Validation And Application Of Retrieval Algorithm For Remote Sensing Of Euphotic Zone Depthin The EasternChina

Euphotic zone is the topmost layer of ocean in which there is sufficient light for net primary production, i.e. where the energy fixed by photosynthesis exceeds that lost by respiration. Euphotic zone depth is the depth where only1%of the surface photosynthetic available radiation (PAR) remains. The depth of the photic zone is generally proportional to the level of primary productivity that occurs in that area of the ocean. In this study, the performance of retrieval algorithm of Zeu, which has great potential applications, was validated in the Eastern China Seas. On this basis, the spatial/time distributions of Zeu in the Eastern China Seas were obtained from the ocean color satellite data (MODIS), to satisfy the study requirement of ocean biology.Firstly, the retrieval algorithm for Zeu based on the inherent optical properties(IOPs) was validated with in situ measurements. The in situ optical data set, which consists of irradiance, absorption, scattering, transparency, and etc., was collected from several cruises in the Eastern China Seas. The remote sensing reflectance at the sea surface was derived from the measurements of radiometers with certain data processing procedures. The 'true' values of Zeu used for validation was obtained from the radiative transfer simulations (RTS) with the inputs of scattering and absorption measurement data. Besides, the values of Zeu, which are considered as another 'true' data set, were obtained from secchi disk depth based on the empirical algorithm. Then, the performance of the retrieval algorithm was evaluated by these two data sets. The results show that the retrieval algorithm based on IOPs has good performance in the Eastern China Seas. Secondly, the validated retrieval algorithm was applied to the MODIS data (Level2) in the Eastern China Seas. The Zeu from the MODIS is compaired with the Zeu from the measured data, RMSE is9.25%, the validated retrieval algorithm is reliable. The monthly distributions of Zeuwere obtained by averaging over7years (2005-2011) MODIS data in the Eastern China Seas. The results shows the distributions of Zeu from validated retrieval algorithm possess seasonal variation characteristics, and the results are reasonable.