The Soil Moisture Active Passive (SMAP) "Soil Moisture 9 km (L2, Passive, Night, Dual Channel Algorithm)" layer displays surface soil moisture in cm³/cm³ derived from the Dual Channel Algorithm (DCA), one of four optional soil moisture algorithms, for the 6:00 p.m. ascending (Night) half-orbit passes of the SMAP radiometer. The SMAP radiometer measures natural thermal emission emanating from the soil surface. 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. In the DCA, both the vertically and horizontally polarized brightness temperatures are used to solve for soil moisture and vegetation optical depth.

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 L2 Radiometer Half-Orbit 9 km EASE-Grid Soil Moisture

Data field: soil_moisture_option3