CN114295604A - Rapid soil nutrient detection system and method for LIBS and NIRS spectrum synchronous acquisition - Google Patents
Rapid soil nutrient detection system and method for LIBS and NIRS spectrum synchronous acquisition Download PDFInfo
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Abstract
The invention discloses a soil nutrient rapid detection system and method for LIBS and NIRS spectrum synchronous collection, belonging to the field of optical and soil nutrient detection. The detection method provided by the invention corrects the corresponding nutrient characteristic spectral line intensity obtained by LIBS detection by fitting the linear relationship between the content of different matrix chemical substances and the characteristic spectral line intensity of each nutrient and establishing an NIRS prediction model for predicting the content of each matrix chemical substance, thereby effectively eliminating the interference of matrix effect on spectral detection and realizing high-precision stable detection of soil nutrients.
Description
Technical Field
The invention belongs to the field of optical and soil nutrient detection, and particularly relates to a soil nutrient rapid detection system and method for LIBS and NIRS spectrum synchronous acquisition.
Background
The soil provides various nutrient elements for the growth of crops, and the abundance and shortage of nutrients of the soil have important influence on the growth condition and the yield of the crops. In order to meet the demand of population growth on food yield, fertilizers are widely applied in agricultural planting. Due to the lack of a soil nutrient rapid detection technology meeting the actual production requirements, excessive use of chemical fertilizers is often adopted in production to guarantee the growth vigor and yield of crops. According to statistics of data, the usage amount of the chemical fertilizer in 2015 in China is about 6000 million tons, but the actual utilization rate of the applied chemical fertilizer is less than 40%. A large amount of chemical fertilizer which is not absorbed and utilized by crops enters 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 on the high-precision soil nutrient detection technology suitable for actual agricultural production has important significance for guiding scientific and accurate fertilization, improving the utilization rate of the fertilizer and reducing agricultural non-point source pollution.
Although the traditional agro-chemical analysis method has high detection precision for measuring soil nutrients, the traditional agro-chemical analysis method has the defects of strong operation specificity, long consumption time, sample pollution caused by chemical reagents and the like. 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 spectroscopy (ICP-MS) have high detection accuracy and high analysis speed, the methods require complicated sample pretreatment and have expensive equipment price, 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 good potential in soil nutrient analysis, and both spectrum analysis technologies have the advantages of being simple to operate, free of complex sample pretreatment, high in detection speed and the like. However, because the soil matrix is complex in structure, the LIBS detection is seriously affected by the difference of the soil moisture content, the organic matter content and the like, and the accuracy and the stability of the LIBS detection are difficult to meet the actual production requirements. In addition, NIRS has good detection performance for indexes such as soil nitrogen, water content and organic matters, but it is difficult to realize measurement of indexes of elements such as phosphorus and potassium in soil.
Disclosure of Invention
Aiming at the defects and improvement requirements of the prior art, in order to thoroughly eliminate the interference of soil matrix effect on nutrient LIBS detection, the invention provides a soil nutrient rapid detection system and method synchronously acquiring LIBS and NIRS spectra. In addition, the detection system and the detection method synchronously acquire the LIBS and NIRS spectral information of the sample, have the advantages of simple operation, high detection efficiency and the like, and effectively reduce the influence of the time-space change of the sample on the detection precision.
In order to achieve the above object, in a first aspect, the present invention provides a system for rapidly detecting soil nutrients by synchronously collecting LIBS and NIRS spectra, comprising:
the system comprises a sample stage, an LIBS collection device, an optical assembly, a sample moving device and a sample cell assembly which are positioned above the sample stage, and an NIRS collection device which is positioned below the sample stage;
the bottom of the sample cell component is closed and light-transmitting and is used for placing a sample to be detected;
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 centers of the light sources 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 center of the circle is positioned; m is more than or equal to 2;
the sample table is provided with a hole, and the hole, the optical fiber collimating mirror probe and the optical assembly are coaxial so as to ensure that the spectral data acquired by the LIBS acquisition device and the NIRS acquisition device come from the same sample.
Further, the diameter L of the circle formed by the light source centers and the distance H from any one of the light source centers to the upper surface of the light source support frame satisfy that L is 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 the center of any one light source and the lower bottom surface of the light source support frame meet the condition 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 meet that D is more than or equal to 1.2L and less than or equal to 1.6L.
