Application of Wavelet Transform to the Infrared Diffusion Reflectance Spectrum of Rocks
DENG Da-wei1,2,SONG Ning1,2,LI Qi-nan3,XU Xiao-xuan1,2,ZHANG Cun-zhou1,2*
1. Photonics Center of School of Physics, Nankai University, Tianjin 300071, China 2. The Key Laboratory of Advanced Technique and Fabrication for Weak-Light Nonlinear Photonics Materials, Ministry of Education, Nankai University, Tianjin 300457, China 3. Laboratory of Optical Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100080, China
Abstract：The infrared diffuse reflectance spectra of hydrocarbon source rocks with different particle sizes were measured. The result indicated that the absorbency of the raw spectrum decreased with the reduction of particle size, but the relationship turned to be reverse after we pretreated the original spectra by using wavelet transform to eliminate the background and calibrate the baseline drift, both of which were caused by scattering. The reversed relations showed that the spectral lines were influenced deeply by the scattering of the samples. So the particle size of the samples to be measured and the particle size of the model samples must be consistent to reduce the error. The low frequency part of the spectrum filtrated by wavelet transform corresponds to the scattering, and the authors used it to set up a model at the latent absorbance wave number (near 2 820 cm-1) to forecast the particle size. By comparing this model with the other model based on the original spectrum the authors found that the pertinence of the anterior model is higher than the latter one and the value reaches 0.999 7. So the authors can accurately forecast and control the distribution of the particle size by this model, which can be used to improve the accuracy in the quantitative analysis of the infrared reflectance spectrum. Also the study validated that both scattering and absorption coefficients are inversely correlated with the particle size.
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