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Published September 2017 | public
Journal Article

Soil Moisture Estimation Using Differential Radar Interferometry: Toward Separating Soil Moisture and Displacements

Abstract

Differential interferometric synthetic aperture radar (DInSAR) measurements are sensitive to displacements, but also to soil moisture mv changes. Here, we analyze whether soil moisture can be estimated from three DInSAR observables without making any assumptions about its complex spatio-temporal dynamics, with the goal of removing its contribution from the displacement estimates. We find that the referenced DInSAR phase can be a suitable means to estimate m_v time series up to an overall offset, as indicated by correlations with in situ measurements of 0.75–0.90 in two campaigns. However, the phase can only be referenced when no displacements (and atmospheric delays) occur or when they can be estimated reliably. We study the separability of displacements and m_v using two additional DInSAR observables (closure phase and coherence magnitude) that are sensitive to m_v but insensitive to displacements. However, our analyses show that neither contains enough information for this purpose, i.e., it is not possible to estimate m_v uniquely. The soil moisture correction of the displacement estimates is hence ambiguous too. Their applicability is furthermore limited by their proneness to model misspecifications and decorrelation. Consequently, the separation of soil moisture changes and displacements using DInSAR observations alone is difficult in practice, and—like for mitigating tropospheric errors—additional data (e.g., external m_v estimates) or assumptions (e.g., spatio-temporal patterns) are required when the m_v effects on the displacement estimates are comparable to the magnitude of the movements. This will be critical when soil moisture changes are correlated with the actual displacements.

Additional Information

© 2017 IEEE. Manuscript received October 21, 2016; revised January 11, 2017 and February 14, 2017; accepted May 4, 2017. Date of publication June 13, 2017; date of current version August 25, 2017. This work was supported by the Helmholtz Alliance HA310 Remote Sensing and Earth System Dynamics. The authors would like to thank the European Space Agency for the data acquired within the NoSREx campaign. They would also like to thank S. Leinss for his assistance with processing the NoSREx data, A. Berg for insightful discussions about the CanEx-SM10 campaign, and R. Hanssen and P. Rosen for discussions about the implications for displacement studies. Three anonymous reviewers provided helpful comments that improved this paper.

Additional details

Created:
August 19, 2023
Modified:
October 17, 2023