ABI Research’s competitive analysis evaluates GNSS IC vendors across innovation and implementation parameters
The GNSS market is slowly shifting in new directions, according to ABI Research. While the smartphone market continues to grow, new opportunities are also emerging in automotive, insurance, wearables, unmanned aerial vehicles (UAVs) and the Internet of Things (IoT).
Overall, the GNSS market is forecast to continue to grow strongly, with ubiquitous location and market-specific IC design as key differentiators.
In its latest competitive analysis of GNSS IC vendors, ABI Research evaluates a variety of innovation and implementation parameters to determine emerging competitive threats and technologies, the companies best positioned for success and those in danger of losing out.
Unchanged for the past three years, the market’s two top IC vendors remain Qualcomm and Broadcom, soon to be acquired by Avago. Both companies continually illustrate the ability to lead the way on cutting-edge innovation, which in turn drives their dominant market-share position, ABI Research said.
Beyond just GNSS, both companies also offer comprehensive location technology platforms in HULA (Broadcom) and Izat (Qualcomm), which will enable smartphone OEMs to begin offering ubiquitous location in 2016. Qualcomm’s work on LED/VLC and LTE Direct illustrates the gap that now exists between it and pure-play GNSS IC vendors.
u-blox, a well-established GNSS IC company, has shown continuous growth each year by implementing new technologies and making acquisitions, culminating in its first ever third place ranking, ABI Research said. The company continues to lead the way in its core markets, while also expanding into the emerging IoT space.
“The big surprise this year has been MediaTek dropping to fourth place,” said Patrick Connolly, principal analyst at ABI Research. “This is primarily due to a lack of new GNSS or indoor location products. However, this did not affect its IC market share, or its ability to win an important GNSS IC win with Fitbit in wearables. MediaTek has a history of delivering when its customers need new innovation. As a result, ABI Research expects new product announcements from the company in 2016, especially around indoor location.”
Ranking fifth, STMicroelectronics is seeing customers migrate to its TESEO III platform. Its modular, high-performance approach should also enable it to move beyond its traditional markets of automotive and recreational/fitness, especially as it has begun to leverage the company’s expertise in sensor fusion.
As new opportunities for GNSS continue to develop in markets such as wearables, IoT, personal tracking and UAVs, there will also be a number of new or emerging companies looking to claim a share in the stakes. Analysis findings point to the Chinese regional market as one such area that has potential to demonstrate strong growth trends in future years.
“There’s big opportunity for emerging Chinese start-ups, such as CEC Huada, to meet new, indigenous, market demand over the next 10 years, while also working their way toward becoming major international competitors,” concluded Connolly. “Additionally, Galileo Satellite Navigation, an emerging company focused in software GPS, is reporting impressive results in trials. As consumer electronics start supporting software GPS, it will be interesting to watch whether or not it can achieve volume shipments in 2016.”
These findings are part of ABI Research’s Location Devices Service, which includes research reports, market data, insights and competitive assessments.
Galileo Satellite Navigation Ltd. (GSN), an Israeli startup, is demonstrating a navigation solution that can “pull the sword out of the stone,” said Uri Michon, sales and marketing manager for GSN.
The company has developed its own GNSS software receiver, and is now in the final stage of integration to a Korean (long-term evolution) LTE integrated circuit (IC) manufacturer platform.
As opposed to a standard hardware receiver convention of one size fits all, GSN offers a tailor-made flexible solution that accommodates each customer’s use cases, performance needs and system resource tradeoff.
The receiver requires any regular RF front-end, simple glue logic and existing platform digital signal processor (DSP)/central processing unit (CPU). The receiver is hardware agnostic and has already been demonstrated working on CEVA, Cadence, ARM and Intel processors.
While reducing the need for an external IC, the customer gains the ability to install only the GNSS constellation required, reducing inventory and solution costs. The customer can also introduce upgrades (new constellation features) and updates when available.
GSN is targeting the cellular market, but the company said its flexibility and ability to create a low resource solution has its best fit for the rapdily evolving markets of machine-to-machine (M2M), the Internet of Things (IoT) and wearables.
Part 1 of this series appeared in the June Survey Scene newsletter, Part 2 appeared in the August newsletter, and Part 3 appeared in the October newsletter. Upcoming Survey Scene newsletters will carry additional columns in this series.
Basic Procedures and Tools for Ensuring GNNS-Derived Ellipsoid Heights Meet the Project’s Desired Accuracy
David B. Zilkoski
In Part 1 of this series, I discussed the basic concepts of GNSS-derived heights; the article discussed the three types of heights involved in determining GNSS-derived orthometric heights: ellipsoid, geoid, and orthometric.
Part 2 discussed guidelines for detecting, reducing, and/or eliminating error sources in ellipsoid heights. It focused on guidelines for establishing accurate ellipsoid heights in a local geodetic network. It discussed procedures that need to be followed to detect, reduce, and/or eliminate error sources to estimate accurate GNSS-derived ellipsoid heights, and procedures for evaluating published NAD 83 (2011) ellipsoid heights.
Part 3 in this series described the differences between a scientific gravimetric geoid model and a hybrid geoid model, and why it is important to use both geoid models in your analysis. It highlighted that the latest published United States National Geodetic Survey (NGS) hybrid geoid model, Geoid12B, is made consistent with the United States national vertical height reference frame, that is the North American Vertical Datum of 1988 (NAVD 88). It emphasized that this means a user will be consistent with NAVD 88 when using GEOID12B to estimate GNSS-derived orthometric heights, but it doesn’t guarantee that your GNSS-derived orthometric heights are accurate. It demonstrated how to use these geoid models and ellipsoid heights to identify potential issues with published NAVD 88 heights.
This column (the fourth in this series) will focus on basic procedures and tools that should be used to establish accurate GNSS-derived ellipsoid heights for a project. It will provide basic procedures for ensuring a project’s GNSS-derived ellipsoid heights are meeting the desired accuracy. The accuracy of the adjusted ellipsoid heights must be evaluated first, so if there is an issue with the difference between the GNSS-derived orthometric height and published NAVD 88 height, the user will know if the ellipsoid height or the orthometric height is the problem.
NGS has developed guidelines that address the establishment and densification of vertical control networks through the use of GNSS surveys and valid NAVD 88 orthometric control. NGS has documented these procedures in NOAA Technical Memorandum NOS NGS-59, titled “Guidelines for Establishing GNSS-derived Orthometric Heights (Standards: 2 cm and 5 cm). The document provides basic rules and procedures that need to be adhered to for computing accurate NAVD 88 GNSS-derived orthometric heights. However, before we can validate NAVD 88 height constraints used to estimate GNSS-derived orthometric heights, we first need to ensure that the GNSS-derived ellipsoid heights are accurate to the desired requirements. It is impossible to describe all situations in a short newsletter, so this column will address the basic procedures with a few caveats.
Validating Your GNSS Survey Project’s Ellipsoid Heights
Part 2 discussed guidelines for detecting, reducing and eliminating error sources in ellipsoid heights (NGS 58). It focused on evaluating published NAD 83 (2011) ellipsoid heights. This column will discuss a few basic procedures for analyzing a GNSS project’s data to ensure the desired ellipsoid height accuracy standard has been met.
GNSS data can be evaluated by analyzing repeat baseline differences, network loop closures and residuals from a minimum-constraint least-squares adjustment. It was noted in the second article that if GNSS users follow the NGS guidelines, they will reduce and/or eliminate errors in ellipsoid heights and, at a minimum, they will detect problems or errors in data. It was also mentioned that the basic concepts are very simple, but they all need to be followed exactly as prescribed. For example, “the observing scheme for all stations requires that all adjacent stations (baselines) be observed at least twice on two different days and at two different times of the day.”