Furthermore, 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 detected is placed on the first light-transmitting glass, and a standard white board is placed on the second light-transmitting glass.
Further, the LIBS detection device comprises a LIBS spectrometer, a laser, a digital delayer, a LIBS detection optical fiber and a LIBS detection probe, wherein the external trigger input ports of the laser and the LIBS spectrometer are respectively connected with the output ports T1 and T2 of the digital delayer through digital signal lines, the LIBS detection probe is fixed on the 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 comprises an optical lens fixing bracket, a first focusing convex lens, a dichroic mirror and a second focusing convex lens; the center of the dichroic mirror is flush with a light outlet of the laser; the first focusing convex lens and the second focusing convex lens 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 includes UP2The control panel, the switching power supply and the stepping motor driver;
wherein, the switching power supply is UP respectively2The control board, the halogen lamp and the stepping motor driver provide direct current voltage; UP2The control panel is respectively connected with the LIBS spectrometer, the NIRS spectrometer and the digital time delayConnector connection, UP2The GPIO output port of the control panel is connected with the stepping motor driver; the stepping motor driver is connected with the stepping motor.
Further, the sample moving device comprises a screw sliding table, a coupler, 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 spindle of the stepping motor is connected with a screw of the screw sliding table through the coupler.
In a second aspect, the invention provides a method for rapidly detecting soil nutrients by synchronous collection of LIBS and NIRS spectra, which comprises the following steps:
s1, adding different matrix chemical substances into soil samples with the same known nutrient content by adopting a standard addition method to prepare different new samples; performing LIBS detection and NIRS detection on each new sample to obtain corresponding LIBS and NIRS spectral data;
s2, fitting linear relations between the contents of different matrix chemical substances and the characteristic spectral line intensities of the nutrients by taking the content of the matrix chemical substances as an independent variable and the characteristic spectral line intensities of the nutrients as a dependent variable based on the LIBS spectral data, and taking the slopes corresponding to the linear relations as matrix effect spectral line intensity correction coefficients 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 correction coefficient of each matrix effect spectral line intensity in S2 and the content of each predicted matrix chemical substance in S3; constructing a calibration curve between the corrected corresponding nutrient characteristic spectral line intensity and the nutrient content reference value;
s5, acquiring LIBS and NIRS spectral data of soil to be detected, predicting the content of each matrix chemical substance in the soil to be detected by using the spectral prediction model, and obtaining the corrected characteristic spectral line intensity of each nutrient in the soil to be detected by combining the correction coefficient of each matrix effect spectral line intensity; and obtaining the content of each nutrient in the soil to be detected according to each calibration curve.
Further, in S4, the corrected corresponding nutrient characteristic line intensity is expressed as:
wherein, IjcFor corrected j-th nutrient line intensity, Ij0J-th nutrient characteristic spectral line intensity, k, directly obtained for LIBS detectionijCorrection factor for matrix effect line intensity of ith matrix chemical substance to jth nutrient, QNIRiAnd predicting the content of the ith matrix chemical substance for the spectrum prediction model, wherein n is the total number of the matrix chemical substance types generating the matrix effect.
Generally, by the above technical solution conceived by the present invention, the following beneficial effects can be obtained:
(1) the rapid detection system for soil nutrients synchronously acquired by LIBS and NIRS provided by the invention can ensure that the LIBS acquisition device and the NIRS acquisition device can synchronously acquire the soil nutrients through reasonable layout, and the acquired spectral data come from the same sample, so that the influence of the time-space change of the sample on the detection precision is effectively reduced.
(2) The M halogen lamps 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 mirror probe is positioned on a vertical line where the center of the circle is located, the design structure is compact, the detection distance between the lower surface of a sample and the optical fiber probe is easily ensured to be gathered by the irradiation focus of the light source, the detection device is very suitable for development of detection equipment, and the design can effectively isolate the interference of external environment light on detection.
