CN105699322B - The method that the stable carbon isotope ratio of soil is quickly detected using near infrared spectrum - Google Patents
The method that the stable carbon isotope ratio of soil is quickly detected using near infrared spectrum Download PDFInfo
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- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
- G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
- G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
- G01N21/35—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light
- G01N21/359—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light using near infrared light
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Abstract
The present invention provides a kind of methods for the stable carbon isotope ratio detecting soil using near infrared spectrum, and described method includes following steps：1) the stable carbon isotope ratio of multiple calibration pedotheques is measured；2) the diffusing reflection spectrogram of the near infrared band of acquisition calibration pedotheque, obtains original spectrogram；3) original spectrogram is smoothly pre-processed, spectrogram after being handled；4) vector machine method is used to establish the causes after the processing of calibration pedotheque between spectrogram and stable carbon isotope ratio；5) the diffusing reflection spectrogram for acquiring the near infrared band of pedotheque to be measured, the stable carbon isotope ratio of pedotheque to be measured is calculated according to causes.Method provided by the invention can quickly detect soil stabilization carbon isotope ratio using near-infrared spectra.
Description
Technical field
The present invention relates to field of ecology, more particularly to a kind of method of the stable carbon isotope ratio of detection soil.
Background technology
Stable carbon isotope ratio (δ13C) analysis method can be used to indicate that the source of the soil organism, research soil have
The degree of decomposition of machine matter and its component and turnover, reproduction C3/C4The change histories of vegetation, in soil organism research and ecology
In be increasingly becoming a strong tool.
Measure soil δ13C generally uses stable isotope ratio mass spectrography (IRMS), its working principle is that：Soil passes through height
Temperature burning, organic carbon therein are transformed into gaseous state CO2；After chromatographic column or adsorption column are separated with other gases, in ion source
In be ionized；After ion beam line focus and acceleration, into mass analyzer；Under magnetic fields, ion stream presses certain lotus
Matter ratio (m/z) deflects, and since the quality (m) of various isotopes is different, the degree of ion stream deflection is also different；Each is same
The ion beam of position element reaches ion acceptor by the track of oneself, and the amplified ion intensity of flow for recording each isotope is surveyed
Go out isotopic ratio.Stable isotope ratio mass spectrometer is expensive, and special messenger is needed to operate, and test period is long, corresponding test at
This is also high.Therefore, isotope ratio mass spectrometry (IRMS), which measures soil δ 13C, following deficiency：1, expensive equipment, test at
This height；2, technology requires high, not easy to operate；3, test period is long；4, it is not easy to promote.
Application of the infrared spectrum technology in soil analysis is risen in last century the eighties.Currently near infrared spectrum
(NIR) and middle infrared spectrum (MIR) technology is widely used in point of the various physicochemical properties of soil in conjunction with Chemical Measurement means
Analysis, it is as a result satisfactory.Such as：Total carbon content, total nitrogen content, content of tatal phosphorus, moisture, the soil texture, potassium (K), calcium (Ga),
Content, the Microbials of metals such as iron (Fe), manganese (Mn), magnesium (Mg) etc..NIR, MIR spectroscopic analysis methods are a kind of indirect analyses
Method needs first to be measured the physicochemical property of a large amount of representative pedotheques with reference method, by being associated with sample spectra
Calibration model is built with its physicochemical property；Then the composition and property of unknown pedotheque are predicted with calibration model.Therefore, quilt
The pedotheque of survey will include the range of the type and physicochemical property of predicted pedotheque as far as possible, and to its each component
Physicochemical property carries out Accurate Determining.
Near-infrared (NIR) SPECTRAL REGION refers to electromagnetic wave of the wavelength within the scope of 780~2500nm, spectral information source
In the frequency multiplication and sum of fundamental frequencies of intramolecule vibration, and mainly reflect hydric group (such as C-H, N-H, O-H, S-H etc.) in molecule
Frequency multiplication and sum of fundamental frequencies absorption of vibrations.Many organic matters have characteristic absorption, and the absorption intensity of different-waveband in the SPECTRAL REGION
There are correspondences with the molecular structure and concentration of the substance.In infrared (MIR) SPECTRAL REGION be wavelength in 2500~25000nm
Electromagnetic wave in range, substance are that fundamental frequency, frequency multiplication and sum of fundamental frequencies absorb in the absorption peak of this range.Different compounds have it special
Infrared absorption spectrum, intensity, position, shape and the number of bands of a spectrum are related with compound and its state.MIR and NIR spectra
It is the frequency multiplication of material molecule internal vibration and the absorption of sum of fundamental frequencies difference lies in, near infrared spectrum, different component and functional group
Bands of a spectrum are easier to overlapping and information strength is weaker, cause spectrum elucidation relative difficulty, institute's established model easily to be influenced by extraneous factor, surely
Qualitative difference；And the fundamental frequency that middle infrared spectrum is intramolecule vibration absorbs, information strength is stronger, and information extraction is relatively easy.
