CN110907375B - Full-spectrum water quality online monitoring device and method - Google Patents
Full-spectrum water quality online monitoring device and method Download PDFInfo
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- CN110907375B CN110907375B CN201911253221.9A CN201911253221A CN110907375B CN 110907375 B CN110907375 B CN 110907375B CN 201911253221 A CN201911253221 A CN 201911253221A CN 110907375 B CN110907375 B CN 110907375B
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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
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- G—PHYSICS
- G01—MEASURING; TESTING
- 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
- G01N21/27—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands using photo-electric detection ; circuits for computing concentration
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Abstract
The invention discloses a full-spectrum water quality on-line monitoring device and a full-spectrum water quality on-line monitoring method, wherein the device comprises the following steps: the light is split by the concave grating and then imaged on a photoelectric array detector, each pixel of the photoelectric array detector receives optical signals with different wavelengths, the optical signals are converted into electric signals, and data communication is achieved through a data acquisition and communication circuit; the spectrum of the narrow-band filter is measured, the measurement results of different instruments are compared, and the spectrum measurement results are corrected according to the change of the center wavelength of the spectrum of the filter, so that the consistency of the detection spectra of different instruments is improved. The method comprises the following steps: the standard normal transformation is adopted to eliminate the noise and the light source drift influence; different frequency components in the absorption spectrum are extracted based on characteristic component decomposition, and the spectrum slow change and the absorption characteristics caused by turbidity are separated, so that the quantitative analysis of various water quality pollution factors is realized; and aiming at components with partially overlapped absorption peaks, respective absorption characteristics are extracted by adopting a two-dimensional spectrum, so that the quantitative analysis precision is improved.
Description
Technical Field
The invention relates to the field of water quality online monitoring, in particular to a full-spectrum water quality online monitoring device and method.
Background
With the economic development and the acceleration of urbanization process in China, the problem of environmental pollution is becoming more and more serious. Water resources are closely related to production and life of people, and the water environment is seriously damaged by illegal discharge of industrial wastewater, use of chemical pesticides, substandard treatment of urban domestic wastewater and the like. The most direct impact of water pollution is a serious threat to human health, and according to the survey reports of the world health organization, more than 70% of diseases in developing countries are related to water pollution. Meanwhile, the influence of water pollution on industry and agriculture also harms the development of national economy. According to relevant statistics, the water environment quality in China is not optimistic, the surface water is slightly polluted overall, even part of urban river reach is seriously polluted, and the proportion of monitoring points of poor underground water and extremely poor water quality is 59.6%. Therefore, how to effectively control or treat water pollution, protect water environment and promote the sustainable development of national economy becomes an important social and economic problem.
The traditional water quality detection technology mainly takes off-line measurement, and usually needs a plurality of steps of manual on-site sampling, water sample pretreatment and laboratory instrument analysis. Although the laboratory offline measurement has complete analysis means and higher repeatability and precision, the laboratory offline measurement also has the defects of large sampling error, requirement of professional operation, low detection frequency, incapability of reflecting the water pollution change in real time and the like, and cannot meet the requirement of effective management of governments or enterprises on the water environment. The chromatographic separation technology is mainly applied to the test of substances such as benzene series, pesticide residues and the like in water and has the advantages of high analysis precision, good repeatability and the like, but the chromatographic separation technology has the problems of complex and expensive analytical instrument, high maintenance cost, pretreatment of a sample, long test period, need of operation of professional personnel and the like. The mass spectrometry technology and the instrument have the defects of expensive equipment, complex analysis and the like in water quality detection, have a limited analysis range, and are only suitable for analyzing the amount of industrial organic matters such as polycyclic aromatic hydrocarbon and the like in water or determining pesticide residues in water. The water quality detection is developing on line, in real time and in an automatic direction.
