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

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 (
SM
), soil temperature, soil salinity, and vegetation, using L-band microwave brightness temperature (
T_B
) observations and retrievals from the soil moisture ocean salinity (SMOS) and soil moisture active passive 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
SM
outperformed CLSM
SM
when evaluated against field data, and the forward L-band
T_B
simulations derived from in situ
SM
and soil temperature performed better than those derived from CLSM estimates when evaluated against SMOS
T_B
observations. The surface salinity for the sampled pixels was on average only 4 mg/g and only locally influenced the
T_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
T_B
simulations over the entire Dry Chaco, the RTM was inverted using 10 years of multiangular SMOS
T_B
data and constraints of CLSM
SM
and soil temperature. However, the latter modeled
SM
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.