The Study On Key Techniques For The Field Mineral Near-Infrared Spectroscopy Analysis

Near-Infrared Spectroscopy (NIRS) analysis technique is a physics method to analyze the matter's chemistry composition and content by its emission or absorption spectra reflecting its atoms'and molecules'characters. It is a modern analysis technique that integrates multi-subject knowledge: spectroscopy, chemometrics, computer application, etc. The laboratorial instruments are used to measure the mineral composition of rocks or soil in situ by portable NIRS analysis techniques. This is a dream of the field geologic workers for a long time. As that the internal portable field mineral NIRS instruments are importation, and the existing external analysis softwares are not fit for internal mineral samples, combined with Chinese geologic investigation item "The study of the field mineral NIRS analysis method and development of instrument"(item number: 199920190116) and Jilin university innovation fund item "The study of the soil environment Near-Infrared detection information analysis system in situ", the key technical problems in three aspects of the field mineral NIRS analysis technique--NIR Spectroscopy instrument, Spectroscopy data processing and application model--have been studied and resolved. The main study work and productions: 1. The optical path and machinery system of the portable field mineral NIR spectrum instrument have designed and realized. Its spectrometer is a cross single optical path grating scan framework to settle the conflict between the setting space of parts and the system volume—to supply the enough setting space for the integrating sphere and the modulator, and to ensure the system volume is small. Its machinery includes the precise parts, inching institutions, and a sines gearing to ensure its precise is enough. The capability test and experiment comparison with the congener foreign instrument have done. Its results indicate its main technical parameters have been close to the level of the congener foreign products. 2. The characteristics and processing methods of minerals NIRS data have been researched. The characteristics of minerals NIRS diffuse reflectivity data are that the NIRS data of the same mineral sample have a holistic excursion and range variety, the dynamic range of NIRS data of the same composition minerals is large, the signal-to-noise of different NIRS data are not same. The mathematics model of mineral NIRS data has been concluded. It's: y = byt +a+n. 3. The three classes of pretreatment methods for spectrum data have been concluded by the numbers, their application effects have been analyzed, and their application principles have been concluded. The spectrum pretreatment can eliminate or decrease the errors brought by spectrum stability and sample characters. The de-noise pretreatments can eliminate or decrease the spectrum noise. The matrix pretreatment can enlarge the differences between the data of the modeling samples, and be used to process the sample data set before modeling. The combining application of the three classes mutual benefit pretreatment approaches can heighten the accuracy and robustness of the model. The application effect of every kind of data pretreatment has relation with its processing data, so the data pretreatment approaches should be ensured after comparing and analyzing all kinds of the approaches. 4. The establishing methods of application model on the mineral NIR analysis have been studied. With Partial Least Squares (PLS) and Artificial Neural Net (ANN) modeling methods, and simulative data, the factors affecting the model performance have been educed. Those are the relativity, the errors of constant and simple part, and spectrum noise of the modeling data. The methods to avoid those factors have been brought forward, their applying impacts have been studied, and their accuracy and robustness have been compared. Conclusions drew from the two modeling methods are same by and large. The relativity of the modeling data affects the accuracy of the model. The errors of constant and simple part, and spectrum noise of the spectrum data depress the accuracy or and robustness of the model. The elimination of those effects can befulfilled by the mutual beneficial approaches to do spectrum, den-noise pretreatment, and matrix pretreatment. Standardization and normalization are two better spectrum pretreatments that are efficient in eliminating the errors of constant and simple part of the data. And used matrix pretreatment at the same time, the model accuracy will be advanced. The den-noise pretreatment can reduce the influence of spectrum noise to the model performance. There are three methods of den-noise in this paper: Savitzky-Golay convolution smoothing, wavelet den-noise and Fourier den-noise. The efficiency of the three den-noise methods are better for smaller spectrum noises (60dB), but its efficiencies are not satisfying for bigger spectrum noise(40dB),the determinant of test set is smaller than 95%. The accuracy of each modeling method has relation with the relativity of the modeling data, the spectrum pretreatments approach, and the size of spectrum noise. The robustness of the ANN modeling method is better than those of the PLS. 5. The half-quantity NIRS analysis software for the field mineral composition have been designed for self-producing portable field mineral NIR spectrometer. And its core modules have been developed. simulative data and actual data are separately used to test the software. The result indicates the software runs all right and is practicable. Main innovative work: 1. The cross single optical path grating scan framework as the spectrometer of portable mineral NIR spectrum instrument has been designed and realized. 2. According to character of the spectrum data measured by the self-made NIR mineral spectrum instrument, the mathematics model has boiled. It applies to the field mineral NIRS reflectivity data by the single optical path diffuse reflection spectrum instrument. Base on this model, three classes of pretreatment methods for spectrum data have generalized. Those are den-noise, spectrum and matrix pretreatment. Mutual beneficial principles when using these methods are clarified. 3. According to the requirement of the field mineral half-quantify analysis, the post-treatment method to deal with the analytic data has been provided, and its software has been designed. The study of this paper is useful because: (1) The process of the study on the field mineral components using NIR spectrum analysis techniques will be speeded up. (2) It will lay foundation for developing the NIRS mineral analysis instrument and software which should have independent knowledge right and suitable for our country.