Amplitude Calibration Method for Synthetic Aperture Radiometer Based on Cold-sky Observation Unit

Microwave radiometers obtain the accurate brightness temperature of the target scene through calibration, which is a necessary means for quantitative data application. The synthetic aperture microwave radiometer consists of multiple radiometer units, and the calibration requirement extends from a single receiver to all units. Noise injection is a calibration method for fixed antenna beam radiometers, including synthetic aperture microwave radiometers. However, the noise diode used as the calibration reference encounters issues such as short-term fluctuation caused by temperature and long-term drift resulting from the aging of the device, leading to the deterioration of the system's calibration accuracy. To address the aforementioned problems, this paper proposes a method of amplitude calibration for synthetic aperture radiometers based on a special cold-sky observation unit. By designing a dedicated cold-sky observation radiometer channel, the common noise source of the synthetic aperture radiometer is calibrated in real-time, reducing the influence of noise temperature uncertainty on the amplitude calibration of all observation channels in the synthetic aperture radiometer system. Based on the system scheme of the K-band one-dimensional synthetic aperture radiometer in the Microwave Imager Combined Active and Passive of China’s Ocean Salinity Detection Satellite, the radiometer system model and calibration model are established, and numerical simulations and prototype calibration experiments are carried out. Simulation and experimental results validate the effectiveness of the proposed method.