Can InSAR Coherence and Closure Phase Be Used to Estimate Soil Moisture Changes?

Zhong Lu,Yusuf Eshqi Molan

doi:10.3390/rs12091511

Zhong Lu, Yusuf Eshqi Molan

Open Access

https://doi.org/10.3390/rs12091511

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Journal: Remote Sensing	Publication Date: May 9, 2020
Citations: 8	License type: CC BY 4.0

Affiliation: Southern Methodist University

Abstract

We studied the influence of the statistical properties of soil moisture changes on the Interferometric Synthetic Aperture Radar (InSAR) coherence and closure phase to determine whether the InSAR coherence and closure phase can be used to estimate soil moisture changes. We generated semi-synthetic multi-looked interferograms by pairing n real single-looked pixels of an observed SAR image with n synthetic single-looked pixels. The synthetic SAR data are generated from the real SAR data by applying soil moisture changes with a pre-defined mean and standard deviation of changes. Our results show that the diversity of soil moisture changes within the multi-look window gives rise to decorrelation, a multi-looked phase artifact, and a non-zero phase triplet. The decorrelation and closure phase increase by enlarging the diversity of soil moisture changes. We also showed that non-soil moisture changes can lead to larger decorrelations and closure phases. Furthermore, the diversity of phase changes, decorrelation, and closure phases are correlated with land cover type. We concluded that the closure phase and coherence are independent of the magnitude of soil moisture changes and are inappropriate tools to estimate soil moisture changes. Coherence, however, can be used as a proxy for soil moisture changes if the diversity and magnitude of soil moisture changes within a multi-looked pixel are strongly correlated.

Highlights

Interferometric Synthetic Aperture Radar (InSAR) can remotely sense mm to cm-scale surface deformation [1,2,3]
Our analysis showed that InSAR coherence and the closure phase are functions of the diversity of soil moisture and non-soil moisture changes
The results of the real data confirm that, compared to soil moisture changes, vegetation and surficial processes lead to much larger closure phase and decorrelations

Summary

Introduction

InSAR can remotely sense mm to cm-scale surface deformation [1,2,3]. InSAR has been used successfully to map surface deformations associated with different mechanisms, such as landslides, sinkholes, volcanism, subsidence, and permafrost [4,5,6,7,8]. Two SAR images of the same area with the same looking angle taken at different times can be used to generate an interferogram. The change in water content leads to changes in the InSAR phase and SAR intensity [9]. This in turn can influence the inferred deformation and potentially affect InSAR coherence

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