The spectrum technology has the advantages of no need of pretreatment, high analysis speed and capability of realizing simultaneous detection of various components on line, and is widely applied to qualitative and quantitative analysis research of various substance components. The water quality detection technology based on the ultraviolet-visible spectrum method has the advantages of low instrument cost, convenience and rapidness in operation, high detection speed, no secondary pollution and the like, and has wide application prospects in the field of online water quality monitoring. The core technology of the water quality ultraviolet-visible spectrum detection system mainly comprises a continuous spectrum detection technology and a quantitative analysis method aiming at different substance components. The spectral monitoring instrument determines the measurement resolution, stability and reliability; the chemometric analysis method suitable for a specific system and a specific scene determines the analysis speed and the analysis precision of the system. At present, the water quality detection technology by ultraviolet-visible spectrum analysis is mainly applied to the analysis and test of parameters of water such as COD, TOC, TURB, NO3-N and the like. The method has obvious advantages in the online and in-situ measurement of surface water, domestic sewage and industrial wastewater, and is an important development direction for the research of online water quality detection instruments.
The development of related technologies and instruments in the world is early, and an immersed ultraviolet-visible spectrum water quality analyzer is developed by a research team of Vienna agriculture university, can simultaneously measure parameters such as COD, TSS and NO3-N, and has good repeatability and measurement precision. On the basis, the team provides a sudden water pollution disaster early warning method based on the ultraviolet-visible spectrum method. A UVASecosc type ultraviolet absorption online analyzer produced by HACH company in America adopts a double-beam reference framework to correct turbidity influence, so that COD online monitoring is realized. The UVM-4020 ultraviolet absorption method on-line water quality COD detector produced by the SHIMADZU of Japan adopts a weighted multi-wavelength method, thereby further improving the detection precision. The full spectrum on-line measuring system of STIP-scan CAS74 produced by Germany E + H company realizes the simultaneous detection of a plurality of pollutants.
The main problems of the prior water quality monitoring device and method based on the spectrum method in application are as follows: the spectrum measuring instrument has narrow coverage wavelength range and can not completely cover the absorption characteristics of different water quality pollution components, and in addition, the consistency of the measured absorption spectrum among different instruments is poor, thereby influencing the quantitative analysis precision. In addition, the water quality has more pollution components, and the measurement precision of the absorption spectrum is influenced to a certain extent due to turbidity change caused by scattering particles. Some substances in water sample pollutants, such as blue algae and chlorophyll, have similar absorption characteristics, have the phenomenon of overlapping absorption peaks, and bring certain difficulty to quantitative analysis of the substances.
Disclosure of Invention
The invention provides a full spectrum water quality on-line monitoring device and a full spectrum water quality on-line monitoring method, which utilize different optical path measurement results to improve the quantitative analysis precision of trace components in water quality and realize the quantitative analysis of various water pollution parameters, and the detailed description is as follows: a full-spectrum water quality on-line monitoring device comprises: a light source and a spectrometer are arranged in the shell,
the light source adopts a halogen lamp and a concave reflector, and focuses light source energy into the optical fiber; the spectrometer adopts a detection unit of a concave grating and a photoelectric array detector, a built-in wavelength correction unit based on a filter wheel set and a data acquisition and communication circuit;
the light is split by the concave grating and then imaged on a photoelectric array detector, each pixel of the photoelectric array detector receives optical signals with different wavelengths, the optical signals are converted into electric signals, and data communication is achieved through a data acquisition and communication circuit;
the filter wheel set is provided with narrow-band filters with different wavelengths, the narrow-band filters are connected with the motor to realize automatic switching, the measurement results of different instruments are compared by measuring the spectrums of the narrow-band filters, and the spectrum measurement results are corrected according to the spectrum center wavelength change of the filters, so that the consistency of the spectrums detected by different instruments is improved.
