Near‐surface soil moisture retrieval from ASAR Wide Swath imagery using a Principal Component Analysis

Abstract

The new ENVISAT Advanced Synthetic Aperture Radar (ASAR) Wide Swath Mode (WSM) data provide good potential for routinely monitoring near surface soil moisture due to the increased temporal revisit capability compared with ERS2 SAR. In this paper, we propose a Principal Components Analysis (PCA) to retrieve near‐surface soil moisture from ASAR WSM data. The results demonstrate that PCA transformation can at least partially separate or group the effect factors, such as surface roughness, land cover, vegetation, and topography within the limitations of our datasets. The second principal component which was consistent with soil moisture and rainfall‐runoff dynamics was representative of the soil moisture Saturation Potential Index over a large area. Validation against field measurements and against the UK Met Office Surface Exchange Scheme shows the retrieval performs with reasonable accuracy.

Acknowledgements

The authors would like to thank ESA for providing satellite images as Category‐1 customers. Also, thanks are due to the Met Office and Joint Centre for Hydro‐Meteorological Research, Wallingford for providing the MOSES 2.2 model and to CEH for providing Land Cover 2000 data. Morley Meteorological data were provided by the Arable Group. Thanks to Mr Andrew Thurston at Morley for access to field sites. We also wish to thank the two anonymous reviewers for providing constructive and helpful comments.