Access all areas: emerging approaches for GPS-denied operations

Transcription

1 Access all areas: emerging approaches for GPS-denied operations [Content preview Subscribe to Jane s International Defence Review for full article] GPS jamming and spoofing have been experienced across the contemporary operating environment, Huw Williams examines some of the systems under development to counter the threat GPS technology is prevalent on the modern battlefield and underpins many systems. With applications including simple dismounted navigation, precision strike, and as a key enabler in the operation of unmanned aerial vehicles (UAVs), it is unsurprising that GPS denial has emerged as a significant disruptive capability. GPS signals are vulnerable to active jamming or spoofing, and have limited application in buildings and certain environments, such as dense forest canopies or urban canyons. As such, significant attention is being paid to providing the utility offered by GPS through other means. The use of alternative technologies for navigation is not something new, with inertial navigation systems (INS) in widespread use, and the likes of LORAN (long range navigation) technology, terrain contour matching (TERCOM), and celestial navigation systems having a number of applications. Efforts to enhance existing technologies and harden GPS continue, with anti-jamming systems developed and fielded and resources put into improving the performance of INS and other navigational aids. The US Department of Defense also has efforts to modernise GPS (M-code GPS) which should bring an additional level of protection through the combined use of high-gain directional antennas and wide-angle antennas to broadcast the M-code from next-generation GPS III satellites. Elsewhere, US Army concepts for the use of pseudolites envisage surrogate systems for GPS, such as a manned aircraft or UAV flying outside the reach of an enemy s interference to broadcast a GPS signal to an area of operations, or ground-based installations transmitting the GPS signal, although these could not account for localised jamming and would require a level of control over the battlespace. Alternatives that leverage multiple technologies often in a blended approach are emerging and taking advantage of reductions in size, weight, power, and cost (SWaP-C) in the enabling technologies, such as sensors, measurement units, and computer processors, as well as software developments. Vision-based navigation The US Defense Advanced Research Projects Agency s (DARPA s) Fast Lightweight Autonomy (FLA) programme aims to develop perception and autonomy algorithms that will enable highspeed navigation in cluttered environments. Page 1 of 9

2 The participants in DARPA's FLA programme utilise COTS hardware for the air vehicle. (Draper) FLA is focused on enabling air vehicles that are small enough to fly through windows to operate autonomously at speeds of up to 20 m/s, with no communication to the operator and without GPS waypoints. For FLA, the participants are using a commercially available platform in the form of a DJI Flamewheel 450 airframe that is equipped with E600 motors, 12-inch propellers, and a 3DR Pixhawk autopilot. The programme is taking an incremental approach and is demonstrating a sequence of capabilities, beginning with lower-clutter, fly-by missions and progressing to higherclutter, fly-through missions. US-based research and development organisation, Draper, has partnered with the Massachusetts Institute of Technology (MIT) for FLA and the team is using a vision-based navigation system that features its SAMWISE (Smoothing And Mapping With Inertial State Estimation) sensor-fusion algorithm. Our team s approach is focused on a minimal set of sensors; we believe we can accomplish this task with just an IMU [inertial measurement unit] and a single monocular camera, explained Ted Steiner, a senior member of Draper s technical staff. The reason why this is such a valuable sensor combination is because you could potentially shrink a UAV down to be very small and carry only these two sensors. When you look at some of the small UAVs that have already been developed and which are flown manually, these are almost always the two sensors that are present. We re also using a laser altimeter to get more accurate altitude, which is especially helpful for take-off and landing, but the only sensors we truly need are a camera and an IMU, Steiner told Jane s. To date, the team has been able to achieve flight speeds of up to 45 mph, and mph when flying around obstacles. Page 2 of 9