(3) According to the method for rapidly detecting the soil nutrients synchronously acquired by LIBS and NIRS spectrums, provided by the invention, the corresponding nutrient characteristic spectrum line intensity obtained by LIBS detection is corrected by fitting the linear relation between the contents of different matrix chemical substances and the characteristic spectrum line intensity of each nutrient and establishing a spectrum prediction model for predicting the contents of the matrix chemical substances, so that the interference of matrix effects on spectrum detection is effectively eliminated, and the high-precision stable detection of the soil nutrients is realized.
Drawings
FIG. 1 is a schematic view of a structure of a soil nutrient rapid detection system for LIBS and NIRS spectrum synchronous collection provided by the invention;
FIG. 2 is a schematic diagram of a top view structure of a soil nutrient rapid detection system for LIBS and NIRS spectrum synchronous collection provided by the present invention;
FIG. 3 is a schematic diagram of an axial structure of a soil nutrient rapid detection system for LIBS and NIRS spectrum synchronous collection provided by the invention;
FIG. 4 is a schematic 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 view of a front view of an 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 of the present invention;
FIG. 8 is a schematic diagram of an axial measurement configuration of the NIRS light source and detection assembly provided by the present invention;
FIG. 9 is a cross-sectional view of a NIRS light source and detection assembly provided in accordance with the present invention;
FIG. 10 is a schematic flow chart of a method for rapidly detecting soil nutrients by LIBS and NIRS spectrum synchronous collection provided by the present invention;
the same reference numbers will be used throughout the drawings to refer to the same or like elements or structures, wherein:
the system comprises a LIBS spectrometer, a spectrometer support plate, a LIBS detection device, a laser support plate, a digital delayer, a sample cell component connecting plate, a switch power supply, a control device, a ground foot, an NIRS spectrometer, an NIRS detection optical fiber, a NIRS detection device, a NIRS light source and detection component, a screw rod sliding table, a sample moving device, a stepping motor, a coupler, an optical component, an optical lens fixing support, a LIBS detection probe, a LIBS detection optical fiber, a lead screw sliding table, a sample moving device, a stepping motor, a coupler, an optical component, an optical lens fixing support, a lead screw, a machine box, a telescopic support, a touch single-control single-touch control single-control-panel, a touch-control single-control single-control-touch-control single-control single-control single-control-system, and single-control-system, and-control-system, wherein the LI-control-system comprises a computer, and-controlYuan, 26. touch screen, 27.UP2The test device comprises a control board, 28, a stepping motor driver, 29, a sample table, 30, a fixed base, 31, a sample cell assembly, 32, a second focusing convex mirror, 33, a dichroic mirror, 34, a first focusing convex mirror, 35, a connecting transition piece, 36, soil to be tested, 37, a sample cell frame, 38, a standard white plate, 39, first light-transmitting glass, 40, second light-transmitting glass, 41, a light source support frame, 42, a bottom cover, 43, a fiber collimating mirror probe and 44, a halogen lamp.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.
In the present application, the terms "first," "second," and the like (if any) in the description and the drawings are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order.
Example one
Referring to fig. 1 and fig. 2 to 9, the system for rapidly detecting soil nutrients by synchronously collecting LIBS and NIRS spectra provided in this embodiment includes: the device comprises an LIBS acquisition device 3, an NIRS acquisition device 13, an optical assembly 19, a sample moving device 16, a control device 9, a sample cell assembly 31, a touch unit 25, a case 23, a sample table 29, feet 10 and the like; the four feet 10 are positioned at the lowest part of the whole detection system, the case 23 is positioned right above the feet 10, and the 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 inside of the case 23, and the sample table 29 and the case 23 are connected together through bolts; the LIBS detection device 3 is positioned in the case 23 and above the left of the sample table 29; the optical assembly 19 is positioned inside the case 23 and on the upper right of the sample table 29; the sample cell assembly 31 is located directly below the optical assembly 19, above the sample stage 29; the sample moving device 16 is positioned right behind the sample cell assembly 31, above the sample stage 29; the control device 9 is positioned inside the case 23 and on the lower left of the sample table 29; the NIRS detection device 13 is positioned inside the case 23 and at the lower right of the sample table 29; the touch unit 25 is located on the outer right side of the case 23.