Diffusing reflection is a kind of common near-infrared acquisition method, and basic principle is：When illumination is mapped to loose solid-like
When the surface of product, in addition to some is reflected by sample surfaces and (is known as mirror reflected light) immediately, remaining incident light exists
Sample surfaces generate unrestrained transmitting, or toss about reflection gradually decaying between sample particle, or to penetrate dissipating of turning back again after internal layer
It penetrates.The light for being diffusely reflected or scattering out after these contact sample microparticle surfaces has absorption-attenuation characteristic, and here it is unrestrained anti-
Penetrate the fundamental cause for generating spectrum.The effect of diffusing reflection device be exactly maximum intensity these diffusion, the luminous energy that scatter out
Pinching gets up to be sent into detector, so as to get the spectral signal with good signal-to noise ratio.The spectral technology that diffuses is fast in the past 20 years
A kind of detection method of speed development, this method is easy to operate, quick, can be carried out fast, accurately to various samples to non-demolition
Analysis, the development of the digitlization of analytical instrument and chemometrics method in addition can be well with chemometrics method
The extraction and the influence in terms of background interference for solving spectral information so that it plays important function in many fields, and takes
Obtained preferable social and economic benefit.
Either NIR or MIR spectrum are done in collected spectral information including some can generate Spectral Signal
The information disturbed, to influence the foundation and prediction of model, it is therefore desirable to carry out Pretreated spectra.Common preprocessing procedures
Have data smoothing, baseline correction, centralization, multiplicative scatter correction, standardization, derivative, Fourier transform and more than several sides
Method is used in combination.In addition, the effective information rate in signal Analysis, main method can be improved in spectrogram compression and information extraction
There are principal component analysis (PCA), wavelet analysis, simulated annealing (SAA), genetic algorithm (GA), moving window (MWPLS) etc..
One of the core technology of NIR and MIR spectrum analyses is to establish function between spectral information and component physicochemical property
Relationship establishes calibration model.The common analysis method of spectrum regression analysis has:Multiple linear regression (MLR), principal component regression
(PCR), Partial Least Squares returns (PLSR), artificial neural network (ANN), support vector machines (SVM) etc..MLR, PCR and
PLSR is chiefly used in solving linear correction problem, and ANN and SVM are chiefly used in solving the problems, such as gamma correction.
Influence due to factors such as the state of spectrometer, measuring environments to spectrum belongs to non-linear mostly, also some matter
The relationship for measuring parameter and spectrum is also non-linear.Support vector machines (SVM) is as the multivariate calibration methods under nonlinear regression, energy
The problems such as avoiding over-fitting existing for other methods and local minimum, is also widely applied in recent years.Support vector machines
(SVM) initially by Vapnik in the 1990s propose, be it is a kind of grown up by Statistical Learning Theory it is a kind of novel
Modeling method, it has stronger study generalization ability, preferably solves using structural risk minimization principle as theoretical foundation
The problems such as non-linear, high dimension, small sample, starts to become a kind of difficult preferable approach of tradition such as solution " cross and learn ",
The fields such as pattern-recognition, signal processing are successfully applied.The basic principle of support vector machines is fixed by interior Product function
The input space is transformed to a higher dimensional space by the nonlinear transformation of justice, and input variable and output are found in this higher dimensional space
A kind of relationship between variable.
It yet there are no and utilize near-infrared (NIR) spectral detection soil δ13The report of C values.
Invention content
In view of the drawbacks described above of the prior art, the present invention provides a kind of new detection soil δ13The method of C values will solve
Certainly the technical issues of is quickly to detect soil δ using near-infrared (NIR) spectrum13C values.
To solve the above problems, the technical solution adopted by the present invention is that：It is a kind of to detect the steady of soil using near infrared spectrum
Determine the method for carbon isotope ratio, described method includes following steps：
1) the stable carbon isotope ratio of multiple calibration pedotheques is measured；
2) the diffusing reflection spectrogram of the near infrared band of acquisition calibration pedotheque, obtains original spectrogram；
3) original spectrogram is smoothly pre-processed, spectrogram after being handled；
4) vector machine method is used to establish quantifying between spectrogram and stable carbon isotope ratio after the processing of calibration pedotheque
Relational model；
5) the diffusing reflection spectrogram for acquiring the near infrared band of pedotheque to be measured calculates soil to be measured according to causes
The stable carbon isotope ratio of earth sample.