The light source shading shell is used for isolating the working light source from outside light and playing roles in dust prevention and heat insulation. The online monitoring device further comprises: a measurement interface, the measurement interface comprising: the system comprises an incident optical fiber interface and three acquisition optical fiber interfaces, wherein the three acquisition optical fiber interfaces respectively acquire water quality samples in three corresponding sample tubes, and the three sample tubes have different optical paths; the three acquisition optical fiber interfaces are respectively connected with the 1 × 3 optical switches, and three paths of absorption spectrum signals are output through the output optical fibers by switching of the optical switches. The correcting the spectrum measurement result specifically comprises:
combining the absorption spectrum of the narrow-band filter with a correction method, and calculating a spectrum measurement correction coefficient between two instruments through two standard filter spectrums;
and correcting the spectrum measured by the second spectrometer by using the wavelength data of the three optical filters by using the first spectrometer as a target spectrometer to obtain a correction coefficient matrix, and enabling the spectrum measured by the second spectrometer to be consistent with the target spectrum through the correction coefficient.
A full-spectrum water quality online monitoring method comprises the following steps:
in the spectrum preprocessing, standard normal transformation is adopted to eliminate noise and light source drift influence;
in quantitative analysis, different frequency components in an absorption spectrum are extracted based on characteristic component decomposition, and spectrum slow change and absorption characteristics caused by turbidity are separated to realize quantitative analysis of various water pollution factors;
and aiming at the components with partially overlapped absorption peaks, respective absorption features are extracted by adopting a two-dimensional spectrum, so that the quantitative analysis precision is improved.
The technical scheme provided by the invention has the beneficial effects that:
by adopting the technical scheme, the invention develops the multi-parameter, low-cost and high-performance water quality detection prototype, realizes the rapid real-time online detection of the multi-parameter of the water quality without pretreatment, reagent and secondary pollution, and has the following advantages:
1. the invention has wider spectrum measurement range, adopts the integrated design of the concave grating and the linear array detector, improves the stability of spectrum measurement, is internally provided with the wavelength calibration unit, adopts the narrow-band optical filter, can realize the spectrum calibration of different instruments and reduces the spectrum difference between different instruments;
2. the spectrum measurement light source and the spectrum detection unit both adopt standard optical fiber interfaces, are convenient to be connected with other measurement accessories and can be applied to various occasions;
3. the invention provides a variable optical path water sample measuring device, which is provided with an optical fiber interface and an optical path variable flow cell and can be used for simultaneously measuring the transmission spectra of a water quality sample under different optical paths;
4. the invention provides a method for decomposing turbidity and absorption characteristics in a water quality sample based on characteristic matrix decomposition, which reduces the influence of different turbidity changes on the quantitative analysis precision of an absorbing substance in the water quality sample;
5. the invention provides a quantitative analysis method based on different optical path absorption spectrum correlation processing aiming at the problem of large spectral absorption peak overlap of blue-green algae in a water quality sample, so that blue-green algae absorption characteristics are extracted, and the quantitative analysis precision is improved.
Drawings
Fig. 1 is a schematic structural diagram of a full spectrum measuring device for online monitoring of water quality;
in the drawings, the components represented by the respective reference numerals are listed below:
1: an optical fiber interface; 2: a concave grating; 3: a filter wheel set; 4: a motor; 5: a photo array detector; 6: an instrument light-shielding housing; 7: a data acquisition and communication circuit; 8: a halogen lamp; 9: a concave reflector; 10: a light source shading shell; 11: and a sample cell.
FIG. 2 is a schematic structural diagram of a transmission spectrum measurement interface for water quality samples with different optical paths designed by the present invention;
fig. 3 is a flow chart of the water quality parameter detection method based on full spectrum measurement designed by the invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, embodiments of the present invention are described in further detail below.
The invention discloses a water quality parameter online monitoring instrument and method covering an ultraviolet-visible spectrum range based on a full spectrum principle aiming at the online monitoring requirement of multiple parameters of water quality in environment monitoring. The full spectrum detection instrument adopts the design of an integrated concave grating and a linear array detector, and a wavelength correction device is arranged in the full spectrum detection instrument, so that the correction of the measurement spectra of different instruments can be realized, and the consistency of the spectra of samples is ensured. The invention also designs a transmission-type multi-optical-path detection device for the water quality sample, and the precision of quantitative analysis of the trace components in the water quality is improved by using the measurement results of different optical paths.