GNSS can provide “absolute” and relative positioning information much easier, faster and more precisely than some classical techniques. However, the wrong station can still be occupied, the height of the antenna can be measured wrong or incorrectly entered during the baseline reduction processing phase, the receiver can malfunction, an abnormal atmospheric condition can cause large errors in the height component, or some “unknown Gremlin” can be causing an error source.
Classical techniques of establishing horizontal and vertical control used networks that consisted of many loops, triangles and braced quadrilaterals. This design provided enough redundant observations to detect data outliers. NGS guidelines for establishing GNSS-derived heights were designed with this same concept in mind. Since all baselines must be repeated and adjacent station observed, analyzing repeat baseline differences, loop closures and residuals from minimum-constraint least-squares adjustments are very effective analysis tools for detecting data outliers.
Comparing Ellipsoid Height Differences from Repeat Baselines
This procedure is very simple: subtract one ellipsoid height difference from another, for instance, the ellipsoid height difference from baseline A to B on day 1 minus the ellipsoid height difference from baseline A to B on day 2. If this difference is greater than 2 cm, one of the baselines must be observed again. Comparing ellipsoid height differences from repeat baselines is a very simple procedure, but it’s also one of the most important. Many users complain about having to repeat baselines, but requiring an extra occupation session in the field can often save many days of analysis in the office. In addition, repeating the baseline provides the redundancy necessary to obtain the desired relative accuracy of the survey (that is, repeat measurements help to derive a more accurate result than a result derived from a single measurement).
Figure 1 depicts the network design of a 2015 North Carolina Geodetic Survey (NCGS) GNSS Height Modernization Project. The data from this GNSS project was provided to me by the North Carolina Geodetic Survey (James G. Gay, chief of Western Field Operations, North Carolina Geodetic Survey, Division of Emergency Management/Risk Management, North Carolina Department of Public Safety, 2090 US 70 Highway, Swannanoa, NC 28778). It should be noted that these results should be considered preliminary and have not been finalized by NCGS personnel. This is an excellent example of a GNSS project that followed the guidelines outlined in NGS 58. The network design includes short baselines with many loops. The average length of baselines is 2.9 km, the maximum baseline is 13.5 km, and there are 465 baselines connected to 182 stations. All baselines were repeated, making the analysis easy.
Figure 1. Plot depicting the Network Design of the NCGS Rowan County Height Modernization GNSS Project.
Figure 2 is a plot of the differences between repeat baselines. First, it should be noted that most baselines are less than 5 km and most repeat baselines differences are less than +/- 2 cm. There are some outliers, which is not unusual when performing GNSS surveys even when following all guidelines outlined in NGS 58. What is important is that these outliers are identified, and then additional observations are performed to meet the guidelines and obtain the desired accuracy of the survey.
The repeat baseline procedure helps to identify these outliers such as the baselines highlighted in figure 2. As noted in figure 2, the largest outliers are on two different baselines. These baselines should be re-observed to meet the NGS 58 guidelines. The requirement is to repeat the baseline on different days and at different time of the day. The reason for the requirement is to get two observations under different conditions and different satellite geometry. The user needs to determine which baseline is the outlier so he can ensure that he has two baselines with different satellite geometry. When a network is properly designed with short baselines and many loops, the results from a minimum-constraint least-squares adjustment can help identify the outlier.
Figure 2. Plot of repeat baselines for the NCGS Rowan County Height Modernization GNSS Project (does not include re-observations of repeat baselines that did not meet the 2 cm guideline).
Analyzing Loop Closures
Loop closures can be used to detect “bad” observations. If two loops with a common baseline have large closures, this may be an indication that the common baseline is an outlier. The following statement appeared in Part 2: “Please be aware that repeatability and loop closures do not always disclose all problems, and that is why it is important to adhere to the procedures outlined in NGS’ publications.” So why is it okay to use loop closures now?
Since users must repeat baselines on different days and at different times of the day, there are several different loops that can be generated from the individual baselines. If a repeat baseline difference is greater than 2 cm, then comparing the loop closures involved with the baseline may help determine which baseline is the outlier. As previously stated, according to NGS 58 guidelines, if a repeat baseline difference exceeds 2 cm, one of the baselines must be observed again, and baselines must be observed at least twice on two different days and at two different times of the day. If it can be determined which baseline is the potential outlier, the user will know which time of the day to re-observe the baseline. Therefore, loop closures can be very helpful in isolating errors when the user followed all of the guidelines outlined in the NGS 58 document.
Plotting Ellipsoid Height Residuals from Least Squares Adjustments
It is important that during the analysis of the GNSS-derived ellipsoid heights, the user performs a minimum-constraint least-squares adjustment and identifies potential outliers. This ensures that the GNSS-derived ellipsoid heights meet the user’s desired standards. This is not a complex procedure if the user knows how to perform a least-squares adjustment of GNSS data. Explaining least-squares adjustments is beyond the scope of this column. Today, most GNSS manufacturers provide support software that includes performing least-squares adjustments. NGS also provides software tools for validating data formats and performing adjustments. These tool can be found here. I used these tools to analyze and adjust the survey data of the Rowan County GNSS Height Modernization Project.
If users follow NGS guidelines and evaluate all repeat baselines, the adjustment results should confirm what has already been determined. For example, if a repeat baseline indicates a large difference between two vectors, then typically one of the residuals of one baseline should be larger than the other. Following NGS guidelines usually provides enough redundancy for the adjustment process to detect outliers and usually apply the residual to the appropriate observation, that is, the bad vector.
Like comparing repeat baselines, analyzing ellipsoid height residuals is also important. During this procedure, the user performs a 3D minimum-constraint least-squares adjustment of the GNSS survey project (constrain one latitude, one longitude and one ellipsoid height), plots the ellipsoid height residuals, and investigates all residuals greater than 2 cm.
Figures 3 and 4 depict the dU residuals from a least-squares adjustment of the Rowan County Height Modernization Project. NGS’ adjustment program provides the vector residuals in dX, dY and dZ; and dN, dE and dU (local geodetic horizon coordinate system). dU residuals are not the same as dh residuals, but for all practical purposes can be analyzed just like dh residuals. Looking at Figures 3 and 4, a few items should be noted. First, all dU residuals are less than 2 cm except for five baselines. Four of the five baselines had repeat baselines that exceeded the 2 cm repeat baseline requirement (see Figure 2). For example, the plot of repeat baseline differences indicated that baseline between station 296 and 442 disagreed by 5.25 cm (see Figure 2). The plot of dU residuals (Figure 4) from the least-squares adjustment shows that one of the baseline’s residual is -4.4 cm and the other is 0.9 cm. The adjustment results are indicating which baseline needs to be re-observed to meet the guideline’s requirement of repeat baselines on two different days at two different times of the day. That’s all there is to it, when the user follows NGS guidelines exactly as prescribed.
Figure 3. Plot depicting absolute dU residuals from the NCGS GNSS Height Modernization Project (does not include re-observations of repeat baselines that did not meet the 2 cm guideline).Figure 4. Plot of all residuals from the NCGS Rowan County GNSS Height Modernization Project (does not include re-observations of repeat baselines that did not meet the 2 cm guideline).