Preferably, in the step 1), the method for measuring the stable carbon isotope ratio of calibration pedotheque is to stablize
Isotope ratio mass spectrography.
Preferably, in the step 1), the specific steps for preparing calibration pedotheque include：After soil sample is removed water, mill
Carefully, 60 mesh sieve is crossed.
Preferably, in the step 1), multiple calibration pedotheques include the sample of Oe and Oa layers of soil.
Preferably, in the step 3), original spectrogram, which is carried out smooth pretreated specific steps, includes：The atmospheric background
Inhibit, absorbance conversion, automatic baseline correction and the processing of Norris first derivative filterings.
Preferably, in the step 4), the specific steps for establishing causes include：With SPXY methods respectively by light
Spectrum information and stable carbon isotope ratio are divided into calibration set and verification collects, and being supported vector machine using RBF kernel functions calculates,
Best kernel functional parameter g and penalty parameter c are determined using Web search method and by 5 folding cross-validation methods, with calibration set
Spectral information is independent variable, using stable carbon isotope ratio as dependent variable, establishes regression model, and examine correction using verification collection
The precision of model.It is highly preferred that the ratio of the sample number of calibration set and verification collection is 3：1.It is highly preferred that described searched using network
It seeks method and by staying more cross-validation methods to determine best kernel functional parameter g and penalty parameter c the step of includes：Allow penalty parameter c
With kernel functional parameter g 2-10To 210Between discrete value；For taking fixed kernel functional parameter g and penalty parameter c, by calibration set
As initial data and using 5 foldings stay more cross validations choose the kernel functional parameter g that makes calibration set verify mean square error minimum with
Penalty parameter c；Have multigroup when making calibration set verify the kernel functional parameter g of mean square error minimum and penalty parameter c, then chooses punishment
One group of parameter c minimums is used as optimal parameter；It is minimum when choosing penalty parameter c, it is corresponding with multigroup kernel functional parameter g, then is chosen
The first group of kernel functional parameter g and penalty parameter c searched is as optimal parameter.Straightening die is examined it is highly preferred that being collected with verification
The specific steps of the precision of type include：It is that index investigates model performance, and makes with prediction related coefficient and predicted root mean square error
Model is evaluated with prediction relation analysis error.
Preferably, the specific steps for preparing pedotheque to be measured include：It is levigate after soil sample is removed water, cross 60 mesh sieve.
Beneficial effects of the present invention are：1, this method can quick, accurate, easy, low price measurement soil δ 13C values.2、
Easy to operate, popularization is strong, has a wide range of application.3, it is suitable for the various ecosystems such as forest, farmland, meadow.
The technique effect of the design of the present invention, concrete structure and generation is described further below with reference to attached drawing, with
It is fully understood from the purpose of the present invention, feature and effect.
Description of the drawings
Fig. 1 be in the embodiment of the present invention 1 and 2 sample 6, Pinggu different depth soil near infrared absorption spectrogram.
Fig. 2 is the schematic diagram of spectral model in the embodiment of the present invention 1 (including Oe and Oa) predicted value and actual value correlation.
Fig. 3 is the signal of spectral model in the embodiment of the present invention 2 (not including Oe and Oa) predicted value and actual value correlation
Figure.
Specific implementation mode
Specific implementation mode as one preferred, it is provided by the present invention quickly to detect soil using near infrared spectrum
The method of stable carbon isotope ratio includes the following steps.
(1) standby soil sample to be checked
It by the impurity elimination of mineral layer soil, air-dries, crushing, crosses 60 mesh sieve, drier saves backup；By Oe and Oa layers of soil (two
The different degrees of Litter leaf not decomposed completely of kind) 48h are dried in 60 DEG C to eliminate moisture, it crushes, crosses 60 mesh and sieve, drier preserves
It is spare.Totally 200 samples come from seven different regions (Pinggu, Hong Yashan, Bai An, Huang Zangyu, Xinyang, Mount Huang, the Yunshan Mountain)
The pedotheque of different depth (Oe, Oa, 0-2,2-5,5-10,10-20cm) in cork oak forest.
Sample preparation details：Forest soil sample is solid particle in irregular shape, size, shape and the uniformity coefficient of particle
All spectroscopic data is had a huge impact；By pulverizing and sieving, it can get smaller soil particle degree, increase the uniform of sample
Degree, reduce particle scattering effect as far as possible influences caused by spectra collection.
