Hurricane Matthew, which formed Sept. 28 and dissipated Oct. 10, brought torrential rains to the Carolinas, causing widespread flooding. The above is a screenshot from a drone inspection video.
In the wake of Hurricane Matthew, Verizon used drones for cell-site inspections in North Carolina and South Carolina. The aerial survey shortened cell-site recovery to hours compared to potentially days, based on the severity of flooding.
The quadcopter used was operated by Measure UAS, which conducted the flights with Federal Aviation Administration (FAA) authorization.
Flights used a two-person crew that included a ground pilot for the UAS, and a visual observer of the operation for safe, legal and insured operations, Verizon said.
While Verizon was able to access most hurricane-affected sites quickly to assess damage, some sites were not accessible because of extreme flooding. That’s where the UAS came in.
Streaming in HD
The UAS was able to livestream and record high-definition video and high-resolution photographs of a cell site.
The first flight to a site surrounded by water near Elm City, North Carolina, and the Tar River Reservoir showed engineers that the base-station equipment — which was elevated on stilts — was not underwater and had not suffered visible damage.
After determining the site was safe to access, Verizon’s Network team secured an air boat and refueled the generator, bringing the site back into service within hours.
Verizon completed successful cell site inspection trials earlier this year in New Jersey providing valuable 3D imagery and system performance data via UAS.Now the company has several vendors to aid Verizon’s network maintenance and operations.
airborne service
In October, Verizon conducted the first trial with Verizon’s Airborne LTE Operations during an emergency management and disaster recovery exercise in Cape May, New Jersey.
The exercise simulated how Verizon’s network could provide 4G LTE coverage from a 17-foot wingspan UAS operated by American Aerospace Technologies (AATI) to first responders in an area impacted by a severe weather event where no wireless service is available.
While this is the first simulation in an emergency scenario, AATI and Verizon are conducting trials nationally testing connectivity between manned and unmanned aircraft and Verizon’s 4G LTE network, including in-flight connectivity.
Drones could soon be inspecting powerlines in India, thanks to a partnership between Sharper Shape and Sterlite Power.
Sharper Shape, based in Palo-Alto, California, offers automated drone-based asset inspections. Sterlite Power is a power transmission company in India.
The Sharper Shape Sharper A6 drone is designed for beyond-visual-line-of-sight (BVLOS) flights.
Sharper Shape has already spearheaded the adoption of long-distance commercial drone flights for utilities in Europe. In the U.S., Sharper Shape is part of the EEI Sharper Utility partnership, an industry collaboration aimed at demonstrating and developing commercial long-distance drone flights for electric companies.
As part of the cooperation, Sterlite Power will make a minority investment in Sharper Shape to foster Indian market growth and continued technology development. The companies signed a partnership agreement during Make in India Week in Mumbai in February, an event held to spur innovation, design and sustainability.
Sterlite Power and Sharper Shape are awaiting approvals from India’s Directorate General of Civil Aviation for large-scale, long-distance inspection flights. Long-distance drone flights could provide significant benefits with safe, efficient and fast inspections compared to manned helicopter flights.
Utilities in India. The partnership also intends to provide services for other utilities in India. India has a power transmission network of more than a million circuit kilometers, which undergoes double-digit growth annually. The use of drones will increase the uptime of the grid, reduce transmission tariffs, avoid grid blackouts, and save the environment by reducing deforestation along the line corridors.
Sterlite Power has already introduced lidar for surveys and helicopters to avoid disturbances to farm activities and speed the process to commission much-needed infrastructure in India. Soon, it will deploy heli-cranes to erect transmission towers in the challenging terrains of Jammu and Kashmir.
In the United States…
In August, Sharper Shapesubmitted a waiver application to the U.S. Federal Aviation Administration (FAA), requesting approval to perform beyond-visual-line-of-sight (BVLOS) flights. The waiver would allow members of the Edison Electric Institute (EEI)-Sharper Shape partnership to demonstrate and develop commercial long-distance flights for electric company asset inspections.
BVLOS flights are able to travel 10–20 miles, compared to roughly one-third of a mile under visual-line-of-sight regulations.
The test flights will leverage Sharper Shape’s new Sharper A6 drone and Sharperscope 5.0 payload. The A6 is optimized for BVLOS asset inspections, using four redundant cellular networks to make it virtually impossible for the drone to lose communication with ground-control operators, the company said.
Sharper Shape leverages the LTE commercial multi-billion-dollar networks, while other vendors use point-to-point, which can’t communicate beyond line of sight, or satellite connection, which suffers from high costs and invariable latency that increases the response time and impedes a pilot’s ability to make quick adjustments during flight.
The University of Maryland (UMD) Unmanned Aircraft Systems (UAS) Test Site, along with and Shore Regional Health, conducted on Aug. 24 the state’s first civil unmanned aerial delivery of simulated medical cargo. Engineers from UMD flew a Talon 120LE fixed-wing aircraft across the Chesapeake Bay with saline solution simulating four vials of Epinephrine to demonstrate the key role that UAS can play in emergency situations.
First Responsders. “This is a major achievement for our test site and for the University of Maryland,” said Darryll Pines, dean of the School of Engineering. “What this flight demonstrates is the incredible potential that UAS have in assisting first responders in emergencies. As more of these aircraft enter the skies, demonstrations of their use in service to humanity will grow substantially.”