3 The main challenges in delivering the capability can be broken down into three areas, Steiner said: navigation, perception, and planning. The Draper/MIT solution for DARPA's FLA programme utilises vision-based navigation and employs a single monocular camera. (Draper) Critical navigation information pertains to location and state i.e. how fast is the air vehicle moving and which direction is it pointing, We re using a camera and an IMU to estimate our relative position compared to where we started, [the IMU measures] acceleration and rotation rates, and we integrate those to get position data and correct the signal using feature tracking measurements that cut down on error, Steiner explained. Perception is focused on providing an awareness of the air vehicle s surroundings and obstacles that it needs to avoid, What we re doing in the perception area is using a technique that is fundamentally called stereo from motion. That allows us to generate a point cloud of the environment based on a single camera moving around, and we know how far the camera moves from [SAMWISE]. The way that we have sped up our obstacle detection and avoidance pipeline is Page 3 of 9

4 through an algorithm developed by our MIT partners that is able to compute obstacles across a graph mesh, which saves a lot of computation, so that s been an enabling technology for us. The team applies an innovative approach to addressing the planning task, The reason why this is challenging is because many algorithms that currently exist take quite a bit of time to process an optimal trajectory we very quickly produce many candidate trajectories and select the best one. So we evaluate the goodness of trajectories as opposed to optimising the best trajectory, Steiner explained. Further sensors could be brought on board to improve performance, Steiner noted, but this would have to be balanced by the increase in SWaP, One sensor that we have experimented with is a magnetometer, but we ve found that in the indoor environment that tends to have too much noise, but outdoors it s still a valuable sensor, he said. To date, Draper and MIT have demonstrated the ability of their system to operate in a warehouse environment; in outdoor, very open environments; in a profile that has both indoor and outdoor settings, where it flies in and out of buildings; and in a scenario that combines elements of all three profiles. DARPA has now tasked the FLA participants with operating in outdoor urban environments, as well as introducing a search element, as opposed to just fast flight, Steiner said. While FLA is primarily targeted at lower altitude flight, vision-based navigation can also be applied at high altitudes. Leidos has developed an airborne vision-based navigation approach that matches live sensor images to overhead satellite imagery databases. The tremendous capability that modern processors have in a small SWaP-C factor, combined with the prevalence of high-resolution satellite imagery databases for pretty much all of the world, have been the two enablers that have allowed us to do real-time navigation with vision aiding, explained Kevin Betts, Leidos position, navigation, and timing director. He added, The best mode to operate in is if you take the live camera image and match it to what you have in your database; the fact that you already have geo-registered information allows you to match the image you are seeing to what s in the database and then go through the reverse transformation to calculate the position and attitude of the aircraft. Betts said that in the majority of terrain, they have achieved sub-10 m accuracy with the system when operating below the cloud ceiling. Betts added that available hardware is mature enough to support this vision-based approach to navigation, in no small part due to the high quality of the electro-optical/infrared camera payloads that are typically carried by UAVs, for example. With regards to the currency of the satellite imagery databases, Betts said that these can be and are updated frequently, meaning that typically there are not gaps in coverage that might allow significant changes on the surface to conflict with the database employed by the aircraft. One limitation of the system, of course, is its inability to function independently over water. While the sweet spot for the operation of the system is 2,000 10,000 ft; it can also operate at higher altitudes and at low level typical to those flown by quadcopter UAVs, as long as the fieldof-view is wide enough, Betts said. Page 4 of 9

