Detection limits for sideways looking MTI radars

Airborne surveillance radars provide powerful tools for addressing a variety of ground surveillance activities ranging from terrain height mapping to moving target detection. Two common modes for ground surveillance are the synthetic aperture radar (SAR) mode for static target detection and ground moving target indication (GMTI) for the detection of ground moving targets. While the concept of operating in different modes on a common radar is straightforward, optimising the overall design is not. For example, the preferred orientation for the SAR and GMTI modes are different with the SAR needing to look sideways to the aircraft flight path and the GMTI preferring to look ahead of the aircraft. When we add the constraints imposed by airframe design we inevitably arrive at a compromise solution which is a moderately sized antenna mounted in a sideways looking configuration. The GMTI must now operate in a manner which allows a good detection performance to be recovered in this sideways looking mode. The solution is to use displaced phase centre antenna (DPCA) or space time adaptive processing (STAP) techniques. These techniques allow the GMTI system to differentiate between unwanted static clutter and slowly moving targets of interest. We consider how effectively these modern GMTI techniques may operate. To do this we need to understand both the operation of the processing and detection algorithms and the statistical properties of the targets and clutter. This paper presents a theoretical description of the GMTI detection limits and compares these predictions with experimental airborne data.