CN114295604B - LIBS and NIRS spectrum synchronous acquisition soil nutrient rapid detection system and method - Google Patents
LIBS and NIRS spectrum synchronous acquisition soil nutrient rapid detection system and method Download PDFInfo
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Abstract
The invention discloses a system and a method for rapidly detecting soil nutrients by synchronously collecting LIBS and NIRS spectra, which belong to the field of optical and soil nutrient detection. According to the detection method designed by the invention, the linear relation between the content of different matrix chemical substances and the characteristic spectral line intensity of each nutrient is fitted, the NIRS prediction model for predicting the content of each matrix chemical substance is established in a combined mode, the characteristic spectral line intensity of the corresponding nutrient obtained by LIBS detection is corrected, the interference of matrix effect on spectral detection is effectively eliminated, and the high-precision stable detection of soil nutrients is realized.
Description
Technical Field
The invention belongs to the field of optics and soil nutrient detection, and particularly relates to a system and a method for rapidly detecting soil nutrients by synchronously acquiring LIBS and NIRS spectra.
Background
The soil provides various nutrient elements for the growth of crops, and the nutrient deficiency of the soil has important influence on the growth condition and yield of the crops. In order to meet the demand of population growth for grain yield, fertilizers are widely applied in agricultural planting. Due to the lack of a rapid detection technology for soil nutrients meeting actual production requirements, excessive use of chemical fertilizers is often adopted in production to ensure crop growth vigor and yield. According to data statistics, the chemical fertilizer use amount of China is about 6000 ten thousand tons in 2015, but the actual utilization rate of applied chemical fertilizer is less than 40%. A large amount of chemical fertilizers which are not absorbed and utilized by crops enter water resources such as lakes, estuaries, underground and the like through runoff loss and leaching loss, so that serious agricultural non-point source pollution such as water eutrophication and the like is caused. Therefore, the research of the high-precision soil nutrient detection technology suitable for actual agricultural production has important significance for guiding scientific and precise fertilization, improving the utilization rate of chemical fertilizers and reducing agricultural non-point source pollution.
The traditional agrochemistry analysis method for measuring soil nutrients has the defects of strong operation specialization, long consumption time, sample pollution caused by chemical reagents and the like although the detection precision is high. Although the methods such as Atomic Absorption Spectroscopy (AAS), inductively coupled plasma atomic emission spectroscopy (ICP-AES), inductively coupled plasma-emission spectroscopy (ICP-OES), and inductively coupled plasma mass spectrometry (ICP-MS) have high detection accuracy and high analysis speed, they require complex sample pretreatment and are expensive in equipment, and are not suitable for large-area popularization and use. A large number of research results show that laser-induced breakdown spectroscopy (LIBS) and near infrared spectroscopy (NIRS) have better potential in soil nutrient analysis, and both spectroscopic analysis techniques have the advantages of simple operation, no need of complex sample pretreatment, high detection speed and the like. However, due to the fact that the soil matrix is complex in structure, the LIBS detection is seriously affected by the difference of the soil moisture content and the organic matter content, and the accuracy and stability of the soil nutrient LIBS detection are difficult to meet actual production requirements. In addition, NIRS has better detection performance on indexes such as nitrogen, water content, organic matters and the like of soil, but measurement of element indexes such as phosphorus, potassium and the like in soil is difficult to realize.
Disclosure of Invention
Aiming at the defects and improvement requirements of the prior art, the invention provides a soil nutrient rapid detection system and method for synchronously collecting LIBS and NIRS spectra in order to thoroughly eliminate the interference of soil matrix effect on the detection of nutrient LIBS, which sufficiently utilizes rich matrix information provided by NIRS to correct the characteristic spectral line of soil nutrient LIBS detection, fundamentally eliminates the influence of matrix effect on the detection of nutrient LIBS caused by the content difference of matrix chemical components in a sample, and provides a new device and method for realizing high-precision rapid stable detection of soil nutrient. In addition, the detection system and the detection method adopt LIBS and NIRS spectrum information of the sample obtained synchronously, so that the detection system and the detection method have the advantages of simplicity in operation, high detection efficiency and the like, and the influence of sample space-time variation on the detection precision is effectively reduced.
To achieve the above object, in a first aspect, the present invention provides a soil nutrient rapid detection system for synchronous acquisition of LIBS and NIRS spectra, comprising:
a sample stage, a LIBS collection device, an optical assembly, a sample movement device and a sample cell assembly positioned above the sample stage, and a NIRS collection device positioned below the sample stage;
the bottom of the sample cell assembly is sealed and transparent, and is used for placing a sample to be measured;
the sample moving device is connected with the sample cell assembly and is used for moving the sample cell assembly so that light emitted from the surface of the sample to be detected is collected by the LIBS collecting device after passing through the optical assembly;
the NIRS acquisition device comprises M halogen lamps, a light source support frame and an optical fiber collimating mirror probe, wherein the M halogen lamps are uniformly distributed on the light source support frame at equal angles, the light source centers of the M halogen lamps are connected into a circle, and the optical fiber collimating mirror probe is positioned on a vertical line where the circle center of the circle is positioned; m is more than or equal to 2;
the sample stage is provided with a hole, and the hole, the optical fiber collimator lens probe and the optical component are coaxial so as to ensure that the spectrum data collected by the LIBS collecting device and the NIRS collecting device come from the same sample.