The reader may have noticed that one large residual on the residual plot, baseline 442 to 253 (11.5 km), did not show up as a large different on the repeat baseline plot. There are several reasons why this could occur. For example, the stations involved in the baseline are not adjacent stations, so the baseline wasn’t repeated; the repeat baseline closure was large, but not greater than 2 cm; or the pair of stations are involved with many vectors and the one vector is inconsistent with the other vectors. Regardless of the reason, if there’s enough redundant observations to and from a station and the repeat baselines don’t indicate a problem, then the adjustment is doing what it’s designed to do; that is, detecting outliers and reducing their influence on the final adjusted height. In this particular case, the repeat baseline closure between stations 442 and 253 was 1.84 cm, which meets the NGS 58 guideline of 2 cm. The adjustment uses all of the data to determine the best set of coordinates. Based on the repeat baselines and loops surrounding the two stations, the adjustment indicated that one of the vectors fits better with the other vectors surrounding the two stations. Per the requirement of NGS 58 guidelines, the NCGS re-observed all five baselines with large residuals.
After all outliers are detected and removed from the adjustment, the user should compare the adjusted ellipsoid heights with the latest published ellipsoid heights, that is, NGS published NAD 83 (2011) ellipsoid heights. Figures 5 and 6 are plots of the adjusted ellipsoid heights from a minimum-constraint least-squares adjustment minus the NAD 83 (2011) ellipsoid heights. Since this was a minimum-constraint adjustment (that is, only one latitude, one longitude and one ellipsoid height value were constrained), a bias shift based on the average differences was removed from all differences. Most of the differences agree within +/- 2 cm. There are several that are greater than +/- 2 cm, but only one is greater than +/- 4 cm.
As mentioned in Part 2, many of the older GPS survey projects that were part of the NAD 83 (2011) network adjustment were not Height Modernization projects and were not performed following the NGS 58 guidelines. That is, most baselines are greater than 10 km and were not repeated. Therefore, in my opinion, many of the published ellipsoid heights local-height accuracies may be optimistic. The user should consider this when determining whether their results are more accurate than the published values. NGS’ Constrained Adjustment Guidelines for incorporating GNSS project data into NAD 83 (2011) state, “As a general rule, if the adjusted values of the constrained coordinates of a station shift by more than 2 cm horizontally and/or 4 cm in height, its horizontal coordinates and/or ellipsoid height, respectively, should be unconstrained.”
The stations that have height differences greater than 4 cm should be investigated. In addition, stations that have large relative height differences (greater than 4 cm) between closely spaced neighbors should also be investigated. For example, station Jockey’s difference is 3.6 cm, and two of its neighbors’ differences are only -0.5 cm. The relative difference exceeds 4 cm [3.6 cm – (-0.5 cm)] between two closely spaced stations.
Figure 5. Plot of adjusted ellipsoid height minus published NAD 83 (2011) Ellipsoid Heights (the number is the difference for that particular station; units = cm).Figure 6. Plot of adjusted ellipsoid height minus published NAD 83 (2011) published heights.
It is important to understand the quality of the adjusted ellipsoid heights. When analyzing the project’s ellipsoid heights, the user should compute the local ellipsoid height accuracy values. Part 2 discussed NAD 83 (2011) network and local accuracies. NGS’ adjustment program has an option of computing network and local accuracy values.
Figures 7 and 8 are plots of NCGS Rowan County GNSS Height Modernization median local ellipsoid height accuracy values. Stations that have local ellipsoid height accuracy values greater than 2 cm should be investigated. Figure 7 highlights the two largest median local ellipsoid height values [Camping (3.19 cm) and Buffalo 2 (2.46 cm)]. The observations and residuals of the baselines in the area should be closely analyzed.
Figure 8 is a plot of the local ellipsoid height accuracy value with the absolute dU residual values. If the user follows all of the NGS 58 guidelines, then all baseline residuals should be small (less than 2 cm). In this project, the largest “dU” residual is 1.86 cm. Saying that, the network design could be modified to try to improve a station’s median local ellipsoid height accuracy value.
For example, station Buffalo 2 has a median local ellipsoid height accuracy value of 2.46 cm (see Figure 7). It’s only involved in one loop, and it’s relatively large. The loop has five baselines consisting of lengths of 13.5 km, 9.8 km, 7.9 km, 4.6 km and 0.7 km. Two of the baselines lengths are greater than the guideline’s average baseline recommendation of 7 km, but all repeat baselines meet the 2 cm guidelines, and all residuals are “reasonable.” Adding another baseline between two different stations to create two smaller loops from the one larger loop would decrease the size of the loop and increase the redundancy in the network.
In this particular case, station Buffalo 2 has a published NAD 83 (2011) ellipsoid height, and the difference between the adjusted height and the published height is only 1.1 cm (Figure 5), indicating the new survey is consistent with the old survey. Station Camping also has a published NAD 83 (2011) ellipsoid height, and the difference between the adjusted ellipsoid height and published height is -1.9 cm (Figure 5). Once again, this indicates that the Rowan County GNSS survey is consistent with the previous survey.
This column focused on describing procedures for analyzing a project’s GNSS-derived ellipsoid heights. As previously stated, it important to ensure that your GNSS-derived ellipsoid heights meet the desired accuracy of the project before using the survey data to estimate GNSS-derived orthometric heights.
Figure 7. Plot of NCGS Rowan County Height Modernization project’s median local ellipsoid height accuracy values.Figure 8. Plot of NCGS Rowan County Height Modernization project’s median local ellipsoid height accuracy values and absolute dU residuals.
So far, this series has addressed the following topics:
basic concepts of GNSS-derived heights
NGS’ guidelines for establishing GNSS-derived ellipsoid heights (NGS 58)
differences between hybrid and scientific geoid models, and
procedures and tools for detecting GNSS-derived ellipsoid height data outliers.
These four columns were meant to provide the reader with basic concepts and procedures for estimating GNSS-derived ellipsoid heights.
My next column, which will appear in the February 2016 Survey Scene newsletter, will discuss procedures for estimating GNSS-derived orthometric heights. Determining valid NAVD 88 published heights is very important when using GNSS data and geoid models to estimate GNSS-derived orthometric heights. NGS has documented these procedures in NOAA Technical Memorandum NOS NGS-59. The NGS 59 guidelines are separated into three basic rules, four control requirements and five procedures that need to be adhered to for computing accurate NAVD 88 GNSS-derived orthometric heights. The next column will address the NGS 59 guidelines.
Topcon Positioning Group is collaborating with DAQRI, an augmented reality company, on wearable technology designed to change the way construction and survey professionals interface with the job site.
DAQRI is the creator of the DAQRI Smart Helmet, an industrial-grade wearable that seamlessly connects humans to their work environments by providing information about the world around them.
Topcon and DAQRI will work together to create a solution designed to make workers on the job safer and more productive through the use of augmented reality technologies. They plan to do this by integrating DAQRI’s hardware and software solutions with Topcon positioning solutions.
The DAQRI Smart Helmet was designed for the industrial workplace. It includes an advanced sensor package, an intuitive user interface that requires zero calibration, and a battery that lasts a full shift.
Powered by 4D Studio, DAQRI’s software platform for positioning, the partnership will allow construction workers to view information from their projects in the real-world work environment to make their workflows safer and more efficient.
The collaboration is designed to bring wearable technology to a wider AEC (architecture, engineering and construction) user base, empowering the wearer with a hands-free tool that can be used on the job, Topcon said in a news release.
“DAQRI is a leader in providing solutions in outdoor environments, which will meld well with our positioning and software innovations,” said Jason Hallett, Topcon vice president of product management. “It’s the first step in utilizing our mutual synergies to develop rugged, heads-up display technology for our marketplace.”
