The Soil Moisture Active Passive (SMAP) “Freeze/Thaw 36 km (L3, Passive, Night)” layer displays freeze/thaw state posted on a 36 km EASE-Grid 2.0 for Global land surface areas and land surface areas north of 45°N latitude from the SMAP radiometer. Freeze/thaw is detected by identifying the temporal response of the normalized polarization ratio (NPR) of the brightness temperature, which is sensitive to changes in the dielectric constant of the landscape components that occur as the water within the components transitions between frozen and non-frozen conditions.

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 Radiometer Global and Northern Hemisphere Daily 36 km EASE-Grid Freeze/Thaw State

Data field: freeze_thaw