Further, the diameter L of the circle formed by the center of the light source and the distance H from any center of the light source to the upper surface of the light source support frame satisfy l=2h; the distance S between the upper surface of the optical fiber collimating mirror probe and the lower bottom surface of the light source support frame and the distance h between any light source center and the lower bottom surface of the light source support frame satisfy that S is more than or equal to 0.65h and less than or equal to h; the inner diameter D of the light source support frame and the diameter L of the circle are more than or equal to 1.2L and less than or equal to 1.6L.
Further, the sample cell assembly comprises a sample cell frame, first light-transmitting glass and second light-transmitting glass, wherein the first light-transmitting glass, the second light-transmitting glass and the sample cell frame form a sample cell with a closed bottom and light transmission, soil to be measured is arranged on the first light-transmitting glass, and a standard white board is arranged on the second light-transmitting glass.
Further, the LIBS acquisition device comprises a LIBS spectrometer, a laser, a digital delay, a LIBS detection optical fiber and a LIBS detection probe, wherein an external trigger input port of the laser and the LIBS spectrometer is respectively connected with output ports T1 and T2 of the digital delay through digital signal lines, the LIBS detection probe is fixed on an optical assembly, one end of the LIBS detection optical fiber is connected with the LIBS spectrometer, and the other end of the LIBS detection optical fiber is connected with the LIBS detection probe.
Further, the optical assembly includes an optical lens fixing bracket, a first focusing convex lens, a dichroic mirror, and a second dimer Jiao Tujing; the dichroic mirror and the horizontal surface form an included angle of 45 degrees and are fixedly arranged in the middle of the optical lens fixing support, and the center of the dichroic mirror is flush with the laser light outlet; the first focusing convex lens and the second focusing convex lens Jiao Tujing are horizontally and fixedly arranged on the optical lens fixing support and are respectively positioned right above and right below the dichroic mirror.
Further, the system also comprises UP 2 Control panel, switching power supply and step motor driver;
wherein the switching power supplies are UP respectively 2 The control panel, the halogen lamp and the stepping motor driver provide direct current voltage; UP (UP) 2 The control panel is respectively connected with the LIBS spectrometer, the NIRS spectrometer and the digital delayer, and UP 2 The GPIO output port of the control board is connected with the stepping motor driver; the stepper motor driver is connected with the stepper motor.
Further, the sample moving device comprises a screw sliding table, a shaft coupling, a stepping motor and a sample cell assembly connecting plate, wherein one end of the sample cell assembly connecting plate is connected with a sliding block of the screw sliding table, the other end of the sample cell assembly connecting plate is connected with a sample cell frame, and a stepping motor main shaft is connected with a screw of the screw sliding table through the shaft coupling.
In a second aspect, the invention provides a method for rapidly detecting soil nutrients by synchronously collecting LIBS and NIRS spectra, which comprises the following steps:
s1, respectively adding different matrix chemical substances into soil samples with known same nutrient content by adopting a standard adding method to prepare different new samples; LIBS detection and NIRS detection are carried out on each new sample, and corresponding LIBS and NIRS spectrum data are obtained;
s2, based on the LIBS spectrum data, taking the content of the matrix chemical substances as independent variables, taking the intensity of each nutrient characteristic spectral line as dependent variable, fitting the linear relation between the content of different matrix chemical substances and the intensity of each nutrient characteristic spectral line, and taking the slope corresponding to each linear relation as a matrix effect spectral line intensity correction coefficient of the corresponding matrix chemical substances to the corresponding nutrients;
s3, establishing a spectrum prediction model based on the NIRS spectrum data, wherein the spectrum prediction model is used for predicting the content of each matrix chemical substance;
s4, correcting the corresponding nutrient characteristic spectral line intensity obtained by LIBS detection by using the matrix effect spectral line intensity correction coefficients in S2 and the content of each matrix chemical substance predicted in S3; constructing a calibration curve between the corrected corresponding nutrient characteristic spectral line intensity and the nutrient content reference value;
s5, LIBS and NIRS spectrum data of the soil to be detected are obtained, the content of each matrix chemical substance in the soil to be detected is predicted by utilizing the spectrum prediction model, and the corrected characteristic spectral line intensity of each nutrient in the soil to be detected is obtained by combining the correction coefficients of the matrix effect spectral line intensity; and obtaining the nutrient contents in the soil to be measured according to the calibration curves.
