GPS World

Category: Survey

  • GPS 24+3 Configuration: A Closer Look

    In the few years I’ve been writing this column, very few subjects have warranted back-to-back newsletter coverage. The new GPS 24+3 onfiguration is one of them. The reason I’ve continued with this discussion is because it will significantly affect your GPS operations, especially if you’re using RTK or DGPS.

    What is the new 24+3 GPS configuration?

    If you didn’t read my last column, you might want to read it so you have a common frame of reference. Essentially, the effect of the 24+3 configuration will be to increase the visibility of more GPS satellites throughout the day at a given location. In addition to have more satellites in view, you will generally see lower PDOP values which can result in an increase in accuracy; but certainly the increased satellite visibility is the major upside with 24+3.

    Remember that the GPS satellites are configured in 6 orbital planes (A, B, C, D, E, F) with X number of satellites in each plane that are referred to as “slots.” For example, slot A1 is the first satellite in the A plane, slot B4 is the fourth satellite in the B plane. Note that the slots aren’t necessarily in numerical order. Following is a graphic presented by the U.S. Air Force in September 2009 to provide an illustration of the planes, and slots within each plane. GLAN is the Geographic Longitude of the Ascending Node.

    On the graphic above, note that many of the satellites are paired together. When GPS satellites are paired together, there is little benefit to the user on the ground because the satellites aren’t “spread out”. Ideally, the user on the ground needs the satellites to be “spread out” in the sky which will result in a lower PDOP value (better constellation geometry) and ultimately better accuracy. The satellites are in this configuration today because GPS policy defines a 21+3 configuration. Since there are 30 operational GPS satellites in orbit (six more than required), the six spares are placed near other operational satellites. This isn’t optimal for the user on the ground.

    The concept behind the 24+3 configuration is to spread out the satellites more than the current configuration to benefit users on the ground. This involves significantly repositioning three GPS satellites (SVN24, SVN26, SVN49) and slightly repositioning three other GPS satellites (SVN56, SVN46, SVN55).

    Following is a tabular listing of each slot in the 21+3 configuration. Please note that the graphic above is a rough graphic for illustration purposes (referencing GLAN) while the tabular data below are the actual values.

     

     

    Notes:

    Epoch: 00:00:00 UTC, 1 July 1993
    Greenwich Hour Angle: 18h 36m 14.4s
    Orbital Slot IDs are Arbitrarily Numbered
    * Orbital Slots Marked by an Asterisk are Expandable

     

    In the 24+3 configuration, slots B1, D2, F2 are split to B1F/B1A, D2F/D2A, and F2F/F2A. The F designation is Fore and the A designation is Aft.

    Following is the tabular data for the expanded slots:

    On the B plane, SVN49 is repositioning to slot B1F while SVN56 is moving slightly to slot B1A.

    On the D plane, SVN24 is repositioning to slot D2F while SVN46 is moving slightly to slot D2A.

    On the F plane, SVN26 is repostioning to slot F2F while SVN55 is moving slightly to slot F2A.

    You can refer to the graphic at the beginning of this article to reference the current location (approximate) of each SVN as well as the slot id. The SVN number is to the left of the symbol while the slot id is to the right.

    SVN24 has the furthest distance to travel. It began its journey late last month and will arrive in January 2011. SVN49 and SVN26 will both arrive at their destination slots in May 2010.

    If they were in a hurry, the satellite travel time could be reduced, but according to folks I’ve spoken to they have to conserve fuel. After the satellite reaches its destination slot, it must have enough fuel to occasionally maneuver as well as retain enough fuel for an end of life boost which could happen many years in the future.

    The description of 24+3 configuration is detailed in the September 2008 release of the Global Positioning System Standard Positioning Service Performance Standard document. You’ll see this is the source of the two tables I’ve shown above.

     

    Exactly how many more GPS satellite will my receiver “see”?

    I was hoping to publish satellite visibility charts in this column for different regions of the world to illustrate the upside of 24+3. This is where the “rubber meets the road.” I’ve been experimenting with a modified GPS almanac in satellite visibility software to generate these, but I want to confirm the accuracy of the plots before I publish them. I’m close, but not quite there yet.

    Also, I want to publish a separate satellite visibility chart for DGPS users. Remember from my last column that SVN49 is a tricky one. It’s still unhealthy since it was launched into orbit last March. Most likely, it will never be usable by SBAS (WAAS, EGNOS, MSAS) and DGPS receivers and will effectively reduce the 24+3 configuration to a 24+2 configuration for those users. Mind you, even if SVN49 is not usable by SBAS and DGPS, the new configuration will still be an improvement over the current configuration.

    Look for continuing coverage on the 24+3 configuration. It will be the most relevant GPS topic for day-to-day GPS users in 2010.

    Follow me on Twitter at http://twitter.com/GPSGIS_Eric

  • Leica Builder Series Designed for Varying Jobsite Needs

    The Leica Builder Series Total Stations, just introduced by Leica Geosystems, is designed for construction contractors or anyone on a construction site requiring an easy-to-operate, full-feature measuring tool.

    From simple tasks to professional all-day use, the Leica Builder offers a scaled product family of five different models to meet the varying needs of most construction jobs, Leica said. Contractors can choose from the 100-, 200-, 300-, 400-, or 500-series models.

    The Leica Builder Series is designed for non-technical construction professional to easily perform positioning, layout, or dozens of other daily construction-site tasks. To facilitate data transfer, some models feature a USB port-an industry first-while the 500 Series also has Bluetooth functionality.

    The Leica Builder Series offers the choice of two operation modes. Contractors can operate in stand-alone mode via the on-board PowerSite construction programs with the memory capabilities to collect, store and download data. Alternatively, an application is available for contractors who prefer to use a data collector. The Builder can be coupled with the Leica DX-10 data collector and Siteforeman software.

    On-board PowerSite software is designed specifically for construction applications, eliminating surveying features that contractors may not need, Leica said. Contractors do not require a surveying background in order to use the PowerSite software.

    Intended for the construction site, the Leica Builder is designed to withstand dust, water, and other environmental conditions with an IP55 rating.

    The entry model Leica Builder 100-Series is an electronic digital theodolite for horizontal and vertical angle measurements. Other models — Leica Builder 200, 300, 400, and 500 — are total stations available with reflectorless and/or prism measurement capabilities, data storage via USB memory stick, and wireless communication for more useful functionality. All instruments are equipped with theft protection and support many different languages of which three can be uploaded and switched at the push of a button. The Leica Builder is delivered packaged in a crush-proof transport case with a set of accessories for out-of-the-box use.

  • The New GPS 24+3 Constellation: What Does it Mean to the Surveying and GIS User?

    Last week, the U.S. Air Force announced it is reconfiguring the GPS constellation. The Air Force is changing the constellation from a 21+3 configuration to a 24+3 configuration. The result will be more satellites in view, on average.

    This is great news for the GPS surveying and GIS mapping user. In my  opinion, it was the only achievable short/medium-term solution to the GPS “brownout” problem that has plagued GPS surveying and mapping users for years, and has worsened in recent months.

    In short, a GPS “brownout” is a time of the day when a GPS user is unable to utilize his or her GPS receiver because there aren’t enough satellites in view to achieve the desired accuracy. GPS “brownouts” primarily affect high-precision RTK users because that technology requires that the GPS receiver is tracking at least six satellites for a reliable position. With the current GPS constellation, there are times during the day when this is not possible given the satellite configuration and local conditions (obstructions such as trees, buildings, and terrain). This problem puts a serious damper on GPS productivity.

    Even though there are currently 30 operational GPS satellites, they are configured in a 24-satellite constellation. Essentially, several satellites are “paired up” so they add no value to users on the ground. They are designated as back-up satellites in case of a failure. I wrote a detailed article on this subject in October 2009 titled GPS Constellation Management: Playing Not to Lose that summarizes the problem.

    The New 24+3 Configuration

    Announcements from various publications and online newsgroups have different interpretations of the Air Force announcement. Some are emphasizing increased accuracy and others are citing increased coverage in Afghanistan. While both are correct, the major benefit to the surveying/mapping user community is increased worldwide satellite visibility. In other words, more GPS satellites will be in view at a given time during the day.

    More satellites in view = greater RTK and mapping productivity.

    The reason that increased accuracy is mentioned in the announcement is because PDOP values will be lower in general due to the increase of satellites in view…and there’s a direct correlation between accuracy and PDOP. Just how many more satellites will be in view is not clear yet. I’m working on producing some mission planning charts that will illustrate the benefits of 24+3 compared to 21+3.

    The three satellites being repositioned are SVN24, SVN26, and SVN49. SVN24 and SVN26 are two of the oldest satellites (Block-IIA) in the GPS constellation. SVN24 was declared operational in August 1991. SVN26 was declared operational in July 1992. SVN49 is a newer Block II-RM that was launched last March and has never been declared operational due to an anomaly discussed here before. More on SVN49 further down.

    The time to reposition each satellite is significant. SVN24, with the furthest distance to travel, began its journey last week and will take 12 months to reach its destination slot according to the Air Force. SVN49 will begin its journey on January 21, 2010, and will take four months (May 2010). SVN26 will begin its transition on February 8, 2010, and will reach its destination slot in approximately three months (May 2010), according the Air Force.

    Which Users Will Benefit the Most?

    After (and maybe during) the transition, RTK users will see an increase in the number of visible GPS satellites throughout the day. As I mentioned above, I’m still working on producing satellite visibility charts to better and more accurately illustrate this, so stay tuned. Of course, the benefit is going to vary depending on where you are located.

    Another group who will benefit is GIS mapping users, especially those working in difficult GPS conditions such as in forestry, urban/municipal areas, and areas where there is rugged terrain. An increased number of GPS satellites in view will allow GIS mapping users to operate in areas where it may not have been possible before and perform better in areas that were difficult.

    Consumer GPS users will benefit the least. Even during times of GPS “brownouts,” the pushback from consumer GPS has been minimal. Automobile navigation systems perform without a hiccup for the most part and handheld receivers behave reasonably well. The primary reason is that both of those types of receivers aren’t selective about the satellite signals they accept. Accuracy is way down the list of important design features in those receivers. That’s not the case with RTK and professional GIS mapping receivers. RTK and GIS mapping receivers require high-quality measurement data from GPS satellites.

    Will RTK Users Still Need GLONASS?

    Certainly, GPS-only (non-GLONASS) RTK users will see an increased benefit with the 24+3 configuration, particularly those who are operating in relatively clear-sky environments like precision agriculture. However, as we’ve seen with this technology, users will keep pushing the GNSS envelope to use it in marginal conditions where GPS 24+3 won’t be enough. GLONASS will still contribute more satellite measurements, on average, than GPS 24+3. Therefore, GLONASS will still be a desirable feature.

    But, I think we may see mainstream GNSS receiver manufacturers selling the GLONASS option at a lower price (or offering it for free) as it will be required in fewer instances. Russia is continuing to launch GLONASS satellites three at a time with the most recent launch being in December 2009 and the next scheduled one being later this spring.

