X波段天气雷达回波强度衰减订正方法的对比研究
Comparative Study on Attenuation Correction schemes for X-Band Weather Radar Reflectivity Factor
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摘要: 近年来,国内建设了几百部X波段天气雷达,获取了大量的探测数据。但X波段的电磁波波长短,容易受到降水的衰减,中到大雨的衰减比较明显,暴雨的衰减很严重,影响了回波强度数据的可靠性。为了利用受衰减的X波段雷达回波数据,需要采用可靠的订正算法,对回波数据进行衰减订正。作为双偏振雷达的参量之一,KDP具有不受降水衰减的特性,因而被广泛地应用于衰减订正。本文利用成熟的ZH-KDP方法和全新的k-LWP方法,对两次降雨个例的四组X波段雷达回波数据进行了订正试验,并和邻近的S波段雷达回波数据进行对比分析,结果表明:(1)上述两种方法都有良好的订正效果,相比较来说,k-LWP方法的订正效果更好,不容易出现“过量订正”;(2)ZH-KDP方法只能用于双偏振雷达,但k-LWP法可用于各种天气雷达,具有更好的实用性和稳定性;(3)KDP受地物和冰雹等目标的非瑞利散射影响大,导致了获取KDP的困难,但LWP受地物的影响小,并且比ZH-KDP方法更简单。个例试验表明, k-LWP方案可以很好地用于X波段雷达的衰减订正。Abstract: In recent years, hundreds of X-band weather radars have been deployed in China. Vast amount of radar measurement data has been archived. However, these data suffered from precipitation attenuation due to the short wavelength of X-band. The attenuation evidence is obvious in the case of moderate to heavy precipitation, and the attenuation gets severe if the precipitation is intense, degrading the reliability of X-band radar measurement of reflectivity factor. Therefore, believable attenuation correction becomes necessary for the application of X-band weather radar measurement. KDP, one of polarimetric radar variables, is widely used to correct the attenuation by precipitation because it is immune to attenuation. The reliable scheme ZH-KDP and the innovative scheme k-LWP are used in the study for attenuation correct effect analyses, the sample data consists of 4 datasets collected by X-band weather radar during 2 storms, and the adjacent S-band radar data is used to evaluate the correction effects of the 2 schemes. The results indicate that: (1) Both schemes have good performance on attenuation correction, and k-LWP has advantage over ZH-KDP because of less possibility of over-correction. (2) ZH-KDP scheme is valid only on dual-polarization radar, but k-LWP scheme can work on both polarimetric and non-polarimetric radar with good practicality and robustness; (3) KDP is prone to be affected by non-Rayleigh scatters like ground object and hailstone, increasing the difficulty to get precise KDP. In contrast, LWP is hard to be affected by ground objects and hailstones, and calculation of k-LWP scheme is simpler. Case studies verify that the k-LWP scheme is highly effective for the attenuation correction of X-band radars.
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