An examination of propagation effects in rainfall on radar measurements at microwave frequencies

Bringi, V. N. ; Chandrasekar, V. ; Balakrishnan, N. ; Zrnic, D. S. (1990) An examination of propagation effects in rainfall on radar measurements at microwave frequencies Journal of Atmospheric and Oceanic Technology, 7 (6). pp. 829-840. ISSN 0739-0572

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Propagation effects in rainfall are examined at three microwave frequencies corresponding to S (3.0 GHz), C (5.5 GHz), and X (10.0 GHz) bands. Attenuation at horizontal polarization, as well as differential attenuation and differential propagation phase between horizontal (H) and vertical (V) polarizations are considered. It is shown that at the three frequencies both attenuation and differential attenuation are nearly linearly related to differential propagation phase (ΦDP). This is shown through simulation using (a) gamma raindrop size distributions (RSD) with three parameters (N0, D0, m) that are varied over a very wide range representing a variety of rainfall types, and (b) measured raindrop size distributions at a single location using a disdrometer. Measurements of X-band specific attenuation and S-band specific differential phase in convective rainshafts using the National Center for Atmospheric Research CP-2 radar are presented in order to experimentally demonstrate the linear relationship between attenuation and differential propagation phase. Correction procedures for reflectivity and differential reflectivity (ZDR) are developed assuming that differential propagation phase is measured using a radar that alternately transmits H and V polarized waves with copolar reception through the same receiver and processor system. The correction procedures are not dependent on the actual rainrate profile between the radar and the range location of interest. The accuracy of the procedure depends on, (a) RSD fluctuations, (b) variability in the estimate of differential propagation phase due to measurement fluctuations, and (c) nonzero values of the backscatter differential phase (δ) between H and V polarizations. Simulations are used to gauge the accuracy of correction procedures at S- and C-bands assuming δ is negligible. The correction accuracy for attentuation at S-band is estimated to be ∼0.05 dB while at C-band it is estimated to be within 1 dB if ΦDP≤60°. Simulations further indicate that C-band differential attenuations effects can be corrected to within ∼35% of the mean value.

Item Type:Article
Source:Copyright of this article belongs to American Meteorological Society.
ID Code:1040
Deposited On:25 Sep 2010 11:13
Last Modified:16 May 2016 12:12

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