應用同步衛星資料估算東亞地區之風場

Applying Geostationary Satellite Data to Estimate Wind Field of Eastern Asia Area

劉振榮(Gin-Rong Liu) ； 徐健瑤(Jiann-Yau Shyu) ； 林唐煌(Tang-Huang Lin)

《大氣科學》 23卷2期 (1995/06) Pp. 265-285

摘要

由於傳統探空測站每天在正常情況下僅觀測兩次，而且探空測站一般亦只分佈在人口綢密的陸地範圍，因此不僅大氣運動資料的時間解析度不足，對於廣大的洋面上或人跡罕至的高山，沙漠或叢林地區則更是缺乏資料。由此可知傳統的探空觀測資料不論在空間上或時間上均存有極大的空隙，而目前由於可接收2-4顆繞極軌道衛星，因此間隔不到6小時衛星即可觀測一次，而同步衛星更是每天24小時中每隔1小時或半小時即可傳送一次觀測資料，此外更由於衛星觀測涵蓋範圍的寬廣與連續，使得衛星觀測資料在時間和空間上的解析度均遠優於傳統的觀測，也因此本研究即嘗試應用衛星來估算東亞地區之風場，以彌補傳統探空觀測在大洋面或人跡稀少處風場資料之不足。同步衛星所觀測的雲圖傳統均應用於觀測天氣系統的變化情形，不過由於其良好的時間解析度，更是用來觀測雲運動的最佳工具。而由於大部份的雲移動可視為雲受到風吹拂所致，因此雲運動又可代表雲所在高度層上的風向風速，所以藉由東亞地區內各雲塊之移動晴形，即可估求得當時之風場。本研究即利用日本GMS-4地球同步衛星逐時所觀測得之雲圖作雲追蹤，首先利用環形電影法選擇適合追蹤之雲塊，再由互相關法決定雲塊之移動及距離，以決定風向和風速，最後由紅外線所求得之雲頂溫度決定風向風速所代表之高度，而整個東亞地區之目標雲塊均追蹤求得風向風速後，最後步驟則編輯全部結果並去除不合理的部份，即可估求得東亞地區當時之合理風場。本研究所估求之風場即與同時之探空觀測風場相比對，以驗證應用本研究之準確性。研究中最大誤差可能來自於雲高度之決定，這也是未來在改進風場估算準確度上值得進一步研究之方向。本研究採用了GMS-4四個觀測日期資料，研究結果與當時的探空資料比較，風向相差在30度以內者為66.3%，風速相差在15 knots以內者為90.2%，結果尚佳。

關鍵字

風場 ； 衛星遙測

並列摘要

Normally the traditional radiosonde station just observes twice daily. And usually the stations locate in the land area where are dense in population. Thus, not only the time resolution is worse in atmospheric motion data, but also the data are scare in the areas of wide open ocean, mountain, desert and jungle. Therefore, there exist larger data-scare area in the traditional radiosonde observations no matter in space or in time. Because one can receive the observing data of 2 to 4 polar orbital satellites daily, the time interval of observations of the polar orbital satellites is less than 6 hours. Besides, the geostationary satellite can provide 1 or half hour interval observations every day. And the satellite observing coverage is wide and continuous in space. These will make the satellite observations superior than the traditional radiosonde observations in time and space resolution. Thus, this research tries to apply geostationary satellite data to estimate the wind field of East Asia in order to increase the wind data in the wide open ocean or less population area where traditional observations are scare.Typically the geostationary satellite observed cloud images are used in monitoring the development of weather systems. But owing to its excellect time resolution, it is also good in estimating cloud motion. Because almost all the cloud motion cause from the blowing of wind, the cloud motion can represent the wind of the cloud level. Therefore through the measurement of every individual cloud motion in East Asia the wind field of this area can be estimated. Cloud images observed by the Japanese GMS-4 geostationary satellite in every hour are tracked in this research. The movie loop is applied to choose the tracked cloud., and the cross-correlation method is used to determine the speed and direction of the cloud motion. The speed and direction of the wind is estimated from the speed and direction of the cloud motion. The height of the wind is determined by compaired the vertical temperature profile and the cloud top temperature observed by GMS-4 IR channel. Finally the wind field is complied by removing the unrealistic wind. The results of this wind field estimation are compared with the radiosonde observations to verify its accuracy.Four GMS-4 IR data are used in this study, and the results are compared with the radisonde ovservations. The percentage of those difference less than 30 degrees in wind direction is about 66.3% and the percentage less than 15 knots in wind speed is about 90.2% of the samples.

並列關鍵字

Wind field ； Satellite remote sensing