The AMSR-U2 Soil Moisture Normalized Polarization Difference (Night) layer indicates the amount of soil moisture over land masses in grams per cubic centimeters (g/cm³). This layer was constructed by using the Normalized Polarization Difference (NPD) algorithm using resampled brightness temperature data. The AMSR-E/AMSR2 Unified Level-2B land product provides a long-term data record by combining AMSR-E and AMSR2 data. The imagery resolution is 25 kilometers, and the temporal resolution is daily.

The Advanced Microwave Scanning Radiometer 2 (AMSR2) instrument provides global passive microwave measurements. It is a remote sensing instrument that measures weak microwave emissions from the surface and the atmosphere of the Earth. AMSR2 also provides microwave emission and scattering intensity measurements.

References: NSIDC: AMSR-E/AMSR2 Unified L2B Half-Orbit 25 km EASE-Grid Surface Soil Moisture, Version 1; AMSR2 Global Soil Moisture Retrievals using the Normalized Polarization Difference (NPD) algorithm and Single Channel Algorithm (SCA) Algorithm Theoretical Basis Document