The invention also designs a water quality parameter detection method of the ultraviolet-visible waveband spectrum, which adopts a characteristic vector decomposition method to realize the extraction of different frequency components in the absorption spectrum, separates the turbidity change and the absorption characteristics of the water quality sample and improves the quantitative analysis precision; aiming at the problem of overlapping of the absorption characteristics of blue-green algae in water, the respective absorption characteristics of the blue-green algae are extracted by adopting a different optical path absorption spectrum related processing method and are subjected to quantitative analysis. The device and the method of the invention can realize quantitative analysis of various water quality pollution parameters.
In order to solve the problem that not only absorbent substances exist in a water sample for water quality detection, but also turbidity and other scattering substances can influence a measurement spectrum, the characteristic vector decomposition mode of a spectrum matrix is utilized to decompose the absorption and turbidity spectrum characteristics. The general spectral analysis method starts from absorption characteristics, and changes caused by scattering are not concerned, so that the method for separating absorption from scattering in the spectrum by using characteristic decomposition is an innovative method. Aiming at the components with partially overlapped absorption peaks, respective absorption features are extracted by adopting a two-dimensional spectrum, and the method belongs to a specific method and is innovatively applied to spectral absorption feature extraction.
Example 1
The invention designs a full spectrum water quality on-line monitoring device, which is shown in figure 1 and comprises the following components: the halogen lamp 8 and the concave reflector 9 are adopted as the light source, so that the energy of the light source can be effectively focused into the optical fiber through the optical fiber interface 1, and the light source efficiency is improved.
The invention adopts the optical fiber interface 1, and can be conveniently installed with other measuring accessories. Namely, the light source is composed of a halogen lamp 8, a concave reflector 9 and an optical fiber interface 1.
The spectrometer adopts a detection unit of a concave grating 2 and a photoelectric array detector 5, a built-in wavelength correction unit based on a filter wheel set 3 and a data acquisition and communication circuit 7.
The concave grating 2 has the functions of dispersion and light beam focusing, no ghost line exists after light splitting, stray light is extremely small, the dispersion ratio and the resolution ratio are greatly improved, and the effects of leveling the field and improving the resolution ratio are remarkable.
The light is split by the concave grating 2 and then imaged on the photoelectric array detector 5, each pixel of the photoelectric array detector 5 receives optical signals with different wavelengths and converts the optical signals into electric signals, and the data communication with other equipment can be conveniently realized through the data acquisition and communication circuit 7.
The filter wheel set 3 is provided with narrow-band filters with different wavelengths, the narrow-band filters are connected with the motor 4 to realize automatic switching, in the process of spectrum measurement, the spectrums of the narrow-band filters can be measured, the measurement results of different instruments can be compared, the spectrum measurement results can be corrected according to the spectrum center wavelength change of the filters, and the consistency of the spectrums detected by the different instruments is improved.
The connection control between the narrowband filter and the motor 4 and the automatic switching by the program inside the motor 4 are well known to those skilled in the art, and are not described in detail in the embodiments of the present invention.
The optical fiber interface 1 is adopted by the spectrometer, so that the spectrometer can be conveniently connected with other measuring accessories.
And the light source shading shell 10 is used for isolating the working light source from external light and simultaneously playing a role in dust prevention and heat insulation.
And a sample cell 11 for containing a sample to be measured. Referring to fig. 2, the measurement interface includes: the system comprises an incident optical fiber interface and three acquisition optical fiber interfaces, wherein the three acquisition optical fiber interfaces respectively acquire water quality samples in three corresponding sample tubes, and the three sample tubes have different optical paths; the three acquisition optical fiber interfaces are respectively connected with the 1 × 3 optical switches, and three paths of absorption spectrum signals are output through the output optical fibers by switching of the optical switches. The measurement interface can simultaneously measure the transmission spectra of the water quality samples in different optical paths, adopts the optical switch to switch different measurement channels, has high speed, has switching delay time less than 1ms, and has higher stability.
