The Backscattering Properties Of Red Tide Alga And The Remote Sensing Inversion Model

Backscattering coefficient is an important parameter in ocean optics, and also is one of the important inherent optical properties, it is determined by the concentration of water constituents. Recently, while considerable research has been conducted on the backscattering properties of water with the development of optical instruments, most of this research is focused on the particle backscattering characteristics of case1water and coastal turbid water. The phytoplankton backscattering coefficient (bbP) and the causes of its variability are still poorly known. This hinders the expansion of the remote sensing model to a considerable extent. Variability of the backscattering characteristics about the alga Aureococcus anophagefferens、Skeletonema costatum、Amphidinium carerae hulburt and Prorocentrum micans which represent for the picophytoplankto、 nanophytoplankton and microphytoplankton respectively are examined. At the same time, the cell density remote sensing inversion model of the red tide alga is first builded. And the main researches contents and achievements were as follows:(1) Variability of backscattering properties about different red tide alga. Particulate backscattering coefficients and backscattering ratio are obtained for the experimental cultures by calculating the in-situ measured data, the results show that the backscattering coefficient and the backscattering ratio increase with an increase in the chlorophyll concentration, but every alga has its own spectral shape, and the shape of the particulate backscattering coefficient spectra about the picophytoplankton and nanophytoplankton is also changed with the variation of the chlorophyll concentration, especially at420nm-488nm. Otherwise, the bigger particulate has relatively flattened spectra, it is not regular for the contribution to the water backscattering of different sized alga particles, and a good relationship is observed between the backscattering cross-section and the ESD which provide a good theoretical basis for building the particle size distribution inversion model.(2) According to the variation of particulate backscattering spectra shape, the study investigates the influence of absorption on the backscattering signal, and establishes the characteristic response relationship model between backscattering and absorption on every selected alga. The result indicates that the slope of the backscattering spectrum in the blue for Aureococcus anophagefferens and Amphidinium carerae hulburt shows a strong relationship with absorption and the correlation coefficient R2are0.996and0.93respectively. The slope of the backscattering spectra between442nm and488nm for the Skeletonema costatum and Prorocentrum micans has a weaker, positive linear relationship with the relative absorption(R2is equal to0.57and0.52respectively).(3) Building correlation model between backscattering coefficients and the water quality characteristic parameters. The relationship between backscattering coefficients and chlorophyll concentration, cell desity is studied respctively. And find that the linear regression and nonlinear regression are both fit for showing the relation between the backscattering coefficients and chlorophyll concentration. While the relationship between backscattering coefficients and cell density only fit the nonlinear regression, the determination coefficient at all bands are the same for the Aureococcus anophagefferens; and the relationship of the Amphidinium carerae hulburt’s becomes stronger with the longer wavelengh, especially at the700nm, R2is as much as0.99; moreover, the best fit bands of Prorocentrum micans appears at blue and red, that also lays the good foundation for building cell density distribution inversion model.(4)It develops the cell density remote sensing reversion model from MODIS data and retrieves red tide distribution effectively. After analyzing the spectral data and establishing the relation between inherent optical properties and apparent optical properties, the author builds a cell density remote sensing inversion model from MODIS data in allusion to Aureococcus anophagefferens and Prorocentrum micans, then apply this method to MODIS data on June16,2005, of which the red tide alga is Aureococcus anophagefferens. The results shows that multi-bands inversion model is more accurate than the single band inversion model for the high chlorophyll water, but it is difficult to identify the red tide information from the mixed pixel signal, that leads to the inversion results is larger than the monitoring data especially for high suspended sediment water, while the single band inversion model is more useful for such turbid water, although inversion value is lower than the monitoring results, it is available to eliminating the influence of suspended sediments and the recognition accuracy is more higher.