The LIBS detection device 3 comprises a LIBS spectrometer 1, a laser 4, a digital delayer 6, a spectrometer support plate 2, a laser support plate 5, a LIBS detection optical fiber 22 and a LIBS detection probe 21, wherein the digital delayer 6 is horizontally arranged on the left side of a sample table 29, the laser support plate 5 is positioned right above the digital delayer 6 and is fixed on a rear wall plate of a case 23 through bolt connection, the laser 4 is horizontally arranged on the laser support plate 5, the spectrometer support plate 2 is positioned right above the laser 4 and is fixed on the rear wall plate of the case 23 through bolt connection, the LIBS spectrometer 1 is horizontally arranged on the spectrometer support plate 2, external trigger input ports of the laser 4 and the LIBS spectrometer 1 are respectively connected with an output port T of the digital delayer 61And T2The LIBS detection probe 21 is fixed on the optical assembly 19 through threads by being connected together through a digital signal wire, one end of an 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 light source and detection assembly 14 comprises halogen lamps 44, a light source support frame 41, optical fiber collimating mirror probes 43 and a bottom cover 42, the halogen lamps 44 are fixed on the light source support frame 41 through bolt connection, the number of the halogen lamps 44 is 4, the halogen lamps are uniformly distributed on the light source support frame 41 at equal angles, the optical fiber collimating mirror probes 43 are fixed on the light source support frame 41 through threaded connection, the optical fiber collimating mirror probes 43 are connected with one end of the NIRS detection optical fiber 12 through threads, and the bottom cover 42 is connected with the light source support frame 41 through bolts.
The distance L between the centers of two opposite light sources on the light source support frame 41 and the distance H from the centers of the light sources to the upper surface of the NIRS light source and detection assembly 14 satisfy L-2H, the distance S between the upper surface of the fiber collimator lens probe 43 and the lower bottom surface of the light source support frame 41 and the distance H between the centers of the light sources and the lower bottom surface of the light source support frame 41 satisfy 0.65H-1.6H, and the inner diameter D of the light source support frame 41 and the centers L of the two opposite light sources satisfy 1.2L-1.6L.
The sample cell assembly 31 comprises a sample cell frame 37, first light-transmitting glass 39, second light-transmitting glass 40, a standard white board 38 and soil 36 to be detected, the first light-transmitting glass 39 is adhered to the bottom of the left side of the sample cell frame 37 through glass adhesive, the second light-transmitting glass 40 is adhered to the bottom of the right side of the sample cell frame 37 through glass adhesive, the first light-transmitting glass 39, the second light-transmitting glass 40 and the sample cell frame 37 form a sample cell with the bottom closed and light-transmitting, the standard white board 38 is arranged at the right end of the sample cell, and the soil 36 to be detected is arranged at the left end of the sample cell.
Sample mobile device 16 includes lead screw slip table 15, shaft coupling 18, step motor 17 and sample cell subassembly connecting plate 7, lead screw slip table 15 passes through T type bolted connection to be fixed on the inside back wallboard of quick-witted case 23, sample cell subassembly connecting plate 7 one end is passed through the bolt and is linked together with the slider of lead screw slip table 15, the other end of sample cell subassembly connecting plate 7 passes through the bolt and links together with sample cell frame 37, step motor 17 passes through bolted connection to be fixed on lead screw slip table 15, step motor 17 main shaft passes through shaft coupling 18 with lead screw slip table 15 lead screw and links together.
The control means 9 comprise UP2Control panel 27, switching power supply 8 and step motor driver 28, switching power supply 8 passes through bolted connection to be fixed in quick-witted case 23 bottom plate left side, UP2The control board 27 is fixedly installed on the bottom plate of the case 23 through a copper upright column, UP2The control board 27 is positioned at the right side of the switch power supply 8, the stepping motor driver 28 is fixed on the bottom plate of the case 23 through bolt connection, and the stepping motor driver 28 is positioned at UP2Directly behind the control board 27, the switching power supply 8 is UP through the conducting wires respectively2The control board 27, touch screen 26, halogen lamp 44 and stepper motor driver 28 provide a direct voltage, UP2The control panel 27 is respectively connected with the LIBS spectrometer 1, the NIRS spectrometer 11 and the digital time delay unit 6 through data lines, and UP2The GPIO output port of the control board 27 is connected with the stepping motor driver 28 through a DuPont wire, and UP2The control board 27 is connected to the touch panel 26 through an HDMI video line and a USB signal line, and the stepping motor driver 28 is connected to the stepping motor 17 through a wire.
