The influence of cumulus clouds on fluctuations in down welling microwave radiation of the atmosphere in the resonance absorption band of water vapor 18...27 GHz

Abstract

Problem formulating. The nature of fluctuations in the microwave radiation of the atmosphere remains poorly understood. A number of questions, related to the nature of radiation fluctuations near the lines of resonant absorption of various atmospheric components, the intensity of fluctuations at large spatial and temporal intervals requires further study. The influence of various meteorological factors on the intensity of radiation fluctuations requires a deeper consideration. Goal. The goal is to reveal the spectral features of spatio-temporal fluctuations in downward radiation of the atmosphere in the region of the water vapor resonance 18−27 GHz and to estimate the influence of cumulus clouds of various vertical extent on the intensity of fluctuations. Result. Based on the data of long-term measurements of down welling radiation brightness temperature 18−27.2 GHz, the analysis of the spectra of structural function for wide range of temporal intervals is carried out. It is shown that the spectrum of radiation fluctuations in a cloudless atmosphere is similar to the absorption spectrum in water vapor. The spectra of fluctuations in atmospheric radiation under conditions of cumulus cloud cover of various vertical extent are presented. Practical meaning. Radiation fluctuations should be taken into account when creating systems for remote sensing of the atmosphere and the Earth’s surface. They affect the quality of radiometric measurements and radio astronomy observations. The data on fluctuations in atmospheric radiation gathered during this research can be useful for assessing the spatial and temporal fluctuations in the phase delay, for taking into account the influence of atmosphere during the radio interferometric measurements and when observing radiation sources in the diagrammatic modulation mode.