Estimation of Moving Target Velocity Parameters with Air- and Spaceborne Multi-Channel SAR Systems

Abstract

For traffic monitoring applications using multi-channel synthetic aperture radar (SAR) systems operating on air- or spaceborne platforms the vehicles moving on ground have to be detected and their motion parameters have to be estimated. Up to now, with DLR’s airborne F-SAR system as well as with the spaceborne TerraSAR-X Dual receive antenna mode only two channels of an along-track array have been combined coherently for purposes of ground moving target indication (GMTI) using techniques such as displaced phase center antenna (DPCA) and along-track interferometry (ATI). This work steps from target motion parameter estimation using two-channel techniques (ATI) to multi-channel STAP techniques. The drawback of two-channel target motion parameter estimation techniques such as ATI is that they cannot handle situations where moving target signals interfere with high clutter environments. By use of multi-channel STAP techniques and along-track arrays with more than two channels enough degrees of freedom are available such that even high clutter can be suppressed and at the same time target motion parameters can be estimated. In the frame of this work various STAP parameter estimation algorithms are implemented and tested. The performance of the estimators is tested by use of Monte-Carlo simulations and compared to the Cramer-Rao Lower Bound (CRLB). In a next step the estimators are tested with experimental F-SAR four-channel X-band data and the performance achieved with the real data is compared to the performance predicted by the CRLB and achieved in the Monte Carlo simulations in order to evaluate the quality of the performance prediction. With airborne radar systems and GMTI applications usually high PRF values are used such that the stationary world signals are highly oversampled. This is not possible with spaceborne radar systems due to swath width restrictions induced by the range ambiguities. For spaceborne multi-channel SAR systems range and azimuth ambiguities usually have to be considered for GMTI applications and the choice of the antenna length, the number of channels and the PRF are critical parameters in the multi-channel SAR satellite system design. Since the STAP parameter estimation techniques provide a general processing rule for coherently combining the signals from along-track arrays with arbitrary number of channels, arbitrary arrangement of the channels (as long as the system can be considered quasi-monostatic) and PRF they can also very well be used for the multi-channel SAR satellite system design. The impact of the antenna length, the number of channels and the PRF on the predicted moving target motion parameter estimation accuracy is shown for various near-future multi-channel SAR satellite system concepts.