利用降雨型態分類改進衛星陸上降雨估算的準確度

Using Rain Type Classification Data for Improving the Accuracy of Satellite Rainfall Estimation over Land

蔡明達(Ming-Da Tsai) ； 陳萬金(Wann-Jin Chen) ； 汪建良(Jian-Liang Wang)

《大氣科學》 36卷1期 (2008/03) Pp. 1-19

摘要

在颱風侵台期間以散射指數法(SIL, Scattering Index over Land)，並利用TRMM (Tropical Rainfall Measuring Mission)衛星上的微波(TMI, TRMM Microwave Imager)、降雨雷達(PR, Precipitation Radar)資料及台灣自動雨量觀測站(ARMTS, Automatic Rainfall and Meteorological Telemetry System)降雨資料進行台灣陸上的估算降雨研究。利用TRMM/PR 2A25標準降雨產品的資料進行降雨型態(rain type)的分類，將陸地降雨區分成對流性、有亮帶層狀性及無亮帶層狀性降雨區，並針對不同降雨型態的雨區利用衛星微波資料進行降雨反演的研究，以增進陸地降雨的準確度。
在衛星降雨估算的驗證中，以ARMTS觀測的降雨率爲真值並比較在降雨型態有無分類的情況下降雨估算值差異，結果顯示在對流性降雨區平均降雨率的絶對差值由原先的6.2 mm/hr改進爲1.7 mm/hr；在有亮帶的層狀性降雨區平均的降雨率差值由原先的10.7 mm /hr 改進爲1.8 mm/hr。前面二者的結果經由地面降雨觀測值的驗證皆有明顯的改善，但在無亮帶的層狀性降雨區中，其TMI降雨反演的平均降雨率差值没有改善，由此可見在該類型的降雨率不適合使用SIL法進行反演。

關鍵字

TRMM ； TMI ； 降雨雷達 ； ARMTS ； 降雨型態 ； SIL ； 降雨 ； 微波

並列摘要

In this study, data from the Tropical Rainfall Measuring Mission (TRMM) satellite's Microwave Imager (TMI) and Precipitation Radar (PR) instruments, along with the rain rates measured by the Automatic Rainfall and Meteorological Telemetry System (ARMTS), were employed to quantitatively estimate the precipitation over Taiwan by the scattering index method (SIL, Scattering Index over Land). Based on the rainfall types determined by TRMM/PR, the rainfall areas over Taiwan were classified into convective rainfall areas and stratiform rainfall areas with/without bright band. Analyses in these different rainfall areas were conducted to see if this classification could be used to improve the accuracy of quantitative rainfall retrievals.
With the observational data from ARMTS set as the ground truth, the verification of the accuracy of the satellite rainfall estimation was performed by comparing the discrepancies of the rainfall estimations that had and had not undergone rainfall type classifications. The absolute mean rainfall discrepancy of the convective rainfall areas was reduced from 6.2 mm/hr to 1.7 mm/hr. For bright-band stratiform rainfall areas, they were improved from 10.7 mm/hr to 1.8mm/hr. The rainfall retrieval equations of different rainfall types were tested for the land rainfall estimation over Taiwan. Excluding the case of the stratiform rainfall areas without the bright band, results indicated that the precipitation estimation accuracy was considerably improved in the convective rainfall and bright-band stratiform rainfall areas. In addition, this paper shows that the SIL is not suitable for indirect rainfall retrieval via high-frequency scattering mechanisms for stratiform rainfall areas without bright band..

並列關鍵字

TRMM ； TMI ； PR ； ARMTS ； Rain type ； SIL ； Rainfall ； Microwave