NLR develops new technique for data compression
02-02-2010
Owing to the increase of resolution, bandwidth and sensitivity, radar satellites - or rather SAR (Synthetic Aperture Radar) satellites - produce increasing amounts of sensor data. However, the available bandwidth of the downlinks increases more slowly. Therefore, data compression on board these radar satellites is becoming more important. NLR has developed a new algorithm for more efficient data compression which may avoid the need for another complete ground station.
SAR satellites carry out observations with ever increasing precision of the Earth’s surface. These satellites are used for e.g. detection of illegal oil discharges from ships, for monitoring shipping routes (sea ice) and for the measurement of height changes of dikes. SAR satellites are connected to ground stations, where data is received, stored and transmitted. These stations, including staff, are very expensive to run.
The current compression now has a reduction factor of 2 to 3, but the new algorithm, developed and now implemented by NLR, achieves a reduction factor of 4 to 5, a huge gain. To do this the PowerFFT chip is used: this is the fastest Fast Fourier Transform signal processor in the world. This chip will soon also be available in a spaceworthy version. The latest and fastest technologies are also used for other electronic equipment, to meet the high data rates and required very high computing speed.
Following these technological developments, NLR has started on the design of an onboard processing unit. Here the PowerFFT technology is combined with the Leon processor. This is a processor designed specifically by the company Gaisler (commissioned by the ESA) for space applications. The reason for the development of this onboard processing unit is that it not only carries out data compression but also many other functions, such as intelligent filtering, on board adjustments or complex calculations such as elevation. It is expected that such units will be emplaced during various future missions. The next mission that is targeted is Safari, but if that does not happen, there is a range of other potential missions for which the onboard processing unit can be used.
