레이더 에코 特性을 이용한 非降水 에코의 除去
Elimination of non-precipitation echo using radar echo characteristic
vi, 71 p.
레이더 에코;비강수 에코;
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Precipitation echoes observed by Doppler weather radar are usually contaminated by non-precipitation echoes such as ground echoes and AP(Anomalous Propagation), causing an increase in radar reflectivity and then overestimating of precipitation amount. The quality control of radar reflectivity data is a very important process in radar-based rainfall estimation. The purpose of this study is to develop a new efficient method, which can be used to eliminate non-precipitation echoes for the more accurate estimation of rainfall amount. The fuzzy logic procedures in the present study were applied to eliminate nonprecipitation echoes, based on the membership functions of radial velocity, standard deviation of reflectivity, and vertical gradient of reflectivity. Each membership function of these three parameters was obtained for four reflectivity classes of each parameter, yielding twelve membership functions. The probability distributions of the three parameters for both cases of precipitation and clear air were obtained from the analysis of the data from MRO (Marshall Radar Observatory) radar observations of five cases each of precipitation and clear air. To assess the fuzzy logic procedures, two steps were taken. One was the selection of two precipitation events: one with precipitation event contaminated by both ground echo and AP, and the other contaminated by AP alone. The other was estimation of rainfall amounts for the two precipitation events by radar reflectivity and polarimetric method. The precipitation accumulation maps for six hours by radar reflectivity were made after eliminating the non-precipitation echoes by fuzzy logic. In addition, the precipitation accumulation maps for six hours were acquired by the precipitation amount obtained by the polarimetric parameters. These precipitation accumulation maps by both methods were compared with each other by assuming that the precipitation amount obtained by the polarimetric method as a reference. The result of the comparison shows that the non-precipitation echoes were well removed by both methods. However, the fuzzy logic procedures reduced the amount of rainfall slightly beyond 60 km from the radar site, compared to the rainfall amount by the polarimetric method. The isolated non-precipitation echoes were not removed by the polarimetric method. A direct comparison between the present method and others was not made. Compared with Kissenger's method(1999) which is very similar to the present method, it obtained higher CSI(Critical Success Index) for the two precipitation events. The present study indicates that for the operational radar which produces the three parameters, the fuzzy logic developed is very useful for the estimation of accurate rainfall amount.