Using MODIS Imagery to Estimate Secchi Depth Turbidity of Taiwan Coastal Water

• Main Authors: Che-Chuan Kang, 康哲銓
• Other Authors: Chi-Kuei Wang
• Format: Others
• Language: zh-TW
• Published: 2008
• Online Access: http://ndltd.ncl.edu.tw/handle/46946053188192720280

碩士 === 國立成功大學 === 測量及空間資訊學系碩博士班 === 97 === 　　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.