Estimation of absorption and electrical path length at 22.235 GHz

Abstract

Radiometric studies at the weak water-vapour-resonant frequency centered at 22.235 GHz have been made during clear sky conditions. Data obtained in presence of rain and cloud cover have been intentionally discarded. Monthly variations of absorption in clear weather have been compared with those obtained by using radiosonde data. The results reveal that the

absorption is maximum during the months of July through August. A difference was found to exist between the measured values of atmospheric noise temperature and those obtained by calculation, which is discussed in terms of mean medium temperature and ground temperature. The monthly variation in the excess wet-path length at 22.235 GHz, determined from the measurements of brightness temperature, is also considered. Comparison have been made between the calculated and measured values of this excess electrical path length. The maximum excess path length experienced by the microwave signal is about 40 cm, occurring in the monsoon season. This is due to the high abundance of water vapour during the monsoon season over Calcutta. The minimum path length deduced was 15 cm in the non-monsoon season.