国外应用微分光谱反射率估测水中悬浮物含量的研究简介

DERIVATIVE REFLECTANCE SPECTROSCOPY TO ESTIMATE SUSPENDED SEDIMENT CONCENTRATION

利用光谱反射率（Ｒλ）估测水中悬浮物含量的基础是水体中悬浮物含量与水体反射光谱之间存在一定的相关性，但这种相关性要满足下述条件才能成立，即在研究的波段范围内，环境变化因子（照度、子像元、云等）影响很小，或者这种影响对所有的波段都是一个附加常数。而这样的条件往往是不会成立的。在国外又研究出一种估测水中悬浮物含量的新方法，即微分光谱反射率（ｄＲλ）方法，目前在实验室和海上两种环境条件的应用研究中，都取得了很好的效果。

Abstract Remotely sensed data can be used to estimate successfully the concentration of sediment in water. Such estimation has relied on relationships between suspended sediment concentration(SSC) Cs and radiation in one or two broad wavebands where it is assumed that the effects of environmental variability (irradiance, subpixel cloud, etc.) are either small, or can be considered as spectrally additive constants in all wavebands.Where these assumptions do not hold, an alternative and theoretically more robust relationship is proposed, that between Cs and derivative radiation (change in radiation per unit wavelength). Measurements of spectral reflectance (Rλ), derivative spectral reflectance(dRλ) and Cs were measured in the laboratory, where the effects of environmental variability were small and at sea where the effects of environmental variability were large. There was a strong correlation between Cs and dRλ both in the laboratory (λmax= -0.98) and at sea (λmax=-0.83) and dRλ was used to estimate Cs in the laboratory to an error of less than 8% of the mean SSC. The correlation between Rλ and Cs was weaker at sea (λmax= 0.46) than in the laboratory (λmax= 0.96). This was due to the presence of large and spectrally variable environmental effects. We recommend the use of derivative spectra for the estimation of Cs when continuous spectra are available.