An attempt for ocean color products of the turbid water in the clean-sky and cloud-free coastal regions

摘要

There are two kinds of atmospheric components effecting atmospheric correction. One is Rayleigh scattering term from air molecules which is most stable. The other is aerosol scattering term (including Rayleigh-aerosol interactions) which changes so much. Rayleigh term can be got from Rayleigh lookup table but aerosol term is hard to be extracted, especially for the turbid ocean waters. Moreover, this aerosol estimation will cost a lot of time and the corresponding near real-time system will be not easy to be established. Is it necessary to consider the effect of the aerosol scattering term all the time for anywhere all over the world? After all, there are many turbid coastal regions with clean-sky, cloud-free around the globe, especially the relatively unpolluted Southern Hemisphere. In this paper, we propose a new approach to estimate ocean color products in clean-sky, cloud-free coastal region from the remote sensing data. According to the successful control of air pollution in the Tokyo Bay from Japan government and the Tokyo Bay coastal region containing some of the most consistently highly turbid coastal waters to be found along the coast line, we use in-situ CDOM data of the Tokyo Bay to test this method. Since 2010, the short expeditions have been conducted in the Tokyo Bay. Through these expeditions, waters are sampled to determine chlorophyll-a concentrations, nutrients, CDOM, as well as the CTD profiling of temperature, salinity, and photo-synthetically available irradiance. The MODIS (MODerate-resolution Imaging Spectroradiometer) data from the AQUA and TERRA are received and processed at the satellite ground receiving station of Chiba. The band ratio and non-linear regression analysis are applied to build the new algorithm to estimate CDOM from the in-situ CDOM and the Rayleigh-corrected radiance at the top of the atmosphere. As a complementary algorithm of these ocean color algorithms, the direct method proposed in this paper can be used to estimate CDOM absorption coefficients from MODIS visible Rayleigh-corrected radiance ratio and in situ CDOM data. Our data analysis results suggest that the method proposed in this paper can deal with clean-sky, cloud-free coastal region at near real-time speeds, especially the turbid coastal region in the relatively unpolluted Southern Hemisphere.