    SVN49 – What No One Is Talking About

    One of the three GPS satellites being repositioned for 24+3 is SVN49. If you’ve kept up with the GPS constellation over the past six months, no doubt you’ve read about the SVN49 problem. It was launched last March and still hasn’t been declared healthy due to an irreparable problem. There has been much debate about what to do with SVN49. You can read about it here and here and here.

    Most likely, the problem that SVN49 has will not affect RTK users. In other words, if SVN49 is set healthy, RTK users will be able to utilize it like the other normally operating GPS satellites.

    However, GIS mapping users won’t benefit from SVN49. The Federal Aviation Administration (FAA) has said it won’t incorporate corrections for SVN49 in WAAS. Although the U.S. Coast Guard (USCG) and Department of Transportation (DOT) haven’t commented, I doubt they will broadcast DGPS corrections for SVN49 either. For code phase post-processing, I doubt manufacturers will modify their post-processing software to accommodate the SVN49 anomaly.

    So, for GIS mapping users, it’s likely going to be a 24+2 configuration instead of a 24+3 configuration.

    Either way, this is good news across the board for the GPS surveying and mapping user community.

    I agree with what Don Jewell wrote in his column recently, that this subject is going to be written about and discussed a lot over the next few
    months as SVN26 and SVN49 are repositioned, and over the next year as SVN24 reaches its destination.

  • The Federal Radionavigation Plan

    I’ve intended to write about the 2008 Federal Radionavigation Plan (FRP) for quite some time. It is an important document because it is the official policy document that drives the United States’ radio navigation (including GPS) program planning. According to the FRP, it includes the introductions, policies, radionavigation system user requirements, system descriptions, and operating plans of various radionavigation systems. The FRP is updated biennially. The 2008 FRP was approved in January 2009.

    The FRP preface states that it is prepared jointly by the Department of Defense, Department of Homeland Security, and Department of Transportation with assistance from other government agencies. The document covers radionavigation systems used by both the civilian and military communities. It does not cover radionavigation systems used exclusively by the U.S. military.

    The FRP is a fascinating document because it encompasses GPS, GPS augmentation systems, and “back-up” systems. In this column, I’m going to extract several statements from the FRP and comment on them. If you’d like to read the FRP in full (184 pages), you can do so here. Briefly, the FRP includes the following navigation technologies: GPS, WAAS, DGPS, LORAN, and VOR/DME/TACAN/ILS/MLS/NDB (all aviation-oriented).

    By way of background and according to the FRP, the first version of the FRP was released in 1980 as part of a Presidential Report to Congress.

    For the remainder of this column, I’ll provide quotes from the FRP that I think are relevant and add some commentary.

    From the executive summary:

    “A major goal of DoD and DOT is to ensure that a mix of common-use (civil and military) systems is available to meet user requirements for accuracy, reliability, availability, continuity, integrity, coverage, operational utility, and cost; to provide adequate capability for future growth; and to eliminate unnecessary duplication of services. Selecting a future radionavigation systems mix is a complex task, since user requirements vary widely and change with time. While all users require services that are safe, readily available and easy to use, unique requirements exist for military as well as civil users. For example, the military has more stringent requirements including performance under intentional interference, operations in high-performance vehicles, worldwide coverage, and operational capability in severe environmental conditions. Similarly, civil users desire higher accuracy and integrity for future highway, rail, and other safety-of-life applications. Cost is always a major consideration that must be balanced with a needed operational capability.”

    EG Comment: As I did, you may think the “civil user desires” described in the executive summary are a small subset of actual consumer users, and that’s true. But, it’s important to remember that this document is focused on U.S. government users rather than commercial users.

    However, it does raise a point about the consideration given to civilian users when program decisions are being made regarding GPS such as features, satellite launch schedules, ground infrastructure, and constellation management. I’m sure when a congressperson, who is making decisions regarding budgets, is researching the subject he or she will read this executive summary. The statement “civil users desire higher accuracy…” will mislead the reader. While there is a demand for high accuracy in the commercial civil user community, there is a much larger demand for products in the low and medium accuracy commercial markets.

    While I’m not criticizing the executive summary for being incorrect, it seems to me that the people who control the purse strings (Congress) may not be given enough information to grasp the “big picture” regarding the GPS user community.

     

    “Interoperability considerations —

    “National and international radionavigation systems are sometimes used in combination with each other or with other systems. These combined systems are often implemented to provide improved or complementary performance. In the case of GPS, the USG encourages future interoperability with foreign space-based PNT systems for civil, commercial, and scientific uses worldwide. Examples of existing or future foreign space-based PNT systems are Russia’s Global Navigation Satellite System (GLONASS), the European Union’s Galileo, Japan’s Quasi Zenith Satellite System (QZSS), China’s Compass, and India’s Regional Navigation Satellite System (RNSS). Properly designed receivers that take advantage of these systems may benefit from additional satellite signals, increased redundancy, and improved performance over that obtained from just one system alone. A critical aspect of system interoperability is ensuring compatibility among radionavigation services. For example, the USG has concerns about radionavigation signal structures that could adversely impact the military and civil use of GPS. The USG has also fostered the use of interoperable augmentations through its adherence to international standards for DGPS and space-based augmentation system services.These include Maritime DGPS and the Wide Area Augmentation System.”

    EG Comment: I have to say that the U.S. government has done a good job in the area of interoperability. In the 2001 Federal Radionavigation Plan, interoperability wasn’t discussed nearly to the degree it is in the 2008 FRP.

    From the 2001 FRP: “Radionavigation systems are sometimes used in combination with each other or with other systems. These combined systems are often implemented so that a major attribute of one system will offset a weakness of another.…a few manufacturers have of navigation and positioning equipment have developed combined GPS/GLONASS receivers to take advantage of these benefits. Some receivers are on the market with others in the planning stage.”

    From 2001 to 2008, the U.S. government’s position has morphed from recognizing that some GPS/GLONASS receivers exist to actually encouraging interoperability with all “foreign-based PNT systems for commercial, civil, and scientific uses worldwide.” That’s quite a transformation.

     

    “General policy statement —

    “As the full civil potential of GPS services and its augmentations are implemented, the demand for services provided by other Federally provided radionavigation systems is expected to decrease. The USG will reduce non-GPS-based radionavigation services with the reduction in the demand for those services. However, it is a policy objective of the USG not to be critically dependent upon a single system for PNT. The USG will maintain back-up capabilities to meet: (1) growing national, homeland, and economic security requirements, (2) civil requirements, and (3) commercial and scientific demands. Operational, economic, safety, and security considerations will dictate the need for complementary PNT systems. While some operations may be conducted safely using a single radionavigation system, it is Federal policy to provide redundant radionavigation service where required. Backups to GPS for safety-of-life navigation applications, or other critical applications, can be other radionavigation systems, or operational procedures, or a combination of these systems and procedures to form a safe and effective backup. Backups to GPS for timing applications can be a highly accurate crystal oscillator or atomic clock.”

    EG Comment: I wrote to someone the other day about this. Back-ups to GPS is a serious issue. I think very few would argue that it’s not. The reality is that
    there is no single back-up for GPS. It depends on the application. In aviation, it’s maintaining a minimal infrastructure of VOR/DME/ILS rather than Loran, according to the FAA. In maritime, it’s the legacy visual aids and charts according to the U.S. Coast Guard. For high precision users, it’s legacy technology like optical instruments and new technology like Locata and pseudolites.

     

    “GPS backup —

    “With respect to transportation to include aviation, commercial maritime, rail, and highway, the DOT has determined that sufficient alternative navigation aids currently exist in the event of a loss of GPS-based services, and therefore Loran currently is not needed as a back-up navigation aid for transportation safety-of-life users. However, many transportation safety-of-life applications depend on commercial communication systems and DOT recognizes the importance of the Loran system as a backup to GPS for critical infrastructure applications requiring precise time and frequency.”

    EG Comment: The continuing Loran saga.

     

    “Civil Signals —

    “In addition to the L1 Coarse/Acquisition (C/A) signal, the USG will add three additional coded signals to support future civil applications:

    • L1C, frequency 1575.42 MHz, providing better performance than the current C/A signal being used by civilian receivers;

    • L2C, frequency 1227.6 MHz; and

    • L5, frequency 1176.45 MHz, to meet the needs of critical safety-of-life applications, such as civil aviation.

    “The L1C signal is designed to be interoperable with the European Galileo system and is being promoted as a future world standard for incorporation into Global Navigation Satellite Systems (GNSS). The next generation of GPS satellites, GPS III, will begin broadcasting L1C around 2014.

    “The performance specifications in the current SPS PS apply to users of the L1 C/A (1575.42 MHz) signal. As new modernized GPS civil signals (L1C, L2C, and L5) achieve initial operating capability (IOC), performance standards for services utilizing these signals will be developed.”

    EG Comment: Nothing new here, but the schedule of actually implementing the new civil signals is a moving target. There are only seven satellites broadcasting L2C at this time. The first Block IIF satellite with L5 should launch in the first or second quarter of this year. Satellites broadcasting L1C (Block III) won’t launch until at least 2014 and a full constellation won’t be operational for many years after that.

     

    “Discontinuation of codeless and semi-codeless GPS access —

    “As published in the Federal Register on September 23, 2008 (Volume 73, Number 185), the USG commits to maintaining the existing GPS L1 C/A, L1 P(Y), L2C and L2 P(Y) signal characteristics that enable codeless and semi-codeless GPS access until at least 31 December 2020. To enable an orderly and systematic transition, users of semi-codeless and codeless receiving equipment are expected to transition to using civil-coded signals by this date.”

    EG Comment: I’ve written a lot about this. You can read some here.

     

    “Military signals —

    “Currently, GPS military users are provided P(Y) code signals on L1 and L2. These will be supplanted in the future by the M-Code, the next generation military GPS signal. The first GPS Block IIR-M satellite began broadcasting M-Code in September 2006. M-Code will significantly improve exclusivity of access because, in addition to being encrypted, it will be spectrally separate from civilian signals and other radionavigation satellite service signals, thereby enabling U.S. navigation warfare operations through spectral separation. Navigation warfare involves protecting U.S. and allied use of GPS while simultaneously preventing hostile forces access to GPS services and preserving peaceful civil GPS use outside of an area of military operations. The M-Code will permit higher power operation than the present signal design and will facilitate localized tactical denial of GPS civil signals to prevent their use by hostile forces. Military GPS receivers, when tracking the encrypted military signals, are much more resistant to interference than commercial GPS equipment. The newest generation of military GPS receivers that can access military GPS signals directly are even more resistant to interference; however, future improvements in signal availability and receiver performance will continue to be necessary.”

    EG Comment: The key phrase is “localized tactical denial of GPS civil signals…”. Wow, what can I say about that? Come on GLONASS/CDMA, and Galileo, hurry up!