Two innovative points of the present invention：One, depth, general soil test will not all be added Oe and Oa layers, but more and more
Studies have shown that the Oe and Oa layers of important component because containing a large amount of soil organism and forest soil；Two, it adopts
Sample region, the sample that the present invention acquires come from 5 provinces on a latitudinal gradient, at a distance of 1500 kilometers from north to south, from north
The warm temperate zone in portion is gradually transitions the subtropical zone in south.
(2) δ of soil sample to be checked is measured using stable isotope ratio mass spectrography13C values
(3) spectra collection
The cross section that an internal diameter 11mm is placed on low-hydroxy-group squartz glass is the stainless steel cylinder of annular, to bottom
The white light penetrated up is unobstructed, and the 200mg soil samples accurately weighed are placed in it, then to have weight be 4g, diameter is also by one
The bottle of 11mm, is gently placed in soil sample, can make that thickness of sample is uniform, has enough dress sample depth and will not press too tight
Generate mirror-reflection.Using designed, designed of the present invention and the sample stage built, the diffusing reflection spectrogram of infrared band, instrument in acquisition
It is configured to：Fourier transformation infrared spectrometer, attachment are near-infrared integrating sphere, white light source, CaF2Beam splitter, InGaAs detections
Device；Acquisition parameter is：Using Jin Jing as background, scanning range 10000-4000cm-1, resolution ratio 4cm-1, scan 64 times.
Innovation about harvester：General extensive acquisition soil sample has fixed-size automatic sampling apparatus, but its
Instrument price and testing cost can be improved, and uses underaction.Based on practical angle, designed, designed of the present invention is simultaneously built
The irreflexive sample stage of pedotheque, purpose are mainly to maintain that thickness of sample is uniform, has enough dress sample depth and will not press
Tightly generate very much mirror-reflection.
(4) data prediction
Software Omnic 8.2 is carried by original spectrogram whole wave band (i.e. 10000-4000cm with instrument-1) carry out the air back of the body
Scape inhibits, and changes into absorption spectrum, then carry out automatic baseline correction.After spectroscopic data is imported software matlab7.8, Norris is used
(7,7,1) derivation exponential smoothing is handled, and first 7 indicates 7 points of smooth, second 7 expression, 7 differential widths, 1 expression one in bracket
Order derivative.Norris derivations smoothing processing can eliminate noise, be eliminated as much as unrelated information variable.
The pretreatment of pedotheque near infrared spectrum can efficiently reduce system deviation, noise, granularity and wave crest mistake
The influence of point etc..In some common preprocessing procedures, baseline drift is mainly eliminated in baseline correction；Smoothing processing master
If eliminating noise information；Derivative processing (first derivation or second order derivation) can effectively eliminate needle position misalignment, reduce peak and peak it
Between overlapping, obtain more effective informations；Multiplicative scatter correction is to eliminate solid particle size, surface scattering and light
Influences of the Cheng Bianhua to solid diffusing reflection spectrum.
The cross-reference of preprocess method not of the same race has its corresponding prediction model different improvement and influence, so,
The modelling effect for comparing Norris first derivatives filtering and Norris second dervative filterings herein also compares and adds
The modelling effect of multiplicative scatter correction and Norris first derivative filterings when being not added with multiplicative scatter correction.
(5) soil near infrared spectrum and δ are established using support vector machines method13Quantitative relationship between C values
By soil δ13C values are also introduced into matlab softwares.Test sample is pressed 3 with SPXY algorithms:1 ratio is respectively by light
Spectrum information and δ13C values are divided into calibration set and verification collects, and are respectively used to model foundation and verification.
The innovative point that the present invention is divided about sample set：Many researchs are all pre- around how to choose best spectrum when modeling
Processing method, the division methods of less relatively calibration set and verification collection, but the selection of calibration set and verification collection sample is more to spectrum
Meta analysis correction is most important.Common Method of Sample Selection includes mainly randomized (RS) and K-S (Kennard-Stone) at present
Method and SPXY (sample set partitioning based on joint x-y distance) method.Randomized randomness
Greatly, do not ensure that selected sample there are enough representativenesses；The big sample of SPECTRAL DIVERSITY is selected into calibration set by K-S methods,
Remaining sample is included into verification collection, but for the range that content is low or concentration is low, spectrum change very little between sample is often selected
Sample also do not have representativeness；SPXY algorithms are a kind of sample set selection methods based on statistical basis, with spectrum-physics and chemistry value
Symbiosis distance is used as foundation to ensure utmostly to characterize sample distribution, to improve model stability.The present invention is based on Norris
The spectrum of first derivative filtering processing, compares the effect of SPXY methods and K-S methods institute established model.
