A LIBS-NIR dual-spectrum integrated system and detection method for soil component detection

Abstract

The application belongs to the field of soil analysis and detection, and discloses a LIBS-NIR dual-spectrum integrated system and detection method for soil component detection. The system comprises a near-infrared light emitting unit, a first focusing lens, a beam splitter, a dichroic mirror, a second focusing lens, a third focusing lens and a NIR spectrometer. The near-infrared light emitting unit emits a near-infrared light beam which is incident into a soil sample after passing through the first focusing lens, the beam splitter, the dichroic mirror and the second focusing lens. The near-infrared spectrum signal enters the NIR spectrometer after passing through the second focusing lens, the dichroic mirror, the beam splitter and the third focusing lens. The system further comprises a pulsed laser, a fourth focusing lens, a fifth focusing lens and a LIBS spectrometer. The pulsed laser is incident into the same position of the soil sample through the dichroic mirror and the second focusing lens. The plasma emission spectrum signal is transmitted to the LIBS spectrometer through the fourth focusing lens and the fifth focusing lens. Through coaxial light path integrated design, the position consistency of the near-infrared spectrum and the LISB spectrum in the acquisition process is realized.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of soil analysis and detection, and more particularly relates to a LIBS-NIR dual-spectrum integrated system and detection method for soil component detection. BACKGROUND

[0002] Traditional soil analysis methods rely on chemical and physical analysis techniques in the laboratory, such as atomic absorption spectroscopy, inductively coupled plasma emission spectroscopy, and gas chromatography. These methods are accurate and precise, but often require complex sample pretreatment, and different detection indicators require different measurement instruments and methods, resulting in long detection time, high cost, and complex operation. Laser-induced breakdown spectroscopy (LIBS) and near-infrared spectroscopy (NIR) are two emerging spectral analysis techniques that have the advantages of rapidity, non-destructiveness, and simultaneous detection of multiple elements or components, and are gradually being applied to soil analysis and detection. LIBS uses the plasma emission spectrum generated by high-energy pulsed laser ablation of soil samples to obtain elemental information in the soil. NIR obtains molecular structure and composition information of organic matter and minerals in the soil through infrared absorption spectrum generated by near-infrared light irradiation of soil samples. However, soil is a complex natural matrix, and the diversity and interaction of its components often make it difficult for a single spectral technique to accurately detect its quality indicators.

[0003] A LIBS and NIR spectrum synchronous acquisition soil nutrient rapid detection system and method is disclosed in Chinese patent document CN114295604B, which uses NIR spectrum to predict soil organic matter, soil matrix information such as moisture, and then corrects LIBS spectrum to improve the prediction performance of soil nutrient elements. However, the detection system disclosed in this patent has two independent spectral systems, LIBS and NIR, distributed on both sides of the sample, which cannot obtain LIBS information and NIR information at the same position of the sample. In the detection process, NIR spectrum is only used to correct LIBS spectrum information, ignoring the relationship between NIR and LIBS spectra, and not realizing information fusion between spectral data. Finally, the system only detects soil nutrient elements, ignoring soil cation exchange capacity, physical composition, and other analysis indicators. SUMMARY

[0004] In view of the defects of the prior art, the purpose of the present application is to provide a LIBS-NIR dual-spectrum integrated system and detection method for soil component detection, aiming to realize rapid, efficient, and accurate analysis of chemical components and physical composition in soil.

[0005] To achieve the above-mentioned purpose, the present application provides a LIBS-NIR dual-spectrum integrated system for soil component detection, which comprises a near-infrared spectrum signal acquisition unit and a LIBS spectrum signal acquisition unit.

[0006] The near-infrared spectrum signal acquisition unit comprises: a near-infrared light emitting unit, a first focusing lens, a beam splitter, a dichroic mirror and a second focusing lens, and a third focusing lens and a NIR spectrometer, which are coaxially arranged in sequence along the near-infrared light propagation path; the near-infrared light beam emitted by the near-infrared light emitting unit is sequentially incident into the soil sample via the first focusing lens, the beam splitter, the dichroic mirror and the second focusing lens, and generates a near-infrared spectrum signal; the third focusing lens is arranged beside the beam splitter, and the near-infrared spectrum signal is sequentially transmitted to the NIR spectrometer via the second focusing lens, the dichroic mirror, the beam splitter and the third focusing lens.

