Application of wavelet transformation in detection of organic matter content based on visible/near infrared reflectance spectroscopy

The hyper-spectral reflectance of soil was measured by a ASD FieldSpec within 400～1 000 nm,and processed by logarithmic transformation for getting A value of soil spectra.Next,first order derivative operation was conducted for the original soil spectra and A value.Then,the two types of first derivative spectra of soil above were denoised by the threshold denoising method based on wavelet transformation.In the two kinds of denoised spectra,spectrum response feature due to different soil organic matter content was discussed;and the sensitive bands for organic matter content estimation were initially determined by applying correlation.Results showed that:(1) Because of much noise,it is difficulty to identify contour and response feature in the two types of first derivative spectra resulting from different organic contents.(2) By the threshold denoising method based on wavelet transformation,noise in the two types of first derivative spectra is removed effectively,and the spectra contour and response feature can be identified easily.(3) Within 567～598 nm,there are high and stable negative correlation coefficients between soil organic matter contents and denoised first derivative spectra of soil.(4) Within 524～535 nm,there are high and stable positive correlation coefficients between soil organic matter contents and denoised first derivative A value of soil.