Example 2
Based on the device, the invention also designs a water quality pollution parameter detection method based on the ultraviolet-visible band spectrum, which comprises the following steps: the spectrum preprocessing and quantitative analysis method adopts a standard normal transformation algorithm to eliminate noise and light source drift influence in the spectrum preprocessing. In the quantitative analysis, a method based on characteristic component decomposition is adopted to extract different frequency components in an absorption spectrum and separate the spectrum slow change and the absorption characteristics caused by turbidity, thereby realizing the quantitative analysis of various water quality pollution factors. And aiming at the components with partially overlapped absorption peaks such as chlorophyll, blue algae and the like, the respective absorption characteristics are extracted by adopting a two-dimensional spectrum, so that the quantitative analysis precision is improved.
The water quality parameter detection method based on the full spectrum is described by combining the attached drawings and an embodiment, and the flow of the water quality parameter detection method based on the full spectrum is shown in fig. 3 and can be divided into the following steps:
(1) Water sample absorption spectrum measurement under different optical path
The spectrum measuring device designed by the invention is used for measuring the absorption spectrum of water samples in the range of 190-800nm under different optical paths, and the measuring process specifically comprises the following steps: measuring spectrometer dark noise I d Then, the background spectrum I is collected under the condition that no water sample exists in the sample pool 0 Then introducing the water sample into a sample cell to collect the sample lightSpectrum I, and thus the absorbance A of the water sample at different optical paths is calculated as follows:
the multi-optical path transmission measurement accessory designed by the invention can realize the simultaneous measurement of water sample spectra in different optical paths.
(2) Spectral preprocessing
And a standard normal transform (SNV) algorithm is adopted to eliminate the influence of noise and light source drift. This method assumes that the absorbance at each wavelength point in the spectrum will reach a certain distribution, e.g., a gaussian distribution. Based on this assumption, each spectrum is calibrated. First, the average of the spectrum is subtracted from the original spectrum, and the result is then divided according to the standard deviation.
(3) Measurement spectral correction
Aiming at the difference of measurement spectrum errors among different spectrometers, the spectrum is respectively measured by adopting a standard optical filter arranged in the spectrometer, and a correction coefficient is obtained after certain algorithm processing is carried out according to the spectrum of the standard optical filter measured by different instruments, so that the spectrum correction among different instruments is realized. The correction process is as follows:
three wavelengths of the standard filter are respectively lambda 1 ，λ 2 ，λ 3
The spectrometer 1 measures three standard filter spectra which can be expressed as:
the three standard filter spectra measured by spectrometer 2 can be expressed as:
wherein, A 1 ，A 2 ，A 3 Measured absorption spectra at three wavelengths respectively.
The spectrometer 1 is taken as a target spectrometer, the spectrum measured by the spectrometer 2 (namely a slave) is corrected by adopting three optical filter wavelength data, and the calculation process of a correction coefficient matrix F is as follows:
wherein F is a correction coefficient matrix.
