Associations Of Clay Minerals Content Of Soil On SWIR Spectral Response

Clay mineral is the amorphous silicate minerals with aqueous layer or layer chain, generally distributed in the soil with dispersed state size (<2microns); it has strong adsorption, ion exchange and dilatability, and makes the soil have certain self cleaning capacity. The type, content and structure characteristics of clay minerals in the soil can lead to physical and chemical properties change of soil; it has indicative function for geological prospecting and oil and gas exploration, and also has been used for the study of ancient climate and environmental pollution. Clay minerals have diagnostic spectral features in hyperspectral shortwave infrared, laboratory spectrometric method is the foundation for the application of remote sensing to monitor the content of clay minerals in the soil study. For these reasons, the objective of this study was to analysis the relationship between diagnostic spectral reflection information and the physical and chemical parameters of soil to establish the SWIR spectroscopy forecast models of soil physic-chemical parameters for accurately quantifying the contents of kaolinite, illite and montmorillonite in soil. The mainly research results are described as follows:1. Determined the content of soil clay minerals and abtained the spectral data. A total of367soil samples were collected from the study area. Each sample was divided into two groups, some of the samples was sent to the laboratory for determining the content of22kinds of elements and oxides which are used for quantitative measurement of kaolinite, montmorillonite and illite content, other samples was scanned by Portable Near Infrared Spectrometer, get367soil samples reflective curves with SWIR spectral range. According to the research needs, we chose the24soil samples from the A and B layer soil in Bei Zi Fu area, B and C layer of soil samples of70in Jin Chang Gou Liang area. To analysis spectral curve, we found that sample with different layers of soil; its spectral response in the shortwave infrared was different. C layer soil spectral reflectance is highest; followed by B layer soil, and A soil layer spectral reflectance is the lowest. The environmental impact is heavy on A soil layer.2. Short wave infrared spectral characteristics research and modeling. The spectral reflectance of soil samples determined in laboratory contains some interference factors which have nothing to do with the test samples, such as instrument noise and baseline drift, etc. We have carried on the first order differential, logarithmic, inverse mathematical transformation, etc, to avoid the influence of undesirable interference factor affecting the spectral measurement. Clay minerals have diagnostic spectral feature in the shortwave infrared, so continuum removal method was used to extract the absorption peaks of kaolinite, montmorillonite and illite from the USGS standards spectral library. Based on three kinds of the clay minerals’characteristic absorption peak positions to extract the reflectance of soil samples, and using the multiple linear regression method to establish forecast model between spectral reflectance of different layers soil and clay mineral contents of soil. A layer of soil is affected by the weathering, changed the original soil composition which is different from B layer, so that the model between A layer of soil spectral reflectance and B layer of clay mineral contents is not ideal. B layer of soil affected by external environment influence is small and the C layer soil is closer to the parent rock, its stability is strong, so the B and C layer of soil have similarity components. The correlation relationship between B layer of soil spectral reflectance and C layer of clay mineral contents is better, so the prediction models could be used for estimation the kaolinite and illite contents.3. Application of the prediction model. The principal component analysis (PCA) and ratio analysis were employed to extract the altered information of magnesium hydroxy and aluminium hydroxyl in the research area. The clay minerals content calculated from the prediction models were basically consistent with the degree of alteration, the higher content, the higher the degree of alteration. The method of quantitative inversing soil clay minerals content by laboratory hyperspectral remote sensing can be used for verifying field alteration information, which has a guiding role for field prospecting.