GNSS antenna maker Tallysman has introduced the TW7875 magnetic mount GNSS antenna, which is designed for precision dual-frequency positioning. It is capable of receiving GPS L1/L5, GLONASS G1, BeiDou B1, Galileo E1/E5a and NavIC L5.
The TW7875 employs Tallysman’s Accutenna technology, which provides superior multipath signal rejection due to its low axial ratio across the full bandwidth, the company said.
The antenna also provides a linear phase response and tight phase center variation at a new economical price point, according to the company, which said it provides performance comparable to higher priced dual-band GNSS antenna.
It is designed for precision agriculture, autonomous vehicles and other applications where precision matters.
The TW7875 is housed in a magnetic mount IP67 rated housing. It can also be ordered without the magnet since it can also be mounted by screws or double-sided adhesive tape.
Model TW3875 is the embedded antenna version of the TW7875. It is available with a wide selection of connectors and custom cable lengths, and can be custom tuned by Tallysman to ensure optimum performance within the customer’s enclosure.
A capture of the Buffalo and Erie County Botanical Gardens in Buffalo, New York, taken in May 2018. (Image: Nearmap)
Fresh off an eye-grabbing appearance showcasing its new 3D products at last week’s Esri User Conference, Nearmap will deliver a free “Cooking with GIS” webinar Thursday, July 26.
The hour-long session will highlight ways that the company’s vertical, oblique and 3D aerial imagery can bring competitive advantage to surveyors, construction managers, telecomm engineers, city planners, realtors and investors, building contractors, property and natural resource managers, and many others. Using their geographic information systems (GIS) skills, these professionals can perform deep analysis and make decisions with confidence using detailed and up-to-date visual insights.
Nearmap won 2017 Esri’s Best New Content Partner Award in 2017, and the free webinar, subtitled “Esri + Nearmap,” focuses on the key advantages of seamlessly integration the company’s high-resolution aerial imagery into Esri mapping and software products.
Esri is an international supplier of geospatial information systems with more than one million users in 200 countries around the world. Nearmap’s ArcGIS Image Service Online provides users an easy and efficient way to incorporate high-resolution PhotoMaps within Esri ArcGIS Online. ArcGIS users can instantly access current 2.8” imagery within days of capture while also showing change over time using Nearmap’s historical archive.
A New York City building site with temporary covered pedestrian walkway. (Photo: Nearmap)
As an integral partner in the ArcGIS ecosystem, Nearmap helped integrate their imagery with a wide range of Esri software solutions—both off the shelf and bespoke. Coupled with Portal for ArcGIS, the Nearmap ImageServer can be used in any application that is able to talk to ArcGIS Server, delivering power to the platform.
3D. Nearmap recently brought dramatic change to the aerial imagery market, announcing a national survey program providing high-resolution oblique imagery and derivative 3D products from its patented HyperCamera2 technology. The new camera system provides a high degree of overlap from different angles, so Nearmap can reconstruct the real world in detail, producing not only high-resolution orthomosaic and oblique imagery, but also surface and terrain models, natural color point clouds and textured 3-D meshes.
Users can immerse themselves in 3D textured mesh models, improving analysis and design activities. They can see different elevations and line of sight using the 3-D information. These features become important in many use cases, including airport or utility planning, or to determine the best location for a crane before a construction project.
Other applications include wireless telecommunications network modeling, solar panel design, tactical resource deployment, real estate development promotion, property valuation, insurance underwriting and smart cities.
Delivery. Nearmap is delivered through a user-friendly interface called MapBrowser or accessed via Esri, Autodesk and other third-party solutions.
Nearmap captures urban U.S. imagery multiple times per year, processes massive amounts of visual data, and uploads up-to-date aerial maps to the cloud within days. Patented imaging and processing technology delivery at speed of high-resolution aerial imagery as a service: orthographic (vertical) maps, multi-perspective panoramas and oblique aerial views.
The fully cloud-based PhotoMaps are accessible instantly via desktop and mobile, with 70% of the U.S. covered in major metros.
Clarity, color and 2.8″ GSD detail help users identify and accurately measure ground features with ease, detect change over time or monitor progress through the company’s library of precisely georeferenced historical imagery.
Nearmap imagery is refreshed up to three times per year principal coverage areas, with three orthomosaic captures incorporating one oblique capture. Nearmap’s orthomosaic imagery already covers nearly 70 percent of the U.S. population dating back to 2014.
Speakers on the July 26 webinar include Kevin Kwok, Nearmap technical product manager; Chuck Dostal, Nearmap geospatial technical engineer; and customer Mike Otillio, director of research for Colliers International, servicing the commercial real estate industry.
F-35Bs can use JPALS for precision landings in zero visibility conditions.
Early in 2018, U.S. Marine Corps F-35B Lightning II fighters deployed to the Pacific aboard the USS Wasp amphibious assault ship, and used Raytheon Company’s Intelligence, Information and Services business’ Joint Precision Approach and Landing System (JPALS) to guide them onto the ship’s deck.
An F-35B Lightning II prepares to land on the flight deck of the USS Wasp while underway in the Philippine Sea, March 23, 2018. (Photo: U.S. Marine Corps/Lance Cpl. Amy Phan)
JPALS is a differential, GPS-based precision landing system that guides aircraft onto carriers and amphibious assault ships in all weather and surface conditions, including rough waters.
It uses an encrypted, jam-proof datalink, connecting to software and receiver hardware on the aircraft and an array of GPS sensors, mast-mounted antennas and shipboard equipment, the company said.
“We’re asking our pilots to land in some of the most difficult conditions on Earth,” said U.S. Navy Captain B. Joseph Hornbuckle III, program manager, Naval Air Traffic Management Systems Program Office. “JPALS goes a long way toward ensuring the safety of our aircrews and the success of our missions.”
JPAL’s precision navigation is equally effective ashore. A land-based version of the system can be small enough to be either dropped into an austere environment via parachute or driven in on a trailer.
