Influence of air humidity on microwave depolarisation in semi-arid areas

The subject of the work is the role of synoptic conditions in a change in the original polarisation of an electromagnetic field. The depolarisation may be provoked by any inhomogeneities in the structure of the medium. More or less dense volumes are randomly formed by the large number of solid nuclei suspended in humid air and attracting water vapour; especially in the ground atmosphere of the Northern Negev desert, where high levels of coarse aerosol concentration and humidity are typical. The electrical features of such irregularities are characterised by the permittivity of the suspended grains ε, which depends on the rate of nuclear moistening. Since ε differs strongly from the permittivity of clear air, displacement of the incoming wave from its original orientation takes place. The dependence on ε of the amount of reradiated power (received as an additional field component orthogonal to the primary transmitted signal) is assessed according to the theory of depolarisation and the Rayleigh approximation. After the removal of the meteorological factors (from six recorded parameters), the relative humidity is found to be a main parameter influencing the depolarisation rate; the rate is observed to be proportional to the humidity level