The touch unit 25 includes a touch screen 26, a telescopic support frame 24 and a fixing base 30, the fixing base 30 is fixed on the outer side of the wall plate on the right side of the case 23 through a bolt, one end of the telescopic support frame 24 is connected with the fixing base 30 through a revolute pair, and the other end of the telescopic support frame 24 is fixedly connected with the touch screen 26 through a bolt.
Example two
Referring to fig. 10, the present invention further provides a method for rapidly detecting soil nutrients by synchronous collection of LIBS and NIRS spectra, comprising:
s1, adding different matrix chemical substances into soil samples with the same known nutrient content by adopting a standard addition method to prepare different new samples; performing LIBS detection and NIRS detection on each new sample to obtain corresponding LIBS and NIRS spectral data;
s2, fitting linear relations between the contents of different matrix chemical substances and the characteristic spectral line intensities of the nutrients by taking the content of the matrix chemical substances as an independent variable and the characteristic spectral line intensities of the nutrients as a dependent variable based on the LIBS spectral data, and taking the slopes corresponding to the linear relations as matrix effect spectral line intensity correction coefficients 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 correction coefficient of each matrix effect spectral line intensity in S2 and the content of each predicted matrix chemical substance in S3; constructing a calibration curve between the corrected corresponding nutrient characteristic spectral line intensity and the nutrient content reference value;
s5, acquiring LIBS and NIRS spectral data of soil to be detected, predicting the content of each matrix chemical substance in the soil to be detected by using the spectral prediction model, and obtaining the corrected characteristic spectral line intensity of each nutrient in the soil to be detected by combining the correction coefficient of each matrix effect spectral line intensity; and obtaining the content of each nutrient in the soil to be detected according to each calibration curve.
Further, in S4, the corrected corresponding nutrient characteristic line intensity is expressed as:
wherein, IjcFor corrected j-th nutrient line intensity, Ij0J-th nutrient characteristic spectral line intensity, k, directly obtained for LIBS detectionijCorrection factor for matrix effect line intensity of ith matrix chemical substance to jth nutrient, QNIRiAnd predicting the content of the ith matrix chemical substance for the spectrum prediction model, wherein n is the total number of the matrix chemical substance types generating the matrix effect.
It should be noted that the detection method can be applied to the detection system provided in the first embodiment, and can also be applied to an existing detection system.
The following describes the detection method in detail by taking the detection method applied to the detection system provided in the first embodiment as an example. The method comprises the following steps:
step 1: optimizing and setting parameters, namely selecting a soil sample with higher nutrient content to be detected, compressing the soil sample, placing the compressed soil sample into a sample groove on the left side of the sample cell assembly, and placing the standard white board 38 into a white board groove on the right side of the sample cell assembly 31; moving the standard white board 38 in the sample cell assembly to the detection window of the sample table 29 through the control of the touch screen 26, starting an NIRS detection light source, selecting the integration time when the maximum reflection peak intensity of an NIRS spectrum is 65000 as the integration time of NIRS detection, and setting the average scanning times and the sliding average width as 3; according to the set NIRS acquisition parameters, acquiring the spectral data when the NIRS light source is turned on and storing the spectral data as a white reference, and acquiring the spectral data when the NIRS light source is turned off and storing the spectral data as a black reference; the touch screen 26 is used for controlling to move the compressed soil in the sample cell assembly 31 to a detection window of the sample stage, so that the sample moves rightwards at a constant speed, LIBS spectral data under different laser energy, delay time and door width parameters are respectively collected, the characteristic spectral line of the nutrient to be detected is determined by contrasting the atomic spectrum library, the signal-to-noise ratio of the LIBS spectral data under various parameter conditions is calculated, and the parameters such as the optimal laser energy, the delay time and the door width for LIBS detection are determined and set according to the signal-to-noise ratio; the spectral data can be acquired according to the optimization and setting of the parameters, and NIRS spectral drift correction is needed for continuous long-time spectral detection;