“Deploying with the F-35 is a good start, but it’s just the beginning,” said Matt Gilligan, Raytheon vice president of Navigation, Weather and Services. “There are many fixed and rotary wing aircraft around the world and across the services that deploy to harsh, low-visibility environments where JPALS would be extremely valuable.”
The system is slated to go into production in 2019 and will be outfitted on the U.S. Navy’s newest fighter — the F-35 Lightning II — allowing pilots to land with accuracy.
The European Union (EU) project BLUEGNSS has been developing GNSS applications in selected European airports to increase safety and airport accessibility, according to the European Commission’s Community Research and Development Information Service (CORDIS).
BLUEGNSS’s focus has been on advancing the adoption of the Galileo system in Greece, Italy, Cyprus and Malta. The four countries together form the Blue Med functional airspace block (FAB): airspace in which air traffic is managed irrespective of national boundaries. Blue Med is one of the nine FABs formed in Europe to reduce the fragmentation of the European air traffic network.
Three-dimensional GNSS approaches are being designed for 11 airports in the Blue Med FAB: four each in Greece and Italy, two in Cyprus and one in Malta.
The primary aim is to harmonize the implementation of required navigation performance approaches among the four countries, CORDIS said. This will enable aircraft to fly along precise flight paths with greater accuracy, and will make it possible to pinpoint aircraft position with precision and integrity.
Three new procedures. So far, substantial progress has been made towards safety and airport accessibility in the target countries. Since the beginning of 2018, three new GNSS procedures have been validated for Italian airports Cuneo, Lamezia and Parma, followed by another two for Larnaca and Paphos in Cyprus.
The poor weather conditions under which the Cyprus GNSS approaches were validated served to demonstrate the benefits of GNSS vertical guidance. Since its launch in 2016, BLUEGNSS has designed and validated 14 GNSS procedures.
Augmented performance of Galileo has been achieved through the European Geostationary Navigation Overlay Service (EGNOS). EGNOS is a satellite-based augmentation system that improves GNSS positioning. Its three satellites and network of more than 39 reference stations in 24 countries enable it to provide greater accuracy than Galileo alone.
EGNOS’s safety advantages and lower investment costs greatly benefit small and regional airports, which usually can’t afford the high costs of installing and maintaining ground-based navigation aids.
For this reason, BLUEGNSS has promoted its use in this geographically challenging Mediterranean region.
“The southeast Mediterranean region lacks full EGNOS coverage,” said GNSS expert Patrizio Vanni of ENAV S.p.A., project coordinator and Italy’s air navigation service provider. “To make things even more challenging, each airport involved in the project presents a very different operational environment.”
The project hasn’t only focused on designing and validating GNSS approaches at airports where no such procedures have been available up to now. It has also provided the necessary training and monitoring to support implementation by the Blue Med FAB countries.
Now close to completion, BLUEGNSS (Promoting EGNSS Operational Adoption in Blue Med FAB) is the first project of its kind to be coordinated at FAB level. It may serve as a catalyst to spread required navigation performance approach know-how in the region and beyond, to the whole of Europe.
Comtech Telecommunications Corp. has been awarded $1.9 million navigation contract by a U.S. automotive manufacturer, according to the company. The automaker’s identity was not revealed.
The contract is with Comtech’s Enterprise Technologies group, which is part of Comtech’s Commercial Solutions segment, and is for developing a new navigation product for two of the automaker’s top vehicle programs, including motorcycles.
“With this agreement, our turnkey navigation solution will be introduced to an entirely new automotive segment and is included as a lead product for this manufacturer supporting multiple languages and is deployed globally across all major markets,” said Fred Kornberg, president and chief executive officer of Comtech Telecommunications Corp. “It also represents a new stage of growth for our navigation and mapping applications, made possible through our Location Studio platform that has been a leading source of product customization for OEMs across a number of vertical markets.”
The Enterprise Technologies group specializes in precise device location and messaging platforms. Its fully virtualized and API solutions are available to mobile network operators, enterprises, internet of things (IoT) developers and automotive manufacturers.
Comtech Telecommunications Corp. designs, develops, produces and markets innovative products, systems and services for advanced communications solutions. It sells products to a diverse customer base in the global commercial and government communications markets.
The SensLynx GPS Management Accelerator Program (GMAP) can enable start-ups or enhance existing business portfolios with the addition of tracking solutions, the company said.
GMAP requires no upfront investment or inventory warehousing, and is structured to deliver recurring revenue via new sales channels, while also being compatible with legacy business models to capitalize on similar customer profiles.
Because SensLynx white labels its solutions under certain criteria, entrepreneurs earn significant margin on hardware sales, plus monthly subscription income from the customers they will own outright.
“We believe in the entrepreneurial spirit,” said Rob Garry, co-founder and CEO of SensLynx. “Not only does this Accelerator Program help us grow our IoT Fleet sector on a grass roots level, it inspires others to strike out on their own or expand.”
The GMAP program is built around SensLynx’s bundled solution components, which include Fleet & Asset Tracking, Electronic Logging Device, Routing Application, Video/DashCam capture and Workforce Management for smartphones.
At its heart is comprehensive fleet/asset tracking software, packed with features like data handling, parsing, database, mapping, alerting, reporting, dispatch, maintenance logging, e-logs, local posted speed limits, addressing, geofencing, interstate miles, open API-based software and more.
The complete bundled solution with software, hardware and data connectivity is packaged at one guaranteed monthly price.
Senslynx’s GMAP program includes initial training, planning for rollout, conducting telemarketing for launch, developing website content, providing custom-branded marketing materials and online demo support, accessible through the streamlined GMAP Reseller Portal where businesses can also easily manage supply chain and customer accounts.
China sent a Beidou-2 backup navigation satellite into orbit on a Long March-3A rocket from the Xichang Satellite Launch Center, in the southwestern Sichuan Province, at 4:58 a.m. on July 10, according to Xinhua.net.
China started to construct the third-generation of Beidou system in 2017, and eight Beidou-3 satellites are now in space. The satellite just launched is a second-generation Beidou-2, and the 32nd of the Beidou navigation system.
