Exploiting frequent Sentinel-1 observations for soil moisture retrieval
Balenzano, Anna; Satalino, Giuseppe; Mattia, Francesco

The forthcoming European Space Agency (ESA) Sentinel-1(S-1) C-band SAR constellation will provide continuity of data, with unprecedented capabilities in terms of revisit time (six days exact repetition time and near daily coverage over Europe and Canada), coverage and timeliness (data delivery within 3 hours). These features open new opportunities for the monitoring of the soil moisture content at the high spatial (e.g below 1km) and temporal resolution, with important consequences on operational land services. In this context, a soil moisture retrieval algorithm, named ''Soil MOisture retrieval from multi-temporal SAR data'' (SMOSAR), has been recently developed in order to exploit the S-1 Interferometric Wide Swath images for a systematic near-real time soil moisture retrieval at a high spatial resolution [1]. SMOSAR takes advantage from the frequent S-1 acquisitions by inverting the temporal changes of radar backscatter, which enhance the dependence on the fast soil moisture changes (few days) and impair the slow (few weeks) changes of the others surface parameters (e.g. soil roughness and vegetation biomass). The algorithm has been validated over time-series of ASAR and RADARSAT-2 data, simulating the S-1 products in terms of repeat cycle, collected over well-documented test sites during the ESA AgriSAR'06 and AgriSAR'09 and Italian ENVISAT'04-'05 campaigns. The paper presents the concept underlying the soil moisture retrieval from dense time-series of SAR acquisitions, discusses its strengths and limitations, and shows new results concerning the application of the method to time-series of ASAR WS data at VV polarization. [1] Mattia F., Satalino G., Balenzano A., Pauwels V., De Lathauwer E., (2011), GMES Sentinel-1 soil moisture retrieval algorithm development, European Space Agency contract n. 4000101352/10/NL/MP/ef, Final Report.