1. data normalization.To prevent dimension between data different, generally first by the spectrum number of calibration set and verification concentration
According to and δ13C values all carry out the normalized of [- 1,1], after the foundation and prediction of calibration model to be done, then renormalization, meter
Calculate the precision of prediction of model.
2. finding optimal parameter c and g.For nonlinear problem, support vector machines (Supporting vector
Machine, SVM) main thought of homing method is the line for converting former problem to by nonlinear transformation some higher dimensional space
Sex chromosome mosaicism, and linear solution is carried out in higher dimensional space, we select that the radial direction of computational complexity in training process can be reduced
Base kernel function (Radial basis function, RBF)
K(||x-xi| |)=exp (- | | x-xi||2/2g2)
Wherein xiFor kernel function center, g is the width parameter of function, controls the radial effect range of function to realize this
One process.Influence SVM model performances factor it is usual there are two, i.e. kernel functional parameter g (core width) and penalty parameter c (canonical
Change parameter) value.C controls to sample beyond the punishment degree for calculating error, and g then control function regression errors, and straight
Connecing influences initial characteristic value and feature vector.G is too small to lead to over-fitting, and the excessive then models of opposite g are too simple, to shadow
Ring precision of prediction.Therefore, it in order to improve study and the generalization ability of SVM, needs to carry out kernel functional parameter g and penalty parameter c
Optimization.
We choose best penalty parameter c and kernel functional parameter g using 5 folding cross verifications.Its basic process is to allow c
With g all 2-10To 210Between discrete value (variation of its value is 2-10, 2-9.5, 2-9..., 29, 29.5, 210), for taking fixed c
With g the calibration set at this group of c and g is obtained using 5 folding validation-cross (5fold-CV) methods using calibration set as raw data set
Mean square error (MSE) is verified, is finally taken so that group of c and g of calibration set verification MSE minimums are as optimal parameter.If there is more
Group c and g corresponds to minimum verification mean square error, then that minimum Selecting All Parameters c group is optimal parameter；If corresponding minimum c
There is multigroup g, with regard to choosing the first group of c and g searched as optimal parameter.Reason for this is that excessively high c can cause to learn
State occurs, i.e. calibration set MSE is very low and verifies collection MSE very high (generalization ability of grader reduces).
3. establishing regression model, data renormalization, prediction.Using grid-search method, pass through 5 above-mentioned folding validation-cross
After method determines best Radial basis kernel function parameter c and g, using the infrared spectrum in calibration set as independent variable, with δ13C values are because becoming
Amount, the two is mapped in higher dimensional space, soil near infrared spectrum and δ are established13Support vector regression model between C values.
And the spectral information of individual authentication collection is substituted into the model and calculates δ13C values, by being concentrated with verification after data anti-normalization processing
Survey δ13C values compare, testing model precision of prediction.
It is missed with prediction related coefficient (Correlation coefficient in prediction, R), prediction root mean square
Poor (Root mean square error in prediction, RMSEP) is that index investigates model performance, and good model should
Have coefficient height and the low feature of error.In addition, using prediction relation analysis error (Residual predictive
Deviation, RPD) model is carried out to go deep into evaluation；Think that model has preferable predictive ability when RPD values are more than 3, it can
With into the quantitative control of row index.The near-infrared diffusing reflection of the similar soil of unknown, property can be believed after model foundation is good
Breath substitutes into the model, calculates its δ13C values.
The present invention acquires the atlas of near infrared spectra of cork oak forest soil (from different places and depth), to initial data
After carrying out series of preprocessing, in conjunction with the SVM in Chemical Measurement, can it is accurate, quickly, it is easy, detect various soil at low cost
δ in earth13C values.
It is an advantage of the invention that：
(1) accurate.Prediction related coefficient R is more than 0.96, and predicted root mean square error is less than 0.68, RPD and is more than 3.
(2) quickly.One sample collection only needs 3min, can acquire within one day at least 200 infrared spectrums, at subsequent data
Reason can be completed in 1h.
(3) easy to operate.Sample pre-treatments are simple, and instrumentation is simple.
(4) testing cost is low.Compared to stable isotope ratio mass spectrometer, infrared spectrometer is cheap.
(5) popularization is strong, easy to spread.Instrumentation is simple, and price is relatively cheap.
(6) applied widely, it cannot be only used for the detection of forest soil, it can also be used to other ecosystems such as farmland, grassland
System.