Weighing 22 pounds at take-off, the small UAS was hand launched from the shores of Flag Ponds Nature Park in Lusby, and landed at Ragged Island Private Airport in Cambridge, flying 12 miles over 28 minutes. The flight was autonomous with man-on-the-loop with ability to intercede.
The UAV was greeted by a security officer from Shore Regional Health who retrieved the package and transported it to the Shore Medical Center at Dorchester.
“We wanted to simulate a situation when weather, traffic or other disaster made more traditional means of transportation impossible. UAS are faster to deploy, less weather dependent and less expensive,” said Matthew Scassero, director of the UMD UAS Test Site.
Flight path as recorded by aircraft GPS. The loiter midway allowed confirmation of the radio monitoring/control signal handoff. Loiter will not be necessary for operational flights.(Image: UMD)
The test also helped Shore Regional Health explore new ways of providing access to medical care to rural areas, according to William Huffner, Shore’s chief medical officer. UAS technology has the potential to bring supplies not only to medical staff, but also directly to patients in isolated areas.
“In emergency situations, every second counts,” Scassero said. “Imagine being able to deploy insulin or another critical medication to someone in need by landing or dropping it right in their backyard.”
Talon UAV. The Talon 120LE is made of 7075 aircraft-grade aluminum, foam and composite materials. Scassero said that the team chose a Talon 120LE because of its “payload capacity, stability and reliability.” With an endurance of greater than two hours, its modular nose payload section and wing pods, it can carry payloads up to 2.5 pounds. The aircraft flies autonomously and lands on its belly.
Scassero said the use of UAS will be critical in future emergencies. “Using UAS for cargo will allow them to operate in tandem with manned aircraft to work together for these types of humanitarian missions and others, such as search and rescue,” he said.
Next Steps. Following this successfull test, the test site is looking at different operational control paradigms (suc as network or satellite), health IT cueing of the system, different vehicles for various applications, and different flight environments.
Aeropoints are desgined for for companies across the industrial sector — including mining, construction, quarries and landfills.
Propeller Aero has introduced AeroPoints — smart ground-control points designed to make it easy to capture surveyaccurate mapping using drones.
The patent-pending technology provides a simple solution to a major roadblock to widespread commercial drone adoption: accuracy.
Typical ground control requires establishing precise geolocation position using surveying equipment, and then securing a visible ground marker exactly on the pre-marked GPS point.
AeroPoints are portable ground-control markers, visible from the air and capable of quickly capturing their own positions down to 2-centimeter absolute accuracy.
AeroPoints work with any camera or drone, and integrate seamlessly with Propeller’s cloud-based data platform and processing engine (see above story). They’re solar-powered, durable and weather resistant, and they don’t require any onsite connection.
To use AeroPoints, customers simply lay them down, fly their drone, and then pick them up again. They automatically connect to a wireless or mobile hotspot when back in range to upload captured positional data — and precision georeferencing is done.
DJI and Datumate have begun offering a drone, software and app package that fully automates and expedites site surveys.
Tailored for professional surveying jobs, the DJI-Datumate Site Survey Solution simplifies the surveying and mapping processes, while maintaining superior accuracy. Shenzhen-based DJI is the world’s top aerial-imaging company. Israel based Datumate is a leader in automated “field-to-plan” surveying solutions.
The DJI-Datumate Site Survey Solution is a comprehensive and professional package of imagery and mapping tools that help surveying, construction, inspection and infrastructure companies quickly generate a working model, site visualization, analytics and plan.
The solution includes “Triple D” bundles of DJI Drone, DatuFly tablet app for an automated and expeditious aerial photography, as well as DatuGram 3D photogrammetry software that converts aerial and ground images to high-precision, geo-referenced 2D maps and 3D models.
“New drone regulations expedite the adoption of drones in a wide range of surveying related applications,” said Paul Xu, DJI’s director of enterprise solutions. “We believe that DJI-Datumate Site Survey Solutions offer a professional and cost-effective end-to-end solution for the surveying, infrastructure-mapping and inspection markets.”
DatuFly software generates a flight and image-taking plan for the DJI Drone, based on the best practice requirements of DatuGram 3D photogrammetry, ensuring survey-grade accuracy, high quality and quick results.
“We are excited to partner with DJI to automate and digitize the entire field-to-plan process. Our mutual solution brings site visualization and analytics quickly to the office, keeping field and office work effortless and safe,” said Datumate CEO Tal Meirzon. “DJI-Datumate Site Survey Solutions are an important step forward in professional surveying, construction infrastructure-mapping and assets inspection.”
DJI-Datumate Site Survey Solutions are available globally from the DJI online store, as well as through DJI and Datumate dealers.
SenseFly introduced the eBee Plus, its newest fixed-wing system for survey-grade photogrammetric mapping, at Intergeo 2016.
senseFly eBee Plus S.O.D.A. results
For photogrammetric-quality mapping, upgradeable RTK/PPK functionality and flight time of almost an hour, the UAV is designed for professionals working in fields such as surveying, construction and GIS who require efficient data collection with survey-grade accuracy.
