Interrupted Synthetic Aperture Radar (SAR)

High and ultra-high resolution Synthetic Aperture Radar (SAR) are increasingly used for surveillance. These high resolution modes require a significant coherent integration time (CIT) to achieve the high cross range resolution. Persistent surveillance sensing modes require continuous collection of SAR data. The reality of sensor resource management is that this kind of time dedicated to SAR may not be achievable. Instead the sensor must be periodically interrupted so that other functions such as air-to-air situational awareness (search, track, and track maintenance), terrain following/terrain avoidance (TF/TA), electronic attack (EA), electronic protection (EP), and communications. A further complication occurs due to the crowded spectrum which is especially true for UHF foliage penetrating radar. In these lower frequency bands there are frequent gaps in collected radar spectrum due to interference or transmit restrictions. This interrupted SAR mode results in imaging artifacts that serious degrade the performance of subsequent exploitation algorithms. This effort will explore not only the impact of varying levels of interruption on SAR exploitation but also study several techniques for mitigating the effects of interruptions. BENEFIT: This research will result in mitigation of artifacts in SAR data that seriously degrade the performance of change detection algorithms used for persistent surveillance. The approach will be immediately beneficial to low frequency foliage penetrating SAR where interference in frequency is high and large integration times are needed to achieve cross range resolution. The technique will also facilitate novel sensor resource management approach to allow multi-function sharing of an aperture. The technique not only has applications to military sensors but also commercial foliage penetrating interferometric radars used in terrain mapping applications.