[0007] The LIBS spectrum signal acquisition unit comprises: a pulsed laser, a fourth focusing lens, a fifth focusing lens and a LIBS spectrometer, which are arranged in sequence along the pulsed laser propagation path; the pulsed laser is used for emitting a pulsed laser, and the pulsed laser is sequentially incident into the same position of the soil sample irradiated by the near-infrared light beam via the dichroic mirror and the second focusing lens, and generates a plasma emission spectrum signal, and the plasma emission spectrum signal is sequentially transmitted to the LIBS spectrometer via the fourth focusing lens and the fifth focusing lens.

[0008] Compared with the prior art, the above technical scheme conceived by the present application can make the near-infrared light beam sequentially incident into the soil sample via the first focusing lens, the beam splitter, the dichroic mirror and the second focusing lens, and the pulsed laser emitted by the pulsed laser via the dichroic mirror and the second focusing lens into the same position on the soil sample, and then make the subsequently collected near-infrared spectrum signal and plasma emission spectrum signal be the signals at the same position of the soil sample, so that the integrated system is easy to operate, and the accurate collection of the two spectrum signals at the same position on the soil sample can be completed without additional operation.

[0009] Further, the first focusing lens is a non-spherical plano-convex lens, which is used for collimating the near-infrared light beam into a first parallel light beam; the mirror surface of the beam splitter forms a 45° angle with the propagation direction of the first parallel light beam, and is used for dividing the first parallel light beam into a transmitted light beam and a reflected light beam.

[0010] Further, the second focusing lens is a non-spherical plano-convex lens, the horizontal surface of which faces the soil sample, and is used for focusing the transmitted light beam to irradiate the soil sample, and is also used for collimating the near-infrared spectrum signal into a second parallel light beam to be incident into the dichroic mirror.

[0011] Further, the second parallel light beam is reflected by the dichroic mirror to obtain a near-infrared spectrum reflection signal, and an optical axis of the near-infrared spectrum reflection signal is perpendicular to an optical axis of the near-infrared light beam.

[0012] Further, the mirror surface of the dichroic mirror is at an angle of 45° with the propagation direction of the near-infrared light beam, and is at an angle of 90° with the mirror surface of the beam splitter, the dichroic mirror is used for filtering the near-infrared spectrum signal of the non-working wave band, and is also used for changing the propagation direction of the pulsed laser so as to be incident into the second focusing lens (5).

[0013] Further, the dichroic mirror is at an angle of 45° with the propagation direction of the pulsed laser emitted by the pulsed laser, and is used for reflecting the pulsed laser into the second focusing lens and focusing the pulsed laser by the second focusing lens to be incident into the soil sample.

[0014] Further, the dichroic mirror is a long-wave pass dichroic mirror.

[0015] Further, the beam splitter is a non-polarized beam splitting cube.

[0016] Further, the fourth focusing lens and the fifth focusing lens are two aspheric plano-convex lenses arranged coaxially, and the plane mirror surfaces of the two aspheric plano-convex lenses are arranged to face away from each other.

[0017] Further, the system further comprises a sample displacement platform and a digital signal generator, the digital signal generator is used for respectively controlling the emission of the near-infrared light, the pulsed laser and the collection of the near-infrared spectrum signal and the plasma emission spectrum signal, and the movement of the sample displacement platform; preferably, the system further comprises a data analysis unit, the data analysis unit is used for respectively reading and analyzing the near-infrared spectrum signal collected by the NIR spectrometer and the plasma emission spectrum signal collected by the LIBS spectrometer.

