Microwave propagation characteristics a study over Assam valley with respect to hydrometeors

Abstract

The basic aim of the research work is to study the microwave propagation characteristics with respect to hydrometeors (specially rain) and to analyse system responses towards microwave attenuation. This aim is built on the fact that the radiowaves above 10GHz suffer attenuation due to absorption and scattering by raindrops. This study has been carried out at Guwahati (260 12'N, 920E), over a line-of-sight (LOS), short haul (3.2 kms) microwave link operating at 11 GHz by PandT department. A standard observational procedure is adopted to impliment the aim. Microwave field strength measurements are taken during the period 1991-93, by tapping the AGC output of the receiver. In order to associate the attenuation with rainfall rate and raindrop size distribution, the data on rainfall and raindrop size and shape are collected simulteneously by the instruments developed for the purpose. The observational study on rainfall, raindrop size, shape and microwave attenuation is presented. Correlation between rainfall rate and microwave attenuation is computed. The observed results are then studied under the light of standard existing models like CCIR, Negative exponential, Lognormal and Global model. The observed results are also compared with those reported from various stations. Modelling on thunderstorm rain attenuation is made with an aid of dipole polarisation in raindrops of different shapes. Based on the observed results on rainfall, the rainfall rate distribution over Assam is modelled in which the rain climatic zones of Assam are classified. The thesis is organized into six chapters: CHAPTER 1: GENERAL INTRODUCTION CHAPTER 2: THEORIES AND NUMERICAL MODELS ON RAIN ATTENUATION : A REVIEW CHAPTER 3: EXPERIMENTAL TECHNIQUES CHAPTER 4: OBSERVATIONS AND ANALYSES CHAPTER 5: COMPARISON OF OBSERVED RESULTS WITH STANDARD MODELS AND MODELLING OF RAIN ATTENUATION AND RAINFALL RATE CHAPTER 6: RESULTS, DISCUSSIONS AND CONCLUSIONS CHAPTER 1 gives a brief introduction to the present work. Necessity for going to microwave frequencies...