“We are committed to developing innovative solutions that power the future of work and Topcon is at the forefront of the industry with some of the most innovative products that are being used by millions of workers across a variety of environments,” said Matt Kammerait, vice president of product, DAQRI. “This makes them the perfect partner to integrate the Smart Helmet into existing workflows. We look forward to seeing how our partnership re-defines the nature of ‘work,’ by setting a new standard for wearables in the AEC space.”
The three BeiDou satellites launched this year are sending twice as many signals as their predecessors, reports the Economic Times, following tests of the orbits and key technology.
The 18th and 19th satellites are the first BeiDou satellites that can communicate with each other, helping with distance measurements, said Wang Ping, chief engineer on the project.
After the tests, they are working as intended and in all weather, according to a newsletter from the China Academy of Space Technology.
AeroVironment has received an order valued at $13 million for RQ-20A Puma AE small unmanned aircraft systems (UAS) and initial spares packages for the United States Marine Corps.
The Marine Corps employs the Puma AE system as the long-range solution for its small unit remote scouting system (SURSS), complementing the AeroVironment RQ-11B Raven and RQ-12A Wasp AE UAS.
The Puma AE unmanned aircraft system delivers situational awareness directly to its operator in ground, to help provide information superiority on the battlefield.
AeroVironment received the order from ADS Inc. on behalf of the U.S. Marine Corps through the Defense Logistics Agency Tailored Logistics Support program. Delivery is scheduled within 12 months.
The Puma AE weighs 13.5 pounds, operates for more than 210 minutes at a range of up to 15 kilometers, and delivers live, streaming color and infrared video as well as laser illumination from its pan-tilt-zoom Mantis i23 AE gimbaled payload.
Launched by hand and capable of landing on the ground or in fresh or salt water, the Puma AE provides portability and flexibility for infantry, littoral or maritime reconnaissance operations.
A proposed national drone registration system should be based on the pilot, not the craft, recommends an FAA task force. It should also be free, electronic and immediate, and not apply to UAVs weighing 250 grams or less.
In October, U.S. Transportation Secretary Anthony Foxx and Federal Aviation Administration (FAA) Administrator Michael Huerta announced the creation of the task force to develop recommendations for a registration process for unmanned aircraft systems (UAS).
The Task Force agreed that it was outside its scope to debate the Department of Transportation (DOT) Secretary’s decision to require registration of sUAS or the legal authority for the implementation of such a mandate.
Immediately following the DOT’s announcement in October, the FAA brought together retailers, pilots, industry representatives and others to talk about the proposal and submit comments on how the system should work.
Task force members interviewed FAA officials, met for three days and prepared final recommendations. They agreed on three basic requirements: Owners must fill out an electronic form, immediately receive a certificate of registration and number for use on all UAVs they own, and mark all applicable drones with a registered number.
The Task Force recommendations for the registration process are:
Fill out an electronic registration form through the web or through an application (app).
Immediately receive an electronic certificate of registration and a personal universal registration number for use on all sUAS owned by that person.
Mark the registration number (or registered serial number) on all applicable sUAS before their operation in the National Air Space (NAS).
The Task Force recommended an exclusion from the registration requirement for any small unmanned aircraft weighing a total of 250 grams or less. The exclusion was based on a maximum weight that was defined as the maximum weight possible including the aircraft, payload, and any other associated weight. In manned aircraft terms, it is the “maximum takeoff weight.”
Jackson Labs Technologies Inc. has made available the M12M Replacement Receiver GNSS module that is form-fit-function compatible to the legacy Motorola M12M and M12+ timing and navigation receivers. It uses an eighth-generation GNSS timing-enabled receiver allowing 72 GNSS-channel reception with any two GNSS systems being received simultaneously.
The M12M adds configurability via USB ports as well as dual in-line package (DIP) switches and various status displays. GPS, GLONASS, BeiDou, QZSS and SBAS (WAAS/EGNOS/MSAS/GAGAN) signals can be received.
The module supports NMEA, Motorola binary and u-blox binary, as well as SCPI (GPIB) communication protocols for easy configuration and monitoring, and is designed to allow plug-and-play retrofit of equipment designed for the legacy Motorola receivers, as well as provide an easy design-in for new customer applications, the company said.
The M12M is certified to operate as a plug-and-play upgrade to legacy equipment such as the Symmetricom/Microsemi XLI server, as well as the Jackson Labs Technologies Fury GPSDO, requiring no setup or configuration to operate in those products, and can thus be used to retrofit products for GLONASS/BeiDou compatibility. In the process, the module enhances all performance parameters such as time to first fix; position, velocity and timing accuracy; tracking sensitivity; the addition of SBAS (differential compensation) capability; and the addition of external interfaces such as USB and a synthesized frequency output.
The module supports a satellite tracking sensitivity of down to -167 dBm, allowing indoor reception in typical environments, a 1PPS output with better than 5-nanosecond real-mean-squared (rms) stability (quantization corrected), and a positioning accuracy of typically better than 0.3 meters rms (survey-in) or better than 0.7-meter rms horizontal even in high-dynamic environments such as aircraft missions.
Dynamic auto Kalman filter configuration software allows using changing Kalman filter parameters in real time for improved accuracy, with filter parameters being automatically set dependent on actual mission dynamics. The GNSS timing receiver also supports Auto Survey (Survey-in) operation with Position Hold mode and TRAIM, allowing single-satellite timing reception in challenged or denied stationary environments.
The module integrates a UTC (GNSS)-synchronized NCO synthesizer with buffered output that can generate a user-adjustable frequency from 0.25 Hz to over 10 MHz with extreme frequency accuracy when locked to the satellites. Additional features include operation from various power sources such as USB, or 3V via the M12M compatible connector, as well as a 7-segment LED status display, and numerous DIP switches for easy software-less configuration of the operating modes and desired GNSS systems to be enabled, Jackson Labs said. The module displays Satellite Status information including signal strengths and systems received, and can thus be used as a handheld antenna- and satellite signal distribution-system monitor.
Various optional programs can be used to configure, control and monitor the unit such as GPSD/NTP, GPSCon, Z38xx, u-blox uCenter, TimeKepper, TeraTerm Pro, WinOncore-12 and others. The industry-standard SCPI software interface supports easy-to-use English-language commands such as GPS?, HELP?, and others to monitor and configure the unit, while all advanced GNSS receiver functions such as capturing carrier phase data, assisted start, satellite setup and gating, and health monitoring features are also supported.
M12M Replacement Receiver module samples ship from stock, and are priced at $220 each.
CACI International has released SkyTracker, a precision system to protect high-value assets and support public safety against the escalating threat posed by the inadvertent or unlawful misuse of unmanned aircraft systems (UAS).
SkyTracker’s UAS detection, identification, and tracking system uses the drone’s radio links to precisely identify and locate UAS flying in banned or protected airspace, and has the unique capability to locate UAS ground operators. This proprietary CACI technology has been demonstrated to address a variety of UAS threat scenarios. The system is widely applicable, from protecting airports to safeguarding critical infrastructure or events — anywhere UAS pose a potential risk to people or assets.
On Oct. 7, the FAA announced a Pathfinder agreement with CACI to test SkyTracker in the airport environment to ensure successful operation without disruption of airport communications.
SkyTracker accurately detects, identifies, and tracks UAS threats. The system’s mitigation capability provides responders with precise information in a defined geographic location in order to initiate countermeasures that, unlike other technologies, do not interfere with legitimate electronics or communications systems in the area, or with UAS that are being operated responsibly as determined by the U.S. government.
