B.S.T.J. Briefs: Effects of Sandstorms on Microwave Propagation

Effects of Sandstorms on Microwave Propagation By T. S. CHU (Manuscript received August 29, 1978) Low rainfall volume suggests the promise of long paths using higher microwave frequencies for radio communication in desert areas. The pursuit of this promise gives rise to the need for understanding the effects of sandstorms on microwave propagation. First, a distinction should be made between large sand grains and fine sand dust.1 Sand grains of greater than about 0.2-mm diameter are driven by the wind as a low-flying cloud with a height of less than about 2 meters above the ground. This limited height is expected to be lower than most antenna heights of a microwave station. On the other hand, dust-like sand particles can rise in dense clouds to a height of one kilometer or more. This latter type of sandstorm, which is essentially a misnomer for dust storm, may lie in the terrestrial and earth-space paths of microwave radio; hence, path attenuation data are required. Precise calculation is hampered by the uncertainty about the dielectric constant and the size distribution of sand particles. However, useful analysis and frequency dependence of the sandstorm effects can be obtained without precise knowledge of these parameters. The relation between microwave attenuation and optical visibility will be of interest because visibility provides a convenient measure of dust density. The visibility is inversely proportional to the optical attenuation coefficient. A proportionality constant of 15 dB* will be assumed for the visibility distance in the following calculations.