A Study of Precipitation Effect on Tropospheric Electromagnetic Wave Propagation at Frequency 19.5 GHz

  • Author(s): Shun-Peng Shih
  • DOI: 10.3319/TAO.2008.19.3.309(AA)
  • Keywords: Precipitation, Rain attenuation, Ka-band, Drop size distribution, Terrestrial propagation link
  • Citation: Shih, S. P., 2008: A study of precipitation effect on tropospheric electromagnetic wave propagation at frequency 19.5 GHz. Terr. Atmos. Ocean. Sci., 19, 309-319, doi: 10.3319/TAO.2008.19.3.309(AA)

In this article, we take advantage of a terrestrial propagation link at Ka-band 19.5 GHz located on the campus of the National Central University in Chung-Li City to carry out a tropospheric radio propagation experiment. Data collected in 2004 were used in data analysis to provide a deeper understanding of the precipitation effect on tropospheric electromagnetic wave propagation at Ka-band. The results indicate that the relation between specific attenuation ©§e of 19.5 GHz radio wave amplitude and the measured rain fall rate R (in unit of mm hr-1) is of the form: κe = aRb (in unit dB km-1) with a = 0.0699 and b = 1.0984, which is fairly close to that obtained by assuming Laws-Parsons drop size distribution. In order to study the overall attenuation characteristics of Ka-band radio wave influenced by precipitation particles, we used a ground-based 2D disdrometer to measure the terminal velocities of raindrops and their size distributions. The result shows that the relation between raindrop diameter and terminal velocity in terms of the Power-Law relation, i.e., V(D) = ADB, and the drop size distribution can be expressed in the form of a Gamma distribution function, i.e., N(D) = N0Dμ exp(-δD). With these results, the corresponding rain attenuation of the electromagnetic wave at Ka-band is estimated and discussed in this article.

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