    “Military use of GPS civil signals —

    “DoD does not have an operational requirement to use the GPS civil signals, designated L1C, L2C, and L5, or the Wide Area Augmentation System (WAAS), with the exception of the Army validated WAAS requirement documented in the Global Air Traffic Management (GATM) Operational Requirements Document (ORD). Since DoD policy prohibits the use of civil signals or augmentation systems in wartime environments and dual equipage is not fiscally practical, type approval of military aviation receivers is required to eliminate the need for civil GPS equipage on military aircraft. This will provide an enhanced capability to span the operational environment for military aviation—from flight in civil airspace in peacetime to combat operations worldwide. Commercial operators of Civil Reserve Air Fleet (CRAF) airframes may elect to equip with L5 and/or WAAS if there is a demonstrated.”

    EG Comment: Interesting.

     

    “Mitigating Disruptions in Aviation Operations —

    “A loss of GPS service, due to either intentional or unintentional interference, in the absence of any other means of navigation, would have varying negative effects on air traffic operations. These effects could range from nuisance events requiring standard restoration of capabilities, to an inability to provide normal air traffic control service within one or more sectors of airspace (the NAS is divided into hundreds of air traffic control sectors. A single air traffic controller has the responsibility to keep aircraft safely separated from one another within each sector and from other sectors. Sector dimensions vary, and are established based on predominant traffic flows, altitude, and controller workload) for a significant period of time.

    “In addition to FAA plans of retaining a minimum network of VOR, DME, and ILS facilities to serve as a backup to GPS for the
    near future, several other solutions have been identified to help mitigate the effects of a satellite navigation (SATNAV) service disruption:

    “The L5 civil frequency planned for GPS will help mitigate the impacts of both solar activity and unintentional interference, but it may be 2018 before a full constellation of dual-frequency satellites (L1 and L5) is available. The dual frequency capability with L5 will address ionospheric scintillation by enabling receivers to calculate
    actual ionospheric corrections, thereby preserving LPV capability during severe ionospheric storms.

    • Modern transport-category turbojet aircraft with inertial systems may be able to continue navigating safely for a period of time after losing radionavigation position updating depending on the route or procedure being flown. In some cases, this capability may prove adequate to depart an area with localized jamming or proceed under visual flight rules during good visibility and high ceilings, however, inertial performance without radionavigation updates degrades with time and will eventually fail to meet airspace requirements.

    • Integrated GPS/inertial avionics having anti-jam capability could reduce the area affected by GPS jamming or unintentional interference. Industry research is proceeding to develop this technology, with an expectation that it might be marketed to the general aviation community at some point in the future.

    • Users may have an option to equip with instrument flight rules (IFR)-certified Loran avionics, pending the improvements needed to achieve a nonprecision instrument approach capability with eLoran. A combined eLoran/SATNAV receiver could provide navigation and nonprecision instrument approach service throughout any disruption to SATNAV service.

    EG Comment: This is a good description of the GPS strategy for aviation operations. But, honestly, if there’s a disruption once the National Airspace System (NAS) is fully reliant on GPS, it’s hard to see there not being major, major hiccups in the air traffic system.

     

    “Mitigating disruptions in land operations —

    “Surface transportation users currently use radionavigation services from GPS and its augmentations to supplement other available nonradionavigation systems. Under this operational paradigm, users seamlessly use other existing techniques to mitigate both the short-term loss of GPS due to obstructions and the longer-term loss due to failed on-board user equipment and adverse operating environments. In future applications, accuracy requirements are expected to become much more stringent, and GPS and its augmentations are likely to play a more critical role. The loss of GPS and its augmentations will be carefully evaluated within the overall operational environment to ensure continued safe and efficient operation of the land transportation system.

    “Surface transportation agencies are working with industry to ensure that safety critical systems that use GPS and its augmentations consider the loss of these radionavigation services and are able to mitigate its effects in order to continue safe and efficient operation of the nation’s surface transportation infrastructure. This is accomplished today by outreach to user groups and local transportation agencies and defining minimum operational or functional standards. In the future, training for application developers, state and local highway and transit agencies, and motor carriers on the operational capabilities of GPS as well as what to do when failures occur may be necessary. Finally, since it is expected that signal availability from GPS may not be adequate for surface users experiencing canopy/urban obstructions, alternate systems that perform a verification test on the GPS navigation solution and that support continued operation in the event of a loss of GPS will be employed in a system-of-systems configuration.”

    EG Comment: A great argument for multi-constellation receivers.

     

    “Mitigating disruptions in non-navigation applications —

    “Common positioning applications include: surveying and mapping; precision agriculture; emergency response and law enforcement; fire services; environmental resource management; utility location and management; asset inventory and management; and logistics. These applications have a highly variable duration and involve sporadic areas of operation. Because of the flexible character of positioning applications, operations will typically be halted until the GPS or GPS Augmentation signal is restored in an area. Optical and inertial surveying equipment are back-up options that could meet the accuracy requirements of these applications, depending on the capabilities and preparation of these operators.”

    EG Comment: Multi-constellation receivers have already proven their value in non-navigation applications.

     

    “Operating Plans – GPS —

    “DoD will provide a 48-hour advance notice of changes in the constellation operational status that affect the service being provided to GPS SPS users in peacetime, other than planned GPS interference testing. The USG provides notification of changes in constellation operational status that affect the service being provided to GPS users or if a problem in meeting performance standards is anticipated. In the case of a scheduled event affecting service provided to GPS users, the USG will issue an appropriate Notice Advisory to Navstar Users (NANU) at least 48 hours prior to the event, in accordance with the GPS Standard Positioning Service Performance Standard (Ref. 9).

    “Coordination of planned interference testing activities nominally begins 60 days before testing events. Users are notified by the USCG as soon as an activity is approved, and by FAA typically not earlier than 72 hours before an activity begins. DoD notice will be given to the USCG Navigation Information Service (NIS) and the FAA Notice to Airmen (NOTAM) system. The NIS and NOTAM systems will announce unplanned system outages resulting from system malfunctions or unscheduled maintenance.

    “GPS will be the primary Federally provided radionavigation system for the foreseeable future. GPS will be augmented and improved to satisfy future military and civil requirements for accuracy, coverage, availability, continuity, and integrity. Current policy states that DoD will maintain a nominal 24-satellite constellation, and that replacement satellites will be launched on an anticipated need to maintain the constellation as satellites age and ultimately fail.”

    EG Comment: Good policy statement on notification to civil users. You can sign up to receive NANU’s here.

    Note the statement regarding maintaining a 24-satellite constellation. There are currently upwards of 30 operational GPS satellites. That’s a healthy number, but the problem is that they are still positioned as 24 satellites. In other words, several are “paired up” so the effective constellation is still only 24. There is discussion within the USG about repositioning some of the satellites to optimize the constellation and improve coverage. More on that soon I hope.

     

    “Maritime and nationwide differential GPS —

    “USCG began development of the MDGPS system in the late 1980s to meet the needs of the Coastal and Harbor Entrance and Approach (HEA) phases of
    navigation and to enable automated buoy positioning. MDGPS service was certified fully operational in March 1999 after the network met the performance standards required for HEA navigation. PL 105-66, Title III, § 346 (111 Stat. 1449) authorizes the Secretary of Transportation to improve and expand the USCG’s MDGPS into a Nationwide DGPS, or NDGPS, by adding an inland segment. RITA coordinates this inland program and is acting chair of the NDGPS Policy and Implementation Team. Today, multiple Federal agencies, several states, and scientific
    organizations are cooperating to provide the combined national DGPS utility, with plans to complete NDGPS system coverage throughout the lower 48 states.

    “Each NDGPS facility meets all operating parameters established to qualify a MDGPS facility for operational availability, as established by USCG. NDGPS was not designed to meet aviation integrity requirements.

    “In addition to providing a real-time broadcast of differential corrections, the U.S. DGPS services provide a robust operational backbone to the DOC’s CORS application for post-processing survey applications and Webenabled location solutions, the National Weather Service’s Forecast Systems Laboratory for short-term precipitation forecasts, and the University NAVSTAR Consortium (UNAVCO) for plate tectonic monitoring. Where operational considerations allow, additional operational capability may be added, such as the broadcast of navigational or meteorological warnings and marine safety information (i.e., NAVTEX data) to support safe navigation at sea.

    “Currently 39 USCG and nine USACE broadcast sites provide service for maritime coverage CONUS, the Great Lakes, Puerto Rico, portions of Alaska and Hawaii, and portions of the Mississippi River Basin. The inland NDGPS segment complements the MDGPS segment and is planned to provide dual coverage of the CONUS and selected portions of Hawaii and Alaska as a combined national DGPS utility. There are currently 38 DOT sponsored sites in the NDGPS network providing 92 percent of the contiguous 48 states with single coverage and 65 percent with dual coverage. The combined DGPS service will provide uniform coverage of the CONUS and portions of Hawaii and Alaska, regardless of terrain, or man-made and other surface obstructions. This coverage is achieved by using a medium frequency broadcast optimized for surface applications. The broadcast has been demonstrated to be sufficiently robust to work throughout mountain ranges, difficult terrain and other obstructions. The combined DGPS service will provide a highly reliable GPS integrity function to users to meet the growing requirements of surface users (transportation, precision agriculture, natural resources and environmental management, emergency management and response, and surveying and construction communities).

    “As each new Nationwide site is added to the DGPS network, it is evaluated and tested to ensure that it meets the full operational capability specifications commensurate with a safety of life service. Once a site is declared fully operational, the site is monitored and maintained by the USCG to ensure support for safety applications. System coverage for a specific location can be obtained from the USCG Navigation Center (NAVCEN) website, http://www.navcen.uscg.gov.

    “The two major deployment milestones have been established as nationwide single station coverage and nationwide dual station coverage (CONUS only). Under single station coverage, predicted to occur no earlier than 2010 (pending funding availability), users anywhere within CONUS will be able to receive at least one DGPS differential correction broadcast. The second major milestone is full coverage by at least two DGPS broadcasts, is expected to occur no earlier than 2012.”

    EG Comment: This is a great example of where policy and the presidential budget don’t necessarily agree. NDGPS has been on the budget chopping block for several years. At this point, DOT has only budgeted to maintain the existing system…about $4.6M annually for the 38 DOT-sponsored sites. The 39 USCG and nine USACE sites provide safety-of-life service so their budgets are secure.

     

    “High Accuracy NDGPS —

    “The HA-NDGPS research program is sponsored by FHWA and FRA to enhance the performance of NDGPS. The first HA-NDGPS station began broadcasting in a test mode in 2001 with funding from the Interagency GPS Executive Board (IGEB). IGEB recognized the potential benefit to many Federal agencies, states, and the general public of having a nationwide high accuracy system. Two HA-NDGPS reference stations are currently operational and providing 10 to 15 cm accuracy throughout the coverage area. Further improvements to accuracy and the development of 1 to 2 second time-to-alarm integrity are anticipated. Once these improvements are complete, a HA-NDGPS standard will be developed.

    “To support this, several approaches are being investigated. They can be grouped into three general categories: improved ionosphere and troposphere prediction; increased data throughput to support broadcast of GPS observables; and the addition of pertinent data to the current broadcast.”