5 Potential enhancements to the system could be brought through even faster processors, Betts noted, as these will enable more real-time integrity checks to be conducted. Improvements in the quality of satellite imagery and wider coverage of 3D databases would assist low-level operation, especially when the camera is not pointing directly at the ground. Dismounted operations Providing navigation and positional data to dismounted personnel operating in GPS-denied environments thus enhancing situational awareness to them and others requires different approaches to those used by aircraft, and is often concerned with indoor operations and increasingly tunnels. In the case of the former, awareness of which floor of a building personnel are operating on is of importance, and as such, a 3D picture must be developed. TRX Systems NEON and NEON Squad Tracker solutions use a blended, multisource approach to providing positional information and navigation, with inertial navigation and dead reckoning as core technologies. The technological pieces that are important to create a commercial off-the-shelf [COTS] solution are there, meaning inertial sensors of the appropriate quality are now at the reasonable price point and size, along with networks that would allow for real-time communications beyond the typical two-way [function], Jeff Kunst, the company s vice-president of product and business development told Jane s. Kunst said the storage and computational capabilities on smart phones have developed to the point that they are capable of running navigation engines that can fuse sensor data locally, rather than having to disseminate it for processing. TRX Systems tracking solutions can provide 3D visualisation. (TRX Systems) We developed a cloud-based system that is deployed with a small tracking unit an IMU, but has other elements as well and that unit gives you sensor data that is sent to a location engine that is on an Android device. The location engine then communicates to the cloud, which then connects into our command software and provides 3D visualisation; so we re providing a 3D location of each user that is calculated directly on the Android, Kunst explained, The command software is really a visualiser, we do some computations in the cloud, but primarily we re doing storage of map data Page 5 of 9

6 and location history, and the cloud handles the messaging service to get real-time data back and forth. We have a very low SWaP and cost device that is COTS available. We re using high quality sensors that are now in cell phones [the device also has] a gyro, an accelerometer, a pressure sensor, and a magnetometer, as well as Bluetooth and ultra-wideband [communications], Kunst explained, adding a combination of all of these sensors can now provide your inertial track and we re able to sense between the inertial data and the pressure data [to determine] whether you re going upstairs, riding in an elevator, going up and down terrain, and then those deltas get sent over Bluetooth [or via USB connectivity] to the Android location engine, and that location engine pulls terrain data from our cloud service, as well as building shape files, and satellite imagery, this allows you to visualise on the Android. The shape files and the terrain data can be correlated with other sensor data in our nav engine, which helps us to reduce the accumulated error from the inertial sensors, so now you can combine that with GPS or in the case of soldier-mounted systems with SASSM [Selective Availability Anti-Spoofing Module] devices or other sources of location data. TRX Systems tracking solution on a smart phone. (TRX Systems) The system can also leverage RF sources to enhance its accuracy, with mapped beacons providing the highest degree of accuracy; while this may not be applicable in operational environments, it has significant utility at training centres, for example. In the military environment, ultra-wideband technology which only requires very low energy levels for short-range, high-bandwidth communications over a large portion of the radio spectrum can be leveraged, with data shared between members of a network; positional information from the member with the best data can be shared and ranges and relative positions established. The accuracy of the system varies and is dependent on a number of parameters, Kunst said, noting that a good original fix is paramount to a high level of accuracy, along with the ability to Page 6 of 9

7 utilise the full range of sources. If you use ultra-wideband in the system, you can be as good as 1 2 m accuracy, but it can be 20 m-type accuracy if you are just using inertial navigation and building shape files. If your use case allows you to use all of your capabilities then generally accuracy is better than 5 m, 95% of the time, but it varies widely depending on how long you are tracking, how big the building is, what constraints you have, what kind of movement you have. The company has conducted exercises with the US military, however, Kunst was unable to go into specifics. With regards to technology developments that will enhance the performance of the systems, he pointed to improvements in the quality and accuracy of map data and the continued maturity and reduction in cost of ultra-wideband communications as beneficial. The US Army has a number of efforts to improve navigation for dismounted personnel in GPSdenied environments, including a soldier-borne vision-aided navigation device. Under development by the Army Materiel Command s Communications-Electronics Research, Development, and Engineering Center (CERDEC), the solution uses cameras with rapid frame rates to take pictures of objects in view and then compares their features in each frame to determine how far, and in what direction, the camera has moved in relation to the object. The system utilises a monocular camera and is aided by an IMU to provide data on distance travelled. The IMU determines approximately how the camera is moving, and therefore the motion of the camera can be compared with what has been determined by the vision element. The system is designed to limit the drift of the IMU by leveraging data collected by the camera. Echo Ridge is developing a handheld navigation system that leverages RF signals of opportunity and interfaces with the Android Tactical Assault Kit. (Echo Ridge) According to the army, during tests in urban environments, soldiers equipped with the system were able to maintain trajectories close to those generated by GPS and other sources. The first application for the system is likely to be vehicle mounted and there is the possibility of introducing a stereo camera configuration SWaP-C permitting. Through a US Air Force Small Business Innovation Research (SBIR) and Small Business Technology Transfer (STTR) programme, Echo Ridge is developing a dismounted navigation system that leverages known RF signals for positional data. Page 7 of 9