“The launch of a backup Beidou-2 satellite will ensure the system’s continuous and stable operation,” said Yang Hui, chief designer of the Beidou-2 series.
Some of the Beidou-2 satellites are nearing the end of their lives and need to be replaced by backup satellites. China launched two backup satellites on March 30 and June 12, 2016.
This new backup is not a simple repeat of previous satellites, but has been upgraded to improve its reliability, Yang said.
It carries redundant rubidium clocks, which is the key to the accuracy of its positioning and timing.
When China began reform and opening-up 40 years ago, its satellites mainly used costly imported rubidium clocks. After the launch of the Beidou program, the United States banned exports of rubidium clocks to China.
Sun Jiadong, chief designer of the Beidou system and an academician of Chinese Academy of Engineering, said China must depend on itself.
China’s first self-developed rubidium clock was tested on a satellite in September 2006. The performance of China’s rubidium clocks was improved on Beidou-2 satellites.
This year will see an intensive launch of Beidou satellites. The system is expected to provide navigation and positioning services to countries along the Belt and Road by late 2018. By around 2020, the Beidou system will go global.
Photo: Xinhua.net
The Beidou-3 satellites can send signals that are compatible with other satellite navigation systems and provide satellite-based augmentation, as well as search and rescue services in accordance with international standards. The positioning accuracy is 2.5 to 5 meters.
The Beidou system will coordinate with other technology, such as remote sensing, the Internet, big data and cloud computing, in future.
In the past five years, the system has helped rescue more than 10,000 fishermen. More than 40,000 fishing vessels and around 4.8 million commercial vehicles in China have been equipped with Beidou, said Beidou spokesperson Ran Chengqi.
China has sold more than 50 million domestically manufactured chips connected to the Beidou navigation and positioning system in the past five years.
By 2020, the value of China’s satellite navigation business is expected to surpass 400 billion yuan (about 58 billion U.S. dollars), of which 240 billion to 320 billion yuan will go to the Beidou system, Ran said.
Harris Corporation has been awarded three multi-award indefinite delivery/indefinite quantity (IDIQ) contracts with ceilings totaling $1.5 billion to provide the National Geospatial-Intelligence Agency (NGA) with geospatial data services for up to 10 years.
Harris will create, manage and disseminate high-quality geospatial-intelligence (GEOINT) information for use by the U.S. intelligence community and military worldwide under contracts that cover all three areas of NGA’s JANUS program — geography, imagery and elevation.
The JANUS program will contribute to and maintain comprehensive, geospatially accurate databases of the world that can be accessed quickly as intelligence, operational and crisis needs arise.
Harris will use its predictive analytics technology to continuously evaluate the health of NGA databases and to guide the acquisition, creation and integration of all forms of geospatial data. Harris’ cloud-based tools will validate and correct the data — pinpointing locations that require updates.
“Winning JANUS continues our long-standing legacy of providing high-quality, responsive GEOINT and analytics to the intelligence and military communities,” said Bill Gattle, president, Harris Space and Intelligence Systems. “Our analytics technology provides NGA with fit-for-purpose data, reduced production costs and cloud-based access to geospatial products and content.”
Harris is investing in new technologies that improve the speed and accuracy of providing GEOINT products. The company has partnered with the NGA for almost 20 years to provide automated geospatial data processing, data management, and geospatial systems design and development. Harris provides high resolution geospatial data content and products under NGA’s Foundation GEOINT Content Management program, and previously supported the Global Geospatial-Intelligence program.
Hexagon US Federal Also Contracted
The NGA also has selected Hexagon US Federal as a prime contractor on two multiple award, indefinite delivery/indefinite quantity contracts for amounts totaling $1.17 billion for the JANUS Geography and JANUS Elevation contracts.
JANUS Geography. Hexagon’s tasks for the JANUS Geography program will support the creation, conflation, integration and enrichment of Foundation GEOINT data used to produce a comprehensive and seamless dataset for NGA partners and customers.
The creation of this dataset will ensure more accurate and readily available geospatial data for military and intelligence operations as well as disaster relief missions saving time and lives.
JANUS Elevation. As a prime contractor on the JANUS Elevation contract, Hexagon will support NGA’s Office of Geomatics with maintenance to an existing worldwide library of digital elevation models. The effort includes products generated, modified or assessed by the office that are a digital representation of the terrain surface of the Earth.
A news story from Australia’s “Today Tonight Adelaide” television show highlights how the DroneShield system can bring down drones that enter restricted airspace or threaten safety. DroneShield countermeasures allow for the controlled management of drone payloads such as explosives, with no damage to common drone models or the surrounding environment.
Did you know Australia doesn’t exist? (Sorry, Aussies.) The entire continent is part of a massive conspiracy designed to confuse you. Anyone who says they’re from Australia is an actor (paid by NASA, probably.) And all the airline pilots are “in on it,” flying people to a carved out section of South America.
The “rationale” (I use the word very lightly) seems to be that Britain just wanted to dump its convicts in the ocean, so made up the continent to tell people where they were taking them.
These and other “theories” spouted by Flat Earthers are akin to falling down a rabbit hole where up is down and round is flat. How can they believe such nonsense?
The 1893 Orlando Ferguson map imagines Antarctica as a wall of ice around the world. (Image: Library of Congress/2011594831)
Last year, the flat Earth idea became national news when rapper B.o.B. used Twitter to jump on the flat Earth bandwagon, even starting a GoFundMe campaign to find Earth’s curve. B.o.B.’s campaign wants to “launch multiple weather balloons and satellites into space” to observe (and try to disprove) what centuries of science and technology have already confirmed. So far, he’s raised less than $7,000 of his $1 million target.
How do Flat Earthers explain GPS? Is there a way to convince them that they’re wrong? Probably not. Anyone who tries is met with an argument that their evidence is faked or faulty. GPS satellites aren’t in space — there’s a “celestial dome” over the Earth. Or the signals are really from giant towers and the G stands for ground. Or Google has laid cables across the oceans to track you.
Astrophysicist Neil DeGrasse Tyson blames the educational system — not for teaching insufficient science subjects so much as needing to improve critical thinking skills. “Our system needs to train you not only what to know, but how to think about information, knowledge and evidence,” he said.
