Principles of Modern Radar - Volume 2 1891121537

724 CHAPTER 16 Human Detection With Radar: Dismount DetectionFIGURE 16-9Illustration ofperformance ofoptimal STAP filteron data for a humantarget in clutter.Doppler Frequency (Hz)8006004002000−200−400−600−800−80 −60 −40 −20 020 40 60 8050403020100−10Doppler Frequency (Hz)8006004002000−200−400−600−800−80 −60 −40 −20 0 20 40 60 806050403020100−10−20−30Angle (degrees)Angle (degrees)(a) Large SINR, prior to STAP(b) Large SINR, after STAPDoppler Frequency (Hz)8006004002000−200−400−600−80050403020100−10Doppler Frequency (Hz)8006004002000−200−400−600−800403020100−10−20−80 −60 −40 −20 0 20 40 60 80−80 −60 −40 −20 0 20 40 60 80Angle (degrees)Angle (degrees)(c) Small SINR, prior to STAP(d) Small SINR, after STAPEquality occurs if and only if α = kβ or Ah opt = k(A H ) −1 s. Solving for the optimumweight vector,h opt = kA −1 (A H ) −1 s = k(AA H ) −1 s = kR −1I s (16.32)The performance of (16.32) as a clutter cancellation filter is illustrated in Figure 16-9,which shows the angle-Doppler maps of a single human target before and after applicationof the optimal STAP filter. In Figures 16-9a and 16-9b, the SINR level of the human signalis large, so that it is clearly visible in the angle-Doppler maps. The clutter cancellationfilter of (16.32) effectively removes the large clutter ridge in Figure 16-9a, leaving aclear target response in Figure 16-9b. However, as the interference levels increase andthe SINR levels decrease, the target signature becomes less and less distinct in the data.Figures 16-9c and 16-9d show angle-Doppler maps for just such a case. Before cluttercancellation, the target signature is so weak due to masking by the clutter that it is barelydiscernable. After clutter cancellation, the clutter ridge is successfully removed, but theremaining target signal, although now visually observable, is still quite weak, limitingdetection performance.For airborne dismount detection applications, where the clutter levels are much higherand the larger distances between the target and the radar diminish the received signal power,it is much more likely to observe the high clutter scenario depicted in Figures 16-9c and16-9d. Thus, while STAP processing is a necessary and critical component of any dismountdetection system, STAP alone does not resolve all of the challenges to human detection,especially in the high clutter case.