Further, in S4, the corrected corresponding nutrient characteristic spectral line intensity is expressed as:
wherein I is jc For the characteristic spectral line intensity of the j-th nutrient after correction，I j0 For LIBS detection, directly obtained characteristic spectral line intensity, k of j-th nutrient ij Matrix effect spectral line intensity correction coefficient for the j-th nutrient of the i-th matrix chemical substance, Q NIRi And predicting the content of the ith matrix chemical substance obtained by the spectrum prediction model, wherein n is the total number of matrix chemical substance types generating matrix effect.
In general, through the above technical solutions conceived by the present invention, the following beneficial effects can be obtained:
(1) According to the soil nutrient rapid detection system for synchronously collecting the LIBS and the NIRS, provided by the invention, the LIBS collecting device and the NIRS collecting device can be ensured to synchronously collect the spectral data from the same sample through reasonable layout, so that the influence of sample space-time variation on the detection precision of the sample is effectively reduced.
(2) The M halogen lamps designed by the invention are uniformly distributed on the light source support frame at equal angles, the centers of the light sources are connected into a circle, the optical fiber collimating lens probe is positioned on the vertical line where the center of the circle is positioned, the design structure is compact, the detection distance between the lower surface of a sample and the optical fiber probe, which is easy to ensure that the irradiation focus of the light source is gathered, is very suitable for the development of detection equipment, and can effectively isolate the interference of external environment light on detection.
(3) According to the method for rapidly detecting the soil nutrients by synchronously collecting the LIBS and the NIRS spectra, provided by the invention, the linear relation between the contents of different matrix chemical substances and the characteristic spectral line intensities of all the nutrients is fitted, the spectral prediction model for predicting the contents of all the matrix chemical substances is established in a combined mode, the characteristic spectral line intensities of the corresponding nutrients obtained by LIBS detection are corrected, the interference of matrix effect on spectral detection is effectively eliminated, and the high-precision stable detection of the soil nutrients is realized.
Drawings
FIG. 1 is a schematic diagram of a front view structure of a soil nutrient rapid detection system for synchronously collecting LIBS and NIRS spectra provided by the invention;
FIG. 2 is a schematic diagram of a top view structure of a soil nutrient rapid detection system for synchronously acquiring LIBS and NIRS spectra provided by the invention;
FIG. 3 is a schematic diagram of an axial measurement structure of a soil nutrient rapid detection system for synchronously collecting LIBS and NIRS spectra provided by the invention;
FIG. 4 is a schematic diagram of a front view of a sample cell assembly according to the present invention;
FIG. 5 is a cross-sectional view of a sample cell assembly provided by the present invention;
FIG. 6 is a schematic diagram of a front view of a NIRS light source and detection assembly according to the present invention;
FIG. 7 is a schematic top view of the NIRS light source and detection assembly according to the present invention;
FIG. 8 is a schematic diagram of an axial measurement structure of the NIRS light source and the detection assembly provided by the invention;
FIG. 9 is a cross-sectional view of a NIRS light source and detection assembly provided by the invention;
FIG. 10 is a flow chart of a method for rapidly detecting soil nutrients by synchronously collecting LIBS and NIRS spectra provided by the invention;
the same reference numbers are used throughout the drawings to reference like elements or structures, wherein:
LIBS spectrometer, 2 spectrometer support plate, 3 LIBS collection device, 4 laser, 5 laser support plate, 6 digital delay device, 7 sample cell component connection plate, 8 switching power supply, 9 control device, 10 ground pin, 11 NIRS spectrometer, 12 NIRS detection optical fiber, 13 NIRS detection device, 14 NIRS light source and detection component, 15 lead screw sliding table, 16 sample moving device, 17 stepper motor, 18 coupling, 19 optical component, 20 optical lens fixing support, 21 LIBS detection probe, 22 LIBS detection optical fiber, 23 chassis, 24 telescopic support, 25 touch unit, 26 touch screen, 27 UP 2 Control panel, 28, stepper motor driver, 29, sample stage, 30, stationary base, 31, sample cell assembly, 32, second polymer Jiao Tujing, 33, dichroic mirror, 34, first focusing convex mirror, 35, connecting transition piece, 36, soil to be tested, 37, sample cell frame, 38, standard white board, 39, first light transmitting glass, 40, second light transmitting glass, 41, light source support, 42, bottom cover, 43, fiber optic collimator probe, 44, halogen lamp.
Detailed Description
The present invention will be described in further detail with reference to the drawings and examples, in order to make the objects, technical solutions and advantages of the present invention more apparent. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the invention. In addition, the technical features of the embodiments of the present invention described below may be combined with each other as long as they do not collide with each other.
