光谱二阶差分Gabor展开法土壤铜铅污染鉴别

土壤是人类生存环境的重要载体，因此，土壤重金属污染问题一直备受关注。随着遥感技术的发展，高光谱遥感在土壤重金属研究中取得了大量的成果，但是，基本上是根据土壤中有机质、铁、粘土矿物等的光谱吸收特征和反演土壤中重金属含量，而不能够区分土壤重金属污染光谱之间的微弱差异。通过盆栽土壤不同浓度铜(Cu)、铅(Pb)污染实验得到不同浓度Cu和Pb污染下盆栽土壤光谱曲线、土壤含水率和有机质含量，提出了一种光谱二阶差分Gabor展开方法探测不同浓度Cu和Pb污染下土壤光谱曲线之间的微弱差异。以二阶差分为基础，首先将土壤光谱转换为稀疏光谱，然后结合土壤稀疏光谱与Gabor展开理论，在频率域中检测不同浓度土壤重金属污染光谱之间的微弱差异，因此，摆脱了单纯通过土壤光谱反射率信息反演土壤重金属含量的研究，而是对土壤重金属污染光谱信息进行时频分析，最终达到检测土壤重金属污染瞬时光谱存在的目的。结果表明：受Cu和Pb污染的盆栽土壤光谱二阶差分Gabor展开系数尺度及等高线分布有较大的差异，Cu污染的盆栽土壤光谱二阶差分Gabor展开系数尺度分布存在两个较高的峰值，且等高线在第1 800~3 600项之间稀疏分布，Pb污染的盆栽土壤光谱二阶差分Gabor展开系数尺度分布存在一个较高的峰值，且等高线在第3 200~3 600项之间密集分布；二阶差分Gabor展开法检测的土壤Cu和Pb污染结果与土壤Cu和Pb含量、土壤含水率、土壤有机质是密切相关的，由于土壤Cu和Pb含量、有机质含量、含水率的不同，土壤Cu和Pb污染二阶差分Gabor展开光谱尺度分布而不同。根据相关性分析结果，分别将土壤Cu和Pb污染划分为三组：Cu(50)~Cu(300)，Cu(400)~Cu(800)，Cu(1 000)以上；Pb(50)以下，Pb(100)~Pb(300)，Pb(400)~Pb(1 200)。

A Spectroscopic Second-Order Differential Gabor Expansion Method for Copper,Lead Pollution Detection in Soil

Soil is an important carrier of the human living environments. Therefore, the problem of soil heavy metal pollution has always attracted attention. With the development of remote sensing technology, much progress has been made in the area of hyperspectral remote sensing, which is used for the study of the heavy metal content of soil. However, this method works basically in accordance with spectral absorption features, as well as the content of soil organic matter, iron and clay minerals, when retrieving the heavy metal content of soil. It has been found to be unable to distinguish the slight differences in the soil heavy metal pollution spectra. In this study, a potting soil pollution experiment with different concentrations of copper (Cu) and lead (Pb) was used to obtain the potting soil spectral curve, as well as the water and organic matter content of the soil under different concentrations of Cu and Pb stress. The purpose of the experiment was to put forward a type of second-order differential Gabor expansion method for the detection of the slight differences between the soil’s spectral curves under different concentrations of Cu and Pb stress. Firstly, based on the second-order difference method, the soil spectrawere converted into sparse spectra by the method, then the sparse spectrum of soil and Gabor expansion theory were combined to detect the weak differences of heavy metal stress spectra in different concentration soils in the frequency domain. Therefore, instead of studying the content of soil heavy metal solely by the spectral reflectance information, this method performed time-frequency analysis on the spectral information of soil heavy metal stress and finally achieved the purpose of detecting the instantaneous spectrum of soil heavy metal pollution. The results showed that the Cu-contaminated potting soil spectra displayed major differences in the scale distribution of the second-order differential Gabor expansion coefficient when compared with the Pb-contaminated potting soil spectra. In addition, the scale of second-order differential Gabor expansion coefficient of the Cu-contaminated soil spectra ranged from 1 800th to 3 600th items sparse, the scale of second-order differential Gabor expansion coefficient of the Pb-contaminated soil spectra ranged from 3 200th to 3 600th items coarctate. By utilizing a second-order differential Gabor expansion method, the detected results of the Cu and Pb pollution in the soil were found to be closely related to soil’s Cu and Pb content, water content and organic matter. As a result of the different Cu and Pb content in the soil, as well as the organic matter content and water content, the second-order differential Gabor expansion spectra of the soil’s Cu and Pb pollution displayed different scale distributions. According to the correlation analysis results, the soil’s Cu and Pb pollution were divided into three grades respectively: Cu(50)~Cu(300), Cu(400)~Cu(800), Cu(1 000) or more；lowerthan Pb(50), Pb(100)~Pb(300), Pb(400)~Pb(1 200).