The eBee Plus offers
built-in RTK/PPK functionality, activated immediately or later on demand, for survey-grade accuracy that the operator controls;
the new senseFly S.O.D.A. RGB camera developed specifically for drone photogrammetry work, featuring a 1-inch sensor and global shutter, capable of capturing images with a spatial resolution of 2.9 centimeters.
eMotion 3 flight and data management software, featuring a full 3D flight environment, mission block flight planning, cloud connectivity and free updates.
High Precision on Demand (HPoD) describes the drone’s built-in upgrade path to real-time and post-processing correction (RTK/PPK) functionality. Once activated by the user, this paid enhancement boosts the system’s achievable horizontal/vertical absolute accuracy to 3 centimeters/5 centimeters without the need for ground control points—dramatically reducing expensive, time-consuming field work.
SimActive Inc., a developer of photogrammetry software, has announced a new subscription-based offering for Correlator3D UAV. The rental option allows users with a dynamic workload to access a high-end product at minimal cost.
“Correlator3D UAV was developed for leading mapping firms, military and government organizations, with a constant emphasis on ease of use,” said Philippe Simard, president of SimActive. “The subscription model now makes the only professional UAV processing tool available for all.”
To download a free trial and view different pricing options, visit www.simactive.com.
To see the latest version of Correlator3D, sign up for SimActive’s next webinar on Tuesday, Oct. 18, at 2 p.m. Eastern Time.
Q: What is the single most important take-away from the new Federal Aviation Administration rule on UAVs?
Al Simon, Marketing Manager, Navigation Products, Rockwell Collins
A: This regulation brings some stability to industry looking to invest in UAS operations and should stimulate technology development that benefits all classes of UAS. This first step should also allow the FAA to turn their attention to the more compelling parts of the market such as Beyond Visual Line of Sight operations and integration into the non-segregated airspace like Class A and Class E.
Mitch Narins, Principal, Strategic Synergies
A: UAV proliferation and safe operation is and will be a continuing challenge. Two of the many concerns I have are: the means that state and local governments will be able to be involved in UAS operations, specifically with privacy issues, as I am sure that the FAA does not want to deal with local complaints; and the FAA’s continued acceptance of GPS/GNSS sole means for positioning, navigation, and timing information and, in the case of UAS, potentially to support command and control links.
Eric Gakstatter Contributing Editor, GIS & UAV, Geospatial Solutions
A: The new UAV FAA Part 107 rules, effective August 29, 2016, opened up the entire United States to the world of UAVs for business use. Part 107 rules significantly lower the barrier to operating UAVs for business by no longer requiring the traditional FAA pilot certificate to operate a UAV for business. The response to the new rules echo the hyper-demand for UAVs for business use. In the first 15 days, more than 5,000 people took the Part 107 test.
NVIDIA and TomTom announced they are partnering to develop artificial intelligence to create a cloud-to-car mapping system for self-driving cars.
The work combines TomTom’s HD map coverage, which spans more than 120,000 kilometers of highways and freeways, with the NVIDIA DRIVE PX 2 computing platform. Together, the solution accelerates support for real-time in-vehicle localization and mapping for driving on the highway.
“Self-driving cars require a highly accurate HD mapping system that can generate an always up-to-date HD map in the cloud,” says Rob Csongor, vice president and general manager of Automotive at NVIDIA. “DRIVE PX 2 for AutoCruise provides TomTom with a real-time, in-vehicle source for HD map updates.”
The NVIDIA DriveWorks software development kit now integrates support for TomTom’s HD mapping environment. The open solution is available for all automakers and tier 1 suppliers developing autonomous vehicles.
UAVs, precision agriculture and robotic guidance require high accuracy at low cost.
Emerging high-volume markets call for RTK technologies previously limited to niche markets by complexity and cost. This article discusses design and implementation of a very precise RTK-based module solution while maintaining cost, size and power consumption as low as possible. Several tests under a range of signal environments benchmark the new module’s performance against existing L1 RTK products.
Real-time kinematic (RTK) positioning has matured over the last few decades into a well-understood technology that, to date, has remained confined to high-end applications by high costs and complexity. Meanwhile, the rapid rise of robotic guidance applications has increased the need for higher accuracy for navigation purposes, fostering an ever-increasing demand for affordable and energy efficient high-precision solutions. Here we discuss the challenges associated with bringing RTK technology to mass markets.
The main challenge for any RTK receivers is resolving carrier-phase ambiguities to their integer values. To do so, an RTK receiver needs clean carrier-phase measurements. In general, high-end RTK receivers typically rely on multi-frequency, multi-constellation solutions and complex estimation models to improve ambiguity resolution performance. However, to reduce size, complexity and power consumption, mass-market receivers typically use narrowband single frequency front-ends, which increase noise and code multipath. Furthermore, mass-market GNSS modules have much less processor and memory resources to call upon. Therefore, to fully integrate the RTK engine, mass-market receivers typically need to restrict the computational burden by optimizing complex RTK algorithms.
Here we discuss our efforts to overcome these challenges while delivering centimeter-level positioning. Performance evaluation under challenging signal environments of a new mass-market L1 RTK module is benchmarked against an existing high-end L1 RTK product.
