A study on channel saturation of atmospheric water vapor detection based on airborne microwave radiometer

183.31 GHz microwave radiometers have advantages in detecting low-content water vapor, yet they also have the problem of channel saturation. Quantitative research on this problem is of great significance to clarify the water vapor detection capability and application range of this type of instrument. Based on the airborne 183.31 GHz microwave radiometer GVR (G-band water Vapor Radiometer, GVR) aboard the precipitation enhancement aircraft Y-12 of the Tianjin Weather Modification Office, this study quantitatively calculates the saturation threshold of the four detection channels and detection sensitivity using the sounding data, and further analyzes the water vapor detection capability and application range of each channel. The results show that the water vapor detection sensitivity and saturation thresholds of the four channels are related to the observation height. When the water vapor content is low, the sensitivity of channel 1 ((183±1) GHz) increases with the increase of the observation height, the sensitivity of channel 3 ((183±7) GHz) and channel 4 ((183±14) GHz) decreases with the increase of the observation height, and the sensitivity of channel 2 ((183±3) GHz) is almost unaffected by the observation height. The higher the observation height of channel 1 and channel 4, the lower the saturation threshold of integrated water vapor detection. On the contrary, the lower the observation height, the greater the saturation threshold. The saturation thresholds of channel 2 and channel 3 are almost unaffected by observation height. The single channel with the strongest water vapor detection capability is selected to retrieve the integrated water vapor content under clear sky condition. When the integrated water vapor content is within 0—1.3, 1.3—4.0 and 4.0—9.8 mm, respectively, channel 1, channel 2 and channel 3 are selected as the retrieval channel correspondingly. The retrieval of integrated water vapor content at different observation heights is applicable. The emission of clouds increases the bright temperature of each channel of the radiometer. The range of bright temperature increase is related to the cloud liquid water content, the distance between the cloud and observation height and the cloud thickness. The greater the cloud liquid water content, the smaller the water vapor detection sensitivity and saturation threshold of each channel. Under cloudy condition, the two channels with the strongest water vapor detection capability are selected to retrieve the integrated water vapor content, and the appropriate water vapor detection channel is selected based on the integrated liquid water path interval. The greater the content of liquid water, the smaller the detectable range of integrated water vapor. To detect the variation of integrated water vapor content at 0.1 mm scale, the application range of airborne microwave radiometer for detecting integrated water vapor content is 0—9.8 mm under clear sky condition. The detection capability is weakened under cloudy condition, and the application range of water vapor detection varies with the cloud liquid water content.