On the Evaluation of Long-term Instrument Calibration Gain Stability Based on Lunar Radiation Observations

Developing high quality climate data records with consistent measurements from different satellite instrument requires a highly stable calibration reference target. Lunar radiation is highly stable in microwave spectrum, attributing to the stable geo-physical property of the Moon’s surface. Therefore, the Moon can be used as a ideal calibration reference for microwave instrument to evaluate the calibration accuracy and assess the long-term calibration stability. The major challenges of using the Moon as a radiometric standard source for microwave sensors include the uncertainties in antenna pattern measurements, lack of measurements of microwave brightness temperature spectrum of lunar surface, and the knowledge of lunar phase lag as a result of penetration depth in different detection frequency. For most of microwave sounding instrument, Lunar radiation can be collected from space view observations during so called lunar intrusion events usually happens several days a month. In this study, a comprehensive lunar brightness temperature model was developed based on two-dimension lunar scan from NOAA-20 ATMS observations and long-term NOAA-18 AMSU/MHS lunar observations.