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Calibration of Multi-Channel Millimeter-Wave Radiometers of Geosynchronous FY-4M Using Brightness Temperature of the Lunar Surface at Millimeter Channels

The Moon is a good calibration source for the millimeter-wave radiometer onboard the Feng Yun-4 Millimeter (FY-4M) satellite. The temperature profiles of the lunar surface can be obtained by solving the one-dimensional heat conduction equation with the thermo-physical properties of regolith. Then, the loss tangent is fitting using the Chinese Chang’e-2 (CE-2) 37GHz brightness temperatures (TB) data against TiO2 abundances, which is derived from Clementine five-bands multispectral data. The calculated surface temperatures and the TBs are validated by Diviner infrared data and CE-2 37GHz TB data. With the theoretical analysis of the radiative transfer, the TBs at FY-4M frequencies of lunar center area is obtained for calibration. In addition, the abnormal thermal emission at "cold spots" should be excluded for calibration.