Preliminary results of a spectral analysis of simulated complex pulse response history of a synthetic aperture radar pixel

Images of a uniform scene produced with a synthetic aperture radar (SAR) frequently appear nonuniform. This phenomenon, called “speckle” is attributed to the coherency of the radar signal and intra-pixel interferometry. Whereas speckle is usually associated with image contrast between adjacent pixels, the same type of contrast exists for one pixel between adjacent azimuthal looks (heading angles). A pixel in a terrestrial scene typically contains numerous scatterers and the phase and amplitude of the reflected radar signal generally varies from pulse to pulse due to intra-pixel interference. This variation in complex response history has been previously simulated by a computer program. In the present effort, the complex response history of a pixel with few scatterers is analyzed by a complex Fast Fourier Transform algorithm. After removing the phase centroid bias and mean phase slope from the original phase history, preliminary results indicate that the spectral responses show correlation with sub-pixel texture when there are one or two dominant scatterers in the pixel for a particular azimuth look. This textural information may be helpful in selecting the optimum resolution and number of azimuth looks for SAR imaging.