Microwave Remote Sensing for Soil Moisture Estimation in Tropical Regions – A Review and SMOS L2 Products Validation

Abstract

The role of soil moisture in the hydrological cycle and climate change monitoring is discussed widely after its designation as an Essential Climate Variable (ECV) by the European Space Agency (ESA). This paper reviews the methods of soil moisture estimation using microwave remote sensing sensors, including the Synthetic Aperture Radar (SAR), Scatterometer, and Radiometer; and the advantages and limitations of using them to estimate soil moisture over tropical regions. The Soil Moisture and Ocean Salinity (SMOS) mission is the first satellite equipped with an L-band radiometer to provide soil moisture products with the best spatio-temporal advantages. Its products have been validated across the world except for the humid tropical regions. An in-situ soil moisture data collection network was set up in Malaysia aimed to provide the first available data to validate SMOS products in the region. This network also aimed to provide data for SMOS retrieval algorithm calibration in the near future. Preliminary result shows unconvincing accuracy between SMOS product and in-situ data.