In the present invention, the terms "first," "second," and the like in the description and in the drawings, if any, are used for distinguishing between similar objects and not necessarily for describing a particular sequential or chronological order.
Example 1
Referring to fig. 1, in combination with fig. 2 to 9, the rapid soil nutrient detection system for synchronous acquisition of LIBS and NIRS spectra provided in this embodiment includes: LIBS collection device 3, NIRS collection device 13, optical component 19, sample moving device 16, control device 9, sample cell component 31, touch unit 25, chassis 23, sample stage 29, anchor 10, etc.; four ground feet 10 are positioned at the lowest part of the whole detection system, a case 23 is positioned right above the ground feet 10, and the ground feet 10 and the case 23 are fixedly connected together through bolts; the sample table 29 is positioned at the middle lower part of the interior of the case 23, and the sample table 29 and the case 23 are connected together through bolts; the LIBS acquisition device 3 is positioned in the case 23, and is positioned at the upper left side of the sample stage 29; the optical assembly 19 is positioned inside the case 23, and at the upper right of the sample stage 29; the cuvette assembly 31 is located directly below the optical assembly 19 and above the sample stage 29; the sample moving device 16 is positioned right behind the sample cell assembly 31 and above the sample stage 29; the control device 9 is positioned inside the case 23, and the lower left part of the sample stage 29; the NIRS detection device 13 is positioned inside the case 23, and at the lower right of the sample stage 29; the touch unit 25 is located on the outer right side of the casing 23.
LIBS collection system 3 includes LIBS spectrometer 1, laser instrument 4, digital time delay 6, spectrometer backup pad 2, laser instrument backup pad 5, LIBS detection optic fibre 22 and LIBS detection probe 21, and digital time delay 6 level is placed in sample stage 29 left side, and laser instrument backup pad 5 is located digital time delay 6 directly over and is fixed on the wallboard behind the quick-witted case 23 through bolted connection, and laser instrument 4 level is placedOn the laser supporting plate 5, the spectrometer supporting plate 2 is located right above the laser 4 and is fixed on the rear wall plate of the chassis 23 through bolt connection, the LIBS spectrometer 1 is horizontally placed on the spectrometer supporting plate 2, and the external trigger input ports of the laser 4 and the LIBS spectrometer 1 are respectively connected with the output port T of the digital delay 6 1 And T 2 The LIBS detection probe 21 is fixed on the optical component 19 through threads by connecting the digital signal wires together, one end of the LIBS detection optical fiber 22 is connected with the LIBS spectrometer 1 through threads, and the other end of the LIBS detection optical fiber 22 is connected with the LIBS detection probe 21 through threads.
The NIRS detection device 13 comprises a NIRS spectrometer 11, a NIRS detection optical fiber 12 and a NIRS light source and detection assembly 14, the NIRS spectrometer 11 is horizontally arranged on the bottom plate of the chassis 23, the NIRS light source and detection assembly 14 is fixed under the detection window of the sample stage 29 through bolt connection, one end of the NIRS detection optical fiber 12 is connected with the NIRS light source and detection assembly 14 through threads, and the other end of the NIRS detection optical fiber 12 is connected with the NIRS spectrometer 11 through threads.
The NIRS light source and detection assembly 14 includes a halogen lamp 44, a light source support 41, an optical fiber collimator probe 43 and a bottom cover 42, the halogen lamp 44 is fixed on the light source support 41 through a bolt connection, the number of the halogen lamps 44 is 4 and is uniformly distributed on the light source support 41 at equal angles, the optical fiber collimator probe 43 is fixed on the light source support 41 through a threaded connection, one ends of the optical fiber collimator probe 43 and the NIRS detection optical fiber 12 are connected together through threads, and the bottom cover 42 and the light source support 41 are connected together through a bolt.
The distance L between the centers of two opposite light sources on the light source support 41 and the distance H between the centers of the light sources and the upper surface of the NIRS light source and detection assembly 14 satisfy l=2h, the distance S between the upper surface of the optical fiber collimator probe 43 and the lower bottom surface of the light source support 41 and the distance H between the centers of the light sources and the lower bottom surface of the light source support 41 satisfy 0.65 h.ltoreq.s.ltoreq.h, and the inner diameter D of the light source support 41 and the two opposite light source centers L satisfy 1.2 l.ltoreq.d.ltoreq.1.6L.