The SkyTracker system design is modular and scalable for application in different environments. It can protect high-value assets in geographically compact locations such as government buildings, embassies and stadiums, as well as provide wide-area defense of airports, military bases and areas under temporary flight bans such as locations experiencing forest fires. SkyTracker provides continuous, automated monitoring, day or night, in any weather condition.
“CACI’s SkyTracker system provides our customers with the unique capability to precisely locate unmanned aircraft systems and their ground operators. Our system has been demonstrated to address a variety of UAS threat scenarios,” John Mengucci, CACI’s chief operating officer and president of U.S. Operations, said. “In addition to the protection of airports, an effort undertaken in our recently announced research and development agreement with the federal government, SkyTracker has broad applications in the protection of critical infrastructure, stadiums, events, or anywhere drones pose a potential risk to people or assets.”
“CACI is proud to advance our SkyTracker solution to address the rapidly escalating threat posed by the misuse of unmanned aircraft systems,” said CACI President and CEO Ken Asbury. “The development of innovative technological solutions in response to complex security threats is in our DNA. We built SkyTracker to address one of the most complex challenges facing those responsible for protecting critical infrastructure.”
CACI provides information solutions and services in support of national security missions and government transformation for intelligence, defense, and federal civilian customers. A Fortune magazine World’s Most Admired Company in the IT Services industry, CACI is a member of the Fortune 1000 Largest Companies, the Russell 2000 Index, and the S&P SmallCap600 Index. CACI provides dynamic careers for over 16,300 employees in 120 offices worldwide.
The European Space Agency (ESA) has named Paul Verhoef its new Director of Galileo Programme and Navigation-Related Activities. Verhoef, former coordinator for Galileo activities with the European Commission, was named as one member of a new senior leadership team after a special meeting of the ESA Council in Paris on Nov. 21.
At the weekend meeting, the agency selected several new managers for key positions. The new leadership team is expected to start work in early 2016.
Space Applications
Director of Telecommunications and Integrated Applications (D/TIA), Magali Vaissiere
Director of Galileo Programme and Navigation-Related Activities (D/NAV), Paul Verhoef
Science and Exploration
Director of Science (D/SCI), Alvaro Giménez Cañete
Director of Human Spaceflight and Robotic Exploration Programmes (D/HRE), David Parker
Space Technology and Operations
Director of Technical and Quality Management (D/TEC), Franco Ongaro
Director of Operations (D/OPS), Rolf Densing
Administration
Director of Internal Services: Human Resources, Facility Management, Finance and Controlling, Information Technology (D/HIF), Jean Max Puech
Director of Industry, Procurement and Legal Services (D/IPL), Eric Morel de Westgaver
A Wide-Area Multi-Application PNT Resiliency Solution
By Stephen Bartlett, Gerard Offermans and Charles Schue
INNOVATION INSIGHTS with Richard Langley
WHERE HAVE ALL THE SYSTEMS GONE, long time passing?
Radionavigation systems, that is (and apologies to Pete Seeger). If we look at the 1990 Federal Radionavigation Plan (FRP), published by the U.S. Departments of Transportation and Defense, as I did in this column in March 1992, we see that there were 10 radionavigation systems in use by different user segments: Loran-C, Omega, very high frequency (VHF) Omnidirectional Range/Distance Measuring Equipment, Tactical Air Navigation, the Instrument Landing System, the Microwave Landing System, Transit, aviation radiobeacons, marine radiobeacons and GPS.
The latest FRP, issued in 2014, includes only seven or six and a half when you consider that marine radiobeacons were mostly phased out in the intervening years. Systems were shut down because with the advent of GPS, they were considered to be redundant. While there were attendant cost savings, the closure of the various systems has resulted in a dangerous virtual sole dependence on GPS for navigation without any backup.
Transit, was the first to go. It consisted of a constellation of six or seven active satellites in circular, polar orbits at altitudes of roughly 1,100 kilometers. The satellites transmitted signals on 150 and 400 MHz, and receivers measured the integrated Doppler frequency shift of the received signals. Transit was terminated at the end of 1996.
Transit was followed by the Omega hyperbolic navigation system. Omega consisted of eight stations around the globe transmitting time-shared carrier-wave signals on four frequencies between 10.2 and 13.6 kHz. The Omega system was closed down in September 1997.
The marine radiobeacons have been mostly shut down in recent years, although aeronautical beacons continue to operate. Radiobeacons are nondirectional transmitters that operate in the low- and medium-frequency bands. Some marine radiobeacons became Differential GPS stations and subsequently part of the Nationwide DGPS network. That network is being scaled back to provide only coastal and Great Lakes coverage.
And that brings us to Loran-C. Like Omega, it was also a hyperbolic navigation system. A receiver measured the difference in times of arrival of pulses transmitted at 100 kHz by a chain of three to five synchronized stations separated by hundreds of kilometers. At one time, the operation of Loran-C was the responsibility of the U.S. Coast Guard. Together with a number of host nations, the Coast Guard operated 17 chains of stations around the world, including one jointly operated with Russia. These stations provided coverage of the coastal areas of North America and the U.S. interior, northern Europe, the Mediterranean Sea, the Far East and the Hawaiian Islands. Additionally, several other countries operated Loran-C stations. Although moves were already underway to update the Loran technology, the Obama administration decided to terminate Loran-C in the U.S., considering it to be an unnecessary antiquated system. The Coast Guard terminated the transmission of all U.S. Loran-C signals in February 2010 and began dismantling stations.
So, is there no longer a viable non-GNSS alternative or backup system for GPS navigation? While there are other possibilities for time transfer, one of GPS’s other applications, there is no widely available substitute navigation system. Currently. However, as we will see in this month’s column, a new version of Loran — Enhanced Loran or eLoran — has been developed and is being tested on the U.S. east coast. Not your father’s Loran, eLoran seems to be the perfect solution for PNT resiliency.
Telecommunications, energy, finance and transportation are just four among the many critical infrastructure / key resource sectors that have come to rely solely on GPS for positioning, navigation and timing (PNT). In fact, the U.S. Department of Homeland Security (DHS) has determined that 11 of the 16 critical infrastructure sectors in the U.S. are critically dependent on GPS for timing. While we can start to imagine what a day without GPS might be like, we’d really rather not — it would be somewhat depressing and really quite dangerous. We would rather imagine a day when there is a wide-area complementary solution available that protects and augments GPS. In this article, we will delve into such a solution: Enhanced Loran, or eLoran for short. We will explain how it works, debunk some myths, speculate on how it could be used in the U.S. (and abroad), highlight the state of current technology and discuss the state of the possible. We will also summarize the state of eLoran in the world and where things might go from here.
What Is eLoran?
eLoran is the latest in the longstanding and proven series of low-frequency, LOng-RAnge Navigation (LORAN) systems, one that takes full advantage of 21st-century technology. It meets the accuracy, availability, integrity and continuity performance requirements for maritime harbor entrance and approach maneuvers, aviation non-precision instrument approaches, land-mobile vehicle navigation and location-based services. It’s a precise source of time (phase) and frequency. Additionally, eLoran provides user bearing (azimuth) and has built-in integrity. In full disclosure, however, eLoran is only a 2D positioning solution unless integrated with a simple altimeter.
eLoran is a low-frequency radionavigation system that operates in the frequency band of 90 to 110 kHz. eLoran is built on internationally standardized Loran-C, and provides a high-power PNT service for use by all modes of transport and in other applications. eLoran is an independent dissimilar complement to GNSS. It allows GNSS users to retain the safety, security and economic benefits of GNSS even when their satellite services are disrupted.
eLoran uses pulsed signals at a center frequency of 100 kHz. The pulses are designed to allow receivers to distinguish between the groundwave and skywave components in the received composite signal. This way, the eLoran signals can be used over very long ranges without fading or uncertainty in the time-of-arrival (TOA) measurement related to skywaves.
