空載透水光達測深系統能夠有效快速的測得沿岸海底地形，然而其作業成本十分昂貴。影響其測深的主要因素之ㄧ為海水的沙奇盤深度，因此，在空載透水光達施測前，進行測區的沙奇盤深度推估分析，評估其施測之可行性，可以有效減少光達作業系統運作之風險，提升其整體經濟效益。

　　本研究利用MODIS衛星影像大範圍取像，以及高時間解析度與多波段的特性，輔以沙奇盤、透光度計與背向散射計等船測資料，推估台灣沿岸海水透視度。船測資料包含2007年5月至2008年5月，共65個深度剖面資料，其中19個測點的採樣時間與MODIS影像取像時間同步。各測點之海水光學性質的代表值，乃是將深度剖面資料兩倍光學深度以內的資料以深度平均處理。本研究深入比較488nm與532nm兩個波段搭配三種不同沙奇盤深度與海水光學性質的關係式，評估MODIS影像求得的6個沙奇盤深度推估值。經與19個測點之船測沙奇盤深度分析結果顯示，532nm波段推估結果優於488nm波段。

　　最後利用推估結果較佳的波段與關係式，將2004年至2007年共計1988張MODIS影像，疊合成1至12月份計12張台灣海域的沙奇盤深度推估影像，並分析其四年的變化，結果顯示台灣海域的沙奇盤深度與吸收係數，以及背向散射係數皆有年的週期性變化。搭配海底地形分析比較後顯示，沙奇盤深度明顯受到海底地形的變化影響，導致沙奇盤深度值會有區域性上的不同；其規律的年週期變化，推論為受到季節性洋流的影響所致。整體看來，每年的夏秋兩季為沙奇盤深度較高的季節，台灣西部海域沙奇盤深度最低，其次為北部，東部與南部海域透視度較高。因此，透水光達於台灣地區最適合的施測時間與地點，應為每年的夏秋兩季與南部以及東部沿岸。

　　Airborne bathymetric lidar system has proved to be cost-effective for mapping coastal waters. Secchi depth is one the most significant factors that affects the performance of the lidar system. Therefore, it can increase the bathymetry survey operation efficiency if the information of the water secchi depth turbidity can be obtained in advance.

　　In this research, the MODIS sensor onboard Aqua satellite is used due to its ability to provide extensive temporal and spatial imagery. The supplemental field measurements of 65 depth profiles are collected using Secchi Disk, Wetlabs AC-9, and HOBI Labs Hydroscat-6 from from May, 2007 to May, 2008. The AC-9 and H-6 profiles are averaged with two optical depth in order to represent the optical properties at a site. Among the 65 profiles, 19 of them are concurrent with MODIS images acquisition. There has been reports of three relationships between optical properties and secchi depth based on either 488 nm or 532 nm. Further investigation are made to compare which combination of optical relationship and wavelength is most reliable.

　　Finally, twelve monthly binning secchi depth maps (January to December) are build by using 1988 MODIS images from 2004 to 2007. The results show annual variation of secchi depth, absorption coefficient, and backscattering coefficient. In addition, Secchi depth in Taiwan is influenced by seasonal ocean current and bathymetry. In general, secchi depth is higher in summer and fall. The west coast of Taiwan has the lowest secchi depth, while the east and south are relative high. In conclusion, it is suggested that the bathymetric lidar survey should take place in the south and east coast of Taiwan in summer and fall.

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