太湖水体反射率的光谱特征波长分析

水体反射率的光谱特征波长分析是解决内陆水色遥感难题的一项重要的基础工作.该文分析了2006-2009年七次太湖综合实验获取的312个采样点遥感反射率,找出反射率曲线出现极大值、极小值、由凹向凸转变的拐点、由凸向凹转变的拐点对应的特征波长,给出了太湖水体反射率350～900nm范围内的光谱特征波长:359,440,464,472,552,566,583,628,636,645,660,676,689,706,728,791,806和825 nm.最后用浮游植物色素的吸收光谱、太湖水体特有的组成成分解释了特征波长.文章分析特征波长的方法,对于各种光谱曲线的特征波长分析都适用,该方法能够有效地区分曲线峰值所在波长和谷值所在波长重叠的情况.该文的研究成果有利于建立反演水质参数的算法,从而提高反演算法的精度.

Characteristic wavelengths analysis for remote sensing reflectance on water surface in Taihu Lake

The research on characteristic wavelengths analysis of reflectance spectrum is a very important and basic task for remote sensing of inland-water color. The present paper analyzed remote sensing reflectances of 312 samples measured in Taihu Lake between 2006 and 2009, and these reflectances were separated into three classes by chlorophyll-a concentrations. The reflectance spectra smoothed by Savitzky-Golay algorithm were calculated by first- and second-order derivatives. Then, zero values were located in the derivatives and counted at all wavelengths. Thus the frequency distribution of zeros at each wavelength was got. At which wavelength a local maximum of the frequencies appears a characteristic wavelength will most likely be there. These characteristic wavelengths are corresponding to maximum, minimum, from-concave-to-convex inflection point and from-convex-to-concave inflection point of a spectrum curve. At last the paper provided the characteristic wavelengths for Taihu Lake water at the spectral coverage from 350 to 900 nm, which are 359, 440, 464, 472, 552, 566, 583, 628, 636, 645, 660, 676, 689, 706, 728, 791, 806, and 825 nm. In addition, these wavelengths we found were explained by absorption of phytoplankton pigments and components of water in Taihu Lake. Being able to distinguish overlaps between peaks and vales at the same wavelength in different measurements, the method to analyze characteristic wavelengths is universally applicable to various spectrum curves. The characteristic wavelengths chosen by the paper are helpful to improving some algorithms of retrieval of water quality parameters.