Although eLoran is based upon Loran-C, it has key differences:
All transmissions are synchronized to UTC (like GPS)
Time-of-transmission control
The ability to use differential corrections (similar to DGPS)
Receivers use “all-in-view” signals
Includes one or more Loran data channels that provide: Low-rate data messaging, added integrity, differential corrections (dLoran and/or DGPS) and other communications including navigation messages.
An eLoran receiver measures the TOA of the eLoran signal:
TOA = TOR – TOT = PF + SF + ASF + ∆Rx
where TOR is time of reception, TOT is time of transmission, PF is the primary factor (propagation delay through air), SF is the secondary factor (propagation delay over sea), ASF is the additional secondary factor (propagation delay over terrain) and ∆Rx is the delay due to receiver electronics and cables.
The primary and secondary factors are well-defined delays and can be calculated as a function of distance. The additional secondary factor delay is mostly unknown at the time of installation. Fortunately, the ASFs remain very stable over time. Any fine changes in ASF over time may be compensated for by one or more differential eLoran reference station sites providing corrections over the Loran data channel.
When eLoran is used for positioning, a minimum of three eLoran transmitting sites are needed to calculate a two-dimensional position fix and time. Time (phase) and frequency can be derived from a single transmitting site as well. With three sites, timing can be derived while a receiver is in motion. An integrated eLoran/GPS receiver can take advantage of combinations of eLoran and GPS transmissions to develop a PNT solution. Any additional measurements provide a means to improve the solution’s accuracy (using weighted least squares) or to protect the solution’s integrity (by receiver-autonomous integrity monitoring).
To achieve the highest accuracy levels, the user receiver corrects its TOA measurements with the published ASF values for the area and differential eLoran corrections received through the Loran data channel. ASF maps for specific geographic areas are distributed to users in a receiver-independent data format that is currently being standardized by the Radio Technical Committee for Maritime Services’ (RTCM’s) Special Committee (SC) 127 on eLoran. The ASF map data would be published by the service provider responsible for aids to navigation.
As described before, the measured ASF values remain stable over long periods of time. Any small changes in the published ASFs due to changes in propagation path characteristics or transmitter-related delays will be compensated for by differential corrections. For this, a differential eLoran reference station site is deployed within 20 to 30 miles (32 to 48 kilometers) of the area of interest. The reference station compares its measured ASFs against the published values and broadcasts corrections to the users through the Loran data channel. Figure 1 shows the principle of differential eLoran positioning in a maritime environment and is representative of its use in other modalities as well.
Figure 1. Overview of a representative eLoran system.
eLoran meets the application requirements shown in Table 1. While unaided, Loran-C does not meet the requirements for a multi-modal, redundant PNT system, specifically the position accuracy requirement. The U.S. first developed eLoran to reduce the positioning error and to enable the system to meet modal performance requirements.
Table 1. eLoran system performance requirements.
eLoran Applications
We are staunch advocates of GPS and believe it should be fully funded, kept technically advanced, protected, toughened and augmented. When GPS is available and trustworthy, it should be used. However, no technology is failsafe, and prudent users should not rely on a sole source for their PNT needs. GPS has been called “a single point of failure” for much of the U.S. economy and critical infrastructure. Applications and requirements vary widely from wireless network communications of ± 1.5 microseconds, to maritime harbor entrance and approach requirements of ± 20 meters, to phasor measurement unit requirements in the electric power grid of ± 500 nanoseconds.
It is important to recognize the challenge of providing assured PNT while also taking advantage of the efficiencies gained by implementing a common solution across all sectors, industries and users. Point solutions can provide complementary PNT for specific individual or modal needs, and any resilient PNT ecosystem includes multiple levels of redundancy.
Some key application areas in which eLoran can provide complementary PNT are telecommunications, energy, finance and transportation. We believe these will be some of the first sectors to adopt and exploit eLoran as a component of their critical infrastructure protection and possibly as a co-primary PNT solution alongside GPS.
Telecommunications Sector. A March 2014 letter from the Alliance for Telecommunications Industry Solutions (ATIS) to the National Security Telecommunications Advisory Committee contained an attached document, Recommended Updates to Telecom Vulnerability to Loss of GPS Signals Documentation, that outlined three areas of concern that ATIS has identified relating to the exposure of commercial communications systems to a loss of the GPS signal. Included in the documentation was the statement: “With the Loran systems decommissioned, GPS is currently the only technology that can meet synchronization requirements for E911 as there is no other widely available access to UTC time of day in the United States.” eLoran’s Loran data channel provides the UTC time-of-day information that the telecommunications industry seeks, as well as providing complementary timing (phase) and/or frequency solutions that would mitigate ATIS’s concerns about: (1) the size of the area and duration effects of a GPS outage, (2) the effects of spoofing, (3) the inability of oven-controlled crystal oscillators (OCXOs) to maintain phase alignment for 24 hours at 1.5 microseconds, and (4) the phase performance of OCXOs in varying temperature environments.
The European Telecommunications Standards Institute Primary Reference Clock mask is one tool used by the telecommunications industry to determine the quality of timing signals in telecommunication applications. Figure 2 shows that eLoran is able to meet maximum time interval error (a measurement of wander or time stability) requirements, often outperforming GPS. Testing was performed independently in a cooperative effort between the United Kingdom National Physical Laboratory and Chronos Technology Ltd., UrsaNav’s reseller in England.
Figure 2. Maximum time interval error plot of eLoran and GPS.
Energy Sector. At present, GPS is the only time source for phasor measurement unit (PMU) (also known as synchrophasor) and frequency data recorder (FDR) sensors used to collect data that measures the state of an electrical system and manages power quality. PMUs/FDRs are a necessary component of the movement to a smart-grid approach to improve energy efficiency on the electrical grid and in businesses and homes. PMUs and FDRs cease to work if the GPS signal is lost or unstable. In 2013, UrsaNav began working with the University of Tennessee at Knoxville (UTK) to demonstrate the capability of eLoran, alongside GPS, to provide the necessary timing accuracy for UTK’s high-precision FDRs to collect synchrophasor data from the U.S. power grid. The required accuracy of the timing reference source is ± 500 nanoseconds, needed by each device performing synchrophasor measurements.
The laboratory setup in Bedford, Mass., used side-by-side FDRs: one using a GPS receiver and one using an eLoran receiver. Other than replacing the GPS receiver with an eLoran receiver in one of the FDRs, no other changes were made. The eLoran signals were being transmitted from a former U.S. Coast Guard (USCG) Loran Support Unit in Wildwood, N.J., more than 300 miles (483 kilometers) from our Bedford laboratory.
“Raw” eLoran was used for the test, that is, with no differential corrections nor continuous receiver antenna calibration. Figure 3 shows the resultant frequency and phase angle comparisons between GPS and eLoran. Green is eLoran; black is GPS. Frequency comparisons are on the left, top and bottom. Phase angle comparisons are on the right, top and bottom. The bottom left graph is a blow-up of the area encircled in red in the top left graph. The bottom right graph is a blow-up of the area encircled in red in the top right graph. In both cases, eLoran performs on par with GPS.
Figure 3. Frequency data recorder outputs from GPS and eLoran.
