“…Based on these algorithms, several global SM products and datasets have been published, such as SMOS, SMAP, AMSR-E, AMSR2 Advanced Scatterometer (ASCAT) and the European Space Agency Climate Change Initiative (ESA CCI). These data have brought great benefits to agricultural and hydrological monitoring, weather forecasting, and climate change research [29][30][31]. However, SM retrieval based on a radiative transfer model using L-band requires a lot of auxiliary information, such as the vegetation optical thickness, vegetation single scattering albedo, soil effective temperature, and soil surface roughness, which limits the global application of these methods [32].…”