step 2: calculating the intensity correction coefficient of the matrix effect spectral line, sequentially adding chemical substances causing serious matrix effect such as water, organic matters, organic carbon and the like into soil samples with the same nutrient concentration to be measured by adopting a standard adding method to prepare different samples, and measuring the reference values of the water content of each sample and the contents of the matrix chemical substances such as the organic matters, the organic carbon and the like by utilizing a traditional chemical analysis method; the prepared sample is compressed and prepared and is placed in a sample groove on the left side of the sample cell assembly 31, the sample moving device 16 is controlled to drive the sample cell assembly 31 to move rightwards at a constant speed, and meanwhile LIBS and NIRS spectral data of the sample are obtained; establishing a linear relation between the soil water content, the content of organic matters, organic carbon and other chemical substances and the characteristic spectral line intensity of the nutrient to be measured, wherein the slope k of the linear relationijI.e. intensity of matrix effect spectral lineA correction factor;
and step 3: NIRS detecting soil matrix information, and respectively establishing a spectrum prediction model of NIRS spectrum data of the soil sample obtained in the step 2 and matrix components such as water content, organic matters, organic carbon and the like by adopting algorithms such as PLSR, MLR and the like;
and 4, step 4: correcting the LIBS detection characteristic spectral line intensity of the soil nutrients, and rapidly determining the water content of the soil sample, the organic matter content Q, the organic carbon content Q and other matrix contents according to the soil NIRS prediction model established in the step 3NIRiAnd (3) detecting the characteristic spectral line intensity I of the soil nutrient LIBS by utilizing the matrix effect spectral line intensity correction coefficient obtained by calculation in the step (2)j0And correcting, wherein the characteristic spectral line intensity correction algorithm is as follows:
and 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 groove at the left side of a sample cell assembly 31, acquiring LIBS and NIRS spectral data of each soil sample under various spectral collection condition parameters set in the step 1, and correcting the LIBS detection characteristic spectral line intensity of each soil sample by using matrix information quickly acquired by NIRS spectrum according to the step 4, so as to obtain the corrected LIBS detection characteristic spectral line intensity I of each samplejcMeasuring 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 establishing and correcting the characteristic spectral line intensity IjcA calibration curve between the reference value and the nutrient index content;
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;
and 7: the method comprises the steps of soil sample nutrient detection, wherein a sample to be detected is compressed and then placed in a sample groove in the left side of a sample cell assembly 31, spectrum data of the sample LIBS and NIRS are synchronously obtained by operating a software interface of a detection system through a touch screen 26, the chemical component content of each matrix of the sample is rapidly predicted by using a soil matrix NIRS detection model embedded in the software interface, the chemical component content of each matrix is substituted into a characteristic spectral line correction algorithm program, a correction value of the characteristic spectral line intensity of the sample to be detected is obtained, and finally the correction value of the characteristic spectral line intensity is substituted into a calibration curve embedded in the software program, so that the content of the nutrient to be detected of the soil sample is rapidly obtained.
Further, in step 1, the NIRS spectrum drift is corrected to 4 hours after each NIRS spectrum is continuously collected, the touch screen 26 is operated to drive the sample moving device 16 to move the standard white board 38 in the sample cell assembly 31 to the detection window of the sample stage 29, and 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 soils in different regions, and the main basis for selecting the matrix chemical substances with the significant difference in chemical component content in different soil samples is.
It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.
Claims (9)
1. A soil nutrient rapid detection system with LIBS and NIRS spectrum synchronous acquisition is characterized by comprising: 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 cell component (31) is closed and light-transmitting and is used for placing a sample to be detected;
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 mirror probe (43), wherein the M halogen lamps (44) are uniformly distributed on the light source support frame (41) at equal angles, the centers of the light sources are connected into a circle, and the optical fiber collimating mirror probe (43) is positioned on a vertical line where the center of the circle is located; m is more than or equal to 2;
the sample table (29) is provided with a hole, and the hole, the fiber collimator lens probe (43) and the optical assembly (19) are coaxial so as to ensure that the spectral data acquired by the LIBS acquisition device (3) and the NIRS acquisition device (13) come from the same sample.
