A NEW POLARIMETRIC METHOD FOR CORRECTING THE EFFECTS OF ATTENUATION AT C-BAND
A NEW POLARIMETRIC METHOD FOR CORRECTING THE EFFECTS OF ATTENUATION AT C-BAND
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一种校正 C 频段衰减影响的新偏振方法
DOI：
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发表时间：
2005
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通讯作者：
P. Tabary
中科院分区：
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作者：
P. Tabary
众所周知，降水介质的分子吸收会降低在相对较短波长下工作的降水雷达的水平反射率 (ZH) 和差分反射率 (ZDR) 值。这种衰减效应在强烈的对流回波之后最为明显。随着偏振分集的出现，差分传播相位测量（ΦDP）具有不受雷达校准误差、衰减效应、冰雹污染和部分波束阻挡影响的优点（Ryzhkov 和 Zrnic 1995）。此外，Holt (1988) 和 Bringi 等人。 (1990) 发现用于校正 ZH 和 ZDR 的系数与 ΦDP 测量值线性相关。图1显示了ZDR和ΦDP的实际观测结果。很明显，ZDR 的低值与 ΦDP 的高值一致。已经出现了几种利用 ΦDP 作为基础来校正由于衰减而导致的 ZH 和 ZDR 减少的方法。本文展示了一种称为平流校正技术的新方法，该方法独立于假设的雨滴尺寸形状模型，b）可以适应与温度相关的衰减，c）是半经验的。这里介绍的技术本质上是跟踪从一个图像到下一个图像的回声，然后假设 ZH 和 ZDR 的任何变化仅是由于衰减效应造成的。针对几种强对流情况生成基于 ΦDP 测量的校正因子。使用邻近雷达收集的数据来比较校正与未校正的反射率测量结果。
Molecular absorption by the precipitation media is known to reduce values of horizontal reflectivity (ZH) and differential reflectivity (ZDR) for precipitation radars operating at relatively short wavelengths. This attenuation effect is most pronounced behind intense convective echoes. With the advent of polarization diversity, differential propagation phase measurements (ΦDP) offer the advantages of being immune to radar calibration errors, attenuation effects, hail contamination, and partial beam blocking (Ryzhkov and Zrnic 1995). Moreover, Holt (1988) and Bringi et al. (1990) discovered that coefficients used to correct both ZH and ZDR were linearly related to ΦDP measurements. Fig. 1 shows actual observations of ZDR and ΦDP. It is evident that low values of ZDR are coincident with high values of ΦDP. Several methods have emerged which utilize ΦDP as a basis to correct for the reduction in ZH and ZDR due to attenuation. This paper demonstrates a new methodology, called the advection-correction technique, that is independent of an assumed raindrop size-shape model, b) may accommodate temperaturedependent attenuation, and c) is semi-empirical. The technique presented here essentially tracks echoes from one image to the next and then assumes that any changes in ZH and ZDR are due to attenuation effects alone. Correction factors based on ΦDP measurements are produced for several cases of intense convection. Comparisons of corrected versus uncorrected reflectivity measurements are made using data collected at neighboring radars.