Cloud Characteristics by Using Doppler Radar over Kolkata.

In present days radio communication scenario, three issues are considered to be the most important. These are reliability, directivity and regulation of transmitted power. All such issues can be taken care provided the characterization of our tropospheric medium is done with good degree accuracy. The radio wave propagating above 10 GHz is affected severely by rain and cloud. In case of rain, the attenuation of radio wave is the main concerned but for cloud along with attenuation, noise temperature generated by cloud is also another issue. Cloud attenuation and cloud noise temperature can be deduced if cloud morphology in terms of cloud coverage, cloud height, cloud thickness, cloud liquid water content etc. is available. The meteorologists of India have studied cloud morphology as well as cloud dynamics for the weather forecasting purposes. But in this paper, an attempt has been made to deduce results on cloud parameters for radio wave propagation studies by utilizing the observations taken by the sophisticated computer controlled Doppler radar belonging to the India Meteorological Department over Kolkata. The Doppler radar operates in C-band at frequency ∼ 2700–2900 MHz with peak power 500 kW. Several cloud parameters viz. radar reflectivity, cloud thickness, cloud height, cloud vertical integrated liquid water content etc. have been studied in probability distribution scale. Based on cloud height, the temperature of the cloud has been determined. It is seen that over Kolkata, the cloud height ∼ 6.5 km occur for maximum percentage of time. The cloud temp has been estimated by using the lapse rate of the temperature with height, which is ∼ 6.5°c km. By using the cloud height, cloud temperature and cloud liquid water content, the attenuation of radio wave due to cloud at microwave and millimeter wave frequency bands, over Kolkata have been derived. It is seen that attenuation value varies from 0.2 dB / km to 30 dB / km over the frequency range from 10 GHz to 100 GHz. The noise temperature generated by cloud has been estimated and found to be from 8°K to 202°K at the frequency range from 10 GHz to 70 GHz with cloud thickness ∼ 1 km and at cloud temperature ∼ 260 °K. Such noise affects the signal to noise (S/N) ratio of the communication system. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]