2. The system for rapidly detecting soil nutrients synchronously acquired by LIBS and NIRS spectra as claimed in claim 1, wherein the diameter L of a circle formed by the centers of the light sources and the distance H from any one of the centers of the light sources to the upper surface of the light source support frame (41) satisfy L-2H; the distance S between the upper surface of the fiber collimator probe (43) and the lower bottom surface of the light source support frame (41) and the distance h between the center of any one light source and the lower bottom surface of the light source support frame (41) meet the condition 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 (41) and the diameter L of the circle meet that D is more than or equal to 1.2L and less than or equal to 1.6L.
3. The system for rapidly detecting soil nutrients through LIBS and NIRS spectrum synchronous collection 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) and the sample cell frame (37) form a sample cell with a closed bottom and light transmission, 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 system for rapidly detecting soil nutrients synchronously acquired by LIBS and NIRS spectra as claimed in claim 1, wherein the LIBS detection device (3) comprises a LIBS spectrometer (1), a laser (4), a digital delayer (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 delayer (6) through digital signal lines, the LIBS detection probe (21) is fixed on the 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. The LIBS and NIRS spectrum synchronous soil nutrient rapid detection system as claimed in claim 4, wherein the optical assembly (19) comprises an optical lens fixing bracket (20), a first focusing convex lens (34), a dichroic mirror (33) and a second focusing convex lens (32); wherein, the dichroic mirror (33) and the horizontal plane form an included angle of 45 degrees and are fixedly arranged in the middle of the optical lens fixing bracket (20), 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 (32) 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 system for rapid detection of soil nutrients with LIBS and NIRS spectral synchronization for collection as claimed in claim 4, wherein said system further comprises UP2A control board (27), a switching power supply (8) and a stepping motor driver (28);
wherein, the switching power supply (8) is UP respectively2The control board (27), the halogen lamp (44) and the stepping motor driver (28) provide direct current voltage; UP2The control board (27) is respectively connected with the LIBS spectrometer (1), the NIRS spectrometer (11) and the digital delayer (6), and UP2The GPIO output port of the control board (27) is connected with a stepping motor driver (28); the stepping motor driver (28) is connected with the stepping motor (17).
7. The system for rapidly detecting soil nutrients synchronously acquired by LIBS and NIRS spectra as claimed in 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. A soil nutrient rapid detection method synchronously acquired by LIBS and NIRS spectra is characterized by comprising the following steps:
s1, adding different matrix chemical substances into soil samples with the same known nutrient content by adopting a standard addition method to prepare different new samples; performing LIBS detection and NIRS detection on each new sample to obtain corresponding LIBS and NIRS spectral data;
s2, fitting linear relations between the contents of different matrix chemical substances and the characteristic spectral line intensities of the nutrients by taking the content of the matrix chemical substances as an independent variable and the characteristic spectral line intensities of the nutrients as a dependent variable based on the LIBS spectral data, and taking the slopes corresponding to the linear relations as matrix effect spectral line intensity correction coefficients 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 correction coefficient of each matrix effect spectral line intensity in S2 and the content of each predicted matrix chemical substance in S3; constructing a calibration curve between the corrected corresponding nutrient characteristic spectral line intensity and the nutrient content reference value;
s5, acquiring LIBS and NIRS spectral data of soil to be detected, predicting the content of each matrix chemical substance in the soil to be detected by using the spectral prediction model, and obtaining the corrected characteristic spectral line intensity of each nutrient in the soil to be detected by combining the correction coefficient of each matrix effect spectral line intensity; and obtaining the content of each nutrient in the soil to be detected according to each calibration curve.
9. The method for rapidly detecting soil nutrients through LIBS and NIRS spectrum synchronous acquisition as claimed in claim 8, wherein in S4, the corrected corresponding nutrient characteristic spectral line intensity is expressed as:
wherein, IjcFor corrected j-th nutrient line intensity, Ij0J-th nutrient characteristic spectral line intensity, k, directly obtained for LIBS detectionijCorrection factor for matrix effect line intensity of ith matrix chemical substance to jth nutrient, QNIRiAnd predicting the content of the ith matrix chemical substance for the spectrum prediction model, wherein n is the total number of the matrix chemical substance types generating the matrix effect.
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