S-Npp Advanced Technology Microwave Sounder: Reflector Emissivity Model, Mitigation, & Verification

The Suomi NPP spacecraft pitchover maneuver revealed an ATMS scan angle-dependent bias when viewing deep space, which is a homogenous and unpolarized source that fills the entire ATMS Field of Regard. Reflector emissivity was investigated as a possible root cause. The emissivity is polarization dependent, which results in a scan-dependent bias with the quasi-vertical channels having a different bias shape than the quasi-horizontal channels. The normal emissivity was empirically estimated by minimizing the scan bias during the pitchover maneuver, and the reflector's temperature was derived from ATMS telemetry. The model, calibration change, and estimated normal emissivity were verified using the ATMS thermal vacuum test data. Reflector emissitivies from approximately 0.2% to 0.4% were derived, resulting in brightness temperature corrections of up to 0.5 K.