Optical Properties And Remote Sensing Retrieval Of Colored Dissolved Organic Materials (CDOM) In Yangtze Estuary And Adjacent Waters

Colored dissolved organic matter (CDOM) is one of ocean color components. The distribution, migration and transformation research of CDOM in estuarine and coastal waters is important for the studying of the ocean color remote sensing. It also has significant biological and spectroscopy significance. In this paper, CDOM absorption coefficient is used as the CDOM concentration index to study the CDOM distribution and its controlling factors of the Yangtze River estuary and adjacent waters, and on this basis, a primary study about the CDOM retrieval is presented.There are significant changes of CDOM absorption coefficient in different monthes. In general, the absorption coefficients in spring are lower than in winter. But the spectral slope value in spring and summer are both larger than in winter.In the downstream of Wusongkou, the effect of imported Huangpu River water is significant. The absorption coefficient increased 43.84 percent in January and 20% in other monthes. Therefore the imported influence of Huangpu River to the Yangtze River can not be ignored.In spring cruise of 2009, CDOM absorptance in the Yangtze River estuary waters descend from the entrance to out sea, and it is higher in the southeast sea waters than in the northeast. There is a high value area of dissolved organic matter near the Zhoushan Islands. It may be the relevant with the warm and cold current intersection near the Zhoushan Islands. In autumn cruise of 2009, from the estuary to the out sea CDOM absorption gradually decreased. And CDOM concentration gradient is smaller than that in the spring cruise. The spatial distribution of spetral slope (Sg) is more complex than that of the absorption.In summer of 2008, the region out of the North Passage contains higher CDOM spectral slope than other waters. In the 2009 spring survey, the highest Sg is 0.017nm-1. In the 2009 fall survey there is a high value area of CDOM spectral slope in the area near the 122.5°E longtitude. The overall distribution trend of spectral slope value is decreasing from the east to south. Compared to other estuaries and coastal waters, CDOM concentration in the Yangtze Estuary is in a medium level. But the Sg gradient is relatively larger than most other waters. In the tidal estuary, the water layer structure is unstable. Owing to this, the CDOM mixing behavior is always varing. Sometimes, the mixing is conservative; and sometimes a non-conservative one it is. Terrestrial input is the major source of CDOM in the estuary. While, CDOM sources also exist in the out sea. But the correlation between CDOM and chlorophyll is not obvious, so that on-site production may be affected by many other factors.CDOM can be retrieved from the remote sensing reflectance. Many retrieval models were presented for different waters. So as to establish a retrieval model suit to the Yangtze estuary and coastal waters, it is attempted to build models with the combination of band ratio in this article. The retrieval results are assessed according to observed data. At last, the multi-band combined algorithm is choosed and the relative retrieval error is about 20%.