Soil of the embodiment 1 including Oe and Oa
(1) soil sample to be checked is prepared.It by the impurity elimination of mineral layer soil, air-dries, crushing, crosses 60 mesh sieve, drier saves backup；It will
Oe and Oa layers of soil dries 48h in 60 DEG C to eliminate moisture, crushes, and crosses 60 mesh sieve, and drier saves backup.Totally 199 samples come
It is different deep from the cork oak forest in seven different regions (Pinggu, Hong Yashan, Bai An, Huang Zangyu, Xinyang, Mount Huang, the Yunshan Mountain)
Spend the pedotheque of (Oe, Oa, 0-2,2-5,5-10,10-20cm), wherein 139, mineral layer soil, Oe and Oa layers of soil totally 60
It is a.
It is not improved using spectral model precision after multiplicative scatter correction pretreatment by table 1, it was demonstrated that sample preparation obtains
Preferably, reduce particle scattering effect as far as possible influences caused by spectra collection.
(2) δ of soil sample to be checked is measured using stable isotope ratio mass spectrography13C values.
(3) spectra collection.200mg soil samples are weighed, the cross section for being placed in 11mm is in the stainless steel column body of annular, and bottom is
Low-hydroxy-group squartz glass, sample top flatten.The diffusing reflection spectrogram of near infrared band is acquired, instrument configuration is：Fourier transform
Infrared spectrometer, attachment are near-infrared integrating sphere, white light source, CaF2Beam splitter, InGaAs detectors；Acquisition parameter is：With
Jin Jing is background, scanning range 10000-4000cm-1, resolution ratio 4cm-1, scan 64 times.By sample for Pinggu, attached drawing 1 is aobvious
The near-infrared spectrogram of 6 depth of soil is shown.
(4) data prediction.Software Omnic 8.2 is carried by original spectrogram whole wave band (i.e. 10000- with instrument
4000cm-1) the atmospheric background inhibition is carried out, absorption spectrum is changed into, then carry out automatic baseline correction.By the spectrum number of 199 samples
After importing software matlab7.8, the processing such as 7 points of smooth, first derivatives are carried out with Norris methods.
The embodiment has attempted 4 kinds of common pretreatments to the near infrared spectrum of pedotheque：1. Norris first derivatives
Filtering+SPXY methods divide calibration set and verification collects；2. multiplicative scatter correction+Norris first derivative filterings+SPXY
Method divides calibration set and verification collects；3. Norris second dervative filtering+SPXY methods divide calibration set and verification collects；④
Norris first derivative filtering+K-S methods divide calibration set and verification collects, and reapply support vector machines (SVM) method and establish soil
Earth δ13The quantitative estimation model of C values.As a result (table 1) shows that different pretreatments method is to built soil δ13C value estimation models
Precision of prediction has certain influence, and (Norris first derivative filtering+SPXY methods divide preprocess method used by this patent
Calibration set and verification collect) spectrum modeling accuracy it is very high, be just slightly below the spectrum modeling accuracy for 2. planting preprocess method.
1 model preprocessing procedures of table and common preprocess method prediction soil δ13The precision of C (including Oe and Oa)
Compare
(5) soil near infrared spectrum and δ are established using support vector machines method13Quantitative relationship between C values.By corresponding 199
A soil δ13C values are also introduced into matlab softwares.Test sample is pressed 3 with SPXY algorithms:1 ratio respectively by spectral information and
δ13C values are divided into calibration set and verification collects, and calibration set contains 150 samples, and verification collection contains 49 samples.Data carry out [- 1,1] and return
After one change processing, it is based on calibration set, the best c of Radial basis kernel function is chosen using grid-search method in 5 folding interactive verification process
It is 1.4, best g is 9.77 × 10-4.Again soil near-infrared is established with calibration set with best c, the g chosen in all-wave spectral limit
Spectrum and δ13Regression model between C values, and the spectral information of individual authentication collection is substituted into the model and calculates δ13C values, data are counter to return
By concentrating actual measurement δ with verification after one change processing13C values compare, testing model precision of prediction.Prediction related coefficient (R) is
0.9573 (attached drawing 2), predicted root mean square error (RMSEP) are 0.6756, and prediction relation analysis error (RPD) is 3.30.
Should the result shows that, this method is suitable for forest soil different depth (Oe, Oa, 0-2cm, 2-5cm, 5-10cm, 10-
δ in 20cm)13The detection of C values can quickly detect soil δ within a short period of time13C values, and satisfied accuracy of detection can be reached.
The embodiment acquires near infrared band modeling by homemade sample stage, achieves extraordinary effect.Combining chemistry meter
Amount is learned when establishing calibration model, and traditional linear correction method (such as PLS) is different from, using a kind of gamma correction model SVM,
Equally obtain extraordinary effect.Meanwhile Norris first derivatives filtering and SPXY methods divide the pretreatments sides such as data set
Method is utilizing near-infrared diffusing reflection technology combination SVM method harmless quantitatives detection soil δ13C plays an important role.In test model
Nearly 200 samples are from the cork oak forest soil across two climate zones and five provinces, different weather conditions and soil
Property can have an impact spectrum.But the model exactly established in such complex condition just has the wider array of scope of application,
Therefore, the near-infrared spectrum technique based on support vector machines method is to be suitble to soil δ13The efficient detection technology of C detections.