Should we bother to convince Flat Earthers they’re wrong? Some on the internet could be trolls toying with arguments and theories. True believers, however, are an extreme minority, and there will always be people who choose to believe in “alternative facts.” Let’s hope they remain a minority.
The UM442 can simultaneously track GPS, BDS, GLONASS and Galileo. It also supports SBAS and QZSS. It uses Uncore’s new-generation Nebulas II chip and UGypsophila real-time kinematic (RTK) algorithm. Based on high-performance data-sharing technology and the simplified operation system of the Nebulas II chip, the UGypsophila RTK algorithm dramatically optimizes matrix processing, enabling the UM442 to track more satellites and shorten the initialization time to 5 seconds.
The MV5-AR inertial sensors are designed for off-highway and military vehicles, marine and mobile robot applications, and the autonomous vehicle market. The rugged, compact sensors use LORD’s fifth-generation high-performance industrial-grade solid-state six-degrees-of-freedom (6-DOF) micro-electromechanical accelerometer and gyro inertial sensor technology. Successfully deployed on ground robots and heavy machinery, applications also include autosteer and terrain compensation; dynamic incline detection (roll, pitch, rotation); vehicle stability and leveling; platform control, alignment and stabilization; operator feedback; and precision navigation. The compact and rugged reinforced housing is fully sealed for immersion and pressure wash. Each sensor is calibrated and temperature compensated.
BeiDou Phase 3 signals are now available on Spirent GNSS RF constellation simulators GSS7000 and GSS9000 — existing users can obtain the software upgrade by contacting Spirent. Phase 3 of the Chinese BeiDou system will extend its coverage from Asia to the entire world, providing receiver developers and integrators with additional GNSS signals to make positioning, navigation and timing systems more accurate, and help to support new applications, such as autonomous vehicles. Customers can test their designs before the system is fully operational in 2020.
The ZED-F9P multi-band GNSS module has integrated multi-band real-time kinematic (RTK) technology for machine control, ground robotic vehicles and high-precision unmanned aerial vehicles applications. It measures 22 x 17 x 2.4 millimeters and uses technology from the u‑blox F9 platform to deliver robust high-precision positioning performance in seconds. The ZED-F9P is a mass-market multi-band receiver that concurrently uses GNSS signals from all four GNSS constellations (GPS, GLONASS, Galileo and BeiDou). Combining GNSS signals from multiple frequency bands (L1/L2/L5) and RTK technology lets the ZED‑F9P achieve centimeter-level accuracy in seconds.
The SA.45s Commercial Space Chip-Scale Atomic Clock (CSAC) is a commercially available radiation-tolerant CSAC suitable for low Earth orbit (LEO) applications. The device provides the accuracy and stability of atomic clock technology while achieving significant breakthroughs in reduced size, weight and power consumption. It provides excellent drift performance and built-in 1 pulse per second (PPS) input for GPS disciplining, making the device well-suited for holdover applications. Commercial and research space applications include satellite timing and frequency control; satellite cross linking; assured position, navigation and timing; and Earth observation.
The long-range, power-efficient eRadio is designed to support high-precision GNSS real-time kinematic (RTK) applications in surveying and precision agriculture. It is enabled with intelligent serial baud rate identification for different RTK devices. It can automatically identify RTK serial baud rate with a radio data cable and provide a plug-and-play form for easy connection between the eRadio and RTK. With its high transmitting power (5-35 Watts), transmission data can be up to 19200 bps/s over a connection distance of 50–80 kilometers. It can work as either a base or repeater with other Harxon radio modems in challenging environments.
Wireless communication with any Android or Windows terminal
Image: SXblue/Geneq
The SXblue Premier GNSS receiver is available in a submetric version (GNSS) or centimetric version (RTK). It is equipped with Pacific Crest Maxwell 6 Trimble technology with BD910 (GNSS version) and BD930 (RTK version) OEM boards, delivering 220 channels to acquire and track GNSS signals from all constellations in view. It makes effective use of GPS, GLONASS, Galileo, BeiDou, QZSS and SBAS signals for precise positioning.
The single-frequency, multi-GNSS Vector V123 and V133 all-in-one smart antennas are multi-GNSS compass systems using GPS, GLONASS, BeiDou, Galileo and QZSS for simultaneous tracking for heading, position, heave, pitch and roll. Both support NMEA 0183 and NMEA 2000. The V123 and V133 thrive in radar/ARPA, AIS, ECDIS, side-scan survey, multi- and single-beam surveys, dredging and general navigation applications.
The Trak4 provides GPS tracking with cell-trilateration fallback. Ping rates can be selected from every two minutes to once a day, with email and text alerts provided for geozone entry and exit or if the high-capacity rechargable battery is low (the battery runs up to 12 months on a single charge.) The Trak4 is designed for tracking vehicles, assets and inventory; it can also be used to track people such as the elderly. Indoor/outdoor weatherproofing allows “anywhere” mounting.
PCTEL’s multi-GNSS L1/L2/L5 antennas combine aerospace-level precision with global satellite compatibility in a highly durable package. They enable critical applications including vehicular automation, 5G network timing synchronization and Positive Train Control (PTC) systems. The antennas increase the accuracy of timing and location information by providing simultaneous access to multiple GNSS signals across multiple frequency bands. The antennas support all relevant GPS, GLONASS, BeiDou and Galileo frequencies with excellent multipath mitigation and high out-of-band rejection for greater signal clarity. Their robust AAR and IP67-compliant design makes them suitable for years of use on railways and in other harsh real-world environments.
Four new GPS handhelds are designed for off-road use, with safety in mind. All four of the OS GPS models have a built-in SIM card with access to the SeeMe subscription-based service and its safety features. With I.C.E (In Case of Emergency), users can send emergency alerts with exact coordinates to family and friends directly from the OS GPS. Live Tracking enables the user to be locatable at all times, sharing location and performance data with up to 20 friends in real time. Aventura, the most advanced navigation device, can be used in all weather conditions.