Multi-Constellation Support
A straightforward approach to improve reliability of the ambiguity resolution is to extend support to other constellations in addition to GPS. GLONASS and BeiDou have respectively reached full and initial (regional) operational status offering significant satellite availability improvements. Both systems broadcast their L1 open service signals using a frequency band that is offset with respect to that of the GPS L1 open service signals and, therefore, concurrent reception of GPS/GLONASS or GPS/BeiDou requires two distinct RF paths. Since the new L1-RTK based module can support reception of GNSS constellations using two independent RF paths, RTK support was implemented for both GLONASS and BeiDou, allowing either of these systems to be used with GPS. On the other hand, the low availability of operational Galileo satellites limits the benefits of a GPS/Galileo solution and, therefore, RTK support for Galileo was not implemented.
GLONASS Ambiguity Resolution
The Russian GNSS transmits L1 signals using a frequency division multiple access (FDMA) technique. While this increases the constellation’s resilience to narrowband interference, it creates two major problems for ambiguity resolution. First, GNSS pseudorange and carrier-phase measurements contain frequency dependent biases related to the receiver’s analog and digital hardware. For GPS (and other code division multiple access [CDMA]-based GNSS), all measurements share the same frequency and the biases cancel out during between-satellite differencing. However, this is not the case for GLONASS where the remaining inter-frequency biases are absorbed by the ambiguities, complicating their resolution. Second, GLONASS signal wavelengths are not common for all satellites within the L1 frequency band.
In addition to the double-difference ambiguity, GLONASS double-difference observations also consist of the between-receiver single-difference ambiguity related to the reference satellite scaled by the wavelength difference of the two signals.
Due to a lack of observability, the single-difference reference ambiguity cannot simply be estimated along with the double-difference ambiguity. On the other hand, merging the two ambiguity terms into a modified one results in an ambiguity that is no longer an integer and therefore cannot be fixed.
Both issues are well understood and several methods have been proposed to circumvent them. However, it is not yet clear whether the performance benefits brought by GLONASS ambiguity fixing outweigh the computational overhead.
BeiDou Ambiguity Resolution
China’s GNSS currently broadcasts B1 open service signals using mixed satellite and signal types, which could complicate ambiguity resolution. The limited orbit variability of BeiDou geostationary and inclined geostationary Earth orbit satellites produces poor carrier-phase ambiguity.
Despite this limitation, recent investigations reported very good dual- or triple-frequency GPS/BeiDou RTK performance, regardless of satellite type. Therefore our approach is to estimate BeiDou ambiguities for all satellites using appropriate weighting of the different carrier phase and pseudorange observations.
Cycle-Slip Detection
Single-frequency RTK inherently offers more limited measurement redundancy than its dual or even triple-frequency counterparts, making cycle-slip detection a difficult task. While a posteriori residuals checks provide a powerful mean to detect outliers, they are computationally expensive and therefore can only be used sparingly. To detect cycle slips prior to the measurement update, heuristic checks are performed on innovation sequences and complemented by systematic analysis of phase lock and C/N0 values.
Configuration Trade-Offs
The RTK positioning modules can concurrently receive and track up to two GNSS systems. By default, the reference receivers are configured for concurrent GPS and GLONASS reception. This can be modified to enable the combined use of GPS and BeiDou.
To optimize the use of processor and memory resources, the number of channels has been limited to 20. This is sufficient for dual-constellation operation almost everywhere except for a limited area in Asia where the number of visible GPS and BeiDou satellites can occasionally exceed 20.
Furthermore, the rover receiver can operate in RTK fixed or RTK float mode. In RTK fixed mode, the receiver will try to resolve ambiguities to their integer values whenever possible whereas in RTK float mode, the receiver will keep the ambiguity estimate as a floating number. The RTK fixed mode will provide the highest level of accuracy but can exhibit position jumps when transitioning from a float to a fixed solution or reliability issues when operating in degraded signal environments where multipath can lead to wrong ambiguity fixes. The RTK float mode, on the other hand, will typically provide dm-level accuracy but a much smoother trajectory.
Static Performance Evaluation
The static test data was collected on the roof of an office building in Singapore in April 2016. Twelve hours of data were collected by four receivers connected to a high-precision receiver forming zero-baseline for both GPS/GLONASS and GPS/BeiDou configurations. This allowed a thorough statistical evaluation of the ambiguity resolution performance for both configurations.
Static Data Processing
The static data sets were post-processed with a software using exactly the same algorithms as those embedded in the receivers’ firmware, allowing for direct comparison of different receiver configurations. The time-to-first ambiguity fix (TTFAF) is often used as a key indicator to assess the ambiguity resolution performance. The TTFAF differs from the time-to-first fix (TTFF) in that it only includes the time required by the ambiguity resolution algorithm to converge. To measure the TTFAF, the software is modified to perform a hot start (where position, time and ephemeris are kept) at regular intervals. This is done to increase the data set sample size and to provide a relevant statistical analysis of its reliability and rapidity.
Static Test Results
As expected, FIGURE 1 shows that the use of the GPS/BeiDou configuration significantly improves satellite visibility over the GPS/GLONASS configuration. The average number of navigation channels used is close to 20 when combining GPS and BeiDou whereas it remains below 16 when combining GPS with GLONASS. This produces faster TTFAF in GPS/BeiDou mode (FIGURE 2).
