Experimentally Based Estimates of Relations between X-Band Radar Signal Attenuation Characteristics and Differential Phase in Rain

Abstract

Correcting observed polarimetric radar variables for attenuation and differential attenuation effects in rain is important for meteorological applications involving measurements at attenuating frequencies such as those at X band. The results of estimating the coefficients in the correction-scheme relations from dual-wavelength polarimetric radar measurements of rainfall involving attenuating and nonattenuating frequencies are described. Such coefficients found directly from measurements are essentially free from different assumptions about drop shapes, drop size distributions, and/or relations between different radar variables that are typically used in many attenuation and differential attenuation correction schemes. Experimentally based estimates derived using dual-wavelength radar measurements conducted during a project in northern Colorado indicate values of the coefficients in the attenuation-differential phase quasi-linear relations at X band in the approximate range of 0.20-0.31 dB deg 21 . The corresponding coefficients in the differential attenuationdifferential phase relations are in the range of 0.052-0.065 dB deg 21 .

Integrated Correction Algorithm for X Band Dual-Polarization Radar Reflectivity Based on CINRAD/SA Radar

“…In Equation 3, Φ DP (X) − Φ DP (0) is a continuously increased X band differential phase value with increasing range and Φ DP (0) (unit: deg) is the estimated initial system phase at each radial due to radar hardware [11,14]. The reflectivity difference ∆Z(S-X) between S and X band pixels in the same space-time, with approximately equal horizontal distances and heights, is approximately equal to the X band PIA at horizontal polarization.…”

“…3. Results Table 2 lists the values of ratio a found through theoretical simulations assuming a mean drop aspect ratio (i.e., minor-to-major dimension ratio) vs. size relations and measured rain temperature in the radar site and using the measurements of the dual-wavelength radar with dual-polarization capabilities introduced by Matrosov et al, 2014 [11]. From Table 2, it can be seen that the values of ratio a generally vary in the range from 0.1 to 0.3.…”

“…Some more sophisticated attenuation correction approaches take into account the variability of ratio a as well [9,11,[13][14][15][16]. Bringi et al, 2001 [13] proposed a self-consistent (SC) method, which iteratively checks Φ DP in each beam resolution volume along each ray and constrains the corrected Z DR on the far side of the rain cell in order to obtain the optimal ratio a at each particular ray.…”

“…S band reflectivity attenuation in rain is typically more than one order of magnitude smaller than it is in X band attenuation and can be usually neglected compared with X band attenuation in dual-frequency measurements [17]. Matrosov et al, 2014 [11] modified the attenuation correction technique suggested by Bringi et al, 1990 [3] to the dual-wavelength observations collected by the CSU-CHILL radar (detailed radar technique parameters introduced in [11]) whose X and S band channels share the same antenna system. The advantages of the modified technique are essentially free of modeling assumptions about their drop shapes, oscillation modes, size distribution, and relations between attenuation characteristics and reflectivity.…”

Characterization of Mediterranean hail-bearing storms using an operational polarimetric X-band radar

“…The common polarimetric approach for compensating rain path attenuation is based on the assumed linearity between specific attenuation as well as differential attenuation and specific differential phase (Bringi et al, 1990;Testud et al, 2000), i.e., A H,DP = γ H,DP K DP . It is known that the coefficients γ H,DP are variable, depending on raindrop size, shape and temperature (Jameson, 1992;Matrosov et al, 2014). Despite the fact that several optimization approaches have been proposed (Carey et al, 2000;Vulpiani et al, 2008), solutions that are totally reliable for operational applications are not yet available.…”