The optical assembly 19 comprises an optical lens fixing support 20, a first focusing convex lens 34, a dichroic mirror 33, a second focusing convex lens Jiao Tujing and a connecting transition piece 35, wherein one end of the connecting transition piece 35 is connected with the optical lens fixing support 20 through a bolt, the other end of the connecting transition piece 35 is fixedly arranged on a rear wall plate in the case 23 through a bolt connection, the dichroic mirror 33 is fixedly arranged in the middle of the optical lens fixing support 20 through a bolt and forms an included angle of 45 degrees with the horizontal plane, the center of the dichroic mirror 33 is flush with a light outlet of the laser 4, the first focusing convex lens 34 is horizontally arranged right above the dichroic mirror 33 of the optical lens fixing support 20 through the bolt, and the second focusing convex lens Jiao Tujing is horizontally arranged right below the dichroic mirror 33 of the optical lens fixing support 20 through the bolt.
The sample cell assembly 31 comprises a sample cell frame 37, a first light-transmitting glass 39, a second light-transmitting glass 40, a standard white board 38 and soil 36 to be tested, wherein the first light-transmitting glass 39 is adhered to the left bottom of the sample cell frame 37 through glass cement, the second light-transmitting glass 40 is adhered to the right bottom of the sample cell frame 37 through glass cement, the first light-transmitting glass 39 and the second light-transmitting glass 40 form a sample cell with a closed bottom and light transmission with the sample cell frame 37, the standard white board 38 is arranged at the right end of the sample cell, and the soil 36 to be tested is arranged at the left end of the sample cell.
The sample moving device 16 comprises a screw sliding table 15, a coupler 18, a stepping motor 17 and a sample cell assembly connecting plate 7, wherein the screw sliding table 15 is fixedly arranged on a rear wall plate inside a machine case 23 through T-shaped bolt connection, one end of the sample cell assembly connecting plate 7 is connected with a sliding block of the screw sliding table 15 through a bolt, the other end of the sample cell assembly connecting plate 7 is connected with a sample cell frame 37 through a bolt, the stepping motor 17 is fixedly arranged on the screw sliding table 15 through bolt connection, and a spindle of the stepping motor 17 is connected with a screw of the screw sliding table 15 through the coupler 18.
The control means 9 comprise UP 2 Control board 27, switching power supply 8 and step motor driver 28, switching power supply 8 is fixed on the left side of the bottom plate of case 23 through bolt connection, UP 2 The control board 27 is fixedly arranged on the bottom plate of the chassis 23 through a copper upright post, UP 2 The control board 27 is positioned on the right side of the switch power supply 8, the stepping motor driver 28 is fixed on the bottom plate of the chassis 23 through a bolt connection, and the stepping motor driver 28 is positioned on the UP 2 Directly behind the control board 27, the switching power supply 8 is connected through conductionLines are UP respectively 2 Control board 27, touch screen 26, halogen lamp 44 and stepper motor driver 28 provide DC voltage, UP 2 The control board 27 is respectively connected with the LIBS spectrometer 1, the NIRS spectrometer 11 and the digital delayer 6 through data lines, and UP 2 The GPIO output port of the control board 27 is connected with the stepping motor driver 28 through DuPont wire, UP 2 The control board 27 is connected to the touch screen 26 through an HDMI interface video line and a USB interface signal line, and the stepper motor driver 28 is connected to the stepper motor 17 through a wire.
The touch unit 25 comprises a touch screen 26, a telescopic support 24 and a fixed base 30, wherein the fixed base 30 is fixedly arranged on the outer side of a right side wall plate of the case 23 through bolt connection, one end of the telescopic support 24 is connected with the fixed base 30 through a revolute pair, and the other end of the telescopic support 24 is fixedly connected with the touch screen 26 through bolts.
Example two
Referring to fig. 10, the invention further provides a method for rapidly detecting soil nutrients by synchronously collecting LIBS and NIRS spectra, which comprises the following steps:
s1, respectively adding different matrix chemical substances into soil samples with known same nutrient content by adopting a standard adding method to prepare different new samples; LIBS detection and NIRS detection are carried out on each new sample, and corresponding LIBS and NIRS spectrum data are obtained;
s2, based on the LIBS spectrum data, taking the content of the matrix chemical substances as independent variables, taking the intensity of each nutrient characteristic spectral line as dependent variable, fitting the linear relation between the content of different matrix chemical substances and the intensity of each nutrient characteristic spectral line, and taking the slope corresponding to each linear relation as a matrix effect spectral line intensity correction coefficient of the corresponding matrix chemical substances to the corresponding nutrients;
s3, establishing a spectrum prediction model based on the NIRS spectrum data, wherein the spectrum prediction model is used for predicting the content of each matrix chemical substance;
s4, correcting the corresponding nutrient characteristic spectral line intensity obtained by LIBS detection by using the matrix effect spectral line intensity correction coefficients in S2 and the content of each matrix chemical substance predicted in S3; constructing a calibration curve between the corrected corresponding nutrient characteristic spectral line intensity and the nutrient content reference value;
s5, LIBS and NIRS spectrum data of the soil to be detected are obtained, the content of each matrix chemical substance in the soil to be detected is predicted by utilizing the spectrum prediction model, and the corrected characteristic spectral line intensity of each nutrient in the soil to be detected is obtained by combining the correction coefficients of the matrix effect spectral line intensity; and obtaining the nutrient contents in the soil to be measured according to the calibration curves.