Zubie Fleet Connect provides real-time GPS fleet tracking, driver check-in and performance reports, and vehicle health alerts. The monitoring and reporting service lets managers of fleets from 2 to 5,000 vehicles optimize business on the road. Wi-Fi connection to the cloud delivers important information about the health and performance of the vehicle, enhancing driver safety. Zubie also works with large enterprises to develop custom data flows and access driving data that can be used to analyze driving patterns, spot geographical trends in activity, or improve fleet asset management based on vehicle wear and tear.
The Heliscope 2.0 provides onboard data collection with speed, efficiency and productivity improvements for the utility inspection industry. It provides a solution for operations over greater distances or in harsher environments than drones can accommodate The system integrates multiple sensor systems into a single, lightweight helicopter payload, capable of simultaneously collecting a range of data types required for utility maintenance and vegetation management inspections. Deployment enables optimized inspection and maintenance schedules, offering potential cost savings in those operational activities by as much as 50 percent. The Heliscope 2.0 has flexible mounting configurations and the ability to adapt for mounting on many different helicopter types.
Based on DJI’s M600 Pro platform, the Leica Aibot system is designed to rapidly and autonomously enable digitizing of critical infrastructure. It enables users to get a complete data set quickly with a user-friendly interface. Using Leica Infinity for point-cloud, digital surface model and orthophoto generation enables surveyors to process and visualize aerial data. For construction projects, Aibot provides access to critical information to perform volume calculations and monitor site progress. Users can see high-definition imagery and 3D mapping of the site and document progress. The UAV data can be combined with other survey technologies such as GPS for a more complete set of information.
Two lightweight, compact antennas are designed for UAVs with a low aerodynamic profile. Antenna model TW1829 is for original equipment manufacturers (OEMs), and model TW8829 is a housed version. Accutenna technology provides high-level rejection of multipath signals, a phase linear response and tight phase-center variations. Pre-filters prevent saturation of the front-end low noise amplifier by strong near frequency and harmonic signals.
The HA32 high-performance antenna supports GPS, GLONASS, Galileo, BeiDou and Hemisphere’s Atlas L-band correction service. It is designed for UAVs, geographic information systems (GIS), surveying, real-time kinematic (RTK) and other applications requiring high-precision positioning and navigation. The HA32 is built on a proprietary four-helix antenna technology that provides superior filtering and anti-jamming performance with features such as a low noise figure of 2.0 dB (typical) and up to 30-dB gain (typical). Suitable for most outdoor and harsh operating environments, the HA32 antenna is sealed in a durable and ruggedized IP67-rated. The lightweight (40 g, typical), compact form factor (40 x 75 mm) makes it resistant to wind when on UAVs.
The technique of precise point positioning (PPP) is making inroads in the positioning industry. However, one issue hampering its more widespread adoption is the convergence time required for the carrier-phase ambiguities to be fully resolved so that the 10-centimeter-accuracy threshold can be surpassed. By using a multi-system, multi-carrier-frequency approach, instantaneous centimeter-level PPP can be achieved.
Innovation Insights with Richard Langley
CARRIER PHASE. It’s one of the two main measurement types or observables used by all GNSS receivers. Fundamentally, it is the instantaneous phase of a GNSS signal’s carrier, an electromagnetic wave of fixed amplitude and frequency (when transmitted), which is (optionally) modulated by a ranging code and a navigation message. It’s measured in radians, degrees or cycles and can be converted to a biased measure of the range between the receiver and satellite antennas by multiplying the value in cycles by the wavelength of the carrier in meters. The other GNSS observable is the phase of the ranging code. Initially measured in code chips or units of time, it is converted to a biased measure of the receiver-satellite range by multiplying it by the speed of light. This value is then typically called the code measurement or the pseudorange. The carrier phase is much more precise than the pseudorange by something like a factor of 100. So, while pseudoranges can be measured to a precision of tens of centimeters, carrier phases can be measured to millimeters or better.
Most GNSS receivers use pseudorange measurements to determine their position. In fact, this is the standard approach to satellite-based positioning that was introduced by GPS in the 1970s. While carrier-phase measurements, or rather their time-rate-of-change, are used for precise velocity determination, it wasn’t originally recognized that carrier-phase measurements could be used for position determination, too. The problem with the carrier phase as a measure of the range is that it has an initially unknown and potentially huge bias. This is because when a receiver starts tracking a signal’s carrier, it doesn’t know the exact number of cycles of the carrier wave stretching all the way from the satellite to the receiver. Hence, carrier-phase measurements are ambiguous as a result of this initial bias. If this ambiguity can be resolved, then carrier-phase measurements can be used for very precise positioning — positioning at the centimeter level or even better.
Over the years, various techniques have been developed to use carrier-phase measurements for positioning, most notably in differential positioning where one or more reference stations are used to position a user receiver or rover. But the technique of precise point positioning, which only requires direct uncombined measurements from the user receiver, is being actively developed and is making inroads in the positioning industry. However, one continuing issue hampering its more widespread adoption is the convergence time required for the carrier-phase ambiguities to be fully resolved so that the 10-centimeter-accuracy threshold can be surpassed. Research by the authors of this month’s article shows that by using a multi-system, multi-carrier-frequency approach, instantaneous centimeter-level PPP can be achieved. They call their technique Optimal Estimation using Uncombined Four-frequency Signals or OEUFS for short. Those of us who remember a smattering of our high-school French will agree that it is quite an eggceptional technique.
Instantaneous centimeter-level positioning used to be synonymous with the single-baseline real-time kinematic (RTK) technique. The rover was constrained to be within a few kilometers of the base station to ensure that errors would remain spatially correlated. Modeling error sources using a regional network of stations later allowed users to retain this level of accuracy within the area of network coverage. A global network of reference stations enabled the determination of precise satellite orbit and clock products, paving the way for precise point positioning (PPP).
