Subspace transformation techniques applied to multi-channel SAR/MTI

Using SAR-systems with several along-track sub-apertures has proven to be a highly sensitive technique for detection and positioning of moving targets. The core of multi-channel SAR/MTI processing is an adaptive filter for clutter suppression. In the SAR environment the processing in the Doppler domain is favourable, since an infinite train of pulses is used. But some problems arise from the large number of degrees of freedom: at the edges of the clutter spectrum the clutter power may be too weak to perform a sufficient adaptation, so that moving target signals are suppressed as well. The objective of this paper is to propose a problem-matched architecture of the clutter adaptation using the technique of “coherent subspace transformation”. This offers stabilisation against rapid flight manoeuvres, coverage of uncertain frequency regions and avoiding the suppression of moving target signals. The proposed processing is illustrated by data gathered with the German “Airborne Experimental Radar” (AER) using four along-track subapertures