    EG Comment: The HA-NDGPS program is one that’s been around a long time. It’s a technology in search of an application. The growth of RTK networks threatens to render HA-NDGPS obsolete. An interesting rumor I heard is that DOT is considering streaming NTRIP data from NDGPS and possibly HA-NDGPS. Essentially, that means one could receive RTCM corrections over the internet via Wi-Fi, mobile phone networks, etc.) and eliminate the bulky and expensive beacon receivers required to use NDGPS today.

     

    “Wide Area Augmentation System (WAAS) —

    “WAAS, an SBAS operated by FAA, provides increased navigation accuracy, availability, and integrity for aircraft navigation during departure, en route, arrival, and approach operations. Although designed primarily for aviation applications, WAAS is widely available in receivers manufactured for navigation use by other communities.

    “FAA commissioned WAAS in 2003. WAAS service supports departure, en route, arrival, and approach operations, including nonprecision approaches and approach procedures with vertical guidance. The WAAS service may support additional capabilities such as advanced arrival and departure procedures (curved and segmented), more efficient en route navigation and parallel runway operations, runway incursion warnings, high-speed turnoff guidance, and airport surface operations.

    “WAAS will be modified to utilize the L5 signal provided by modernized GPS satellites, in lieu of the current semi-codeless L2 signal being utilized to determine ionospheric corrections. New dual-frequency WAAS avionics using L1 and L5 will improve the availability of LPV service.

    EG Comment: Note that WAAS is bypassing L2C. It says something about the future of L2C and if it’s really needed. That’s another discussion altogether. Like GPS, WAAS, and SBAS in general is being used in many applications beyond its original intent. There are hundreds of thousands (several million if you include the consumer WAAS users) that outnumber by orders of magnitude the number of WAAS users in aviation.

     

    “The U.S. Continuously Operating Reference Station (CORS) System —

    “NOAA’s NGS, an element of DOC, has established a CORS system to support non-navigation post-processing applications of GPS, especially precise 3-dimensional positioning at the few centimeter level. More recently, the CORS network has also served the atmospheric science community as a tr
    oposphere and ionosphere monitoring network, and it has     served the geophysics community as a crustal motion monitoring network. Additionally, the CORS system is being modernized to serve as the foundation for future applications that support real and near real-time positioning (that differ from navigation applications by the lack of redundancy and integrity monitoring required for safety-of-life applications). The CORS system provides code range and carrier phase data from a nationwide network of GPS stations for access by the Internet.

    “As of June 2008, data were being provided from more than 1,200 stations. The NGS manages and coordinates data contributions from GPS tracking stations established by more than 200 other groups rather than by building an independent network of reference stations. In particular, use is being made of data from stations operated by components of DOT and DHS that support real-time navigation requirements (mostly WAAS and NDGPS augmentations). These real-time stations make up approximately 17 percent of all CORS stations. Other stations currently contributing data to CORS include stations operated by NOAA, NSF, and NASA in support of crustal motion activities; stations operated by state and local governments in support of surveying and mapping applications; and stations operated by NOAA’s Earth Systems Research Laboratory, in support of meteorological applications. The breakdown of CORS partners is illustrated in Figure 5-1.

     

    “The national CORS system is a GPS augmentation system managed by NOAA that archives and distributes GPS data for precision positioning and atmospheric modeling applications. It serves as the basis for the National Spatial Reference System, defining high accuracy coordinates for all Federal radionavigation systems. Historically, CORS served postprocessing users of GPS, but is being modernized to support real-time users at a similar level of accuracy.”

    EG Comment: What can you say about the CORS system other than that it’s a model for other CORS systems around the world. It says something about the success of the program in that it’s allocated an entire page in the FRP.

     

    Phew, there’s more in the FRP I could quote and discuss but I’ve touched on the major items. Hopefully, this gives you an idea of what the USG thinks about when it makes strategic and tactical decisions about the GPS program. However, keep in mind that in many cases policy and budget don’t match, and if there’s a conflict between the two, budgets usually win.

    As a side note, I’ve started a Twitter. You can find me at http://twitter.com/GPSGIS_Eric.

     

  • Directions 2010: It’s the Economy, Stupid

    At the end of every year, I devote this column to Directions 2010 in which I discuss significant developments, trends, technologies, and companies in the GNSS industry.

    Two years ago, I wrote about the Year of the Who. Not GNSS technology; rather, the people and companies they run.

    Last year, I highlighted 2009 as being the Year of the Other GNSS. The little brother of GPS…GLONASS.

    I’ve thought a lot about this year’s column. Some have said that next year will be the Golden Year for GNSS with the launch of the first Block IIF satellite, possibly the launch of the first GLONASS-K satellite (broadcasting CDMA), launch of Japan’s first QZSS satellite, launch of a GAGAN geostationary satellite, yada, yada, yada.

    The problem with this, as I see it, is that these developments will have very little impact on GNSS users in 2010. All of them have been on the drawing board for years, all have been vetted, and most of them are behind schedule. In a nutshell, it’s beating a dead horse. How many times can one talk about Galileo? Even I get tired of writing about the next satellite launch, the next signal to be broadcast, the next GNSS to be developed, etc.

    From a GNSS technology perspective, do you know what excites me? Optimizing the current constellation of satellites that are already in orbit. That’s where the “rubber hits the road.” With a few tweaks of the GPS constellation, our “brownout” periods would largely disappear immediately. No waiting for new satellite launches, no waiting for new GPS receiver technology to purchase. Just like when Selective Availability (SA) was turned off…boom…an overnight difference. Of course, I know it’s not quite as easy as turning off SA, but I think you see my point.

    However, even though it’s likely that the Air Force will reconfigure the GPS constellation to reduce the GPS brownouts in 2010, that’s not the focus of this column (although it’s a close second).

    Nope. The statement that best defines the GNSS industry for 2010 is one I’ll borrow from Bill Clinton that he used during his campaign for the U.S. presidency in 1992…

    ”It’s the economy, stupid.”

    Why? The current economy is beating the tar out of the GNSS industry.

    Revenue for high-precision GPS/GNSS systems is down significantly. Revenues from Trimble’s Engineering & Construction division were down 22 percent in the third quarter compared to the same period last year. Revenues for Hemisphere GPS, a GPS manufacturer focused on the agriculture industry, were down 31 percent in the third quarter compared to the same period last year.

    When revenue decreases significantly, companies typically react by cutting costs. Some of the first expenses cut are research projects that can lead to revolutionary developments. Companies also review personnel requirements and subsequently reduce headcount.

    Decrease in corporate revenues also trickles down to the distribution channel. The GNSS distribution channel (surveying equipment dealers) have taken a big hit. Layoffs are prevalent and many dealers are reduced to operating with “skeleton crews.”

    In the service sector, I’ve heard from several companies that bid pricing on construction projects is coming in at 20 to 30 percent less than the pre-recession period and bid competition for each project has increased. This results in a lower profit margin for the successful bidder and, as a result, there is less money available in capital equipment budgets for contractors.

    On the flip side, the market for used surveying equipment is hot, GPS/GNSS equipment included. Companies and individuals looking to trade equipment for cash or going out of business altogether are pushing their equipment to the market, primarily using eBay. This flood of “fire-sale” surveying equipment contributes somewhat to the declining revenue for new GPS/GNSS equipment.

    It’s a vicious cycle that’s difficult to recover from.

    In 2005, economics Professor’s Hugh Patrick and David Weinstein from Columbia University and economics Professor Takatoshi Ito from the University of Tokyo wrote about “…a prolonged period of stagnation and malaise…Subpar growth, failing banks, plummeting real estate and stock prices, deflation, unprecedented unemployment, and huge government liabilities have persisted, despite extraordinary fiscal and monetary policy fixes.”

    It reads as though they were writing about today’s U.S. economy, but they were actually writing about the Japanese economy which has been stagnant since 1991. Their book is titled “Reviving Japan’s Economy.”

    It’s a little disconcerting to think about the U.S. recession lasting that long, but I do have a hard time seeing the light at the end of the tunnel. I think real estate prices will continue to depreciate and the effects of the commercial real estate market will reverberate through the economy for several years.

    Let’s face it: high-precision GNSS receivers are a luxury item for the most part. In some cases, the argument can be made that the investment has a ROI (Return on Investment) that justifies the capital expenditure. But in many instances, companies and individuals might decide to save the cash and forego the efficiency that GNSS equipment offers or continue using their legacy GPS equipment that may not be the most efficient technology, but it does the job.

    That, my friends, is the reason that the economy, and not a GNSS technology development or trend, will be the most significant factor in the GNSS industry in 2010.

     

    From the Mailbox

    We received a Letter to the Editor regarding my last column titled “As Loran Fades, Attention Shifts to DGPS and SBAS.” Following is the letter:

    As I read the title of this month’s Survey newsletter column, “As Loran Fades, Attention Shifts to DGPS and SBAS,” it came to my mind that there are many people around the world who do not recognize the difference between a position, navigation, and time (PNT) system and an augmentation of a PNT system — a difference that was not clearly pointed out.  I have heard many PNT users expound on how good an augmentation is and, to my amazement, how the augmentation could provide service despite a GNSS outage. I’ve stopped being surprised. After all, I still remember the days when Galileo was being touted as a backup to GPS.

    Unfortunately, the leadership worldwide has become decidingly less technical over the last decade, and without proper explanation from staffers (who have also become decidingly less technical), the point is lost.

    The simple fact is that augmentations are of little or no use if the system they augment is unavailable. Perhaps this point should be made, and made loudly and strongly — particularly in the case of the scheduled termination of Loran. The same holds for the respective differences between real-time navigation, long-term positioning, and time and frequency — distinctions, again, that are lost to many. While WAAS, NDGPS, and even HA-NDGPS are admirable efforts that highlight what a group of talented, dedicated engineers can do, maybe what we need is a PNT 101 course/flash card set for those “technically challenged” so they can better understand the ramifications of their decisions. It took me and millions of others five years to get a bachelor’s of engineering degree; we cannot expect the leadership to learn engineering overnight.

    I remember fondly the times when, as a junior engineer, I had five layers of management above me that all held engineering degrees. Today I ca
    n’t go up to any level and find a single one. What went wrong?  I do not know, but I do not think it bodes well for the world.

    In any event, best regards to GPS World, and Happy Holidays

    — a wistful engineer

     

    Thanks for the note.

    I believe there are some very smart people in the federal government running these programs. Sadly, I think the demise of programs like Loran are largely the result of political efforts, or lack thereof, rather than a lack of technical understanding. If no one is going to fight for the program, most likely it’s not going to be funded. Furthermore, I think most people agree, engineering educated or not, that GPS is a venerable system. However, it’s debatable whether Loran is a suitable back-up or not.

    Perhaps the title of my article was a bit misleading, too. I don’t think anyone would claim that GPS augmentation is a back-up for GPS. My point was that resources (energy and money) and focus would shift to GPS augmentation as it has become the replacement for Loran in the marine and aviation industries.

