Test of Empirical and Semi-Analytical Algorithms for Euphotic Zone Depth with SeaWiFs Data Off Southeastern China

摘要

This study employs SeaWiFS data over the waters off the southern China to evaluate semi-analytical algorithm for euphotic zone depth(Z). This algorithms is based on water's inherent optical properties (IOPs), which can he near-analytically calculated from spectral remote-sensing reflectance, where remote-sensing reflectance can be derived from the normalized water-leaving radiance provided by SeaWiFS. In the Taiwan Strait, compared with in situ Z (+/- 3 hour within SeaWiFS collection), average error() is l5.0 % and root mean square error (RMSE)is 0074, with Z, in a range of 14-34 m from field measurements. In the South China Sea, compared within situ Z, (+48 hour within SeaWiFS collection), is 5.1% in summer and 22.6 in winter, while RMSE is 0.032 in summer and 0.129 in winter, with Z in a range of 10-82 m from field measurements. For comparison, we also evaluate the performance of the empirical Z algorithm that is based on chromophyll concentration. It is found that the IOP-centered approach has higher accuracy compared to the chlorophyll-a centered approach (e.g. in the South China Sea in winter, is 55.3 % and RMSE is 0.219). The new algorithm is thus found not only worked well with waters of the Gulf of Mexico, Monterey Bay and the Arabian Sea, hut also worked well with waters of the China Sea.