Multichannel Systems for Ground Moving Target Indication

Kurzfassung

The development of a fully operational wide area traffic monitoring system like in the TRAMRAD project (TRAffic Monitoring with spacebased RADar) requires detailed knowledge of the capabilities and limitations of Ground Moving Target Indication (GMTI) techniques. Only with this knowledge it is then possible to end up in an optimized system design. In principle, two processing techniques come into question for radar-based traffic monitoring: Synthetic Aperture Radar (SAR) due to its high resolution imaging capability and Space Time Adaptive Processing (STAP) due to its moving object indication capability. SAR is a well established remote sensing technique which is now routinely used to provide radar images from airborne and spaceborne platforms independent of daylight and weather conditions. On the other hand, several powerful radar techniques have been developed for detecting ground moving targets and estimating their motion parameters mainly for airborne applications in military context. Most of these developments rely in some form on the STAP principle, which evaluates the signals from multiple receive apertures in a spatiotemporal array processing framework. The joint space-time processing is well suited to mitigate the Doppler spreading of ground clutter induced by radar platform motion, thereby enabling a reliable detection of even slow and small vehicles with low radar cross section in heterogeneous environments. However, until today none of these multi channel techniques has been implemented operationally on a spaceborne platform to monitor traffic on the ground. To develop a future fully operational and high resolution traffic monitoring system as envisaged in TRAMRAD it is hence necessary to recapitulate the existing airborne GMTI techniques and algorithms and to adapt them to the traffic scenarios to be observed. This document recapitulates existing GMTI techniques which are based on STAP because from STAP important principles for GMTI using radar can be gained. The influence of system parameters which have to be designed is shown as well as the influence of channel and clutter mismatches to STAP performance. An adaptive system can add robustness to system errors and can handle nonstationary interference. However in real-world environments the adaptation process is critical because clutter statistics vary fast and therefore in general only few samples are available which provide the same clutter statistics as the clutter in the cell under test. A multitude of STAP methods and algorithms has been developed which is aimed on providing fast convergence in the adaptation process. An overview on the methods is given. However the transfer of a typical air-based GMTI system to a space-based GMTI system is not simple: Aspects such as height above ground, platform velocity and platform stability have to be taken into account. A spaceborne GMTI system rather has to combine SAR with STAP principles. The transfer of a STAP processing sheme on a linear multi-channel SAR-system is shown as well as a possibility to transfer STAP on a three-dimensional multistatic array configuration.