Walk Performance Evaluation
Two walk data sets were collected around Priory Park in Reigate, England on October 2015 and February 2016. Approximately one hour of data was collected each time with the equipment depicted in FIGURE 3. The antenna was mounted on a survey pole to ensure the best sky visibility possible. The radio frequency (RF) signal was then split three-way and distributed to a high-precision receiver, our rover receiver and a record and replay simulator. The RTCM correction stream was generated by a high-precision receiver connected to an antenna located on the roof of an office building and made available on a server. Using a Raspberry Pi and a 3G modem the RTCM stream was forwarded to both our receiver and the recorder. As shown in FIGURE 4, the Priory Park was selected because it provides excellent satellite visibility and is located approximately one kilometer away from the the reference station. While the open-sky test aimed at evaluating the performance of the RTK engine under ideal conditions, the tree-loop test was carried out to assess its ability to recover from moderate signal degradations. To this end, several loops were performed through the trees shown in FIGURE 5. [Click on an image to enlarge it.]
FIGURE 1. Number of satellites used vs. time for GPS/GLONASS (top) and GPS/BeiDou (bottom).
FIGURE 2. Zero-baseline TTFAF in Singapore.
FIGURE 3. Walk test set-up.
FIGURE 4. Open-sky walk test in Reigate.
FIGURE 5. Tree-loop walk set in Reigate.
Walk-Test Data Processing
The walk-test data sets were post-processed with a software using the same algorithms as those embedded in the receiver’s firmware. For the tree-loop walk test, the default GPS/GLONASS RTK fixed (Fxd-GR) configuration was used. The reference trajectory was obtained by post-processing the raw measurements from the high-precision rover and reference receivers with NovAtel GrafNav software. As it relies on a forward/backward post-processed dual-frequency GPS/GLONASS RTK solution, the reference trajectory is expected to be reliable and cm-level accurate. It can then be used to evaluate ambiguity resolution performance and baseline accuracy. Additionally, the recorded scenarios were replayed to a high-precision receiver. This receiver has an L1 RTK engine that supports GPS, GLONASS, BeiDou and Galileo constellations and is expected to deliver 1-2 cm positions. While this receiver addresses high-end markets, it was used to benchmark the performance of our RTK solution. Since the high-precision receiver supports the BeiDou and Galileo constellations using proprietary correction messages and not RTCM multi-signal messages (MSM), this direct comparison was only done for the GPS/GLONASS configuration using RTCM RTK messages. The high-precision default configuration will hereafter be referred to as Fxd-GR. The receiver was configured to output, amongst other, the NMEA global positioning system fix data (GGA) message which contains latitude, longitude and altitude data, as well as a quality indicator that can be used to see whether the receiver has achieved an RTK fixed solution.
Limitations of Walk-Test Setup
To generate a reliable and robust reference trajectory, a high-end dual-frequency wideband antenna was used. The antenna has excellent inherent multipath mitigation and phase center stability which is not representative of mass-market applications where the use of affordable patch antennas is likely to result in higher code multipath and lower C/N0. However, these issues can be efficiently mitigated by the use of a ground plane and a carefully selected reference antenna site.
Walk-Test Results
The open-sky walk test was performed in a location with clear satellite visibility so that the number of satellites with continuous phase is close to 20 during most of the test. Continuous phase lock is defined as the amount of time during which the receiver is able to track the satellite using a phase lock loop (PLL). Any interruption in PLL tracking is likely to trigger a reset of the ambiguity estimation. As can be seen in FIGURE 2, ambiguity resolution can take up to a minute, even for zero baselines. As such, having continuous tracking for longer time intervals is required to achieve high rates of RTK fixed solutions. As can be seen in FIGURE 6, this translates into cm-level position errors. Note that the open-sky walk in Reigate started and ended in an office area with low-rise buildings. The degradations brought by these buildings can also be clearly observed in FIGURE 6.
During the tree loop test, signal degradations caused by trees are experienced by the receiver approximately every five minutes, causing the number of satellites to drop to zero at regular intervals.
FIGURES 7 and 8 show the resulting position error for the mass-market and high-precision RTK receivers in Fxd-GR mode. The corresponding position error statistics are summarized in TABLE 1. The statistics are computed over the entire duration of the test and therefore can include position fixes that are computed using code differential or RTK float mode. While the large position errors that sometimes occur in these modes will tend to dominate the statistics, they are deemed representative of field applications.
Both receivers exhibit similar accuracy when they can fix ambiguities but the high-precision receiver sometimes recovers faster from signal loss-of-lock than the mass-market receiver.