Global centimeter-level accuracy can be achieved with PPP, at the cost of a long convergence time, often measured in hours. An additional layer of corrections, including satellite code (pseudorange) and carrier-phase biases, has enabled PPP with ambiguity resolution (PPP-AR). While an improvement in convergence time can be obtained, PPP-AR still cannot compete with RTK or network RTK in terms of time to first fix. Only by providing precise atmospheric information to PPP users, in the form of zenith tropospheric and slant ionospheric delays, can instantaneous centimeter-level accuracy be obtained. This approach led to a unification of PPP and RTK, often referred to as PPP-RTK. This scalable approach has allowed PPP users to obtain accurate positioning globally, while achieving rapid convergence when located within the regional reference network boundaries.
The modernization of GNSS includes satellites transmitting signals on multiple frequencies. The 12 GPS Block IIF satellites currently in orbit already broadcast the L5 signal, and all Galileo and BeiDou satellites launched so far have triple-frequency capabilities. In November 2017, the BeiDou constellation began a new phase of its development with the launch of the Beidou-3S satellites offering new signals compatible with the GPS L1/L5 bands. In March 2018, the European Union decided to open its Commercial Service (CS), offering at no cost the signal and correction stream for the “CS high accuracy” service. As a result, the E6 signal is now available on 14 satellites and can be tracked by modern GNSS receivers. FIGURE 1 depicts the frequency plan of the open GNSS signals, including these last evolutions, as of May 2018.
FIGURE 1. GNSS open signals (as of May 2018). (Image: authors)
With three or more frequencies, a series of widelane ambiguities can be resolved in a cascading scheme. These unambiguous widelane signals can be used to form an ionosphere-free phase measurement with lower noise than code measurements, but typically still at the decimeter level. The availability of the Galileo E6 signal provides a significant step forward for PPP-AR, permitting instantaneous convergence. As a result of frequency separation, unambiguous widelane signals have low noise characteristics, which further benefits the resolution of the whole set of ambiguities. The strategy used in our study is a generalization of the widelaning technique, based on uncombined observations, which we describe as Optimal Estimation using Uncombined Four-frequency Signals (OEUFS).
We explain how instantaneous centimeter-level PPP is achieved by first analyzing the precision of the ambiguity and range parameters in the single-satellite case. The network estimation of the uncombined Galileo phase biases is then described, followed by epoch-by-epoch and 5-minute PPP solutions based on OEUFS.
SINGLE-SATELLITE PROCESSING
To get a first grasp of the benefits of using four frequencies, we first look into single-satellite data. The aim of this analysis is twofold: first, to evaluate the ability of fixing linear combinations of ambiguities and, second, to determine the resulting precision of the unbiased range estimate once these ambiguities are fixed.
Uncombined observations on four Galileo frequencies (E1, E5a, E5b and E6) are used to model an ionosphere-free range, a slant ionospheric delay, and four carrier-phase ambiguities. It should be noted that measurements on a fifth frequency (E5) are available but, due to the proximity of E5 with respect to E5a and E5b, its impact was found to be almost negligible. We will, therefore, restrict ourselves to the four-frequency case. Only two code observations are included in the model — in this case E1 and E5a — since adding other frequencies would require the estimation of differential code biases. Thus, for single-epoch processing, additional code measurements would not usefully contribute to the solution. Observable standard deviations are set to 3 millimeters and 30 centimeters for carrier phase and code, respectively. An analysis using a zero-length baseline revealed that weak correlations do exist between signals, and multipath effects could further increase this correlation. Although taking into consideration correlations among observations would lead to a more realistic covariance matrix, these correlations were neglected in producing the results shown in this article. This is justified by the fact that correlation coefficients are usually not available, especially for real-time processing.
The above-mentioned model was inverted in a least-squares adjustment to perform covariance analysis. While the Least‐squares AMBiguity Decorrelation Adjustment (LAMBDA) method can be used for the identification of optimal linear combinations of ambiguities, the classic widelane ambiguities were found to perform equally well and were used in our work to simplify the exposition. When no ambiguities are fixed, the quality of the solution is driven by the noise on the code observations. TABLE 1 shows that, in this case, the receiver-satellite range parameter can be estimated with a precision of 0.776 meters. This value can be translated into a 3D-position precision by using the position dilution of precision (PDOP) factor. As a rule of thumb, if the PDOP for all satellites in view is equal to 1, the resulting 3D precision should be around 78 centimeters.
TABLE 1. Precision of parameters in the Galileo four-frequency (E1, E5a, E5b, E6) single-satellite case.
Even though the range is not very precise, forming the E5a-E5b widelane ambiguity from the estimated uncombined ambiguities gives a precision of 0.034 cycles, which can be reliably fixed due to the very long wavelength of the signal (9.77 meters). Adding this constraint to the system allows us to estimate the E5b-E6 widelane ambiguity with a standard deviation of 0.041 cycles (although it could also have been fixed initially). Interestingly, fixing both extra-widelane ambiguities does not significantly improve the precision of the range information derived from a single satellite. Nevertheless, due to correlations among ambiguity parameters, a precision of 0.183 cycles is now obtained for the E1-E5a widelane, an improvement of approximately 35 percent over the initial estimate.
While the E1-E5a ambiguity is not sufficiently precise for reliable instantaneous fixing based on single-satellite data from one epoch, using the geometric information from several satellites will enable single-epoch ambiguity resolution for three widelane ambiguities per satellite, as we show in the following sections. Assuming for the moment that ambiguity resolution was indeed successful on all three widelanes, Table 1 indicates that the range parameter can now be estimated with a standard deviation of 19 centimeters, a substantial improvement over the initial 78-centimeter precision. Recalling the PDOP factor introduced above, instantaneous 3D position precision at the 20-centimeter mark should then be possible with good geometry.
Including all available measurements in the model necessarily leads to the best performance. Still, TABLE 2 presents the conditional precision of parameters in three-frequency configurations. The precision for the widelane ambiguity is conditioned on first fixing the extra-widelane ambiguity, while that for the range assumes fixed extra-widelane and widelane ambiguities. The table highlights that frequency spacing plays a key role in the system performance. After fixing two widelane ambiguities, the Galileo E1-E5a-E5b configuration provides a range with a standard deviation of approximately 42 centimeters. The E1-E5a-E6 configuration is the best option, with a precision of the range parameter equal to the four-frequency case. In other words, the contribution of the E5b signal is almost negligible once the E5a-E6 ambiguity, having a wavelength of 2.93 meters, is resolved. For comparison purposes, the values for GPS are included and show that Galileo has the potential for significantly more precise instantaneous positioning.
