台灣附近海域之衛星測高波形重定資料精度評估

Assessment of Retracked Sea Surface Heights Around Taiwan

高煥欽(Huan-Chin Kao) ； 郭重言(Chung-Yen Kuo) ； HyongKi Lee ； 沈嗣鈞(C.K. Shum)

《航測及遙測學刊》 15卷4期 (2010/12) Pp. 307-315

https://doi.org/10.6574/JPRS.2010.15(4).1

摘要

本文之主要目的為進行台灣附近海域之JASON-2 20-Hz和TOPEX/Poseidon（T／P）10-Hz 衛星測高資料波形重定和波形重定演算法之功效評估，並將重定之測高資料與台南安平港驗潮站資料進行比較分析。台灣附近海域海深及海況極為複雜，位於台灣西邊之台灣海峽，其海深均不超過200公尺，而位於台灣東岸之西太平洋海域，其海深可達4000公尺。另外，台灣海峽之海潮潮差較西大平洋大。測高衛星於淺海區域觀測量精度不佳，特別是近海岸處，其主要原為雷達反射脈衝訊號易受到陸地干擾，導致衛星接收之反射波形訊號複雜，因而無法精確求取波形前緣中點，而波形重定（waveform retracking）技術可有效改進此缺點。本研究應用波形重定技術重定台灣附近海域測高資料，應用之波形重定演算法包含Offset Center of Gravity 演算法、門檻值演算法（threshold retracker）、改良型門檻值演算法（modified threshold retracker）與冰原演算法（ice retracker），然後分別計算經由不同演算法重定後之資料改善率（improvement percentages, IMPs），用來評估重定測高資料之精度，以求取各研究區域之最佳波形重定演算法。結果顯示波形重定技術可有效提昇T／P 與JASON－2衛星之近岸資料精度和數量，其IMP可達到82%，而最佳演算法則因地而異。另外，波形重定後之測高海水面高度與安平驗潮站資料，其變化更加吻合。

關鍵字

衛星測高 ； 波形重定 ； 驗潮站

並列摘要

The purpose of the study is to evaluate the accuracy of the retracked TOPEX/Poseidon (T/P) 10-Hz and Jason-2 20-Hz altimetry sea surface heights (SSHs) around Taiwan by comparing to Anping tide gauge records. The sea state and bathymetry in the study area are highly various. Taiwan Strait located at the west of Taiwan has an average bathymetry less than 200 m and its amplitudes of ocean tides are extremely high. In contrast, the western Pacific Ocean located at the east of Taiwan has deep bathymetry of 4000m and relatively low amplitudes of ocean tides. The measurements of radar altimeters are inaccurate in shallow oceans especially near the coastlines because the displacement of the midpoints of leading edges results from the waveforms returning from ocean-land areas. This disadvantage can be effectively overcome by waveform retracking technique. In this study, retracking algorithms including the Offset Center of Gravity, threshold, modified threshold, and ice retrackers were used and the performance of different algorithms were examined by computing the improvement percentages (IMPs). The result shows that T/P and Jason-2 data can be significantly improved by the waveform retracking with the highest IMP at 82% and the optimal retracking algorithm highly depends on the characteristics of the study area. In addition, the retracked Jason-2 SSHs agree better with Anping tide gauge records than non-retracked data.

並列關鍵字

Satellite Altimetry ； Waveform Retracking ； Tide Gauge