    — Eric

  • As Loran Fades, Attention Shifts to DGPS and SBAS

    Few precise-positioning users have employed Loran in a professional sense, although maybe you have in your personal life if you’re a airplane pilot or a mariner. Then again, if you’ve flown as an airline passenger or cruised onboard a ship, you’ve benefited from the back-up to GPS that Loran provides. Similarly, if you’ve used a mobile phone recently; you don’t see it, but the wireless carriers all use Loran as a back-up. That back-up is about to go away.

    Loran was developed initially for marine navigation and then adopted for aviation navigation. I used Loran-C for aviation navigation in the early 90’s after I earned my private pilot’s license. It was much easier than triangulating off of VORs and NDBs. Yes, GPS receivers for aviation were starting to emerge at that time but flying is expensive so a hand-held GPS was an out-of-reach luxury for a newlywed who just bought his first house and was preparing to start a family.

    Loran is a terrestrial (ground-based) system of broadcasting towers, somewhat synonymous with NDGPS. You can read details about the system in the link I provided, but essentially it’s a line-of-sight system in which the Loran receiver antenna needs a direct path to the tower to utilize the signal. Coverage depends on the density of the broadcasting towers. Some regions are covered better than others and when I was using it, there were many areas that were not covered. Accuracy is always an ambiguous subject with respect to navigation technologies, so I’ll go out on a limb and say that Loran-C accuracy is repeatable to about 20 meters. A proposal was floated to upgrade Loran to a system called e-Loran which is reportedly accurate to about 9 meters.

    Anyway, over the past several years there’s been a discussion about what to do with the Loran system because it’s clear that GPS has supplanted Loran as the primary navigation system for marine and aviation. Several articles have been published in GPS World by industry experts with most being in favor of maintaining Loran. The primary argument is that we need a back-up system for GPS, not only for navigation, but for the many invisible ways that GPS supports the national infrastructure (financial networks, wireless communications, transportation).

    Here are several relevant articles, from most recent to further back:

    New Backward-Compatible Technique to Develop GPS+eLORAN User Base

    Coast Guard Jettisons Loran

    LORAN: What the President Meant to Say Was…

    Loran Study Finally Unleashed: Says Keep It, Best Option

    eLoran, Superhero Sidekick

    Loran Gets a Witness

    The Case for eLoran

    In addition to these articles , the U.S. government publishes the Federal Radionavigation Plan (FRP) roughly on a biennial basis. There was one published in 2001, then 2005 and the last one was published in 2008/early 2009. It is the official policy document in which all US navigation systems are planned. According to the FRP, it is prepared jointly by the Department of Defense, Department of Homeland Security, the Department of Transportation and a number of other contributing government agencies.

    If you don’t have time to read the 2008 FRP, following is a telling statement from the document:

    “In March 2007, the DOT Pos/Nav Executive Committee and the DHS Geospatial/PNT Executive Committee accepted the findings of the Institute for Defense Analysis’ Independent Assessment Team and approved to pursue the designation of Enhanced-Loran, commonly referred as eLoran, as a national PNT backup for the U.S. homeland.

    At its March 2007 meeting, the National Space-based PNT ExComm supported this approach and tasked DOT and DHS to complete an action plan that includes identifying an executive agent, developing a transition plan to address funding and operations and requesting the approval by the DOT and DHS Secretaries resulting in a final decision. DoD has not approved eLoran as a GPS backup for military applications.

    In March 2008, the National Space-based PNT ExComm endorsed the DOT/DHS decision to transition the LORAN system to eLoran.

    With respect to transportation to include aviation, commercial maritime, rail, and highway, the DOT has determined that sufficient alternative navigation aids currently exist in the event of a loss of GPS-based services, and therefore Loran currently is not needed as a back-up navigation aid for transportation safety-of-life users. However, many transportation safety-of-life applications depend on commercial communication systems and DOT recognizes the importance of the Loran system as a backup to GPS for critical infrastructure applications requiring precise time and frequency.

    Currently, DHS is determining whether alternative backups or contingency plans exist across the critical infrastructure and key resource sectors identified in the National Infrastructure Protection Plan in the event of a loss of GPS-based services. An initial survey of the Federal critical infrastructure partners indicates wide variance in backup system requirements. Therefore, DHS is working with Federal partners to clarify the operational requirements.”

    By the way, that Independent Assessment Team mentioned in the first paragraph was led by Brad Parkinson, who knows someting about GPS. Further, the government read the report behind closed doors but refused to release it, until forced to do so nearly two years later, by public information access filings.

    There still aren’t any answers to the question about a real back-up to GPS. No doubt it’s a vulnerable system. But that’s a subject for another day.

    What’s Loran got to do with us?

    The reason I’m writing about this is because as support for Loran wanes, attention (resources and focus) shifts away from Loran, it comes to bear more intensely on GPS navigation and its augmentations for marine and aviation; specifically DGPS and SBAS (WAAS/EGNOS/MSAS).

    With a significant policy shift such as this (albeit it has been in the cards), manufacturers stop allocating engineering development resources to the products/technologies with a dim future and shift those resources to products/technologies with a bright future. True, DGPS has been around for better than a decade and SBAS for about half that time so there’s been plenty of time for manufacturer’s to exploit those technologies, but there is still a lot that can be done.

    Engineers are experimenting with and implementing technologies in some interesting areas.

    HA-NDGPS. High accuracy NDGPS. Currently with a high performance DGPS receive
    r, one can attain about meter-level accuracy. Testing with HA-NDGPS, using a dual frequency GPS receiver shows that accuracies in the 10cm (95%) horizontal and 20cm (95%) vertical range are achievable within a 100 mile baseline according to the US DOT Federal Highway Administration Turner-Fairbank Research Center. Test broadcasts are being sent from a site in Hagerstown, MD.

    Broadcasting DGPS/SBAS corrections via NTRIP. The emergence of RTK Networks has spurred the popularity of using the internet to deliver GPS corrections. NTRIP has become a commonly used method of accomplishing this. One of the weak points of DGPS technology has been the reliability and expense of broadcasting DGPS corrections via the 283-325kHz band. Of course, with NTRIP one must have internet access somehow and that typically happens via WiFi or GSM/CDMA mobile phone network. But it’s not that complicated. I’ve been with a GPS user who has pulled the SIM card from their iPhone, plugged it into a GPS receiver, and begin receiving DGPS corrections immediately.

    During my last webinar, someone had posed the question if receiving SBAS corrections is possible via the internet in order to bypass the requirement to maintain visibility of the SBAS geostationary satellite. Streaming SBAS corrections via the internet is already happening in Europe. Users can access EGNOS corrections and bypass the EGNOS geostationary satellites by using SISNeT. A similar type of system could be implemented for any SBAS and not necessarily by the SBAS service provider. It could be a commercial entity.

    I think the internet and GSM/CDMA mobile phone networks are really going to transform the way we transport data from reference stations to our receivers in the field. We’ve been fighting this battle of delivering GPS corrections for better than a decade. In the past, we’ve experimented with FM pagers and landline modems and now we’ve settled on low frequency radiobeacon, VHF/UHF/Spread spectrum and geostationary satellites but none are close to the perfect solution. GSM/CDMA mobile phone networks may be the final solution as the networks continue to build-out towards complete geographic coverage. Of course, we are helped immensely by the mobile phone industry whose focus on data for the many new social networking applications will drive the price of data plans downward.

    By the way, almost all wireless carriers use Loran as a back-up technology; highly precise timing is a key aspect of how wireless communication works. The carriers use GPS for that, but if GPS goes down — as it did in San Diego during a memorable jamming episode a few years ago — so do all cell phones, if the carriers don’t have a timing back-up. In San Diego, they didn’t. Just something to think about, if you are using your mobile phone network to transport data or receive corrections.

  • A Little Q&A Follow-up and Feedback on My Last Column

    I received some feedback on my last column entitled “What’s the Difference Between a Used Car Salesman and a GPS Salesman?” Most of the comments were positive in that the technical content was reasonably deep and thorough. However, I did receive a couple of e-mails from folks who were offended by the comparison.

    The joke has been around for a long time. As I mentioned, I recall hearing it in the early ’90s. I believe it was while I was at a conference somewhere in British Columbia, Canada. Anyway, I used to be a GPS salesman of sorts and I never took offense to it. I figured if I was doing my job correctly, there was nothing to be offended by. But, the fact is the joke has maintained staying power because a number of people do exist who fit that description. Fortunately, they don’t seem to hang around very long in the industry. On the flip side, over the years I’ve met many competent GPS sales professionals that have earned my trust. Many of whom I consider my friends.

    Leftover Webinar Q&A

    There are some lingering questions left over from the last webinar (September). There are still a few questions left after this that I’ll post in future newsletters.

    Question #1: If GLONASS has a full constellation by 2020, would it be fair to say a L1, L2, and GLONASS receiver would be fine because you would really only have a L1 and     GLONASS receiver thus therefore enough sats?

    Gakstatter: The question is referring to the semicodeless sunset I’ve written about in the past. You can read about it here.

    Back to the question. Generally speaking, I would say yes but it’s going to depend on the receiver firmware design. If the receiver is optimized to depend on L2, then the firmware would have to be altered. Then, the question is whether the manufacturer is willing to update the firmware.

    Question #2: If SBAS is made for aviation safety purposes, why it does not cover all of the world? Will the coverage expand in the future?

    Gakstatter: Building an SBAS is very expensive and time-consuming project. If I recall correctly, the US WAAS total expenditure to date is well into several billion dollars. The FY2010 annual budget for WAAS is just under US$100M.

    The nature of SBAS is that they are regional systems. Currently, there are three. WAAS covers most of North America. EGNOS covers most of Western Europe and North Africa. MSAS covers the region around Japan. GAGAN is still in the planning stage and will cover India and surrounding areas.

    This still leaves South America, Australia, and Africa as major land masses not covered by SBAS.

    MSAS has the potential to cover Australia and EGNOS has the potential to cover Africa. Whether that happens or not is more political and financial than technical issues.

    Also, once GPS L5 is broadcast by a full constellation, the requirement for SBAS for aviation will diminish because GPS in aviation will transition to dual frequency (L1/L5) thus mitigating the effects of the ionosphere.  However, there would still be a question about position integrity, which is a central function of SBAS. The debate within some countries that do not currently have SBAS coverage is whether to invest in a SBAS or hold out for GPS L5. However, a full satellite constellation broadcasting GPS L5 will not be operational until ~15 years from now.

    Question #3: Can we obtain SBAS in other regions in the future?

    Gakstatter: India is far along with their GAGAN SBAS. At one point, a test signal was being broadcast. Within the next few months, India reportedly will be launching a geostationary satellite for GAGAN.

    Russia is reportedly in the early stages of developing their SBAS called SDCM (System of Differential Correction and Monitoring).

    The interoperability among SBAS is virtually seamless. A GPS receiver utilizing WAAS in North America is able to use EGNOS in Europe and MSAS in the Japanese region. Most receivers will automatically tune to the local SBAS given the SBAS satellites in view. However, some must be manually set to “look” for the SBAS satellite(s) of that region.

