Holographic Radar Signal Processing

ABSTRACT: In Phase I, TSC and SDL will develop holographic circular SAR (CSAR) processing algorithms that allow a scene to be viewed in three dimensions over 360 degrees in azimuth and with a large elevation angle extent. Our approach is to coherently combine a set of CSAR images collected with different grazing angles to provide vertical resolution using a DTED database as a reference. This holographic SAR imaging will provide target height estimates and additional features for target identification, and will greatly improve the positional accuracy of targets, buildings and terrain. Initial testing of the algorithms will be done using the Gotcha 2006 multiple-orbit data collection. Holographic SAR imaging will eliminate the problematic feature overlay between multiple objects by resolving scatterers in the third dimension. Thus holographic SAR should greatly enhance the Air Force"s ISR capabilities. In Phase II the holographic CSAR algorithms will be fully developed and tested. Also, both L and X-band CSAR data will be collected using the SDL NuSAR radar to demonstrate the performance of the holographic SAR at both low and high radar frequencies. The NuSAR will allow data collection alternatives such as stacked circles, concentric circles, spirals and helical flight paths to be tested. BENEFIT: Holographic CSAR will provide a significantly better target and terrain feature identification capability than a linear flight path SAR, as the target will be viewed over 360 degrees in azimuth and there will be no shadowed areas. Holographic CSAR will also be superior to a single-orbit CSAR, even one using elevation interferometry (i.e. IFSAR) to estimate the target height, because standard IFSAR does not resolve multiple scatterers in height; it merely locates the scatterers in three dimensions. If two scatterers that are displaced in height are not resolved, then the height estimate and horizontal positions of both scatterers will be incorrect in the IFSAR image. In contrast, a true holographic SAR imaging not only provides accurate height estimates for each pixel, it resolves the multiple scatterers displaced in height. It also places the scatterers at the correct geographic location in the image.