Studying Characteristics of the Cloudy Atmosphere Based on Measuring Its Downwelling Microwave Radiation Spectra in the 18.0–27.2 GHz Water Vapor Resonant Absorption Band

Abstract— The paper deals with studying the atmospheric characteristics based on spectral microwave radiometric measurements in the 18.0–27.2 GHz band close to the water vapor absorption line. The results of analyzing the ground-based measurements of clear-sky and cloudy atmosphere radiation with the P22M microwave radiometer-spectrometer performed at Fryazino Branch of Kotelnikov Institute of Radioengineering and Electronics of Russian Academy of Sciences are presented. The measurements have been carried out almost continuously since July 2017. The seasonal variability of clear-sky self-radiation spectra in the 18.0–27.2 GHz frequency band is analyzed. Estimates are made for the error in the linear approximation of the dependence between clear-sky brightness temperature and atmospheric integrated water vapor retrieved from radiosonde data. A possibility of studying the variability of liquid water content in clouds of various types with a spatial resolution about 200 m and a temporal resolution of 10 s is demonstrated. The time series of the brightness temperature spectra may be a basis for an operational analysis of the temporal variability of atmospheric integrated water vapor and cloud liquid water content.