After the F matrix is obtained, the spectrum measured from the machine may then be passed through a correction factor to be consistent with the target spectrum:
A target ＝A Slave machine F (3)
(4) Method for calculating different frequency components of absorption spectrum based on feature vector decomposition
The water sample not only has components with specific absorption peaks, but also has various particulate matters and the like, and the spectral absorption signals are changed to a certain extent. The decomposition steps are as follows:
the sample absorption spectrum can be represented as a matrix a = { a 1 ,a 2 ,a 3 ,...,a n And A is a matrix covariance matrix, wherein the specific calculation process is as follows:
and solving the eigenvalue and the eigenvector of the covariance matrix C by using an eigenvalue decomposition method. For matrix C, there is a set of orthogonal unit vectors Q, and the diagonal elements are eigenvalue sigma matrices, and the specific mathematical expression is as follows:
C＝QΣQ -1 (5)
after the spectral matrix decomposition, the eigenvalues can be sorted according to the principle of decreasing numerical values, and the top k eigenvalues are selected. The data set a is converted into a new space constructed by k feature vectors, namely:
Y＝PA (6)
according to the difference of the selected characteristic values, the obtained spectral characteristics and components represented by the conversion Y are different, and here, according to the variation trend of the absorption spectrum, the slow variation and the fast variation components of the absorption spectrum are obtained by decomposition and respectively expressed as:
Y 1 ＝P 1 a wherein P 1 ∈{λ 1 ，λ 2 ，λ 3 ....λ k }
Y 2 ＝P 2 A wherein P 2 ∈{λ k+1 ，λ k+12 ,λ k+3 ....λ n }
(5) Water turbidity quantitative analysis based on low-frequency component of absorption spectrum
Using slow change Y of spectrum obtained by decomposition 1 Component, calculating the turbidity of the water sample by a least square regression method, wherein the turbidity of the water sample is expressed as H and slowly changes Y according to the absorption spectrum 1 The relationship between the components can be expressed as:
H＝β 1 Y 1 (7)
wherein beta is 1 As a regression coefficient, it can be obtained by measuring the spectrum of a standard sample, and the calculation process is as follows:
β 1 ＝(Y k T Y k ) -1 Y k T C 1 (8)
wherein, Y k As standard sample spectrum, C 1 Is a standard sample concentration matrix.
During the actual sample measurement, respectively 1 And slow change of spectrum Y 1 And substituting the components into a formula to obtain the turbidity value.
(6) TVOC quantitative analysis of absorption spectrum high-frequency component
Using slow change Y of spectrum obtained by decomposition 1 Component, calculating the turbidity of the water sample by a least square regression method, wherein the turbidity of the water sample is expressed as H and slowly changes Y according to the absorption spectrum 1 The relationship between the components can be expressed as:
C TVOC ＝β 2 Y 2 (9)
wherein, beta 2 The regression coefficient can be obtained by measuring the spectrum of the standard sample, and the calculation formula is as follows:
β 2 ＝(Y k T Y k ) -1 Y k T C 2 (10)
in the actual sample measuring process, the components of beta 1 and the spectrum slow change Y1 are respectively substituted into a formula to obtain the turbidity value.
(7) Different optical path absorption spectrum related treatment and blue-green algae quantitative analysis
Because the spectral absorption peaks of blue-green algae in water are overlapped greatly, the quantitative analysis of the concentrations of the blue-green algae and the blue-green algae according to a direct absorption spectrum is difficult. The invention provides a method for correlation analysis based on absorption spectra with different optical paths, which is used for extracting blue-green algae absorption characteristics and carrying out quantitative analysis, and comprises the following specific steps:
and collecting water sample absorption spectra A (lambda, L) in different optical paths L, wherein lambda is the wavelength of the absorption spectrum obtained by measurement.
Calculating the correlation spectrum of the water sample absorption spectrum under different optical paths by the following calculation formula
Ψ(λ 1 ,λ 2 )＝A(λ 1 ,L) T ·N·A(λ 2 ,L) (11)
Wherein N is the number of wavelength points.
According to the correlation spectrum of the absorption spectrum, a PLS model is established, the concentrations of blue algae and green algae are respectively calculated, and the calculation formula is as follows:
C 3 ＝U·Ψ(λ 1 ,λ 2 )+F (12)
C 4 ＝V·Ψ(λ 1 ,λ 2 )+E (13)
wherein E is a fitting residual matrix, U and V are psi (lambda) respectively 1 ,λ 2 ) After the singular matrix decomposition, the decomposition formula can be expressed as:
Ψ(λ 1 ,λ 2 )＝UΣV T (14)
in the embodiment of the present invention, except for the specific description of the model of each device, the model of other devices is not limited, as long as the device can perform the above functions.
Those skilled in the art will appreciate that the drawings are only schematic illustrations of preferred embodiments, and the above-mentioned serial numbers of the embodiments of the present invention are only for description and do not represent the merits of the embodiments.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and should not be taken as limiting the scope of the present invention, which is intended to cover any modifications, equivalents, improvements, etc. within the spirit and scope of the present invention.
