Validation of the Calibrated Microwave Lunar Radiative Transfer Model With the ATMS 2-D Moon Observations at Different Moon Phase Angles

The NOAA-21 Advanced Technology Microwave Sounder (ATMS), launched in November 2022, collected 2-D lunar scan data on March 10, 2023, during its commissioning phase at a Moon phase angle of 34°. The raw data were calibrated using Microwave Calibration Processing System (MiCalPS), a microwave calibration and geolocation tool developed at the University of Maryland. Analysis showed that NOAA-21’s lunar antenna gain is generally lower than NOAA-20’s due to sampling rate differences. After correcting for beam-pointing errors, disk-averaged lunar brightness temperatures ( $T_{B,\text {Moon}}^{\text {DISK}}$ ) were derived for 23–183 GHz. These were compared with NOAA-20 data at 0° phase angle and predictions from the microwave lunar radiative transfer model (MLRTM). The observed model differences were: −3.3 K (K-band), 0.01 K (V), 2.0 K (W), −2.3 K (low-G), and 1.6 K (high-G), consistent with predicted phase delay trends. Further observations at varying Moon phases are recommended to enhance MLRTM validation.