The Soil Moisture Active Passive (SMAP) "Sigma0 3 km QA (L3, Active, XPOL Polarization" layer displays quality assurance (QA) flags for Sigma0 backscatter from the SMAP radar the cross-polarizations (XPOL).
Within the image, green indicates that Sigma0 observations have acceptable quality for science use, yellow indicates that caution should be used with the Sigma0 observations as one or more quality-impacting conditions have been identified, and red indicates that Sigma0 observations are flagged as bad due to unacceptable quality.
References: SMAP L3 Radar Global Daily 3 km EASE-Grid Soil Moisture
Data field: sigma0_qual_flag_xpol