Radiometric measurements of cloud attenuation at a tropical location in India

The effect of the earth's atmosphere on radio waves propagating over an earth-space path is a major concern in the design and performance of satellite communications systems. Some characteristics of cloud and its effect on signal propagation has been studied using multi-wavelength radiometer at a tropical location of Kolkata, India. The liquid water content profile shows high values at higher altitude during pre-monsoon season indicating the presence of cloud above zero degree isotherm. Significant change in attenuation value is observed for same liquid water content due to change in temperature and accordingly a suitable relationship is obtained for the present location. The measurements indicate that ~4 dB and ~12 dB attenuation is caused due to cloud at 0.01% outage probability at the Ka and V band, respectively. ITU-R model is found to be overestimating the cloud attenuation over this location and indicate the need for more experimental measurement from tropical region.