Constraints On Soil Moisture Extraction From Sentinel-1

A comparison between the Sentinel-1 (S1)/Sentinel-2 (S2) derived Soil Moisture Products at plot scale (S
²
MP) and in situ soil moisture measurements at 10 cm depth was carried out for several winter and summer crops (wheat, tomato, cover crops and soybeans) with the aim to provide end users with the strength and limitations of the S
²
MP soil moisture product for their further applications. In dry conditions, the estimated S1 soil moisture (SM) (at ~5 cm depth) highly underestimated the 10 cm SM measurements. Wet conditions due to rainfall or irrigation showed less difference between the S1 estimated SM and the 10 cm in situ SM. Comparison of S1 estimated SM as a function of the vegetation development showed that for the studied crop types the S1 SM estimates are only valid for low and moderate vegetation cover with Normalized Difference Vegetation Index (NDVI) less than 0.7. Results also suggested that the optimal SM estimations by S1 could be mainly obtained at low radar incidence angles.