Further, in S4, the corrected corresponding nutrient characteristic spectral line intensity is expressed as:
wherein I is jc For the characteristic spectral line intensity of the j-th nutrient after correction, I j0 For LIBS detection, directly obtained characteristic spectral line intensity, k of j-th nutrient ij Matrix effect spectral line intensity correction coefficient for the j-th nutrient of the i-th matrix chemical substance, Q NIRi And predicting the content of the ith matrix chemical substance obtained by the spectrum prediction model, wherein n is the total number of matrix chemical substance types generating matrix effect.
It should be noted that the above detection method may be applied to the detection system according to the first embodiment, and may also be applied to an existing detection system.
The following describes the above detection method in detail, taking the detection method as an example of application to the detection system of the first embodiment. The method comprises the following steps:
step 1: parameter optimization and setting, namely selecting a soil sample with higher nutrient content to be measured, compressing the soil sample, placing the compressed soil sample in a sample tank on the left side of the sample tank assembly, and placing a standard whiteboard 38 in a whiteboard tank on the right side of the sample tank assembly 31; moving a standard whiteboard 38 in the sample cell assembly to a detection window of the sample table 29 through the control of the touch screen 26, starting an NIRS detection light source, and selecting the integration time when the maximum reflection peak intensity of the NIRS spectrum is 65000 as the integration time of NIRS detection, wherein the average scanning times and the moving average width are both set to 3; according to the set NIRS acquisition parameters, acquiring spectral data when the NIRS light source is turned on and storing the spectral data as a white reference, and acquiring spectral data when the NIRS light source is turned off and storing the spectral data as a black reference; then, the compressed soil in the sample cell assembly 31 is controlled by the touch screen 26 to move to a sample stage detection window, so that the sample moves rightwards at a constant speed, LIBS spectrum data under different laser energy, delay time and gate width parameters are respectively collected, characteristic spectral lines of nutrients to be detected are determined by comparing an atomic spectrum gallery, signal-to-noise ratio of the LIBS spectrum data is obtained under various parameter conditions is calculated, and parameters such as optimal laser energy, delay time, gate width and the like of LIBS detection are determined according to the signal-to-noise ratio and are set; according to the parameter optimization and setting, spectrum data can be acquired, and NIRS spectrum drift correction is required for continuous long-time spectrum detection;
step 2: calculating matrix effect spectral line intensity correction coefficients, sequentially adding chemical substances which cause serious matrix effects such as water, organic matters and organic carbon into soil samples with the same nutrient concentration to be measured by adopting standard addition to prepare different samples, and measuring reference values of the water content, the organic matters and the organic carbon content of matrix chemical substances of each sample by utilizing a traditional chemical analysis method; the prepared sample is compressed and prepared and placed in a sample tank at the left side of a sample tank assembly 31, the sample tank assembly 31 is driven to move rightwards at a constant speed by controlling a sample moving device 16, and LIBS and NIRS spectrum data of the sample are obtained; establishing a linear relation between the content of chemical substances such as soil moisture content, organic matters, organic carbon and the like and the characteristic spectral line intensity of the nutrient to be detected, wherein the slope k of the linear relation is ij Namely, the matrix effect spectral line intensity correction coefficient;
step 3: NIRS detects soil matrix information, and algorithms such as PLSR, MLR and the like are adopted to respectively establish a spectrum prediction model of the soil sample NIRS spectrum data obtained in the step 2 and matrix components such as water content, organic matters, organic carbon and the like;
step 4: correcting the LIBS detection characteristic spectral line intensity of soil nutrients, and rapidly determining the content Q of matrix such as water content, organic matters, organic carbon and the like of a soil sample according to the soil NIRS prediction model established in the step 3 NIRi Using the calculation in step 2The obtained matrix effect spectral line intensity correction coefficient is used for detecting the characteristic spectral line intensity I of soil nutrient LIBS j0 And correcting, wherein the characteristic spectral line intensity correction algorithm is as follows:
step 5: constructing a soil nutrient calibration curve, actually collecting a batch of soil samples, compressing the collected soil samples, placing the compressed soil samples in a sample tank on the left side of a sample tank assembly 31, acquiring LIBS (laser induced breakdown spectroscopy) and NIRS (laser induced breakdown spectroscopy) spectrum data of each soil sample under various spectrum collection condition parameters set in step 1, and correcting the LIBS detection characteristic spectral line intensity of the soil nutrient according to the matrix information rapidly acquired by using the NIRS spectrum in step 4 so as to obtain the corrected intensity I of each sample LIBS detection characteristic spectral line jc Measuring the reference value of the nutrient index content to be measured of each sample by adopting a chemical analysis method specified in the national standard, and then constructing the corrected characteristic spectral line intensity I jc A calibration curve between the nutrient index content reference value and the nutrient index content reference value;
step 6: embedding the model and the correction algorithm into a software system, and respectively embedding the soil matrix NIRS detection model established in the step 3, the characteristic spectral line correction algorithm in the step 4 and the calibration curve in the step 5 into a software interface of the detection system;
step 7: and (3) detecting nutrients of a soil sample, compressing the sample to be detected, placing the compressed sample in a sample tank at the left side of a sample tank assembly 31, synchronously acquiring sample LIBS and NIRS spectrum data through a software interface of a touch screen 26 operation detection system, rapidly predicting the chemical component content of each matrix of the sample by using a soil matrix NIRS detection model embedded in the software interface, substituting the chemical component content of each matrix into a characteristic spectral line correction algorithm program so as to obtain a correction value of characteristic spectral line intensity of the sample to be detected, and substituting the correction value of the characteristic spectral line intensity into a calibration curve embedded in the software program so as to rapidly obtain the content of the nutrients to be detected of the soil sample.
