Correction for attenuation of radar reflectivity using polarization data

Abstract

SUMMARKAttenuation by heavy rain is a major operational problem in radar estimation of rainfall rates, and one which is increasingly severe at wavelengths shorter than 10 cm. Gate-by-gate correction algorithms, including those using both reflectivity ( Z H ) and differential reflectivity ( Z D R ) , are inherently unstable. In addition values of ZH and ZDK arc affected by hail, which causes little attenuation. Methods dependent upon differential phase shift (KDP) do not give unique solutions but depend upon raindrop size distributions. A new technique which uses both KDP and differential attenuation between the horizontally and vertically polarized radiation (AH-v) is proposed. The total AH.." is measured from the negative ZL)R in light precipitation behind the attenuating region. Theory and observation show that corrections based on the K L )~ -AH-v scheme should he unaffected by hail, stable and accurate. A simpler algorithm may be feasible at C-band in which the total attenuation is derived from the observed total differential attenuation. It appears that the most severe cases of attenuation result from heavy rain consisting of large oblate raindrops. Accordingly, the attenuation would be appreciably reduced if operational radars used vertical polarization rather than the commonly employed horizontal polarization.

Polarimetric rainfall retrieval from a C-Band weather radar in a tropical environment (The Philippines)

“…Therefore, Z DR measurements performed with the antenna pointing at an elevation of 90 o should be 0 dB, and any deviation from that value can be interpreted as the bias of Z DR . However, as we could not manipulate the scan strategy, we followed the suggestion of Smyth and Illingworth (1998) who pointed out that rain drops in regions of light rain were almost spherical and thus Z DR had to be close to zero. Although this approach would not allow for the same precision as the use of a vertically pointing antenna, it appeared reasonable and pragmatic given the expected level of miscalibration.…”

Rain Attenuation Correction of Reflectivity for X-Band Dual-Polarization Radar

“…One is detection range, whereby the echo power received by the radar will decrease with increasing range, and this applies to all radar wavelengths; the other is rain attenuation. With the exception of intense storms, rain attenuation for electromagnetic waves with a wavelength greater than approximately 7 cm is Illingworth [25] for Z DR correction. One of the advantages of the algorithm is that the coefficient α H of the relationship between A H and K DP is estimated from the radar data rather than scattering simulation.…”

Adaptive Attenuation Correction Techniques for C-Band Polarimetric Weather Radars

“…Bringi et al [8] showed that the specific differential phase K DP can be related to the attenuation A h by means of a power law A h = αK DP , where α is sensitive to the temperature. Both A h and K DP are approximately proportional to the fourth moment of the DSD, and therefore, they are quasi-linearly related [10].…”

“…The HB [4] algorithm is given by (7), the Testud et al [11] algorithm (ZPHI) is given by (8), the Bringi et al [12] algorithm (herein referred as BRI) is given by (8)- (10), and the FV algorithm is given by (11).…”

“…Bringi et al [8] showed that the differential propagation phase (K DP ) obtained from a dual polarization (DP) radar can be used to compute the attenuation (A), which, in turn, can be used to correct reflectivity measurements for rain attenuation (see also [9] for circularly polarized radars). Since then, several attenuation correction techniques based on differential phase measurements have been developed [10]- [18]. However, there is a need to assess and validate the different attenuation correction schemes.…”