Mineral layer soil of the embodiment 2 not including Oe and Oa
(1) soil sample to be checked is prepared.It by the impurity elimination of mineral layer soil, air-dries, crushing, crosses 60 mesh sieve, drier saves backup.Altogether
The cork oak that 139 samples come from seven different regions (Pinggu, Hong Yashan, Bai An, Huang Zangyu, Xinyang, Mount Huang, the Yunshan Mountain) is gloomy
The mineral layer pedotheque of different depth (0-2,2-5,5-10,10-20cm) in woods.
It is not improved using spectral model precision after multiplicative scatter correction pretreatment by table 2, it was demonstrated that sample preparation obtains
Preferably, reduce particle scattering effect as far as possible influences caused by spectra collection.
(2) δ of soil sample to be checked is measured using stable isotope ratio mass spectrography13C values.
(3) spectra collection.200mg soil samples are weighed, the cross section for being placed in 11mm is in the stainless steel column body of annular, and bottom is
Low-hydroxy-group squartz glass, sample top flatten.The diffusing reflection spectrogram of near infrared band is acquired, instrument configuration is：Fourier transform
Infrared spectrometer, attachment are near-infrared integrating sphere, white light source, CaF2Beam splitter, InGaAs detectors；Acquisition parameter is：With
Jin Jing is background, scanning range 10000-4000cm-1, resolution ratio 4cm-1, scan 64 times.By sample for Pinggu, attached drawing 1 is aobvious
The near-infrared spectrogram of 4 depth of soil is shown.
(4) data prediction.Software Omnic 8.2 is carried by original spectrogram whole wave band (i.e. 10000- with instrument
4000cm-1) the atmospheric background inhibition is carried out, absorption spectrum is changed into, then carry out automatic baseline correction.By the spectrum number of 139 samples
After importing software matlab7.8, the processing such as 7 points of smooth, first derivatives are carried out with Norris methods.
The embodiment has attempted 4 kinds of common pretreatments to the near infrared spectrum of pedotheque：1. Norris first derivatives
Filtering+SPXY methods divide calibration set and verification collects；2. multiplicative scatter correction+Norris first derivative filterings+SPXY
Method divides calibration set and verification collects；3. Norris second dervative filtering+SPXY methods divide calibration set and verification collects；④
Norris first derivative filtering+K-S methods divide calibration set and verification collects, and reapply offset minimum binary (PLS) method and establish soil
Earth δ13The quantitative estimation model of C values.As a result (table 2) shows that different pretreatments method is to built soil δ13C value estimation models
Precision of prediction has certain influence, and with preprocess method used by this patent, (Norris first derivative filtering+SPXY methods are drawn
Point calibration set and verification collect) spectrum modeling accuracy highest.
2 model preprocessing procedures of table and common preprocess method prediction soil δ13The essence of C (not including Oe and Oa)
Degree compares
(5) soil near infrared spectrum and δ are established using support vector machines method13Quantitative relationship between C values.By corresponding 139
A soil δ13C values are also introduced into matlab softwares.Test sample is pressed 3 with SPXY algorithms:1 ratio respectively by spectral information and
δ13C values are divided into calibration set and verification collects, and calibration set contains 105 samples, and verification collection contains 34 samples.Data carry out [- 1,1] and return
After one change processing, it is based on calibration set, the best c of Radial basis kernel function is chosen using grid-search method in 5 folding interactive verification process
It is 256, best g is 9.77 × 10-4.Again soil near-infrared is established with calibration set with best c, the g chosen in all-wave spectral limit
Spectrum and δ13Regression model between C values, and the spectral information of individual authentication collection is substituted into the model and calculates δ13C values, data are counter to return
By concentrating actual measurement δ with verification after one change processing13C values compare, testing model precision of prediction.Prediction related coefficient (R) is
0.9798 (attached drawing 3), predicted root mean square error (RMSEP) are 0.5934, and prediction relation analysis error (RPD) is 4.22.