Further, in step 1, the NIRS spectrum drift is corrected to be 4 hours after the NIRS spectrum is continuously collected, the touch screen 26 is controlled to drive the sample moving device 16 to move the standard whiteboard 38 in the sample cell assembly 31 to the detection window of the sample table 29, and the white reference data is collected again and stored to cover the original white reference data.
Furthermore, the chemical substances causing the serious matrix effect in the step 2 are not limited to common indexes such as water, organic matters, organic carbon and the like, and can be determined according to the soil in different areas, and the main basis of selection is matrix chemical substances with significant differences in the content of chemical components in different soil samples.
It will be readily appreciated by those skilled in the art that the foregoing description is merely a preferred embodiment of the invention and is not intended to limit the invention, but any modifications, equivalents, improvements or alternatives falling within the spirit and principles of the invention are intended to be included within the scope of the invention.
Claims (8)
1. A soil nutrient rapid detection method for synchronously collecting LIBS and NIRS spectra is applied to a soil nutrient rapid detection system for synchronously collecting LIBS and NIRS spectra, and is characterized in that the system comprises: -a sample stage (29), a LIBS collection device (3), an optical assembly (19), a sample movement device (16) and a sample cell assembly (31) located above the sample stage (29), and-a NIRS collection device (13) located below the sample stage (29);
the bottom of the sample tank assembly (31) is closed and transparent, and is used for placing a sample to be tested;
the sample moving device (16) is connected with the sample cell assembly (31) and is used for moving the sample cell assembly (31) so that light emitted from the surface of the sample to be detected is collected by the LIBS collecting device (3) after passing through the optical assembly (19);
the NIRS acquisition device (13) comprises M halogen lamps (44), a light source support frame (41) and an optical fiber collimating lens probe (43), wherein the M halogen lamps (44) are uniformly distributed on the light source support frame (41) at equal angles, the light source centers of the M halogen lamps (44) are connected into a circle, and the optical fiber collimating lens probe (43) is positioned on a vertical line where the circle center of the circle is positioned; m is more than or equal to 2;
the sample table (29) is provided with a hole, and the hole, the optical fiber collimating lens probe (43) and the optical component (19) are coaxial so as to ensure that the spectrum data collected by the LIBS collecting device (3) and the NIRS collecting device (13) come from the same sample;
the method comprises the following steps: s1, respectively adding different matrix chemical substances into soil samples with known same nutrient content by adopting a standard adding method to prepare different new samples; LIBS detection and NIRS detection are carried out on each new sample, and corresponding LIBS and NIRS spectrum data are obtained;
s2, based on the LIBS spectrum data, taking the content of the matrix chemical substances as independent variables, taking the intensity of each nutrient characteristic spectral line as dependent variable, fitting the linear relation between the content of different matrix chemical substances and the intensity of each nutrient characteristic spectral line, and taking the slope corresponding to each linear relation as a matrix effect spectral line intensity correction coefficient of the corresponding matrix chemical substances to the corresponding nutrients;
s3, establishing a spectrum prediction model based on the NIRS spectrum data, wherein the spectrum prediction model is used for predicting the content of each matrix chemical substance;
s4, correcting the corresponding nutrient characteristic spectral line intensity obtained by LIBS detection by using the matrix effect spectral line intensity correction coefficients in S2 and the content of each matrix chemical substance predicted in S3; constructing a calibration curve between the corrected corresponding nutrient characteristic spectral line intensity and the nutrient content reference value;
s5, LIBS and NIRS spectrum data of the soil to be detected are obtained, the content of each matrix chemical substance in the soil to be detected is predicted by utilizing the spectrum prediction model, and the corrected characteristic spectral line intensity of each nutrient in the soil to be detected is obtained by combining the correction coefficients of the matrix effect spectral line intensity; and obtaining the nutrient contents in the soil to be measured according to the calibration curves.
