Influence of the Statistical Properties of Phase and Intensity on Closure Phase

Nonzero closure phase exists in multilooked pixels. We study the influence of the statistical properties of the intensity and phase changes of single-looked pixels on multilooked phase and coherence. By quantifying the extent of their influences on phase triplet, we show in this article that the statistical properties of the intensity of pixels within a multilooking window can induce changes in interferometric phase and coherence, and contribute to the nonzero closure phase. We demonstrate that the intensity-induced changes increase by increasing the standard deviation of the phase changes, dispersion index of intensity, and the correlation between the intensity and phase changes. We have used ALOS Phased Array type L-band Synthetic Aperture Radar (PALSAR), ALOS-2 PALSAR-2, and Sentinel-1 images to generate real and semisynthetic interferograms to assess our findings. The semisynthetic interferograms are produced by pairing real SAR data and synthetic SAR data; the synthetic SAR data are generated from the real data by adding random vectors with predefined average changes of phase and intensity. Our results show that closure phase is only a function of the statistical properties of the phase and intensity of pixels, and does not possess the information about the magnitude of physical changes. This casts doubt on the effectiveness of methods that exploit phase triplet as a means to estimate soil moisture or any other deforming or nondeforming changes.