Should the result shows that, this method is suitable for the forest soil of different depth (0-2cm, 2-5cm, 5-10cm, 10-20cm)
Middle δ13The detection of C values can quickly detect soil δ within a short period of time13C values, and satisfied accuracy of detection can be reached.This reality
It applies example and near infrared band modeling is acquired by homemade sample stage, achieve extraordinary effect.In conjunction with Chemical Measurement
When establishing calibration model, it is different from traditional linear correction method (such as PLS), using a kind of gamma correction model SVM, equally
Obtain extraordinary effect.Meanwhile Norris first derivatives filtering and SPXY methods divide the preprocess methods such as data set and exist
Utilize near-infrared diffusing reflection technology combination SVM method harmless quantitatives detection soil δ13C plays an important role.139 in test model
For a sample from the cork oak forest soil across two climate zones and five provinces, different weather conditions and soil property are equal
Spectrum can be had an impact.But the model exactly established in such complex condition just has the wider array of scope of application, therefore, base
It is to be suitble to soil δ in the near-infrared spectrum technique of support vector machines method13The efficient detection technology of C detections.
The preferred embodiment of the present invention has been described in detail above.It should be appreciated that those skilled in the art without
It needs creative work according to the present invention can conceive and makes many modifications and variations.Therefore, all technologies in the art
Personnel are available by logical analysis, reasoning, or a limited experiment on the basis of existing technology under this invention's idea
Technical solution, all should be in the protection domain being defined in the patent claims.
Claims (6)
1. a kind of method for the stable carbon isotope ratio detecting soil using near infrared spectrum, which is characterized in that the method
Include the following steps：
1) the stable carbon isotope ratio of multiple calibration pedotheques is measured；
2) the diffusing reflection spectrogram of the near infrared band of acquisition calibration pedotheque, obtains original spectrogram；
3) original spectrogram is smoothly pre-processed, spectrogram after being handled；
4) vector machine method is used to establish the quantitative relationship after the processing of calibration pedotheque between spectrogram and stable carbon isotope ratio
Model；
5) the diffusing reflection spectrogram for acquiring the near infrared band of pedotheque to be measured calculates soil-like to be measured according to causes
The stable carbon isotope ratio of product；
Wherein, in step 4), the specific steps for establishing the causes include：With SPXY methods respectively by spectral information and
The stable carbon isotope ratio is divided into calibration set and verification collects, and being supported vector machine using RBF kernel functions calculates, and utilizes
Web search method simultaneously determines best kernel functional parameter g and penalty parameter c by 5 folding cross-validation methods, with the calibration set
Spectral information is independent variable, using the stable carbon isotope ratio as dependent variable, establishes regression model, and examine using verification collection
The precision of calibration model；
The ratio of the sample number of the calibration set and the verification collection is 3：1；
The best kernel functional parameter g and described is determined using the Web search method and by the 5 folding cross-validation method
The step of penalty parameter c includes：Allow the penalty parameter c and the kernel functional parameter g 2-10To 210Between discrete value；It is right
In taking the fixed kernel functional parameter g and the penalty parameter c, intersect using the calibration set as initial data and using 5 foldings
The kernel functional parameter g for making the calibration set verification mean square error minimum and the penalty parameter c are chosen in verification；It is described when making
The kernel functional parameter g of calibration set verification mean square error minimum and the penalty parameter c have multigroup, then choose the punishment and join
One group of number c minimums is used as optimal parameter；It is minimum when choosing the penalty parameter c, it is corresponding with multigroup kernel functional parameter g, then is selected
Take the first group of kernel functional parameter g searched and penalty parameter c as optimal parameter；
The specific steps of the precision of the calibration model are examined to include with the verification collection：With prediction related coefficient and predict square
Root error is that index investigates model performance, and is evaluated model using prediction relation analysis error.
2. the method as described in claim 1, which is characterized in that in the step 1), measure the stabilization of calibration pedotheque
The method of carbon isotope ratio is stable isotope ratio mass spectrography.
3. the method as described in claim 1, which is characterized in that in the step 1), prepare the specific of calibration pedotheque
Step includes：It is levigate after soil sample is removed water, cross 60 mesh sieve.
4. the method as described in claim 1, which is characterized in that in the step 1), multiple calibration pedotheques
Include the sample of Oe and Oa layers of soil.
5. the method as described in claim 1, which is characterized in that in the step 3), original spectrogram is carried out smooth pre- place
The specific steps of reason include：The atmospheric background inhibits, absorbance conversion, automatic baseline correction and Norris first derivative filterings
Processing.
6. the method as described in claim 1, which is characterized in that in the step 1), prepare the specific of pedotheque to be measured
Step includes：It is levigate after soil sample is removed water, cross 60 mesh sieve.
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| CN103105366A (en) * | 2013-01-22 | 2013-05-15 | 中国科学院安徽光学精密机械研究所 | Method and device for detecting CO2 carbon isotope by infrared spectrum |
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