Tropospheric radiowave propagation over the Bay of Bengal

Abstract

It is known since World War II that supernormal radio wave propagation occurs frequently in the VHF and UHF bands along the east coast of India. This paper presents a study of abnormal propagation observed along the Bay of Bengal coast as well as across the Bay with an S-Band radar located at Madras. Spectacular displays of the Bay coast from Sri Lanka to Orissa and occasionally of the Sundarbans, the Burma coast and Sumatra have been obtained. The seasonal and diurnal variation of such long distance anomalous propagation has been studied in relation to the meteorological conditions and refractive index profiles. The synoptic meteorological features provide a qualitative explanation of the phenomena. The refractive index profiles are however based on routine radiosonde data which do not have sufficient resolution to detect spatial variations over small scales. Hence the utility of the refractivity data to predict the abnormal propagation is found to be limited. To provide guidance to radar and radio engineers, it is necessary to have accurate data of refractivity. In the absence of such data, compiled statistics of observed abnormal propagation may be the most useful data source for the engineer.