Claims (3)
1. A full-spectrum water quality on-line monitoring method is realized based on an on-line monitoring device, and the monitoring device comprises: the light source adopts a halogen lamp and a concave reflector, and focuses light source energy into an optical fiber;
the spectrometer adopts a detection unit comprising a concave grating and a photoelectric array detector, and is internally provided with a wavelength correction unit based on a filter wheel set and a data acquisition and communication circuit;
the light is split by the concave grating and then imaged on a photoelectric array detector, each pixel of the photoelectric array detector receives optical signals with different wavelengths, the optical signals are converted into electric signals, and data communication is achieved through a data acquisition and communication circuit;
the filter wheel set is provided with narrow-band filters with different wavelengths, the narrow-band filters are connected with the motor to realize automatic switching, the spectrum of the narrow-band filters is measured, the measurement results of different instruments are compared, and the spectrum measurement results are corrected according to the change of the central wavelength of the spectrum of the filters, so that the consistency of the detection spectra of different instruments is improved;
wherein, the correcting the spectrum measurement result specifically comprises:
combining the absorption spectrum of the narrow-band filter with a correction method, and calculating a spectrum measurement correction coefficient between two instruments through spectra of two standard filters;
correcting the spectrum measured by the second spectrometer by using the wavelength data of the three optical filters by using the first spectrometer as a target spectrometer to obtain a correction coefficient matrix, and correcting the spectrum measured by the second spectrometer by using the correction coefficient;
the correction process is as follows:
three wavelengths of the narrow-band filter are respectively lambda 1 ，λ 2 ，λ 3 ，
The spectra measured by the first spectrometer to three narrow band filters are expressed as:
the spectra measured by the second spectrometer to three narrow band filters are expressed as:
wherein A is 1 ，A 2 ，A 3 Measured absorption spectra at three wavelengths, respectively; the first spectrometer is taken as a target spectrometer, the spectrum measured by the second spectrometer is corrected by adopting the wavelength data of three optical filters, and the calculation process of a correction coefficient matrix F is as follows:
after obtaining the matrix F, the spectrum measured by the second spectrometer is then corrected by a correction factor:
A target ＝A Slave computer F
Wherein F is a correction coefficient matrix;
the monitoring method is characterized by comprising the following steps:
in the spectrum pretreatment, standard normal transformation is adopted to eliminate noise and light source drift influence;
in quantitative analysis, different frequency components in an absorption spectrum are extracted based on characteristic vector decomposition, and the spectrum slow change and the absorption characteristics caused by turbidity are separated to realize the quantitative analysis of various water quality pollution factors;
aiming at components with partially overlapped absorption peaks, respective absorption features are extracted by adopting a two-dimensional spectrum, so that the quantitative analysis precision is improved;
wherein, based on the decomposition of the eigenvector, different frequency components in the extraction absorption spectrum separate the spectrum slow change and the absorption characteristic that turbidity caused, and the quantitative analysis that realizes multiple water pollution factor specifically is:
1) Computing different frequency components of an absorption spectrum based on eigenvector decomposition
The absorption spectrum of the sample is expressed as a matrix A = { a = { [ a ] 1 ,a 2 ,a 3 ,...,a n The specific calculation process of the covariance matrix C is as follows:
the eigenvalue decomposition method is used for solving the eigenvalue and the eigenvector of the covariance matrix C, for the matrix C, a group of orthogonal unit vectors Q and a sigma matrix taking diagonal elements as eigenvalues exist, and the specific mathematical expression is as follows:
C＝QΣQ -1
after the spectral matrix decomposition, sorting the eigenvalues according to the principle of decreasing numerical values, selecting the first k eigenvalues, and converting the matrix A into a new space constructed by k eigenvectors, namely:
