Sodar as an Indicator of Microwave Propagation Characteristics

Abstract

Studies to show that SODAR is an effective indicator of microwave propagation characteristics are presented. A comparison has been made of observations of sodar atmospheric thermal structures and microwave propagation characteristics of the LOS path between Delhi and Sonepat (42 km) operating at a frequency of 7 GHz. It has been observed that (i) thermal convective structures during daytime and mechanical turbulences due to wind under stable conditions have very little effect on microwave signal strength, (ii) surface-based temperature inversions develop, on an average, an amplitude fading level of 3 dB, (Hi)transitions from unstable to stable conditions develop an amplitude fading level of 2 dB while transitions from stable to unstable (morning rising inversion) develop, on an average, an amplitude fading level of 3 dB, (iv) multiple/elevated layers may develop, on an average, an amplitude fading level of 5 dB with variations of a couple of decibles about the mean value depending upon the nature and height of the multiple/elevated layers and that (v) wave motions/undulations seriously affect microwave signal level and cause amplitude fading as high as 20 dB but have a mean fading level around 7 dB. The effect is most predominant in the pre-monsoon period (1 March to 15 June). Details of the above findings and case studies of certain events are presented.