| 要約: | In this study, new and simple algorithms to retrieve cirrus cloud, sediment
and aerosol optical depth (AOD) from Moderate Resolution Radiospectrometer
(MODIS) imagery is suggested and demonstrated. Techniques used in this thesis
are totally new and never been used before by others researchers. The presences
of cirrus cloud have been detected utilizing gradient technique algorithm. The
algorithm is based on the gradient connecting the 1.38 and 1.24 μm lines of the log–
log graph of apparent reflectance against the MODIS wavelength. This algorithm
has been tested over the Yellow Sea, Gulf of Martaban, Mediterranean Sea and
Atlantic Ocean. The result of this algorithm is then compared with the band ratio
technique and the accuracy was determined with percentage difference below 10%.
The presence of sediment reflectance in the MODIS imagery not only
saturate the ocean color channels, but also enhance the reflectance of near infrared
channels used in the atmospheric correction algorithm. This leads to the
overestimation of the aerosol contributions and underestimation of the derived
water-leaving reflectance in the visible channels. In this study, a new and simple
method to detect and mask the presence of sediment reflectance in the MODIS
imagery is proposed. The algorithm is based on the difference of the gradient of the
line connecting the 0.47 and 2.13 μm channels and 0.47 and 0.66 μm channels of a
log–log graph of the apparent reflectance values against their MODIS wavelengths.
A sample results over Yellow Sea, Gulf of Martaban and Arabian Sea was
demonstrated. The accuracy of the algorithm was tested and determined.
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