Review on the Precise Microwave Brightness Temperature Transfer in the Radiometer Calibration Link

The transfer of precise reference brightness temperature (BT) from the microwave calibration target (MCT) to the receiver antenna is a significant and fundamental issue in achieving accurate microwave radiometer calibration. In addition to the issues of receiver nonlinearity, gain stability et al., this review focuses on the electromagnetic field propagation process. Addressing the precise brightness temperature transfer from the MCT to the receiving antenna in the near-field region, this review systematically summarizes recent research progress by domestic and international scholars on the electromagnetic and thermal emission characteristics of MCT, as well as brightness temperature transfer modeling methodologies and their intrinsic properties. Or in other words, from the perspectives of (1) the accurate BT emission from the MCT, and (2) the accurate transferring in the calibration link, as they are the physical foundation of the radiometer calibration process and corresponding problems took decades to be tackled. This review aims to provide a comprehensive reference encompassing theories, methodologies, and fundamental mechanisms for the progressive establishment of microwave brightness temperature standards and transfer standards by discussing specific issues regarding how MCTs can be accurately characterized and how the BT can be precisely transferred.