The Soil Moisture Active Passive (SMAP) "Soil Moisture 9 km (L3, Passive, Day | Night)" layers display a daily global composite of surface soil moisture in cm³/cm³ derived from the Single Channel Algorithm V-Pol (SCA-V), the baseline soil moisture algorithm, for the 6:00 p.m. ascending (Night) half-orbit passes of the SMAP radiometer. To enhance the grid resolution, Backus-Gilbert optimal interpolation techniques are used to extract maximum information from SMAP antenna temperatures and convert them to brightness temperatures, which are posted to the 9 km EASE-Grid 2.0. The SMAP radiometer measures natural thermal emission emanating from the soil surface. The variation in the intensity of this radiation depends on the dielectric properties and temperature of the target medium, which for the near surface soil layer is a function of the amount of moisture present.

The SMAP spacecraft carries two instruments, a radar (active) and a radiometer (passive), that together make global measurements of land surface soil moisture and freeze/thaw state. It is useful for monitoring and predicting natural hazards such as floods and droughts, understanding the linkages between Earth’s water, energy and carbon cycles, and reducing uncertainties in predicting weather and climate.

References: SMAP Enhanced L3 Radiometer Global Daily 9 km EASE-Grid Soil Moisture

Data field: soil_moisture