Financial Sector. A European Securities and Markets Authority (ESMA) report, dated May 22, 2014, indicates that the majority of trading venues are already coordinated with GPS time, and further states that the deployment of these systems might be costly and technically challenging. ESMA’s view is that each trading venue and market participant should rely on an atomic clock to issue timestamps. An eLoran timing alternative would be less costly, less technically challenging, and, when used in concert with other solutions (such as GPS, atomic clocks or Network Time Protocol / Precision Time Protocol) would also provide trusted time. eLoran would provide absolute time over very wide areas, thereby allowing dispersed markets and users to take advantage of this synchronized time solution. Additionally, eLoran can often provide time indoors, using a magnetic field (H-field) antenna, thereby precluding the permits and expense required for a rooftop antenna installation. ESMA has asked for industry comment on its proposed requirement to synchronize clocks to the microsecond level, and invited industry responses to its preliminary view that business clocks be accurate at least up to the microsecond level.
Transportation Sector – Aviation. PNT use in air traffic management is illustrative. In accord with U.S. Federal Aviation Administration (FAA) planning, a principal surveillance source in the U.S. national air space (NAS) by 2020 will be Automatic Dependent Surveillance-Broadcast (ADS-B), where the required positional accuracy of aircraft relies on GPS position. Moreover, the independent validation and backup of GPS-derived positions relies on accurate time-of-arrival measurements at a network of 650 radio stations in the NAS that currently use GPS-disciplined clocks with accuracy down to 30 nanoseconds. These radio stations are critical infrastructure of the Surveillance and Broadcast Services (SBS) system, which provides ADS-B surveillance to FAA air traffic management (ATM).
The FAA recognizes the need for a backup to surveillance and navigation in the event of local, regional and wide-scale GPS outages, and is examining both near-term and long-term strategies for continuity of operations during those outages. Because of the long lead times for ATM technology insertion, near-term mitigation strategies out to at least 10 years are constrained by existing ATM ground infrastructure and current avionics capabilities. Long-term solutions are not so constrained, and may be based on new signals in space, new ground infrastructure and new avionics capabilities.
Surveillance. Beginning in 2020, ADS-B will be a principal surveillance technology. In recognition of the need for a backup if GPS fails, the FAA is planning to maintain a mix of beacon-interrogation radar and wide-area multilateration (WAM) in the near term. The long-term strategy is still very much in the evolutionary stage.
Navigation. Near-term strategies involve a mix of approaches based upon existing infrastructure and the current capability of avionics. A leading approach, referred to as DME/DME/IRU, uses two-way ranging to multiple Distance Measuring Equipment (DME) facilities augmented by the avionics inertial reference unit (IRU). This approach is practical and applicable more to air carrier aircraft than regional jets or general aviation. Other approaches rely to some extent on the use of very high frequency Omni-Directional Range (VOR) facilities. As with surveillance, the long-term strategy is very much evolutionary.
It is instructive to note that near-term solutions rely on existing radar, DME and VOR infrastructure because it is in place and is compatible with existing avionics. In the long-term view, new technologies with less costly infrastructure are likely to be more cost-effective, especially if they provide benefits beyond ATM applications. eLoran is such a technology.
Transportation Sector – Maritime. There is an increasing awareness in the maritime world that no single system can provide PNT resiliently under all circumstances. At this moment, GPS (with augmentations) is used on most commercial vessels, and in many cases integrated into systems we did not expect would need or use GPS-derived position or time. Even though the introduction of GLONASS, Galileo, BeiDou and other GNSS systems will provide some resilience, the underlying (satellite) technology remains the same, only providing relatively weak signals from space at mostly the same or close-by frequencies for compatibility and inter-operability.
The International Maritime Organization (IMO) recognizes the need for multiple PNT systems on board maritime vessels. The organization developed the e-Navigation concept to increase maritime safety and security via means of electronic navigation, which calls for at least two independent dissimilar sources of positioning and time in a navigation system to make it robust and fail safe. As a follow on, IMO’s Navigation, Communications and Search and Rescue Committee is considering performance standards for multi-system shipborne navigation receivers, which includes placeholders for satellite, augmentation and terrestrial systems.
The most viable terrestrial system providing PNT services that meet IMO’s requirements is eLoran. With three eLoran transmitters in good geometry, eLoran can provide sub-10 meter (95 percent probability level) horizontal positioning accuracy and UTC synchronization within 50 nanoseconds, sufficient to be the co-primary PNT solution with GNSS. The General Lighthouse Authorities of the United Kingdom and Ireland (GLAs) have installed UrsaNav’s differential eLoran reference stations to provide the world’s first initial operational capability (IOC) eLoran system.
Together with Loran transmitters in England, France, Germany, Norway and Denmark, the differential eLoran reference stations provide better than 10-meter positioning accuracy at seven ports and port approaches along the English and Scottish east coast. IOC was achieved at the end of 2014, with full operational capability planned for 2018. Other nations have either begun, or are exploring, similar projects.
Figure 4 shows the accuracy of an eLoran position at the differential reference station on the Humber River in England. Figure 5 shows the position accuracy while on board a vessel transiting outbound on the river from Humber to the North Sea.
Figure 4. Zero-baseline accuracy at Humber reference station.Figure 5. Onboard, en route accuracy on the Humber River.
Current State of eLoran Technology
eLoran technology has been available since the mid-1990s and is still available today. In fact, the state-of-the-art of eLoran continues to advance along with other 21st-century technology. eLoran system technology can be broken down into a few simple components: transmitting site, control and monitor site, differential reference station site and user equipment.
Modern transmitting site equipment consists of a high-power, modular, fully redundant, hot-swappable and software configurable transmitter, and sophisticated timing and control equipment. Standard transmitter configurations are available in power ranges from 125 kilowatts to 1.5 megawatts. The timing and control equipment includes a variety of external timing inputs to a remote time scale, and a local time scale consisting of three ensembled cesium-based primary reference standards. The local time scale is not directly coupled to the remote time scale. Having a robust local time scale while still monitoring many types of external time sources provides a unique ability to provide proof-of-position and proof-of-time. Modern eLoran transmitting site equipment is smaller, lighter, requires less input power, and generates significantly less waste heat than previously used Loran-C equipment.
The core technology at a differential eLoran reference station site consists of three differential eLoran reference station or integrity monitors (RSIMs) configurable as reference station (RS) or integrity monitor (IM) or hot standby (RS or IM). The site includes electric field (E-field) antennas for each of the three RSIMs.
Modern eLoran receivers are really software-defined radios, and are backward compatible with Loran-C and forward compatible, through firmware or software changes. ASF tables are included in the receivers, and can be updated via the Loran data channel. eLoran receivers can be standalone or integrated with GNSS, inertial navigation systems, chip-scale atomic clocks, barometric altimeters, sensors for signals-of-opportunity, and so on. Basically, any technology that can be integrated with GPS can also be integrated with eLoran.
Figure 6 shows a resilient PNT receiver that includes GPS, DGPS, eLoran and a dual-band (100/300 kHz) E-field antenna. The left-hand antenna, shown installed on the P&O Ferries’ Pride of Hull, is the resilient PNT antenna. The right-hand antenna is a standard GPS antenna.
Figure 6. Resilient PNT receiver and dual-band antenna.
World View of eLoran
Nine nations are operating Loran-C or eLoran stations, including Russia and China. It is our understanding that the Republic of Korea, India and the Kingdom of Saudi Arabia are pursuing the installation of eLoran technology or upgrading their Loran-C technology to eLoran.
