水中镉化合物粒子消光系数及其反射率光谱(400～900nm)测量

Measuring the Spectrum of Extinction Coefficient and Reflectance for Cadmium Compounds from 400 to 900 nm

测量出水中镉化合物单位浓度消光系数光谱曲线和镉化合物干燥环境下的反射率光谱曲线是水体镉元素含量遥感反演的关键。首先采用自主设计的透射光测量装置,利用Analytical Spectral Devices(ASD)光谱仪分别测量了相同厚度不同浓度的两种镉化合物粒子溶液(硫化镉和氧化镉)的透射光辐亮度,通过比值法计算出不同浓度的镉化合物粒子溶液的消光系数,最终得到其400~900nm波长范围内的单位浓度消光系数光谱。然后再利用ASD光谱仪在户外晴好干燥的环境下对这两种镉化合物的反射率光谱进行了测量,为日后进一步计算其单位浓度吸收和散射系数打下基础。单位浓度消光系数光谱测量结果表明,硫化镉在675nm出现极大值,在550和830nm出现极小值;氧化镉则随着波长的增加呈逐渐减少的单调趋势;两种化合物在水中的消光作用主要在紫蓝光波段。反射率光谱测量结果表明,硫化镉的反射率从500nm开始快速增大至650nm后趋于平缓;氧化镉从525nm开始呈近线性递增至900nm;二者都具有明显的光谱特征。本文在国内首次专门针对水质遥感领域开展了具有光活性的镉化合物的光学参数测量工作,并获得了这两种化合物的单位浓度消光系数和反射率光谱曲线,是水体镉含量遥感反演模型所必需的光学参数之一,为镉含量遥感反演这一难题提供一个突破口,测量结果可以为镉含量提取的遥感工作波段选择提供有力的参考依据,同时也为水体镉含量的遥感提取提供了模型必需的重要参数。

The key to extract the contents of cadmium in water by using remote sensing technique is to measure the spectrum of extinction coefficient per g·L^（-1） and reflectance for its compounds.So in this paper,firstly,we choose two kinds of cadmium compounds,cadmium sulfide（CdS）and cadmium oxide（CdO）,which are most commonly exsit in natural water,to measure the spectrums of extinction coefficient and reflectance for them.We use the equipment,designed on our own,which can adjust the path length of light passing and make our measuring results more accurate at visible and near-infrared wavelength range than others.Then we use Analytical Spectral Devices（ASD）spectrometer to measure the radiance of the light spot,which is from the direct light passed through cadmium compounds solutions of different concentrations reflected by the standard board.Using the ratio method to eliminate environmental errors and the effects of the thimbleful of suspended solids in water,we obtain the extinction coefficient per g·L^（-1） of these two kinds of cadmium compounds from 400 to 900nm.Secondly,we use ASD spectrometer to measure the reflectance spectrum of them in the sunny day at outdoor.The reflectance we obtain in this paper can help us to calculate the absorption and scattering coefficient per g·L^（-1） in the future.The measuring results show that the extinction coefficient spectrum of CdS has two troughs at 550 and 830nm and one peak at 675 nm.And the extinction coefficient spectrum of CdO decrease from purple to near-infrared.Both of their coefficient spectrums in blue are larger than green and red.And the value of the extinction coefficient per g·L^（-1） of CdS is larger than CdO in the whole measuring wavelength range.The reflectance of CdS in yellow and red is larger than purple and blue,which increases rapidly from 500 to 650nm and then leveling off.While the reflectance of CdO increase linearly from 525 to 900nm.Both have obvious spectral characteristic.According to our results,the largest extinction coefficient appear at blue color,while the largest reflectance appear at yellow and red,which means that those bands are the most sensitive wavelength to detect the change of cadmium concentration in water.This study carries out with optical parameters measurements for optical activity of cadmium compounds specifically for water quality remote sensing for the first time.We conclude that the extinction coefficient and reflectance spectrums we obtained are reasonable,and the results can be used as the base parameter in the remote sensing inversion model for cadmium contents in water,which provides a breakthrough on using remote sensing technique to extract the heavy metal contents in water.Obtained these two optical parameters in this paper can provide powerful reference for band selection of the remote sensing image,which is used to extract cadmium contents in water,as well as provide the necessary important parameters of the remote sensing inversion model of cadmium contents in water.