2. The rapid soil nutrient detection method for synchronously acquiring LIBS and NIRS spectra according to claim 1, wherein the diameter L of a circle formed by the center of the light source and the distance H from any center of the light source to the upper surface of a light source support frame (41) satisfy L=2H; the distance S between the upper surface of the optical fiber collimating mirror probe (43) and the lower bottom surface of the light source support frame (41) and the distance h between any light source center and the lower bottom surface of the light source support frame (41) are more than or equal to 0.65h and less than or equal to S and less than or equal to h; the inner diameter D of the light source support frame (41) and the diameter L of the circle are more than or equal to 1.2L and less than or equal to 1.6L.
3. A method for rapid detection of soil nutrients by LIBS and NIRS spectroscopy synchronous acquisition as claimed in claim 1, wherein the sample cell assembly (31) comprises a sample cell frame (37), a first light-transmitting glass (39) and a second light-transmitting glass (40), the first light-transmitting glass (39) and the second light-transmitting glass (40) form a closed bottom and light-transmitting sample cell with the sample cell frame (37), the soil (36) to be detected is placed on the first light-transmitting glass (39), and a standard white board (38) is placed on the second light-transmitting glass (40).
4. The rapid soil nutrient detection method for synchronously collecting LIBS and NIRS according to claim 1, wherein the LIBS collecting device (3) comprises a LIBS spectrometer (1), a laser (4), a digital delay device (6), a LIBS detection optical fiber (22) and a LIBS detection probe (21), wherein an external trigger input port of the laser (4) and an external trigger input port of the LIBS spectrometer (1) are respectively connected with output ports T1 and T2 of the digital delay device (6) through digital signal lines, the LIBS detection probe (21) is fixed on an optical assembly (19), one end of the LIBS detection optical fiber (22) is connected with the LIBS spectrometer (1), and the other end of the LIBS detection optical fiber (22) is connected with the LIBS detection probe (21).
5. A method for rapid detection of soil nutrients by LIBS and NIRS spectroscopy simultaneous acquisition as in claim 4 wherein the optical assembly (19) comprises an optical lens mounting bracket (20), a first focusing convex lens (34), a dichroic mirror (33) and a second focusing Jiao Tujing (32); the dichroic mirror (33) is fixedly arranged in the middle of the optical lens fixing bracket (20) at an included angle of 45 degrees with the horizontal plane, and the center of the dichroic mirror (33) is flush with the light outlet of the laser (4); the first focusing convex lens (34) and the second focusing convex lens (Jiao Tujing) are horizontally and fixedly arranged on the optical lens fixing support (20) and are respectively positioned right above and right below the dichroic mirror (33).
6. The rapid detection method of soil nutrients synchronously collected by LIBS and NIRS spectra as claimed in claim 4, wherein said system further comprises UP 2 A control board (27), a switching power supply (8) and a stepping motor driver (28);
wherein the switching power supplies (8) are UP respectively 2 A control board (27), a halogen lamp (44) and a stepping motor driver (28) for supplying DC voltage; UP (UP) 2 The control board (27) is respectively connected with the LIBS spectrometer (1), the NIRS spectrometer (11) and the digital delayer (6), and UP 2 The GPIO output port of the control board (27) is connected with the stepping motor driver (28); the stepper motor driver (28) is connected with the stepper motor (17).
7. The rapid soil nutrient detection method for synchronously collecting LIBS and NIRS spectra according to claim 1, wherein the sample moving device (16) comprises a screw sliding table (15), a coupler (18), a stepping motor (17) and a sample cell assembly connecting plate (7), wherein one end of the sample cell assembly connecting plate (7) is connected with a sliding block of the screw sliding table (15), the other end of the sample cell assembly connecting plate (7) is connected with a sample cell frame (37), and a spindle of the stepping motor (17) is connected with a screw of the screw sliding table (15) through the coupler (18).
8. The rapid detection method for soil nutrients synchronously collected by LIBS and NIRS spectra according to claim 1, wherein in S4, the corrected corresponding nutrient characteristic spectral line intensity is expressed as:
wherein I is jc For the characteristic spectral line intensity of the j-th nutrient after correction, I j0 For LIBS detection, directly obtained characteristic spectral line intensity, k of j-th nutrient ij Matrix effect spectral line intensity correction coefficient for the j-th nutrient of the i-th matrix chemical substance, Q NIRi Prediction of the spectral prediction modelN is the total number of species of matrix chemical that produce the matrix effect.
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