| 31 Aug 2026
ASCAT Soil Moisture Estimation using Dynamic Regularised Slope and Curvature
Abstract. Soil moisture content is an essential climate variable driving processes in the hydrosphere, atmosphere and biosphere. Global and multi-decadal records of soil moisture measurements can be realised through spaceborne microwave instruments. The C-band Advanced Scatterometer (ASCAT) provides a global record of backscatter measurements fit for soil moisture retrieval, spanning nearly 20 years. The TU Wien Soil Moisture Retrieval algorithm uses an estimated backscatter-incidence relation to (i) normalise ASCAT backscatter observations from multiple incidence angles, and (ii) to determine reference values for backscatter under dry and wet conditions. A novel method for estimating the backscatter-incidence relation using regularisation was recently developed, resulting in improved short-term dynamics in the estimated time series of the backscatter-incidence relation. In this study, the impact of the regularised estimation backscatter-incidence angle relation on soil moisture retrieval is assessed separately for the backscatter normalisation, and the dry and wet reference calculation. The performance of different configurations in this study are assessed using the Quality Assurance Service for Satellite Soil Moisture Data to validate retrieved soil moisture time series with in-situ measurements provided by the International Soil Moisture Network. Soil moisture retrieval improves over most land cover and climate types when a dynamic regularised backscatter-incidence angle relation is used for backscatter normalisation and the dry wet reference calculation. In particular, short term dynamics of retrieved soil moisture time series are found to improve significantly over most land covers and climate types. Future studies should investigate the use of the dynamic regularised backscatter-incidence angle relation for near real-time soil moisture retrieval, as well as soil moisture retrieval from the ESCAT scatterometer.
Competing interests: At least one of the (co-)authors is a member of the editorial board of Earth Observation.
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