Study on Heavy Metal in Soil Based on Spectral Second-Order Differential Gabor Transform

Abstract

Topsoil was collected from the surroundings of a mining area in Xilin Gol League which was located in Xilinhot of Inner Mongolia Autonomous Region, and measurement was conducted to obtain soil spectral curves and the concentrations of plumbum (Pb), zinc (Zn), copper (Cu), and nickel (Ni) in soil, so as to study the relationship between transform spectrum expansion coefficient contour distribution of different soil samples in this area and heavy metal concentration in soil. The method was based on frequency domain. First, soil spectra were converted to sparse spectra. Then, by combining soil sparse spectra with Gabor transform theory, a conversion to the frequency domain is conducted to detect the subtle difference between soil spectra of heavy metal at different concentrations. This approach helps to get rid of studies which aim to infer the content of heavy metal in soil simply through the information of spectral reflectance in soil, and a frequency domain transform-based analysis of spectral information concerning heavy metal overproof in soil is carried out instead, ultimately achieving the purpose of detecting the existence of transient spectra of heavy metal overproof in soil. This study was to provide a basis for the hyperspectral frequency domain study of soil heavy metal overproof. According to the study, this method could be used to detect the threshold concentration of Pb overproof in the surrounding soil of the mining area in Xilin Gol League. Furthermore, when Pb and Ni concentrations in soil exceeded the background value of soil environment in Inner Mongolia Autonomous Region, an over-standard Zn concentration in this area would lead to changes in transform spectrum expansion coefficient contour distribution and, thus, could be used to detect the threshold concentration of Zn overproof in this area.