Experimental analysis of singular point generation mechanisms in interferometric SAR using optics: The possibility of singular point generation by interference in a single pixel

In principle, we can construct highly precise digital elevation model (DEM) with interferometric synthetic aperture radar (InSAR) observations. However, in actual observed images, we find so many rotaional points, namely, phase singular points (SPs), that we cannot determine the height accurately. It is significantly important to investigate the SP phenomenon. Presently the origin of the SPs is not entirely clear. In this paper, we design a scaled experimental setup in optics to elucidate the mechanisms of the SP generation. From the results, we confirm that low amplitude pixels (dark speckles) are emphasized by multilook process, and that many of these pixels are singular unit pixels. The multilook process is equivalent to interference of multiple complex-amplitude values. In addition, a similar interference is considered to occur in a single pixel of a single-look SAR image. It is suggested that interference of waves from multiple scattering sources in a single pixel can be one of the causes of SP generation.