Ships at sea and vehicles on – and off – roads can be tracked from space using data from radar satellites, says the German Aerospace Center (DLR). It’s not a new idea, but DLR has demonstrated a more accurate way of processing the data.
The demonstration used data from the twin TerraSAR-X and TanDEM-X radar satellites, collected when they were 20km apart in orbit and before they moved into close formation.
Graphic: EADS Astrium
Radar uses the change in frequency in returning signals to distinguish moving targets, but this Doppler shift can move the apparent position of a vehicle several hunderd meters from its actual location, says DLR. In previous experiments on tracking traffic from space, a database of road networks was required to determine vehicle location and speed accurately – but this does not work well in urban areas with many parallel streets, or when vehicles are off road.
Red and green images are both incorrect, but the difference between them is used to calculate the true position, (Photo: DLR)
The traffic processor developed by DLR uses radar images of the same area captured seconds apart by the TerraSAR-X and TanDEM-X satellites. The moving target is shifted from its true position in each image, but the displacement between the two different “incorrect” positions can be used to calculate the location, speed, direction and even acceleration of the vehicle or ship, says DLR.
The traffic processor was used to observe ships in the Strait of Gibraltar. This showed the unprocessed radar images of the ships (white dots on the image below) could be up to 550m away from their true positions (colored symbols). Such accurate position and velocity data could improve traffic management, says DLR.