    Question #4: GNSS improves the productivity. What about the precision? Are there any reports testing/comparing GPS vs GNSS?

    Gakstatter: At this point, the ideal situation would be to only utilize GPS satellites. The quality, integrity and monitoring is world-class. Unfortunately, for RTK users there just aren’t enough of them in orbit to be able to work consistently throughout the day.

    The quality and reliability of GLONASS measurements aren’t as good as GPS yet. The ephemeris data and clock corrections are worse and there isn’t world-wide monitoring of the satellites. Russia’s program managers have stated they are striving to reach the same measurement quality as GPS.

    So, the short answer is no, I wouldn’t expect GPS/GLONASS to improve positioning precision. However, it also depends on the scenario. If the comparison is between a GPS constellation of 5 satellites with a PDOP of 5 against a GPS/GLONASS constellation of 5 + 5 with a PDOP of 2, then I’d vote for the latter.

    There is an extensive report available from The Survey Assocation in the UK. Although it focuses on Network RTK, there’s a valuable discussion in it regarding GLONASS. You can download the report here.

    Question #5: By 2020, is the DOD going to completely get rid of L2 signal?

    Gakstatter: No, not at all. L2 was never intended for use by the civilian community. However, in the 1980’s, some really smart scientists in the commercial sector figured out a way to gain access to the encrypted L2 signal via a technique is referred to as semicodeless.

    Since that time, the Department of Defense (DOD) has respected that technique because it’s been vitally important in the development of the GPS commercial markets. By respected, I mean they have intentionally not made changes to the GPS that would disrupt the semicodeless technique.

    The DOD has now has come to a point that dancing around the semicodeless issue has become a bigger liability than they want to assume. That’s understandable since L2C will allow dual frequency GPS receivers to utilize L2 without using semicodeless techniques, the DOD wants to be released of their liability with respect to L2 semicodeless.

    So, after December 31, 2020, the DOD will no longer guarantee that semicodeless receivers will operate as they do today. It is not a “brick wall” in that it will stop working at midnight on December 31, 2020. In fact, a semicodeless receiver may work perfectly fine most of the time after December 31, 2020, but if it stops working properly, the user assumes the liability.

    Off-topic

    One of the reasons my column is late this week is that I caught a bug earlier this week. It’s nothing serious; it’s just slowing me down a bit because I don’t have the energy I normally have. The fact is that I just don’t get sick beyond my tendency to attract strep throat once every few years.

    This year, I’ve opted out of the flu shot despite a specific call from my mother putting the heat on me to get one. I’ve never gotten a flu shot and probably never will. But, I do admit this is the first year I’ve actually considered it. At one point a few weeks ago, 25% of the primary and middle school-aged kids in our school district
    were absent due to illness. There were significantly fewer Trick-or-Treaters in our neighborhood this year; I believe due to illness.

    I’ve always made an effort to wash my hands, face, nose regularly (no, I’m not obsessive-compulsive) and pay attention to those around me when I’m in public places like malls, movie theaters and airplanes. I absolutely hate getting stuck sitting next to a person on an airplane who is coughing and sneezing. I remember specifically sitting next to a person on a flight back from Phoenix, Arizona, a half-dozen years ago. She looked like death warmed-over…coughing and sneezing horribly. Sure enough, the next day I could feel my body losing the battle. I ended up contracting strep. Ugh.

    Anyway, I want to remind you given that many of the US readers are traveling next week for the Thanksgiving holiday to take care of yourselves and your loved ones.  You’ll be traveling amongst those who haven’t escaped “the bug,” but have still decided to travel. Here are some tips from the Center for Disease Control and Prevention to keep you and your loved ones healthy.

  • ABB Selects Intergraph for North African Gas Pipeline Project

    ABB has selected Intergraph for the development of an oil and gas pipeline network and relevant facilities in North Africa. The pipeline network will be built in the El Merk field, a remote, harsh desert location in Algeria.

    According to Intergraph, geospatial-based pipeline infrastructure management solutions will enable ABB to more effectively design, construct and maintain pipelines and assets and demonstrate a comprehensive pipeline integrity program while reducing the cost of maintaining records. By storing records in a central geographic information system (GIS), the solution makes information readily available for a variety of applications, improving record keeping productivity while assuring compliance with regulatory requirements.

    “An accurate, up-to-date view of all critical assets at any given time is a crucial component of any pipeline implementation project,” said Sergio Casati, ABB Project Manager. “Especially in such challenging terrain conditions, we need to keep our pulse on the status of all assets in near real-time. The strength of Intergraph technology and its more than 40 years of experience in the utilities sector, as well as market leadership in enterprise engineering software, were key factors in our decision to partner with the company on this project. Intergraph’s open, flexible technology platform was also desirable for an initiative like the El Merk project, which involves a consortium of multiple vendors.”

    The announcement said that geospatial technology from Intergraph will play a significant role in the design and installation of the pipeline, field gathering stations, gas distribution manifolds, flow and trunk lines and water and gas re-injection facilities in El Merk. The technology will support the Pipeline Open Data Standard (PODS) model, the most widely implemented pipeline data model in the industry, and all data will be stored in an Oracle Spatial database. The implementation will also include a portal component for the seamless distribution of data to all parties, including field and remote users.

    “The collaboration of Intergraph with ABB Italy on this project marks a significant milestone in Intergraph’s involvement in the oil and gas pipeline industry,” said Maximilian Weber, Utilities & Communications manager for Intergraph in EMEA. “Intergraph has worked with leading pipeline providers around the world including Spectra Energy and Northwest Energy in the U.S., E.ON Ruhrgas in Germany and Chongqing Gas in China. Additionally, our Process, Power & Marine division is the world’s leading provider of enterprise engineering software for the design, construction and operation of plants, pipelines, ships and offshore facilities. We are pleased that ABB has recognized our strength in this industry and has chosen us to ensure the accurate, efficient management of assets, as well as play a key role in protecting this infrastructure.”

  • What’s the Difference between a Used Car Salesman and a GPS Salesman?

    Years ago, I heard a funny joke/maxim. I repeat it often and so do several others I know of so maybe you’ve heard it.

    “What’s the difference between a used car salesman and a GPS salesman?”

    Answer: The used car salesman knows when he’s lying to you.

    I didn’t attend the Minnesota GIS/LIS Annual Conference last week, but I received a report from someone who attended a session in which the presenter seemed to fit the maxim quite well. One of the presenter’s messages was that people should stop using WAAS immediately as a GPS correction source due to the inability of data collection software to handle the ITRF00 > NAD83/CORS96 datum shift. Following is a statement from one of his slides…

    “WAAS Real-time accuracy degraded because of datum shift”

    He claimed that users are “in a panic over it.” In all fairness, the presenter could have very well understood that the datum shift can be handled by a number of data collection software packages…just not the one he represents. After all, he works for a local distributor of GPS equipment. Or, even a scarier scenario would be that he really believed what he spoke.

    I’m not interested in naming names or company names of the offending party, but rather painting the true picture. Of course, the attendee I mentioned above knew better than to believe what the presenter was pitching. His group has been using WAAS as a primary correction source for a number of years and reconciling the datum shift between ITRF00 and NAD83/CORS96. It’s not that hard folks.

    Let’s review.

    ITRF00 is essentially the same as WGS-84(G1150) for sub-meter mapping purposes. WAAS (as well as EGNOS and MSAS) are referenced to ITRF00. You need to be aware that the definition of ITRF/WGS-84 has changed over time. Here is a link to a NIMA WGS-84 document that describes earlier versions of WGS-84 and here’s a link to the current version of WGS84 (G1150) that was adopted in 2002.

    In North America (my apologies to readers from other countries), the generally accepted mapping datum is NAD83. NAD83 has also changed substantially over time. Whereas the original WGS-84 was consistent with the original NAD83 (NAD83/86), today there is a substantial difference between the current WGS-84(G1150) and NAD83/CORS96 and also NAD83/NSRS2007. Here is a graphic from Joel Cusick of the U.S. National Park Service that gives you an idea of the difference over North America:

    Here is a link to a technical report from the National Geodetic Survey (NGS) describing the 14-parameter transformation from ITRF00/WGS-84(G1150) to NAD83/CORS96.

    Sadly and surprisingly, some data collection software today and even some PC-based “GIS” software still treat WGS-84 and NAD83 as the same. This instantly introduces a few feet of error. The irony is that people spend thousands of dollars purchasing high-performance GPS/GIS receivers capable of sub-meter accuracy only to introduce several feet of error by using software that improperly handles the datum transformation.

    What’s the solution if your software doesn’t handle the datum transformation properly?

    As mentioned above, WAAS is based on the ITRF00 datum and not NAD83/CORS96. As most base maps in North America aren’t referenced to ITRF, most likely you’ll need to transform your WAAS-corrected coordinates to NAD83/CORS96. This can be done one of two ways:

    1. As mentioned above, use GPS/GIS data collection software that handles the transformation correctly. This makes the transformation transparent, painless to the user and accurate in real-time.
    2. Apply a datum shift after you’ve collected your data. You can compute the shift by accessing an NGS datasheet near your project area (within 25 miles is close enough). Make sure it was occupied using GPS. Better yet, use coordinates from a CORS. The datasheet will report coordinates in both ITRF00 and NAD83/CORS96. Here is an example of coordinates from the CORS at Wisconsin Point, WI (near Duluth where the MN GIS/LIS Annual Conference was held):

    ITRF00 Position (Epoch 1997.0) – N 46 42 18.20201, W 092 00 54.760208

    NAD83/CORS96 Position (Epoch 2002.0) – N 46 42 18.17201, W 092 00 54.73394

    Simply enter the two coordinates into your favorite mapping software and you’ll be able to compute the distance and direction of the difference.

     

    Once you know this, you can apply the same offset to all of the data for your project. Quick and dirty? Yes. We’re not splitting hairs. WAAS isn’t delivering cm-level accuracy so this sort of transformation is more than adequate…and very efficient.

    The fact of the matter is that many, many organizations have adopted WAAS as a primary source of GPS corrections and are dealing with this datum transformation issue on a daily basis.

    GPS Constellation Management: Playing Not to Lose

    The WAAS/SBAS subject segues perfectly into the second subject of this column which is a follow-up of last week’s column on GPS Constellation Management.

    Last week, I failed to mention that SBAS (WAAS, EGNOS, MSAS) is a valuable contributor to RTK users. Although not designed specifically to aid RTK ground users, some GPS receiver designers have exploited the value of SBAS satellites to enhance RTK operations. In North America, there are two SBAS satellites. In Europe, there are two and there are two in the Japan region. Following is a graphic depicting the regional coverage of the SBAS satellites and their approximate location.

     

    In many regions of the world, users have at least one SBAS satellite available in view. The beauty of SBAS satellites for RTK is that, unlike GPS satellites, SBAS satellites are geostationary. The are available 24/7 as long as their signal path isn’t blocked by trees, terrain or buildings.

