Uncrewed Systems Technology 044 l Xer Technolgies X12 and X8 l Lidar sensors l Stan UGV l USVs insight l AUVSI Xponential 2022 l Cobra Aero A99H l Accession Class USV l Connectors I Oceanology International 2022

8 Platform one Cambridge Pixel has developed a technique for using radar data to support global satellite navigation systems, protecting USVs or ASVs at sea against GPS spoofing, jamming and interference (writes Nick Flaherty). Spoofing is where a GNSS signal from a GPS or Galileo satellite for example is deliberately overwritten with data giving a different location. “If GPS is jammed or spoofed, that presents a real problem for an uncrewed vessel,” said David Johnson, managing director of Cambridge Pixel. “We use information from the radar already installed on the vessel, which gives us information on what is around the craft. We compare that data with a database of terrain and coastline information, and the system can match the data to give an approximate location.” The database uses public data from the Shuttle Radar Topography Mission (SRTM) project at NASA. This has elevation data on a near-global scale using radar interferometry from satellites in 1 x 1 º tiles at 1 arcsecond, giving a resolution of about 30 m. The database is held on the onboard radar computer system, and when the GPS signal is lost the server starts looking in the area of the last known position and uses the terrain data to create an image. This image is then compared to the radar image to provide a location.   “We maintain a store of this on a file system on the computer, creating a picture of what the terrain looks like at that particular position, and it is this image that we compare with the radar data,” said Johnson.  “There are two applications for this. We are always making that comparison in the background and comparing it with what the GPS says. If the data is significantly different then we can generate an alert that GPS might be being spoofed. “If the GPS is jammed or unavailable, we can generate a pseudo-navigation stream. That might not allow the mission to continue but will give the craft information for navigation.” The advantage with this approach is that it doesn’t use any extra equipment on the vessel, such as a camera. The terrain server sits alongside the target tracking and data fusion servers on the onboard rugged PC, and feeds into the mission computer. “We provide the data in a way that fits with our algorithms, and that is taken as an input by the mission planning algorithm,” he said. “We deliberately try not to do something that is specific to the mission planning software.” The accuracy of the positioning is determined by the resolution of the maritime radar, which can have a precision of hundreds of metres. “That just means it takes longer to build up the confidence that there is a problem, maybe a minute or so,” said Johnson. “It’s never going to be a replacement for GPS.” Naturally it doesn’t work in the open ocean, where there is no coastline to monitor. “There has to be coastline around you for this to work, so the technology is best suited to operations in the littoral [coastal] environment,” he said. Marine vessels Data helps stop spoofing June/July 2022 | Uncrewed Systems Technology The technique uses data from a vessel’s onboard radar to prevent GNSS spoofing