Approximate invariance of the inverse of the covariance matrix and its applications

Space-time adaptive processing (STAP) normally requires knowledge of the inverse of the covariance matrix (ICM) of undesired signals for detecting desired target signals. The computation of the real-time ICM is impractical at current computer speeds. Presenting two theorems, this paper shows that the ICM is approximately invariant to clutter changes if radar and platform parameters remain unchanged. Potential applications of this approximate invariance are manifold. One of applications we suggest in the paper is a pre-built space-time non-adaptive processor (PSTAP). Both simulated data generated by the high fidelity simulation software, RLSTAP, and real data collected by the Multi-Channel Airborne Radar Measurements (MCARM) system are tested. The results indicate that PSTAP performs virtually the same as STAP. A moving target has been detected from the MCARM data.