UAV Performance Evaluation
A UAV data set of approximately half an hour was collected around a farm in Reigate, England in April 2016. The UAV test duration is effectively limited by the capacity of the UAV’s battery which, with the payload deployed for this test, was limited to less than 15 min. To extend the test duration, approximately 10 min of static data was recorded at the beginning of the flight while the UAV was standing in the middle of the field with no obstruction around it. The data collection was performed with DJI S900 hexacopter shown in FIGURE 9 and a payload similar to that depicted in FIGURE 3. The patch antenna was mounted on ground plane with a 15 cm diameter to mitigate multipath effects and ensure the best signal reception possible. The RF signal was then split two-way and distributed to our rover receiver and a record and replay simulator. The RTCM correction stream was generated by a high-precision receiver connected to an antenna located on the roof of an office building in Reigate and made available on a server. Using a Raspberry Pi and a 3G modem the RTCM stream was forwarded to both our receiver and the recorder. This farm provides clear satellite visibility and is located approximately three kilometers away from the reference station. It meets all the regulatory requirements to recreationally fly a UAV. The tree-line test was carried to assess the ability of our RTK engine to recover from moderate signal degradations and dynamics. To this end, the UAV was flown repeatedly along the tree line shown in FIGURE 10. [Click on an image to enlarge it.]
FIGURE 6. Position errors vs. time during the open-sky walk test in Reigate for mass-market receiver in Fxd-GR mode.
FIGURE 7. Position errors vs. time during the tree-loop walk test in Reigate for mass-market receiver in Fxd-GR mode.
FIGURE 8. Position errors vs. time during the tree loop walk test in Reigate for high-precision receiver in Fxd-GR mode.
FIGURE 9. UAV test set-up.
FIGURE 10. Tree-line UAV test in Reigate.
Test Data Processing
The UAV test data was processed in a similar fashion as the walk-test data. Two additional configurations, namely GPS/GLONASS RTK float (Flt-GR) and GPS RTK fixed (Fxd-G) were tested with the aim of illustrating their benefits and drawbacks. Due to payload weight restriction, it was not possible to embark a dual-frequency receiver for reference trajectory generation. Instead, the single-frequency raw measurements generated by the mass-market receiver were used. Recorded scenarios were replayed to a survey-grade receiver for performance benchmarking.
The main limitation of the UAV test setup is that the generation of the reference trajectory relies on raw measurements from our narrow-band single frequency rover receiver.. The lack of measurement redundancy and the increased probability of code multipath make the reference trajectory less reliable than that used during the walk test. However, UAV applications typically enjoy more favorable signal environment than their pedestrian counterparts. Additionally, it is possible to confirm the reliability of the reference trajectory using both the GrafNav backward/forward processing option and the reported accuracy.
However, the patch antenna used during the UAV test campaign is representative of mass-market applications. In fact, some tests have been conducted to compare the performance that could be achieved with various antenna types including, but not limited to, a high-precision antenna without its casing and a patch antenna with and without ground plane. The details of this investigation are beyond the scope of this article. Suffice to say that the performance of the patch antenna with a reasonably sized ground plane (15 cm in our case) was deemed the best compromise for mass-market applications in terms of size, weight and cost.
During the tree-line test, moderate signal degradations caused by trees are experienced by the receiver which cause the number of satellites to decrease at regular interval. [Click on an image to enlarge it.]
FIGURE 12. Position errors vs. time during the tree line UAV test in Reigate for high-precisions receiver in Fixed-GR mode.
FIGURE 14. Position errors vs. time during the tree line UAV test in Reigate for mass-market RTK receiver in Fixed-G mode.
FIGURE 13. Position errors vs. time during the tree line UAV test in Reigate for mass-market RTK receiver in float-GR mode.
FIGURE 11. Position errors vs. time during the tree-line UAV test in Reigate for mass-market RTK receiver in Fixed-GR mode.
FIGURES 11 to 14 show the resulting position error for the mass-market and high-precision receivers in Fxd-RD mode as well as those for the mass-marekt reeiver in Flt-GR and Fxd-G modes. The corresponding position error statistics are summarized in TABLE 2. Once again, this table can include position fixes that computed using code differential or RTK float mode.
Comparing the performance of the receivers in Fxd-GR mode, it can be seen that both receivers exhibit similar accuracy when they can fix ambiguities that the high-precision receiver suffers from an erroneous ambiguity fix at take-off which is also reflected in the position error 95 and 100 percentiles.
In Flt-GR mode the mass-market receiver is able to rapidly converge to dm-level accuracy. It is able to maintain this level of accuracy throughout the entire duration of test, highlighting the potential benefits of this mode for applications that do not require the highest level of accuracy but rely on smooth trajectory for guidance control.
For this test the mass-market receiver is able to fix ambiguity as often in Fixed-G mode than in Fixed-GR mode which is linked to the excellent satellite availability in the context of UAV applications. Additionally, the passes that were done close to the tree line were only performed later in the test, when ambiguities had already been fixed. This demonstrates the robustness of u-blox’s RTK engine to mild signal degradations. As a result, the NED position errors in Fxd-G mode are on par with those of the Fxd-GR mode. This highlights the potential benefits of this mode for high-dynamic applications that require higher navigation rate and operate in favorable signal environments.
[Click on an image to enlarge it.]
TABLE 2. NED position error statistics during the tree line UAV test in Reigate for different receivers and receiver configurations.
TABLE 1. Position error statistics during the tree-loop walk test in Reigate for different receivers.
