X-band雷達所觀測之海面影像隱含有表面流資訊在其中。利用雷達影像推算海面流場時，在深水區域，水深對流場計算結果之影響不明顯；但在淺水區域，水深會影響流場計算結果。本文研究目的為探討如何在流場分析過程中輸入適當的水深代表值，以獲得正確的流場分析結果。
為了探討對各種水深、波浪和流速條件下之水深代表值，本文除進行現場觀測外，並發展出一套影像模擬法，可依設定之波浪和流速條件產生影像序列，做為後續研究的素材。在分析過程中，用影像範圍內之任一水深值代入分散關係式均可求得一個流速值，由試誤法求得流速分析值與輸入值小於設定誤差之水深範圍，再用迴歸分析求得水深代表值。
經由以上之計算分析結果顯示，水深代表值與底床斜率間存有良好的相關性，用二次多項式迴歸，其相關性為97%。為驗證結果的準確性，本文將影像求得之流速值與GPS漂流浮標量測之表面流速進行比對，結果顯示代入本文所求得之水深輸入值，確實能改進雷達影像推算表面流速的結果，且在相對水深愈小的區域改進效果愈顯著。

Surface current information is possible to be extracted from the X-Band radar backscatter. The value of representative water depth (RWD) is one of the most important factors in the image process to derive surface current from radar images. It cannot be ignored for the case of that the image is from shallow water area. The purpose of this paper is to study the estimation of RWD in order to find the correct sea surface current.
In addition to the field experiment, an image simulation method is developed to simulate images for further studies from various conditions of water depths, waves and currents. The RWD is tested from the water depth ranges that the image covers. The optimal RWD is then determined by the criteria on minima bias of input and analyzed currents. The result shows that the optimal RWD value has correlation with bathymetry slope. By regression analysis, the coefficient of correlation is 97%. An empirical formula is therefore derived to estimate the RWD.
In order to validity the result from image simulation, a field experiment is arranged. Sea surface current measured from GPS buoy is used for validation of present formula. It is shown that the result of sea surface current derived from radar images is improved by inputting the RWD estimated from the empirical formula in this study. The improvement is significant at the coastal area with small relative water depth.

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