The modernization and upgrade of the U.S. Loran-C system to eLoran was a congressionally mandated program jointly executed by the FAA and USCG from 1997 to 2009, and funded at $160 million. During this time, eLoran was successfully tested and demonstrated in all modes: aviation, maritime, land-mobile, location-based, and timing and frequency. Further, eLoran has been successfully in operation in the U.K. for several years. Every national and international government, industry and academic report has concluded that GNSS is vulnerable and that eLoran is the best complementary solution to help negate those vulnerabilities.
The U.S. terminated its Loran-C service, and thereby its nascent eLoran program, in 2010. Canada followed suit and terminated its Loran-C service as well. Shortly thereafter, DHS/USCG began dismantling or demolishing the modernized infrastructure. However, in December 2014, Congress directed that DHS/USCG preserve the existing, unused U.S. Loran-C infrastructure, unless the Secretary of Homeland Security certifies it is not needed for a system to complement GPS.
In March 2015, U.S. House of Representatives Resolution (H.R.) 1678, a bill that would require establishment of a strong, difficult-to-disrupt terrestrial system to complement GPS, and to serve as another source of PNT when GPS isn’t available, was referred to the Committee on Armed Services. The bill seeks to amend the language that provided for the establishment and management of GPS in Title 10, the section of law that deals with the armed services. We understand that other members of Congress have expressed interest and will be co-sponsoring the bipartisan bill. H.R. 1678 was introduced by Congressman John Garamendi (Democrat, Calif.) with Congressman Duncan Hunter (Republican, Calif.), Congressman Frank LoBiondo (Republican, N.J.) and Congressman Peter DeFazio (Democrat, Ore.) as the initial co-sponsors. In August, the bill was referred to the Subcommittee on Strategic Forces.
Additionally, in May 2015, the DHS and USCG entered into a cooperative research and development agreement with UrsaNav and Exelis (now part of Harris Corp.) to research, evaluate and document at least one alternative to GPS as a means of providing PNT information in the form of eLoran.
It is our understanding that the U.S. Congress is still considerably concerned about the lack of a complementary PNT solution to safeguard U.S. critical infrastructure and key resource sectors, and to protect our economy in the event of a GPS outage. Congress continues to press the administration for a resolution, in the form of a continental U.S. eLoran system, before our nation is placed at further risk.
Acknowledgments
The authors wish to acknowledge the assistance of Dr. Ron Bruno, Harris Corp., and Dr. Paul Williams and Chris Hargreaves, GLAs.
Manufacturers
UrsaNav provided the eLoran receiver and Symmetricom, now Microsemi, provided the GPS receiver for the timing tests shown in Figure 2.
STEVE BARTLETT is vice president of operations at UrsaNav, Inc., North Billerica, Mass.
GERARD OFFERMANS is senior research scientist at UrsaNav engaged in various R&D project work and product development.
CHARLES SCHUE is co-owner and president of UrsaNav.
FURTHER READING
eLoran
“Can eLoran Deliver Resilient PNT?” by N. Ward, C. Hargreaves, P. Williams and M. Bransby in Proceedings of The Institute of Navigation 2015 Pacific PNT Meeting, Honolulu, Hawaii, April 20–23, 2015, pp. 1051–1054.
“eLoran Initial Operational Capability in the United Kingdom – First Results” by G. Offermans, E. Johannessen, S. Bartlett, C. Schue, A. Grebnev, M. Bransby, P. Williams and C. Hargreaves in Proceedings of the 2015 International Technical Meeting of The Institute of Navigation, Dana Point, Calif., January 26–28, 2015, pp. 27–39.
“Implementing a Wide Area High Accuracy UTC Service via eLoran” by G. Offermans, E. Johannessen and C. Schue in Proceedings of the 46th Annual Precise Time and Time Interval Systems and Applications Meeting, Boston, Mass., December 2014, pp. 124–133.
2014 Federal Radionavigation Plan (F, DOT-VNTSC-OST-R-15-01, U.S. Department of Defense, Department of Homeland Security and Department of Transportation, Washington, D.C., available from the National Technical Information Service, Springfield, Virginia, 2015.
1990 Federal Radionavigation Plan, DOT-VNTSC-RSPA-90-3 and DOD-4650.4, U.S. Department of Transportation and U.S. Department of Defense, Washington, D.C., available from the National Technical Information Service, Springfield, Virginia, 1990.
When a GNSS RTK base station is started by assuming an autonomous position, it is necessary and good practice to later adjust and correct the coordinates with a solution referenced from known coordinates. JAVAD’s field software for the TRIUMPH-LS, J-Field, has the ability to adjust the RTK base station coordinates and RTK points surveyed using corrections from that base station.
Three methods can be used to accomplish this.
Manually Entering New Base Station Coordinates
Base station coordinates can be updated manually by entering new coordinates for the base station. These new coordinates can obtained through post-processing the base station data with OPUS or JAVAD’s DPOS web interface. Follow these steps to apply the corrected coordinate to the base station and adjust all the points from this base station through J-Field:
Select an RTK or base station point in the Points screen.
Tap on the blue screen displayed on the right side of this screen to view the Base Rover Statistics screen.
Tap the Base button and you will be prompted to enter the corrected coordinates for the base station.
Enter the new coordinates and tap OK.
J-Field will then search for all the points contained in the current project with the same original matching base station coordinates and apply offsets to adjust all these coordinates into the known coordinate system. The adjusted coordinates along with the original base station and surveyed origin coordinates will still remain stored in the database for documentation purposes and so that adjustments can be undone or modified if necessary.
Base Rover Statistics screen.
DPOS
When a Javad base station is started with J-Field using Base/Rover Setup, the raw GNSS data is automatically saved in the base station receiver. When the base station is then stopped with Base/Rover Setup, the data is downloaded into J-Field so that it will be available for post processing DPOS. To post-process the data, open the DPOS tool found in the CoGo menu and select the base file you wish to process. With the TRIUMPH-LS connected to the Internet, tap the DPOS button to upload the file to DPOS. This automated process will then update the base station and RTK surveyed points using the same algorithm described above.
Shift Mode
The newest feature of J-Field, Shift Mode, allows real-time corrections to be applied to receive base station corrections. A base station can be started with an autonomous position and then corrected by surveying a point with known coordinates. The known point could be a point previously surveyed with a base station setup in a different location. This feature is useful for several scenarios:
You need to move or “leapfrog” your base station to extend the radio range into a new area.
Your original base station point has been lost.
You wish to save time by starting the base station with it mounted to the top of your vehicle. Setting the base station and radio up on the top of vehicle by mounting it a roof rack or using a magnet mount saves time by eliminating the need to set up tripods and can help protect the base station from disturbances or theft in undesirable locations. For the best performance, the base station should be mounted in a level position so that phase center variations and antenna offsets are correctly applied. If you are parked on a sloped surface, it may be necessary to use a tribrach to level the receiver on the top of your car.
The Real-time Position Shift function can be accessed from the Setup menu under Advanced. In this screen, select a point you have collected RTK coordinates from with an autonomous base station, and then the known coordinates of this point. Check the Apply Shift and the shift will be applied to all the RTK surveyed points found in the current project collected from this base station. This shift will continue to be applied to all the points surveyed from this base station.
Position Shift screen.
Real-time Position Shift can also be accessed from the Collect Action screen by clicking the button below the Start button and changing the collection mode to Shift. In this mode, select the Known Point and then press Start from the action screen so that the offset can be calculated. After it has been calculated, you can apply the shift.
Position Shift screen from the Collect Action screen.The Collect Action screen in shift collection mode displaying the Accept/Reject Prompt for the shift.