Conclusion
Static tests showed that with fewer than 20 tracking channels, a single frequency GPS/GLONASS or GPS/BeiDou RTK receiver can successfully fix ambiguities in a reasonable time frame. During the walk and UAV tests, the performance of the mass-market receiver is similar to that of high-end receivers with respect to position accuracy and availability. For example, the availability of the RTK fixed solution was shown to be excellent under open-sky conditions for both but, as expected, in presence of moderate signal degradation and increased receiver dynamics, the availability of the RTK fixed solution decreases in a similar way for both receivers.
The kinematic data sets also served to demonstrate the versatility of the new mass-market receiver’s RTK solution. More specifically, the usefulness of the float-only solution for applications that do not require the highest level of accuracy but rely on smooth trajectory for precise guidance was shown. Similarly, the value of the GPS-only solution for high-dynamic applications operating in favorable environment was highlighted.
Finally, it is important to remember that while the walk-test results shown were obtained using high-end antennas, the UAV test results were obtained using a low-cost patch antenna, validating the suitability of RTK technology for affordable mass-market applications.
Acknowledgments
The authors thank Oscar Miles for his support with the data collection efforts in Reigate, and Alex Parkins for his contributions to the design and implementation of the RTK engine.
Manufacturers
The mass-market receiver described here is manufactured by u-blox. The RTK technology comprises a rover (NEO M8P-0) and a reference station (NEO M8P-2).
Low-cost, precision GNSS receivers will become a reality in the driverless car, drone and even smartphone markets by 2021, finds ABI Research. The automotive industry will be the main driver behind precision GNSS receiver adoption, in which centimeter-level accuracy is essential to complete driver safety systems with the redundancy necessary for autonomous vehicles.
“There is a variety of competing technologies currently under investigation by the automotive industry, but ABI Research forecasts it will move to a hybridized approach, combining LIDAR, HD maps, sensor fusion, machine vision and precision GNSS,” says Patrick Connolly, principal analyst. “As the receivers’ average selling price drops below $50, we expect to see a more immediate market for location technology services, such as AR Heads Up Displays (HUDs), in high-end vehicles. Vehicle-to-Vehicle, or V2V, communication might constitute another use case for high-precision GNSS.”
In addition to autonomous vehicles, the report also identifies opportunities for low-cost, precision GNSS receivers in autonomous unmanned vehicles (AUVs), as well as commercial and consumer devices. Though the average selling prices of such GNSS receivers is $1,000 and higher, ABI Research finds the cost to be one of the most addressable inhibitors to market growth today.
“Precision GNSS achieves sub-meter accuracy through a variety of methods, including a network of reference stations,” Connolly says. “The biggest question mark today is not cost-related, but instead how to achieve reliable, worldwide satellite navigation coverage to support correction techniques, such as real time kinematic, or RTK, and precise point positioning, or PPP. This is an extremely expensive undertaking, with currently no guarantee of a return on investment.”
Competition in the location technologies market ranges from crowdfunded startups to Internet giants, reflecting the scale of the opportunity. Traditional precision GNSS receiver vendors like NovAtel have the intellectual property, engineering experience and ownership of correction networks.
In the consumer GNSS receiver market, u-Blox and Skytraq lead the way, according to the report. Each developed low-cost single frequency PPP and RTK receivers, with a clear roadmap toward dual-frequency. Other consumer GNSS providers, like ST Microelectronics, Broadcom and Qualcomm, also appear active in this space.
Start-ups like North Surveying, NVS Technologies, REACH, and Swift Navigation continue to disrupt the industry, bringing low-cost precision receivers to market, said ABI Research. Their goal is to hit an ASP below $100 in the near future. And Radiosense is a startup that received a lot of attention for its previous work concerning precision GNSS on smartphones. It is now working on automotive solutions in a pilot in Austin, Texas.
Locata has the potential to be the wildcard in the deck, working on a powerful synchronization and location technology that may find its way into consumer technologies by 2021.
“Most interesting in the location technology competitive landscape is the involvement of Internet giants Google and Alibaba,” concludes Connolly. “Google recently announced it will make GPS pseudoranges available to developers, which, although extremely nascent, could open up the door for a lot of innovation. And in China, Alibaba is a major partner in the roll-out of Continuous Operating Reference Stations, or CORS, networks in the region.”
As off-the-shelf unmanned autonomous systems (UAS) become less expensive, easier to fly, and more adaptable for terrorist or military purposes, U.S. forces will increasingly be challenged by the need to quickly detect and identify such craft, especially in urban areas, where sight lines are limited and many objects may be moving at similar speeds.
To map small UAS in urban terrain, the U.S. Defense Advanced Research Projects Agency (DARPA) seeks innovative technologies to provide persistent, wide-area surveillance of all UAS operating below 1,000 feet in a large city. While the newAerial Dragnet program focuses on protecting military troops operating in urban settings overseas, the system could ultimately find civilian application to help protect U.S. metropolitan areas from UAS-enabled terrorist threats.
“Commercial websites currently exist that display in real time the tracks of relatively high and fast aircraft—from small general aviation planes to large airliners—all overlaid on geographical maps as they fly around the country and the world,” said Jeff Krolik, DARPA program manager. “We want a similar capability for identifying and tracking slower, low-flying unmanned aerial systems, particularly in urban environments.”
