臺灣東部高頻雷達表面海流觀測之資料品質管理與初步結果

Abstract

臺灣東部海域為黑潮通過之重要區域,本研究利用臺灣海洋科技研究中心所 提供之和平、綠野、小野柳與旭海等四雷達測站結合國立臺灣大學海洋研究所/海 軍軍官學校合作的蘇澳、漢本兩雷達站做結合,合成出臺灣東部表面海流測流 網。在這些雷達資料中包含了許多環境造成的影響,如自然界電離層隨日夜變化 上下擺動,或是人為設定疏失等導致資料品質會有空間上與時間上的變化。本研 究利用各種統計方法來篩選出可信度較高的雷達資料,排除因為各種干擾的壞資 料。其中包含利用原始自能譜之一階峰訊號與背景訊號之閾值決定可用的徑向流 距離範圍、以長時間統計徑向海流在方位角上之系統性誤差等方式。再將重新後 處理過後的資料與歷史船測資料、歷史浮標資料做比對,可以得到比原始未處理 過得資料更好的相關性。最後利用這些經過品管後的資料來探討表面黑潮的潮流 變化與季節性的變動等。

Since east of Taiwan is Kuroshio flow area, we can verify the accuracy of HF radar data by typical flow pattern of the Kuroshio. Signals received were not only from wave backscatter, but from nature as well. Signals that do not originate from waves are labeled “noise”, which can lead to irregular radial velocity. Data quality decreases as distance increases. Outside of distance, there are two major factors that impact data quality. The first is the variation of the earth’s ionosphere. The second is systematic error in bearings of each HF radar site; long-term reverse current direction for instance. As a result, the total velocity would be interfered with, generating anomalies. With this method, differences between first order signals and noises of different ranges are used to determine appropriate radial currents based on each monopole spectrum. Using statistical methods to calculate high quality data with no significant systematic errors in the azimuths of various radial currents, we can acquire more accurate data. The Kuroshio Current is a strong western boundary current, passing through the east of Taiwan. We can cross-reference HF radar data with Sb-ADCP data to analyze for accuracy. After this data selection process, coefficient of determination (R 2 ) between HF radar and Sb-ADCP data could be increased almost 0.25. Finally, combine selected radial velocity into new and accuracy total velocity vector. After these reprocessed progress, discuss tidal variations and seasonal variations of the surface Kuroshio Current.