TABLE 2. Conditional precision of parameters for three-frequency single-satellite configurations.
NETWORK SOLUTION
To demonstrate the concept of four-frequency ambiguity resolution for PPP, a phase-bias network solution for the Galileo constellation must be generated. Our solution is based on the precise satellite orbit and clock corrections produced by the Centre National d’Études Spatiales (CNES) as a part of the International GNSS Service (IGS) Multi-GNSS Experiment (MGEX). These products contain satellite clock corrections at a 30-second interval, as well as widelane biases allowing for GPS ambiguity resolution in the L1 and L2 frequency bands. For this reason, the following analysis considers both GPS and Galileo constellations.
Consistent processing of multi-frequency and multi-modulation signals requires code-bias corrections. The differential code-bias products from the German Aerospace Center (DLR), including the Galileo E6 signals, are used. Ambiguity resolution for Galileo can only be enabled with corresponding phase biases for all frequencies. To this date, the main contributors to the IGS for E6-compatible receivers are Natural Resources Canada (NRCan), CNES and Geoscience Australia. Since a global network of ground receivers tracking all four Galileo frequencies is not yet available, our solution is computed from a regional, but wide-area, network in Australia. The network consists of six reference stations with multi-system, multi-frequency receivers as depicted with red triangles in FIGURE 2. (Station CEDU is not included in the network solution because it is used later as a rover for PPP testing.) Measurements collected at a 30-second interval are retrieved from the Crustal Dynamics Data Information System (CDDIS) data archive. For the purpose of our demonstration, data from April 1, 2018, from 13:45:00 to 14:35:00 GPS Time is selected. During this period, five Galileo satellites were continuously tracked by the Australian stations, allowing the computation of a Galileo-only solution.
The phase-bias solution is a generalization in the multi-frequency case of the well-known widelane/narrowlane GPS scheme. The first step consists of resolving all integer ambiguities in the network. As we deal with four frequencies, it is required to fix four ambiguities, or their combinations, per satellite-station pass. The first three combinations used for this study are the widelanes defined from E5a-E1, E5b-E1 and E6-E1. Their ambiguities are solved, as for the dual-frequency GPS case, thanks to the Melbourne-Wübbena combination. Then, one remaining integer ambiguity (here, E1) is solved by forming the ionosphere-free phase combination between E1 and E5a (with the corresponding widelane ambiguity already resolved as an integer value). The second step aims at recovering the uncombined phase biases from the estimated linear combinations of biases. By a simple system inversion, it is possible to reconstruct the phase biases on each frequency.
FIGURE 2. Stations used to generate the Galileo phase-bias solution are represented by red triangles, while the PPP user is represented by a black square. (Image: authors)
FIGURE 3 shows the estimated biases for each frequency over the study period. The values were shifted by an integer number of the carrier wavelength for plotting purposes. The uncombined biases obtained are relatively stable, although they vary by a few centimeters over this one-hour period. These fluctuations are correlated among frequencies due to the transformation from linear combinations to uncombined biases. It should be understood that the resulting biases are not true phase biases, but rather biases to be applied to the carrier-phase observations.
FIGURE 3. Estimated Galileo phase biases for the four frequency bands over the study period. (Image: authors)
PRECISE POINT POSITIONING
We assessed the impact of using four frequencies transmitted by Galileo (E1, E5a, E5b and E6) on positioning performance by using station CEDU in Australia (see Figure 2). It is equipped with a multi-frequency receiver collecting multi-GNSS observations at 30-second intervals. Position estimates are derived from the PPP methodology using the satellite orbit and clock corrections, along with the carrier-phase and code biases, described in the previous section.
We computed three different solutions:
a GPS-only solution;
a Galileo-only solution; and
a GPS and Galileo combined solution.
For all solutions, all error sources affecting observations are modeled, including relativistic and wind-up effects, solid Earth tides and ocean loading. The a priori tropospheric zenith delay (TZD) is computed using the Vienna Mapping Function 1 (VMF1) grids, while a priori ionospheric delays are obtained from a global ionospheric map (GIM) generated at the Center for Orbit Determination in Europe (CODE). The eccentricity between the satellite antenna phase centers and the satellite center of mass is obtained from the latest version of the IGS ANTEX file, which includes frequency-dependent phase-center offsets and variations for Galileo. Since there are no Galileo-specific ground-antenna calibrations available, GPS values are used as approximations.
In all cases, we processed uncombined observations corresponding to the OEUFS strategy. For GPS, the L1C and L2W carrier-phase observations are used, along with the C1W and C2W code observations. For Galileo, the L1C, L5Q, L6C and L7Q carrier phases are used, with identical modulations for code measurements. Note that this signal identification uses the RINEX 3 conventions where, for Galileo, the L5 and L7 signals correspond to those in the E5a and E5b bands, respectively. Carrier-phase observations are given a standard deviation of 2 millimeters at zenith, while code observations are deweighted by a factor of 100. An elevation-angle-dependent weighting strategy also assigns lesser weight to satellites closer to the local horizon. Therefore, the value of 3 millimeters used in the single-satellite analysis above corresponds to a satellite tracked at an elevation angle of approximately 40 degrees.
The PPP filter includes states for the three position components, one receiver clock parameter per satellite system, inter-frequency code biases, one phase-bias parameter per frequency, a residual TZD, a residual slant ionospheric delay per satellite and carrier-phase ambiguities. To confirm the theoretical analysis from a previous section, the empirical single-epoch ambiguity-fixing success rate is first evaluated using a bootstrapping algorithm. The full vector of estimated float ambiguities is first decorrelated using the LAMBDA method, and all ambiguities having a success rate larger than 99 percent are fixed to integers. FIGURE 4 shows the number of fixed ambiguities for each solution.
