Microwave Communication Parameters Estimated from Radiosonde Observations over the Indian Subcontinent

Abstract

Emission and absorption of microwaves in atmospheric gases often limit the useful sensitivity of receiving systems in earth-space links. At frequencies below 30 GHz the emission and absorption due to water vapour content in the atmosphere dominate. A main water vapour line occurs at 22.235 GHz where the attenuation and emission noise attain a maximum. An estimate of attenuation, noise, and group delay made at this frequency, therefore, provides an upper limit of water vapour effects at microwave frequencies below 30 GHz. The study is based on the results of water vapour and radio refractivity distribution over the Indian subcontinent presented in two atlases, namely, <i>Atlas of Tropospheric Water Vapour over the Indian Subcontinent,</i> and <i>Atlas of Tropospheric Radio Propagation Parameters over the Indian Subcontinent,</i> published by the National Physical Laboratory, New Delhi; these atlases are based on radiosonde observations made by the India Meteorological Department, Govt. of India.