Experimental Analysis on the Mechanisms of Singular Point Generation in InSAR by Employing Scaled Optical Interferometry

Abstract

Interferograms obtained in interferometric synthetic aperture radar (InSAR) often suffer from decorrelation and singular points (SPs) originating from thermal noise and interference. To analyze the phenomenon, first, this paper presents the results of scaled optical experiment free from thermal noise, where the SP origin is interference. We find that the amplitude of the SP-constructing pixels, namely, singular unit, and of nearby pixels is lower than that of other pixels. This amplitude reduction is enhanced by multilooking process. These results suggest that the number of effective scatterers in a single pixel has reduced to such an extent that individual interference has become visible. We also conduct the same analysis on the SAR data. We find that plain areas show the same features as the optical experiment, implying the same mechanisms of SP generation. In contrast, sea areas present no localization, indicating thermal noise in electronics as the major reason. It is widely known that interference among many incoherent scattered waves presents Rayleigh or similar distribution in its amplitude as a result of central limit theorem. As the number of scatterers reduces, the amplitude becomes log-normal or other distribution. However, no analysis was reported on the local properties in such a case that the central limit theorem does not hold. Investigation of such local properties will also be useful in designing SP filters. The significance of noncentral-limit-theorem situations will increase its importance in the use of SAR data, of which resolution becomes further higher in the near future.