Effects of internal clutter motion on STAP in a heterogeneous environment

Clutter is typically modeled as stationary (i.e., zero Doppler shift) scatter from the surface. Thus for ground-based systems the clutter is contained at zero Doppler while airborne systems will observe clutter spread in Doppler due to platform motion (i.e., the classic angle-Doppler clutter 'ridge'). However, motion internal to the background clutter of vegetation, etc., will result in the clutter having non-zero bandwidth. This effect, generally referred to as internal or intrinsic clutter motion, will tend to increase the rank of the clutter in the space-time adaptive processing (STAP) covariance matrix. We examine the effect of this phenomenon on STAP. We consider the effects of a heterogeneous environment and provide examples based on site-specific terrain data that illustrate the impact on STAP performance.