二类水体短波红外波段大气校正方法的改进

海洋水色遥感技术在海洋生态环境研究中越来越受到重视.大气校正是海洋水色遥感中的一个关键问题,短波红外波段(SWIR)方法是目前在二类水体大气校正中应用较多的一种方法.现有的SWIR方法假设在对数坐标下,大气校正因子在外推波段与基准波段间按线性关系变化.当波段跨度不大时,这一线性近似与辐射传输模型模拟结果相符,而当波段跨度较大时,则存在一定差异.针对这一问题,本文采用分段外推的方法,修正了大气校正因子,对SWIR方法进行了改进.同时,选取2010年10月4日和2012年4月4日两景渤海海域的MODIS遥感图像,先引入浑浊度来分析渤海海域水体清洁程度,进而在区分出的二类水体区域分析改进方法的效果.结果表明,改进后方法的结果比原方法整体偏小,在渤海区域的差异在1%~15%之间.在卫星遥感数据的反演中有必要关注这一问题.

Improvement of SWIR atmospheric correction algorithm for case II water

Ocean color remote sensing technology has drawn more and more attention in marine eco-environmental research. Atmospheric correction is a key issue in ocean color remote sensing. The shortwave infrared (SWIR) algorithm is widely applied in atmospheric correction of case II water. The present SWIR atmospheric correction algorithm assumes that between the extrapolation bands and the reference bands, the atmospheric correction factors change linearly in logarithmic coordinates. When the two bands are close to each other, the linear approximation agrees well with the results of radiative transfer models. However, when the two bands are far away from each other, obvious differences can be observed. A piecewise extrapolating algorithm was adopted to modify the atmospheric correction factors and improve the SWIR algorithm. MODIS remote sensing images of the Bohai Sea on October 4, 2010 and April 4, 2012 were analyzed. Turbid water index was applied to analyze the degree of water cleanliness in the Bohai Sea, and the improved algorithm was evaluated in the case II water area. The results show that the water-leaving radiance of the improved SWIR atmospheric correction algorithm is integrally smaller than the original algorithm and the difference is between 1%~15%. It is necessary to pay attention to this issue in remote sensing.