The imaginary part of the dielectric factor K depends on the temperature and phase of the hydrometeor and the microwave frequency. Dry ice is at least an order of magnitude less lossy than water. This is important since most of the attenuation of decimeter radiation is due to absorption. Wet ice or water-coated hail will be nearly as lossy as a raindrop. The exact Mie theory must be used for wavelengths less than 10 cm; however, the Rayleigh approximation is useful between 10 and 30 cm and is accurate for wavelengths 30 cm and greater. Table 3-1 compares the attenuation coefficient obtained from Equation (3-7) with the distribution of values computed by Schell et al6 (using measured drop size distributions and Mie theory) and the Log Regres- sion fits to attenuation versus rainfall rate scattergrams given by Crane. (2) Also shown are the results of computations based on Equation (3-6) and the exact Mie expressions for . TABLE 3-1 ATTENUATION BY HEAVY RAIN (dB/km) Estimates of the transmission efficiency for propagation through a uniform rainfall are based on the Log Regression model and the mean value of the set of estimates obtained from measured drop distributions at six heavy rain locations.(2) The results are expressed in terms of one-way path attenuation and
RkJQdWJsaXNoZXIy MTU5NjU0Mg==