8 The company is working with the Air Force Research Laboratory s (AFRL s) Sensors Directorate for the effort and has developed a handheld device and algorithm for the task. The algorithm aggregates signals of opportunity to determine its position based on the time difference of the arrival of the signals. The hardware developed by Echo Ridge connects to smart phones that operate with the Android Tactical Assault Kit, on which the navigation information is displayed. The signals measured come from known or discovered locations. The first field test of the system was conducted at Fort Bragg, North Carolina. The US AFRL has also developed a multisource solution for aircraft in the form of its All Source Positioning and Navigation (ASPN) system, which houses multiple sensors in a pod. This is intended to enable the air force to utilise its own navigation algorithms, and the pod includes camera payloads that support vision-aided navigation as well as an INS, magnetometer, GPS receiver, and a highly accurate clock and barometer. The AFRL's ASPN combines a number of sensors in a single pod. (IHS Markit/Patrick Host) While GPS and alternative navigation methods can provide positional information down to submetre accuracy in the best cases, when operating autonomously, land platforms will require much higher precision in support of their movement. UK-based Oxbotica has developed a camera and laser-based localisation system that can achieve accuracy down to a few centimetres when operating along known, mapped routes. The company s Selenium autonomous control system is hardware agnostic and the software uses positional data and local information about the environment around the vehicle to determine a safe route and speed. The system has demonstrated the ability to operate in built-up areas and off-road conditions where there is little structure. Selenium localises the vehicle by comparing real-time imagery to that previously recorded/mapped, and does not require an IMU or other devices to function. Page 8 of 9

9 Oxbotica s CEO, Graeme Smith, told Jane s that a stereo camera system is used for visual odometry, and builds a picture down to the millimetre level. The software draws a memory of a route it has travelled along and multiple maps can be stored for comparison against. In a military environment, Smith said that a typical application could see the system supporting logistics operations, with autonomous vehicles able to follow a route that could have been mapped by another vehicle previously. Smith said that there are a number of technologies on the horizon that could enhance the capability and enable wider utility, notably smaller, smarter cameras that could be soldier borne and enable dismounted units to localise in known areas. Lower cost laser systems and LIDAR could also prove a boon for the system. At sea In the maritime domain, the US Navy has recognised the potential for LIDAR to be used to achieve accurate positional data by measuring space objects that have known orbits, positions, and velocities. The concept requires access to fewer satellites than GPS and does not need active satellites it can use retro-reflectors or even space debris. A high-power LIDAR system, originally designed to track space objects, will be required and the positioning method requires only two measurements range and range-rate a single space object with known ephemeris, and an approximate altitude. Drawbacks to this approach include that the system will be fairly large, expensive, and power-hungry, which means for the time being, it will only be suitable for large ships; it will also be susceptible to interference by weather conditions, with cloud cover being a potential problem. For the full version and more content: Jane's Defence Industry and Markets Intelligence Centre This analysis is taken from Jane s Defence Industry & Markets Intelligence Centre, which provides world-leading analysis of commercial, industrial and technological defence developments, budget and programme forecasts, and insight into new and emerging defence markets around the world. Jane s defence industry and markets news and analysis is also available within Jane s International Defence Review. To learn more and to subscribe to Jane s International Defence Review online, offline or print visit For advertising solutions visit Jane s Advertising Page 9 of 9