Y＝PA
according to the difference of the selected characteristic values, the obtained spectral characteristics and components represented by the conversion Y are different, and according to the change trend of the absorption spectrum, the slow change and the fast change components of the absorption spectrum are obtained by decomposition and respectively expressed as:
Y 1 ＝P 1 a wherein P 1 ∈{λ 1 ，λ 2 ，λ 3 ....λ k }
Y 2 ＝P 2 A wherein P 2 ∈{λ k+1 ，λ k+2 ,λ k+3 ....λ n }
2) Water turbidity quantitative analysis based on slow change component of absorption spectrum
Using a resolved slowly varying component Y of the spectrum 1 Calculating the turbidity of the water sample by a least square regression method, wherein the turbidity of the water sample is expressed as H and is associated with the slow change component Y of the absorption spectrum 1 The relationship between them is expressed as:
H＝β 1 Y 1
wherein beta is 1 The regression coefficient is obtained by measuring the spectrum of the standard sample, and the calculation process is as follows:
β 1 ＝(Y k T Y k ) -1 Y k T C 1
wherein, Y k As standard sample spectrum, C 1 Is a standard sample concentration matrix;
will beta 1 And a slowly varying component Y of the spectrum 1 Substituting the formula H = beta 1 Y 1 Obtaining a turbidity value;
3) TVOC quantitative analysis of fast change component of absorption spectrum
Using the spectrally fast-changing component Y obtained by decomposition 2 Calculating the TVOC concentration value of the water sample by a least square regression method, wherein the TVOC concentration value of the water sample is expressed as C TVOC Which is associated with a fast-changing component Y of the absorption spectrum 2 The relationship between them is expressed as:
C TVOC ＝β 2 Y 2
wherein beta is 2 The regression coefficient is obtained by measuring the spectrum of the standard sample, and the calculation formula is as follows:
β 2 ＝(Y k T Y k ) -1 Y k T C 2
will beta 2 And a spectrally fast changing component Y 2 Substituting into formula C TVOC ＝β 2 Y 2 Obtaining a TVOC concentration value;
for components with partially overlapping absorption peaks, the quantitative analysis steps were as follows:
the spectral absorption peaks of blue and green algae in water are overlapped greatly, and the concentrations of the blue and green algae are difficult to quantitatively analyze according to a direct absorption spectrum; therefore, based on the correlation analysis of absorption spectra of different optical paths, the absorption characteristics of blue and green algae are extracted and quantitative analysis is carried out, and the specific steps are as follows:
collecting water sample absorption spectra A (lambda, L) in different optical paths L, wherein lambda is the wavelength of the absorption spectra obtained by measurement;
calculating the correlation spectrum of the water sample absorption spectrum under different optical paths, wherein the calculation formula is as follows:
Ψ(λ 1 ,λ 2 )＝A(λ 1 ,L) T ·N·A(λ 2 ,L)
wherein N is the number of wavelength points;
establishing a PLS model according to the correlation spectrum of the absorption spectrum, and respectively calculating the concentrations of blue algae and green algae, wherein the calculation formula is as follows:
C 3 ＝U·Ψ(λ 1 ,λ 2 )+F
C 4 ＝V·Ψ(λ 1 ,λ 2 )+E
wherein E is a fitting residual matrix, U and V are psi (lambda) respectively 1 ,λ 2 ) After the result of singular matrix decomposition, the decomposition formula is expressed as:
Ψ(λ 1 ,λ 2 )＝UΣV T 。
2. the full-spectrum online water quality monitoring method as claimed in claim 1, wherein the light source comprises a light-shielding housing for isolating the light source from outside light and performing dust-proof and heat-insulating functions.
3. The full-spectrum online water quality monitoring method according to claim 1, wherein the device further comprises: but measurement interface of simultaneous measurement quality sample transmission spectrum under different optical paths, measurement interface includes: the system comprises an incident optical fiber interface and three acquisition optical fiber interfaces, wherein the three acquisition optical fiber interfaces respectively acquire water quality samples in three corresponding sample tubes, and the three sample tubes have different optical paths; the three acquisition optical fiber interfaces are respectively connected with the 1 × 3 optical switches, and three paths of absorption spectrum signals are output through the output optical fibers by switching of the optical switches.
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