Figure 3-2. Zenith Attenuation Versus Frequency elevation angle to adjust for the longer path. Figure 3-3 compares the integrated gaseous attenuation at a representative northeast (power beam elevation above horizontal ) and southwest () location with the total attenuation along a 10 km path through a moderately heavy rainfall . It can be seen that below 10 GHz the attenuation resulting from molecular absorption is approximately 0. 1 dB or less, depending on the elevation angle. At frequencies less than 3 GHz, gaseous attenuation greatly exceeds the atmospheric loss due to a typical rainfall. 3. 2. 2 SCATTERING AND ABSORPTION BY HYDROMETEORS Attenuation by particles of condensed and solidified water vapor results from both absorption and scattering and depends on the size, shape, statistical distribution and composition. (2,4,5) Generally, dry ice, snow, and hail produce much less attenuation than rain at an equivalent rate. However, wet snow, melting precipitation, and water-coated ice particles can cause significant loss which may be comparable to, and under some circumstances, larger than an equivalent rainfall.
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