On-board Doppler filtering for data volume reduction in spaceborne SAR systems

High-resolution wide-swath (HRWS) synthetic aperture radar (SAR) systems based on digital beamforming (DBF) in elevation are very attractive for the observation of dynamic processes on the Earth´s surface. However, HRWS systems are inherently associated with a huge data volume. Moreover, in order to comply with azimuth ambiguity requirements, a pulse repetition frequency (PRF) much higher than the required processed Doppler bandwidth is often desirable. The data volume can be drastically reduced, if on-board Doppler filtering and decimation are performed prior to downlink. A finite impulse response (FIR) filter with a relatively small number of taps suffices to completely suppress the additional ambiguous components and recover the original impulse response, provided that the filter´s transfer function is compensated for in the processing. This strategy is also applicable to staggered-SAR systems, where on-board Doppler filtering and resampling can be jointly implemented.