The Soil Moisture Active Passive (SMAP) “Soil Moisture 3 km (L3, Active)” layer displays a daily global composite of surface soil moisture in cm³/cm³ from the 6:00 a.m. descending half-orbit passes of the SMAP radar posted on a 3 km EASE-Grid 2.0. The amount of backscatter returned to the radar changes with the amount of moisture in the soil. Wetter soil causes more backscatter to reach the radar. Retrieval of soil moisture from measured backscatter data typically implies an inversion of the radar forward scattering process. The SMAP approach is a multichannel retrieval algorithm that searches for a soil moisture solution such that the difference between modeled and observed backscatter is minimized in the least squares sense.

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 L3 Radar Global Daily 3 km EASE-Grid Soil Moisture

Data field: soil_moisture