Although several systems are being developed for tracking small UAS by extending surveillance methods used in open areas where large line-of-sight buffers mitigate the threat, these systems are impractical for operation in urban terrain. Aerial Dragnet seeks to leapfrog these approaches by developing systems adapted to the fundamental physics of small UAS in urban environments that could enable non-line-of-sight (NLOS) tracking and identification of a wide range of slow, low-flying threats.
The program envisions a network of surveillance nodes, each providing coverage of a neighborhood-sized urban area, perhaps mounted on tethered or long-endurance UAS. Using sensor technologies that can look over and between buildings, the surveillance nodes would maintain UAS tracks even when the craft disappear from sight around corners or behind objects.
Low Cost Sensors, SDR. The output of the Aerial Dragnet would be a continually updated common operational picture of the airspace at altitudes below where current aircraft surveillance systems can monitor, disseminated electronically to authorized users via secure data links. Because of the large market for inexpensive small UAS, the program will focus on combining low-cost sensor hardware with software-defined signal processing hosted on existing UAS platforms. The resulting surveillance systems would thus be cost-effectively scalable for larger coverage areas and rapidly upgradeable as new, more capable and economical versions of component technologies become available.
The Aerial Dragnet program seeks teams with expertise in sensors, signal processing, and networked autonomy to achieve its goal. A solicitation detailing the goals and technical details of the program was posted here. A Proposers Day took place in late September.
Inertial, Gyroscope Take to Space
The concept image above shows the NEA Scout CubeSat with its solar sail deployed as it characterizes a near-Earth asteroid. (NASA)
Sensonor AS of Norway has partnered with the U.S. National Aeronautics and Space Administration (NASA) to supply current and future low- and near-Earth orbit space missions with inertial and gyroscope modules.
The Norway-based company first began supplying its standard inertial measurement unit (IMU) and gyroscope modules for low Earth orbit (LEO) space applications in 2012, Sensonor’s STIM300 and STIM210 inertial products now fly aboard several NASA spacecraft. Current projects using STIM inertial systems include the Raven technology demonstration and Near Earth Asteroid (NEA) Scout.
Raven, which launched to the International Space Station in September, will test key elements of an autonomous relative navigation system. Its technologies may one day help future robotic spacecraft autonomously and seamlessly rendezvous with other objects in motion, such as a satellite in need of fuel or a tumbling asteroid.
The NEA Scout is a robotic reconnaissance mission that will be deployed to fly by and return data from an asteroid representative of NEAs.
The STIM gyroscope modules are often used in combination with GPS or a Star Tracker and Kalman filter to orient and stabilize the satellite, as well as to provide feedback on satellite motion induced by its reaction wheels. In some applications, the gyroscopes are used to stabilize satellite-to-satellite communications.
Lighting Up Indoors for Retail Position
A new indoor positioning system uses LED lighting to pinpoint location for use in the retail industry. Researchers from the University of South Australia have developed an indoor positioning system that tracks movement with greater accuracy than contemporary RFID and Wi-Fi based systems.
Developer Siu Wai Ho said other methods of indoor positioning such as Wi-Fi were only accurate to within 1–2 metres and were easily hampered by radio frequencies from nearby devices, power sources or other wireless electronics. “Our system is more accurate with an error margin of 10cm and unlike some positioning systems our algorithm can calculate the orientation at the same time.”
LiPo uses LED lights as transmitters and photodetectors as receivers because they are both common items in modern societies. Photodetectors are a key component for capturing light and are also commonly found in smart phone cameras. The system uses a specially designed receiver to measure light intensity that is able to calculate position and orientation. Although it currently requires a unique receiver, developers hope to integrate the technology with the photodectors in mobile phones. This would reportedly enable supermarkets to provide customers with relevant information about items nearby.
“If you are in a supermarket you want to see some information for a product in front of you. One or two metres of error is still too big because it maybe gives you a product you are not in front of.”
Other applications could include the identification of objects or machinery in factories, movement aid tools for the elderly and trackers for museums to provide relevant information to tourists as they passed by exhibits.
Munich SatNav Summit Stresses GNSS Back-Up
“Is it Time for GNSS Back-Up?” has been announced as the the theme of the 2017 Munich Satellite Navigation Summit, to take place March 14–16.International experts gather to discuss recent position, navigation and timing develeopment and the necessity for GNSS backup solutions.
Among the topics, in addition to system updates on all major GNSS, we find listed: From Iridium to e-Loran — GNSS in need for a Backup; Galileo after the Brexit; Civil use of the Galileo Public Regulated Service (PRS); and Network-based solutions for GNSS Backup. Go to to www.munich-satellite-navigation-summit.org for registration information.
Xsens Offers Knowledge BASEd Inertial Motion Tracking
Xsens has launched BASE, an online technology platform with a community forum and a knowledge base on 3D motion tracking technology and products. BASE.xsens.com, contains inside information about micro-electro-mechanical system (MEMS) sensors, inertial measurement units (IMU), sensor fusion algorithms, body-motion tracking and motion capture.
It also provides best practices, tips and tricks for the use of Xsens’ MTi series, the MTw and the MVN wearable motion capture solutions. A second section of BASE is the community forum with direct access to Xsens’ engineers and other Xsens users.
There is no need to register for BASE to access the community forum and the knowledge base. To ask questions or comment on articles, registration is possible via SSO or email.