    Since using SBAS satellites for RTK is a relatively new innovation within the past couple of years, not all manufacturers have jumped on the bandwagon yet. The slow adoption of GLONASS was similar. This causes a problem when users want to mix and match RTK receivers from different manufacturers. For example, a user purchases an SBAS-capable L1/L2 RTK rover to be used with their existing L1/L2 RTK reference station. If their existing L1/L2 RTK reference station doesn’t support SBAS for RTK, then the feature on their new RTK rover is worthless.

    Even more important is the lack of support from RTN software designers. “No one’s asking for it” is the answer I get from RTN operators when asked if they are interested in supporting SBAS correctors in their RTN. I believe that users aren’t asking for it because users don’t have a clue how it would help them, and frankly, 99% don’t know the technology even exists. Now, if you would ask users if they’d be interested in one or two extra observables for RTK that would be
    available 24/7 in a geostationary orbit every day, I bet you’d hear some really positive answers.

    RTK users need to be able to utilize every observable that could help them. As Rob Lorimer and I reported last year in our market research report, machine control (based on RTK) will be the fastest growing GNSS segment over the period 2008-2012.

  • GPS Constellation Management: Playing Not to Lose

    In sports, there is a phenomenon that sometimes occurs when a team is leading towards the end of a game. It’s called “playing not to lose”.

    For example, there’s five minutes left in a basketball game and a team is leading by ten points. The leading team wants to run the clock down as much as possible and still maintain their lead. There are two basic strategies the leading team can take. One is to continue being aggressive and using the strategy that put them in a winning position to begin with. The other strategy is to try to “play it safe” until the time clock expires. The problem with the latter strategy is that the other team can sense the change in mentality and feed off of it. It’s called “playing not to lose” instead of “playing to win”. I’ve seen it happen over and over again in team sports and in business. Once an organization has achieved a level of success, they lose the edge that brought them their success.

    The reason you are seeing high HDOP warnings from the NAVCEN and GPS “brownouts” during the day when RTK (GPS-only) isn’t working is because the GPS satellite constellation is sub-optimal. The current design of the GPS constellation is not focused on “playing to win”, but rather “playing not to lose”.

    Even the original GPS Program Manager, Dr. Brad Parkinson, has voiced his concern about GPS brownouts and discussed possible solutions. You can read one of his presentations here. In 2006, noted GNSS consultant John W. Lavrakas published a GPS World article entitled Managing the GPS Constellation for Today’s Needs discussing the disparity between the professional user community needs and GPS constellation management.

    Today, there are 28 operational satellites. There were 30, but PRN08 is offline for maintenance and PRN24 was placed in active reserve after an “unusual failure”. The 31st one, PRN01/SVN49, never has been declared operational since its launch last March due to the issues discussed here before. The current GPS ground control infrastructure can only handle 30 or 31 satellites.

    Given these limitations, GPS looks grim for the GPS-only RTK user, right?

    Not necessarily.

    The GPS constellation is optimized for 24 satellites. When there are more than 24 satellites in orbit, like there has been for many years, the extras are not positioned to benefit the users but rather to be in a position to replace satellite failures. They are sometimes referred to as “paired orbits”. Simply put, the active spares are orbiting very near other satellites that are most likely to fail. This does very little for the user community.

    The current discussion is not whether to launch more satellites, but rather how to reconfigure the satellites that are in orbit. Launching more satellites is a complicated issue. It’s not just an US Air Force (the GPS stewards) technical issue, but a political one because it’s expensive (~$150M per GPS satellite launch). That leaves the Air Force with the option of adjusting the GPS constellation to benefit the user community. Doing this is not completely void of political implications I’m sure, but certainly not near the risk of launching a new satellite and certainly a better bang for your buck to the user community.

    For many years in the GPS scientific community, there have been open discussions in the past of GPS constellations designed for 27 or 30 satellites. The good news is that this is an active discussion within the US Air Force today. It’s quite an important discussion because GPS-only RTK users are increasingly being shut down during the day due to the lack of GPS satellite signals and/or high PDOP. Even a constellation designed for 27 satellites would be a significant gain for GPS-only RTK users.

    During my webinar a month ago, I submitted to the audience the following question:

    “Do you or your crews experience GPS “brownouts” where you have to wait for the GPS constellation to change before you can continue using your GPS system?”

     

    The following results speak for themselves:

     

    Email me your experiences so I can continue to raise awareness of the impact the current GPS constellation is having on GPS-only RTK users. Tell me about your productivity loses, extra mission planning and other time spent dealing with the GPS “brown outs”.

    I’m doing my best to make the Air Force aware of that the current constellation is causing GPS-only RTK users a significant loss in productivity. I have a feeling that the Air Force looks at the millions of consumer GPS users who are happy with their Garmins, TomToms, Magellans, etc. because those folks are able to navigate from Point A to Point B with few difficulties given the current constellation. What the Air Force doesn’t realize are that the GPS demands from the professional user community are much higher. We are the infrastructure people. Without our accurate measurements, the consumer GPS community wouldn’t enjoy the benefits they have.

    RTK users need at least six satellites above 12 degrees and a PDOP below 3.0 for a robust solution. Furthermore, we have to deal with obstructions such as trees, buildings and terrain that will take out, on average, a couple of those. I think the Air Force plugs in a five degree elevation mask back in the office, looks at the sat visibility graph and says “hey, what are these guys complaining about?” The reality is that satellite signals low on the horizon don’t work as well because the data is noisier and many times rejected by the receiver. Secondly, we don’t work in parking lots where we have an unobstructed view of the horizon. We have to deal with trees, buildings and terrain that block satellite signals.

    And the answer is…

    At this point, there is only one solution for RTK users who need better productivity…GLONASS. As much as the Russians have taken a beating in the past for having an unreliable constellation, they hold the key for RTK productivity at this point as the GPS constellation continues to deliver “brownouts” that hamper productivity. It could turn out to be a boon for RTK receiver manufacturers. Although a few include GLONASS as a standard, most RTK receiver manufacturers charge an upgrade fee of several thousand dollars to utilize GLONASS. Even worse for some RTK users, their receiver isn’t upgradeable to utilize GLONASS so they would need to purchase a new receiver(s).

    On a final note, I just spoke to a user in the field who was using a GPS/GLONASS RTK receiver. I asked him to recite to me how many GPS and GLONASS satellites he was tracking. I suppose I shouldn’t be surprised, but it did saddened me a bit. He was tracking more GLONASS satellites (6) than GPS satellites (5). Sigh…

     

  • “What Can GLONASS, GPS L2C, and GPS L5 Do for You?” Webinar Q&A Follow-up

    I hope you’ve enjoyed and benefited from the webinar series as much as I have. I think that given the limited travel budgets in this economy, they are one of the most powerful tools for collaborating. I consider it collaboration because I learn also. Your questions and comments make me think about topics I might not normally consider.

    I also have to give credit to our marketing folks in spreading the word about our webinars. I’ve spoken to others who conduct webinars and I don’t hear of anyone attract the attendance numbers that ours are do (if I may be so bold as to toot our horn). I didn’t see the final attendance numbers on the last webinar, but I think we had over 600 registered. By early next year, I think the number should reach 1,000 for each of the survey/construction/GIS webinars. Hopefully, in the next few months we’ll also start up a webinar series for GeoSpatial Solutions, which I started working on earlier this month.

    As I’ve been accustomed to doing, this newsletter addresses the questions you submitted during the Sept. 15 webinar entitled “What Can GLONASS, GPS L2C, and GPS L5 Do for You?”.

    There were some great questions during the webinar, and a lot of them. There were so many, in fact, that I’m going to break them up into a couple of different newsletter issues. Also, I need to update you on my trip to ION GNSS a couple of weeks ago. I might mix up the next newsletter with more Q&A as well as the ION GNSS update.

    Lastly, don’t feel the need to wait until the next webinar to send me your comments/questions. I can guarantee you that many others have the same questions that you do.

    Question #1: Recent Statement: GLONASS satellite signals are not used nearly as much as the GPS satellite signals (domestically) — is this true? If so, what is the percentage of GPS usage vs. GLONASS in the states?

    Gakstatter: The general statement is true. GLONASS is used predominately in high-precision RTK (real-time kinematic) applications that require centimeter-level accuracy. Even in that segment, I think only a minority of the existing survey receivers utilize GLONASS. But that’s considering legacy receivers that have been in operation for many years. You should remember that GLONASS only became a widely adopted technology in the last few years and it’s still an option on most survey receivers unless you purchase the top-of-the-line model. As recent as five years ago, several mainstream manufacturers still didn’t support GLONASS.

    Also, consider that the popular entry-level GPS L1 survey receivers such as the Magellan ProMark 3 line don’t support GLONASS at all.

    On the GIS front, GLONASS is just starting to make its way into mapping-grade receivers such as the Trimble GeoXH and Topcon GMS-2 Pro. But realize that correctors for GLONASS aren’t supported by real-time correction systems such as WAAS/EGNOS/MSAS or DGPS/NDGPS or OmniSTAR. GLONASS isn’t supported by OPUS or other online post-processing services either.

    But make no mistake about it, GLONASS usage is increasing substantially. This is mainly due to GPS “brownout” periods where there aren’t enough GPS satellites throughout the day to be productive. It’s simply too expensive for work crews to sit idle while waiting for the GPS constellation to improve during parts of the day.

    Lastly, next year the Russians are introducing a significant change with their new generation GLONASS-K satellites. They are going to begin supporting CDMA (vs. FDMA they support now). You can think of this like VHS vs. Beta VCRs of 20 years ago. Today, a GPS/GLONASS receiver is basically two receivers in one box, just like a VCR player that would support VHS and Beta formats. This makes a GPS/GLONASS receiver difficult to design, power hungry and generally inefficient. This is the reason you do not find GPS/GLONASS receivers in the consumer GPS market and rarely in GIS/GPS receivers. However, this is going to begin changing next year as Russia will begin to support CDMA signal structure. This will be the start of a new era in simplifying the design of GPS/GLONASS receivers. I believe it will mark the beginning of the wide-spread adoption of GLONASS. However, this is not an overnight process. It will be many, many years before enough operational GLONASS-K satellites are in orbit to support a CDMA GPS/GLONASS receiver. Of course, it’s also critical that the Russian space program stay focused (politically and financially) in order to achieve this.

    Question #2: Will current GLONASS receivers work with the new (GLONASS) “K” satellites?

    Gakstatter: It is my understanding that the GLONASS-K satellite will support legacy signals and signal structures. Essentially, they would be broadcasting FDMA and CDMA signals. So, the answer is yes. I will report back to you if I hear anything different as this is a critical issue given the large number of GPS/GLONASS receivers in use today.

    Question #3: What does the “k” stand for in RTK?

    Gakstatter: I apologize for “flinging around” acronyms so loosely.

    RTK is an acronym for Real-Time Kinematic. Essentially, it’s a GNSS technology that’s capable of providing centimeter-level positioning in real time while it is moving. RTK utilizes the message carrier (carrier phase) rather than the message itself.