FIGURE 4. Number of fixed ambiguities using a bootstrapping approach for independent, single-epoch, solutions. Number of frequencies in parentheses. (Image: authors)
Not surprisingly, the dual-frequency GPS solution is incapable of reliably fixing ambiguities within a single epoch. During this time period, five Galileo satellites are tracked. If we first consider all four frequencies from Galileo, and use the ambiguities on one satellite to provide the datum, then a total of 16 ambiguities are being estimated in the PPP filter, 12 of which are considered widelanes. Figure 4 confirms that using correlations introduced by the geometry allows instantaneous fixing of all widelane ambiguities for Galileo for most epochs. Adding GPS to the Galileo solution makes Galileo widelane fixing more reliable, but does not allow fixing of additional ambiguities. The three-frequency (E1, E5a and E6) Galileo configuration also enables instantaneous fixing of all eight widelane ambiguities, since the inclusion of E5b brings minimal additional information.
In all subsequent solutions, ambiguity estimation is performed using a more sophisticated method referred to as the best integer equivariant (BIE) approach. Because it is expected that not all ambiguities can be fixed simultaneously, a partial ambiguity resolution scheme is required. The BIE method fulfills this criterion by computing a weighted average of integer vectors. The outcome is a constrained ambiguity vector whose entries take either integer or float values. The key point of this approach is that the BIE float estimates can be improved by the averaging process with respect to the least-squares float estimates. Furthermore, by exploiting the correlations contained in the ambiguity covariance matrix, this method can effectively fix linear combinations of ambiguities. Therefore, we are not explicitly forming widelane ambiguities, but rather optimal linear combinations of ambiguities are fixed through the BIE averaging process. This strategy is implemented using the LAMBDA method to decorrelate ambiguities. Even though the BIE estimates are independent of the decorrelation, this step improves the computational efficiency of the approach.
As we explained in the previous sections, positioning with fixed widelane ambiguities can potentially allow for instantaneous precise positioning. FIGURE 5 demonstrates the epoch-by-epoch position estimates for the three solutions. As the strategy implies, the filter is entirely reset between epochs, and each point in the time series is independently determined. As expected, instantaneous ambiguity resolution with GPS alone is not feasible. Although the external information provided by the GIM is beneficial in reducing the errors, the root-mean-square (RMS) error is at the decimeter level for all components (see TABLE 3).
FIGURE 5. Instantaneous (epoch by epoch) PPP-AR solutions for GPS only, Galileo only and GPS and Galileo combined. Number of frequencies in parentheses. (Image: authors)TABLE 3. RMS errors for each instantaneous PPP-AR solution (meters).
The Galileo-only solution offers a substantial improvement in the horizontal components. These results are explained by the ambiguity-resolved widelane signals providing precise range estimates. It should be noted that only five Galileo satellites are visible during this period with a PDOP slightly exceeding a value of 3. When the full constellation of satellites will be in orbit, even better results could be obtained from a Galileo-only solution. The three-frequency (E1, E5a, E6) Galileo solution offers almost identical position estimates and is not shown here for conciseness. Combining GPS and Galileo yields the best solution with centimeter-level instantaneous positioning (refer to Table 3). For several epochs, a fully converged position is even obtained within a single epoch.
While the RMS errors of the combined GPS + Galileo solution is at the centimeter level, individual epochs can still exhibit decimeter-level errors. To demonstrate the convergence capabilities of the OEUFS strategy, we computed 5-minute PPP sessions. Even though the station is stationary, we added a large amount of process noise to the position states to simulate kinematic processing. FIGURE 6 shows the results of all 10 sessions: horizontal convergence to a few centimeters could be achieved within two epochs in all but one session.
FIGURE 6. Independent 5-minute kinematic PPP solutions using GPS and Galileo. Each trace represents a different session. (Image: authors)
CONCLUSION
We have shown that GNSS modernization is a key component for reducing the convergence time of PPP solutions. Combining multiple constellations strengthens the geometry, and using multiple frequencies allows for improved ambiguity resolution performance. In particular, tracking of the E6 Galileo commercial service signal turns out to be particularly beneficial in terms of instantaneous positioning capabilities. We demonstrated that ambiguities can be instantaneously resolved on Galileo satellites, leading to a range estimate approximately four times better than that provided using code measurements. With good satellite geometry, these frequencies can enable instantaneous 3D positioning with an accuracy of around 20 centimeters. Combining Galileo and GPS allows for single-epoch centimeter-level PPP solutions and full convergence within a few epochs.
We expect that the robustness and accuracy of the OEUFS strategy will improve in the future, with an increasing number of multi-frequency satellites and ground stations. Specifically, the additional frequencies provided by BeiDou and the Quasi-Zenith Satellite System will enhance the geometry of the solution and will further expedite convergence. Within a few years, instantaneous PPP might very well become a practical alternative to RTK for a wide range of applications.
ACKNOWLEDGMENTS
The authors acknowledge Geoscience Australia for making publicly available modernized GNSS data, as well as Paul Collins from NRCan for the review of our manuscript and technical advice. This article is published as NRCan Contribution 20180102.
MANUFACTURER
All of the stations used for the tests described in this article have PolaRx5 reference receivers manufactured by Septentrio (www.septentrio.com).
DENIS LAURICHESSE is a member of the Navigation Systems Department at CNES in Toulouse, France. He has been in charge of the DIOGENE GPS orbital navigation filter, and is now involved in navigation algorithms for GNSS. He is in charge of the CNES IGS real-time analysis center. Laurichesse was the co-recipient of the 2009 Institute of Navigation Burka Award for his work on phase ambiguity resolution.
SIMON BANVILLE is a senior geodetic engineer with the Canadian Geodetic Survey of NRCan, Ottawa, Canada, working on PPP. He obtained his Ph.D. degree in 2014 from the Department of Geodesy and Geomatics Engineering at the University of New Brunswick, under the supervision of Richard B. Langley. He is the recipient of the Institute of Navigation 2014 Parkinson Award.
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