Study On Atmospheric Correction Methods For Water Color In Taihu Lake

The remote sensing can obtain macroscopic radiate information of large water area, overcome deficiencies of the field sampling of discrete points in routine monitoring, realize the monitoring of surface feature, show enormous potentiality in water quality monitoring. However, the global solar radiation received by remote sensor includes little water information (water-leaving radiance). Over 90 percents information comes from rayleigh scattering, aerosol scattering and solar reflectance. So we must make atmospheric correction to obtain the water-leaving radiance which contains the information of water constituents. Separating water information from atmospheric signal is the key for the application of the remote sensing technique, which influences accuracy of following applications such as the inversion of water constituents.Taihu Lake belongs to inland Case-II water, whose optical properties are much more complicated than clean ocean water. Standard atmospheric correction algorithm for ocean color remote sensing may cause big errors. It is necessary to develop atmospheric correction models for inland Case-II water. This thesis firstly demonstrates the principle and methods of atmospheric correction, based on Landsat-5 TM data, synchronous MODIS data and meteorologic records, tries different methods to obtain remote sensing reflectance of water, and analyses the results of atmospheric correction with field spectral data.The main contents of this study are as follows:1,Making atmospheric correction with 6S radiative transfer model, combined with synchronous meteorologic records;2,Making atmospheric correction with the dark-object method, considering influcences ofθ,φ,L_p,T_θ,T_φand E_D;3,Making atmospheric correction with improved Gordon atmospheric correction algorithm, placing emphasis on the calculation of rayleigh scattering, aerosol scattering, oxygen content, whitecap radiance and atmospheric transmission.The results show that:1,Importing synchronous meteorologic records into 6S model improves its atmospheric correction accuracy. The aerosol composition in Taihu area isn't clear, so the standard continent aerosol type was selected here for correction, which caused errors to the result.2,Selecting dark object among lake waters for dark-object method caused over-correction of reflectance in TM bands. The atmospheric parameters computed by synchronous meteorologic records are more accurate than that by the dark object itself. Synchronous meteorologic records are proved to be a complementarity for dark-object method.3,The remote sensing reflectance inversed by improved Gordon atmospheric correction algorithm is close to the field sampling data. Compared with synchronous MODIS data, synchronous meteorologic records computed aerosol scattering more accurately. The relative error its correction is least which is close to the international error criterion for inland Case-II water.