    Question #4: Why will traditional GPS L1/L2 receivers become obsolete after Dec 31, 2020?

    Gakstatter: It’s probably best for you to read the article I wrote about this last year. I also conducted a webinar on the subject you can listen to here.

    It’s important to note that the Dec 31, 2020 date is not a date in which your legacy receiver will stop working. After that date, the US Department of Defense says they won’t guarantee support of semicodeless techniques. In other words, it may work and it may not. The risk is with the user.

    Question #5: What about the accuracy of L2C code? Is it like C/A or P code?

    Gakstatter: L2C provides a pilot carrier for L2. Before L2C, the architects of the original GPS never intended for the civil community to be able to utilize L2. But some very smart engineer/entrepreneurs figured out a way to track the L2 carrier in a “round-about” way via the semicodeless technique mentioned above. With L2C, the semicodeless technique isn’t required any longer so the L2C signal-to-noise (SNR) value is stronger.

    However, there aren’t enough satellites (only 7) in orbit broadcasting L2C at this point to make a significant difference.

    Secondly, L2C has a code similar to C/A code broadcast on L1, but much improved. However, this isn’t being broadcast on L2C at this point due to the ground control segment of GPS not being ready yet. Last indication I received was that it was about two years away from being ready.

    Question #6: If there is a black out in GPS in a GPS/GLONASS receiver, how will it affect? No Black out in GLONASS.

    Gakstatter: I’m assuming you are referring to a total black out of GPS signals. GLONASS isn’t at the point where you can rely on it as a stand-alone system. It lacks a sufficient number of satellites (17) and the quality/reliability of the measurements isn’t nearly as good as GPS.

    Question #7: Are certain frequencies more stable/reliable than others.

    Gakstatter: GPS sign
    als/frequencies (L1 C/A and L2C) are very stable and reliable. They are the most reliable satellite navigation signals in the world. I wouldn’t say that a single GPS signal or frequency is more stable or reliable than another. However, there are a limited number of satellites (seven) that broadcast L2C so it’s not as available as it will be when a full constellation of satellites will be broadcasting L2C (several years from now).

    Many users have GPS/GLONASS receivers. GLONASS, and Russia is very open about this, is not as stable or reliable as GPS yet. While not useful yet as a stand-alone system, GLONASS has proven to be very useful as an augmentation to GPS. This is the reason that GPS/GLONASS receivers have become so popular in recent years in high precision RTK systems.

    Russia has stated that their goal is to match GPS performance in the future.

    Question #8: How will the autonomous accuracy improve with L5 or L2C?

    Gakstatter: Multiple frequencies allow the receiver to directly mitigate the effects of the atmosphere which is the major source error in GPS positioning.

    I’ve heard it been discussed quite widely that decimeter accuracy without correction will be possible with a dual frequency receiver (L1/L5). Furthermore, since both L1 and L5 (and L2C) are open signals (unlike legacy L2), multiple frequency receivers will be widely available and a fraction of the cost of today’s dual frequency receivers.

    Question #9: Will any abilities of the L1/L2 w/ L2C be downgraded when semicodeless is disabled?

    Gakstatter: This is a very good question. The difference I can think of may be the number of satellites broadcasting L2C at that time. If there are still a number of legacy satellites that aren’t broadcasting L2C, one may lose the ability to utilize those satellites.

    Also, it’s important to understand that semicodeless isn’t necessarily going to stop working after December 31, 2020. The DoD merely states that they won’t guarantee it will work after that date. In other words, the DoD might choose to test or utilize a feature that might disrupt semicodeless receivers and they aren’t obligated to inform the civilian community that they are doing so.

    Looking into the future, I’m guessing that receiver manufacturers will create firmware in the receivers (L1 C/A, L2, L2C) that might be capable of detecting this scenario and react accordingly.

    Question #10: If you have a receiver supporting L1/L2/L2c/ glonass where you are tracking 16+ satellites has there been any though on a weighting system for satellites in your solution?

    Gakstatter: Another good question. I’m not sure how the receivers handle this. I will ask a couple of receiver designers I know. I am familiar with some receivers (mapping-grade receivers using code phase) that utilize signals from satellites for which there are no corrections available in order to improve the PDOP. For example, some satellites may not be visible by more than one SBAS reference station and therefore no correction would be issued for that satellite by the SBAS…but the range data from that satellite may still be used to improve the PDOP and position.

    Question #11: Are the ground stations shown in the WAAS slide (SBAS(2) I believe) all operational today?

    Gakstatter: Yes. There are currently 38 WAAS reference stations and all of them are operational today. Twelve were added in the last couple of years (red dots on the map below).

    Four were added in central/eastern Canada, four were added in Alaska and five were added in Mexico. This extended the WAAS service area significantly to the north and south into Canada and Mexico and significantly improved WAAS performance in Alaska.

     

    Question #12: What is the expected accuracy of WAAS in North America and can WAAS be received under canopy (forested) areas?

    Gakstatter: Well, like all questions about GPS accuracy, the answer is “it depends”.

    There are two major factors when considering the accuracy of WAAS.

    The first is the WAAS itself. Looking at the WAAS Performance Report published quarterly by the National Satellite Test Bed, WAAS accuracy throughout North America is well under a meter (horizontal).

    Secondly is the quality of the GPS receiver one is using. A standard consumer-grade GPS receiver using a SiRF (or other) GPS chipset or a GPS-enabled mobile phone is not going to deliver submeter accuracy. Those receivers simply weren’t designed with accuracy as a primary design criterion. On the other hand, there are several GPS receivers available that were designed with professional users in mind that are able to optimize WAAS accuracy and achieve submeter accuracy.

    Operation under tree canopy is even a trickier subject. Among GPS receivers designed for professional users, there is a subset that has been optimized to operate under tree canopy. First, let me be clear that GPS accuracy degrades under tree canopy for all GPS receivers. It’s just a matter of how much it degrades.

    There are two primary issues when operating GPS receivers under tree canopy: accuracy and tracking. Great accuracy is not worth anything if the receiver can’t track satellites. On the other hand, great satellite tracking does little for the professional user if the accuracy is horrible.

    Utilizing WAAS under tree canopy has the additional challenge of the GPS receiver needing to track one of the two WAAS broadcasting satellites (GEOs). Their signal is affected by trees just like GPS satellites. Some companies have developed technology that allows their GPS receivers to temporarily lose track on the WAAS GEO satellite for up to 30 minutes and still maintain WAAS accuracy (or close to it).

    Question #13: Is there a live web page that is good for survey planning, based on GPS satellite positions?

    Gakstatter: There are several GPS satellite planning software packages available as free downloads. Trimble, Topcon, and Leica Geosystems offer them. These require the user to install the software on their computer and update the almanac frequently.

    There is one on-line GPS satellite planning tool from NavCom Tech that’s very convenient for two reasons. First, you don’t have to install any software on your computer. Secondly, it updates the almanac automatically. It has a couple of drawbacks. The major one is that it doesn’t consider GLONASS or SBAS satellites. Secondly, one can’t adjust the elevation mask. Hopefully, NavCom will consider adding those features in the future.

    I wrote an article on this subject recently. You can view it here.

    Thanks and see you next time!

  • ION GNSS/CGSIC annual conference

    I realize the GIS world doesn’t revolve around GPS but I’m going to spend some space on it this month. Currently, I’m in Savannah, Georgia at the annual ION GNSS/CGSIC conference.

    This is where one can peer into the future of where GPS technology (and positioning technology in general) is heading. This is where all of the GPS and GNSS brainpower get together every year. There are a lot of military folks here. The GPS Chief Engineer (Col. David Goldstein), GPS Wing Commander (Col. David Madden), Boeing scientists (GPS satellite builders), Lockheed Martin scientists (GPS satellite builders) and all companies and organizations involved in designing and building GPS infrastructure are here. These are the true rocket scientists. I bet the average IQ would be a pretty good bowling score.

    The way this conference works is that the CGSIC meetings take place on Monday and Tuesday. The ION GNSS meetings take place on Wednesday through Friday.

    CGSIC is an acronym for the Civil GPS Service Interface Committee. CGSIC is coordinated by the US Coast Guard. According to its website, it’s the “recognized worldwide forum for effective interaction between all civil GPS users and the U.S. GPS authorities. It was established and chartered to identify civil GPS user needs (e.g. navigation, timing, and positioning) in support of the Department of Transportation’s (DOT) program to exchange information concerning GPS with the civil user community as part of the GPS “outreach” program. In fulfilling this responsibility, the CGSIC reports its activities to the National Space-Based Positioning, Navigation, and Timing (PNT) Executive Committee and the Office of the Assistant Secretary for Transportation”.

    The CGSIC meetings on Monday and Tuesday consist of briefings from government officials on the status of GPS and various related programs like NDGPS, WAAS, OPUS/CORS and many more. You can view the CGSIC meeting agenda here. There are also many user presentations from various government and commercial entities discussing how they are using GPS/GNSS in their work.

    I’ve been blogging about the meetings while I’ve been in Savannah. You can read my blog here. Of particular interest was the focus on RTK Networks in the Surveying, Mapping and Geosciences Session. RTK is an acronym for Real-Time Kinematic. Essentially, it’s real-time positioning at the centimeter level.

    With respect to GIS and infrastructure mapping, RTK Networks are one of the most significant advancements in GPS you will encounter over the next few years in the Geospatial business. They have the potential to significantly transform the accuracy of infrastructure data that is collected. If you want to learn more about them, you can read some of what I’ve written before about RTK Networks as well as the webinar I conducted on the subject.

    RTK Networks: The Wild, Wild West

    What RTK Users Want; Prospects for Network RTK (Rob Lorimer)

    Webinar – RTK Networks: What, Where, Why

    Here were the subjects discussed regarding RTK Networks at CGSIC:

    PANEL SESSION: Guidelines for Real Time GNSS Networks (RTN)
    A. Site Considerations – Dan Martin, NOAA’s National Geodetic Survey
    B. Planning & Design – Gavin Schrock, Washington State Reference Network
    C. Administration – Gary Thompson, North Carolina Geodetic Survey
    D. Best Methods for Users – Bill Henning, NOAA’s National Geodetic Survey
    Question & Answer Session with Speakers

    Interactive Sessions within Small Discussion Groups
    Group 1. CORS/OPUS
    Group 2. RTN Site Considerations and RTN Planning & Design
    Group 3. RTN Administration and RTN Best Practices for Users
    As I wrote in my blog, this was the place to be if one is interested in Real-Time Networks, from the user perspective to the administrator perspective. There’s a tremendous amount of interest and activity on the RTN space right now.

    While the CGSIC meetings are all about what’s happening now, the ION GNSS meetings are all about what’s going to happen in the future. At ION GNSS, researchers present the results of their hard work. The result of some of this research will be the technology we are using tomorrow.

    Be sure to check my ION GNSS blog. There will be some lag time, but it should all be up by early next week.

    Thanks and see you next week.