Core IdeasSatellites, particularly at Lband frequency, can globally map nearsurface soil moisture.Nearsurface moisture is extended to the root zone using models and data assimilation.Validation uses core monitoring sites, monitoring networks, field campaigns, and multisatellite comparisons.Efforts are underway to associate soil moisture variability dynamics with land surface attributes.This is an update to the special section Remote Sensing for Vadose Zone HydrologyA Synthesis from the Vantage Point [Vadose Zone Journal 12(3)]. Satellites (e.g., Soil Moisture Active Passive [SMAP] and Soil Moisture and Ocean Salinity [SMOS]) using passive microwave techniques, in particular at Lband frequency, have shown good promise for global mapping of nearsurface (05cm) soil moisture at a spatial resolution of 25 to 40 km and temporal resolution of 2 to 3 d. C and Xband soil moisture records date back to 1978, making available an invaluable data set for longterm climate research. Nearsurface soil moisture is further extended to the root zone (top 1 m) using processbased models and data assimilation schemes. Validation of remotely sensed soil moisture products has been ongoing using core monitoring sites, sparse monitoring networks, intensive field campaigns, as well as multisatellite comparison studies. To transfer empirical observations across space and time scales and to develop improved retrieval algorithms at various resolutions, several efforts are underway to associate soil moisture variability dynamics with land surface attributes in various energy and waterrich environments. We describe the most recent scientific and technological advances in soil moisture remote sensing. We anticipate that remotely sensed soil moisture will find many applications in vadose zone hydrology in the coming decades.
