关键词: 无线电波(微波), 传播, 沙尘暴, 能见度

Abstract: Based on present relative studies, the disturbances to radio wave's propagation from sand dust storm include the following aspects:weakening of signal energy by particles' scattering and absorbing; cross polarization resulted from flying particles' ununiform shape and spatial distribution; superrefraction, subrefraction and multipath effects in some way associated with sand dust storms; effects of dust accumulating on antennae. Most studies concentrate on the first and second problems. This paper mainly reviews the present microwave literature on these two subjects and comes the following conclusions:①When predicting the likely effects of sand dust storms on the microwave propagation, we need a critical parameter (permittivity). ②The weakening increases markedly with the rise of the frequency, but at a same frequency, the lower the visibility is, the greater the increment of weakening is; The weakening has a complex relation with particle's moisture content through the medium of permittivity, but when the moisture content is lower than 15%, only a small rise in moisture content will cause a significant increase in weakening. ③For sand dust storms with medium visibility (0.5-5 km), the weakening at a same frequency is mainly controlled by moisture content, but for severe sand dust storms, the effect of visibility is much greater than that of moisture content. ④When the frequency is not too high (f 37 GHz) and the visibility is not too bad (visibility100 m), the weakening caused by sand dust storms is insignificant, especially for the satellite earth link, the effect can be negligible because of its short distance. ⑤The effect of cross polarization is a significant factor, by which sand dust storms affect the microwave propagation. Furthermore, this paper proposes several ways in which the present research can be consolidated:①To establish better models of relation between particle's moisture content and permittivity.② Models concerning air absorption in more detail should be made. ③Cross polarization may be well estimated by a more careful consideration of the relations between dust density and visibility, and the way the dust density decays with height; in addition, particle shape measurements should be extended, possibly to include some measure of the asymmetry, and laboratory tests and theoretical prediction of the canting angle of the particle should be carried out. ④The phenomenon of coupling wind-blown sands with electricity and its effects should be considered. ⑤To compile available geographical and morphological data on sand and dust storms so as to obtain the occurrence frequencies of various visibility in the storms.

Key words: Radio(microwave), Propagation, Sand dust storm, Visibility