L-Band Microwave Satellite Data and Model Simulations Over the Dry Chaco to Estimate Soil Moisture, Soil Temperature, Vegetation, and Soil Salinity

Abstract

The Dry Chaco in South America is a semi-arid ecoregion prone to dryland salinization. In this region, we investigated coarse-scale surface soil moisture (<i>SM</i>), soil temperature, soil salinity and vegetation, using L-band microwave brightness temperature (<i>T</i>_B) observations and retrievals from the Soil Moisture Ocean Salinity (SMOS) and Soil Moisture Active Passive (SMAP) satellite missions, Catchment Land Surface Model (CLSM) simulations, and in situ measurements within 26 sampled satellite pixels. Across these 26 sampled pixels, the satellite-based <i>SM</i> outperformed CLSM <i>SM</i> when evaluated against field data, and forward L-band <i>T</i>_B simulations derived from in situ <i>SM</i> and temperature performed better than those derived from CLSM estimates when evaluated against SMOS <i>T</i>_B observations. The surface salinity for the sampled pixels was on average only 4 mg&#x002F;g and only locally influenced the <i>T</i>_B simulations, when including salinity in the dielectric mixing model of the forward radiative transfer model (RTM) simulations. To explore the potential of retrieving salinity together with other RTM parameters to optimize <i>T</i>_B simulations over the entire Dry Chaco, the RTM was inverted using 10 years of multi-angular SMOS <i>T</i>_B data and constraints of CLSM <i>SM</i> and temperature. However, the latter modeled <i>SM</i> was not sufficiently accurate and factors such as open surface water were missing in the background constraints, so that the salinity retrievals effectively represented a bulk correction of the dielectric constant, rather than salinity per se. However, the retrieval of vegetation, scattering albedo and surface roughness resulted in realistic values.