[0018] According to another aspect of the present application, a method for soil composition detection by using the LIBS-NIR dual spectrum integrated system for soil composition detection according to any one of the foregoing is also disclosed, and the method comprises the following steps:

[0019] S1 controlling the near-infrared light emission unit to emit a near-infrared light beam, the near-infrared light beam is sequentially reflected by the first focusing lens, the beam splitter, the dichroic mirror and the second focusing lens to be incident into the soil sample and to generate a near-infrared spectrum signal; and controlling the NIR spectrometer to collect the near-infrared spectrum signal sequentially reflected by the second focusing lens, the dichroic mirror, the beam splitter and the third focusing lens;

[0020] S2 controls the pulsed laser to emit pulsed laser light, which is sequentially emitted into the same position as the near-infrared light beam in step S1 via a dichroic mirror and a second focusing lens, and generates a plasma emission spectrum signal; control the LIBS spectrometer to collect the plasma emission spectrum signal emitted sequentially via the fourth focusing lens and the fifth focusing lens;

[0021] S3 adjusts the position of the soil sample irradiated by the light beam, and repeats steps S1 and S2 to obtain the near-infrared spectrum signal and the plasma emission spectrum signal at different positions of the soil sample;

[0022] S4 analyzes and processes multiple sets of near-infrared spectrum signals and plasma emission spectrum signals and makes predictions to determine the composition of the soil sample.

[0023] Overall, compared with the prior art, the above technical solutions conceived by the present application mainly have the following technical advantages:

[0024] 1. The present application realizes the consistency of laser-induced breakdown spectroscopy (LIBS) and near-infrared spectroscopy (NIR) in the acquisition process through highly integrated coaxial optical path design. Specifically, by skillfully integrating the focusing optical path system of pulsed laser and near-infrared light beam, the NIR spectroscopy technology and the LIBS system are integrated into one; in addition, the dichroic mirror can accurately filter and separate the near-infrared light beam and the near-infrared spectrum signal according to the specific working wavelength, ensuring that the two spectrum systems do not interfere with each other during data acquisition, significantly improving the efficiency and consistency of dual-spectrum data acquisition, and thus enhancing the reliability of fusion spectrum analysis.

[0025] 2. The present application breaks through the limitations of traditional single spectrum technology in soil quality detection. The near-infrared spectroscopy detection technology is used to obtain the molecular composition information of the soil sample, and the LIBS technology is used to ablate laser at the same position to generate plasma and collect its emission spectrum to obtain element composition information. Through this innovative dual-spectrum information acquisition method and subsequent fusion analysis, the LIBS element information and NIR molecular information in the sample are complementary and mutually verified, forming a comprehensive and collaborative detection of soil element composition and molecular composition, and improving the comprehensiveness and accuracy of soil analysis results. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 is a LIBS-NIR dual-spectrum integrated system for soil composition detection provided by embodiment 1;

[0027] Figure 2 is a method flowchart for soil composition detection using the LIBS-NIR dual-spectrum integrated system provided by embodiment 2.

[0028] In all the drawings, the same reference signs are used to represent the same elements or structures, wherein: 1 - near-infrared light emitting unit, 2 - first focusing lens, 3 - beam splitter, 4 - dichroic mirror, 5 - second focusing lens, 6 - third focusing lens, 7 - first signal collection optical fiber, 8 - NIR spectrometer, 9 - pulsed laser, 10 - fourth focusing lens, 11 - fifth focusing lens, 12 - second signal collection optical fiber, 13 - LIBS spectrometer, 14 - sample displacement platform, 15 - data analysis unit, 16 - digital signal generator. DETAILED DESCRIPTION

[0029] In order to make the purposes, technical solutions and advantages of the present application clearer, the present application is further described in detail below in combination with the drawings and examples. It should be understood that the specific examples described herein are only used to explain the present application and do not limit the present application.

[0030] In the description of the present application, it should be understood that the terms "center", "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and therefore cannot be understood as indicating or implying that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the present application.

[0031] In addition, the terms "first" and "second" are only for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the technical features indicated. Therefore, the features defined with "first" and "second" can explicitly or implicitly include one or more of the features. In the description of the present application, the meaning of "multiple" is two or more, unless otherwise explicitly specified and limited.

[0032] In the present application, unless otherwise explicitly specified and limited, the terms "mounting", "connection", "connection", "fixing" and the like should be understood broadly, for example, it can be fixedly connected, or it can be detachably connected, or it can be integrally connected; it can be mechanically connected, or it can be electrically connected; it can be directly connected, or it can be indirectly connected through an intermediate medium; it can be the communication inside two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0033] Example 1

[0034] To achieve the above-mentioned purposes, as Figure 1As shown, the present application provides a LIBS-NIR dual-spectrum integrated system for soil composition detection, which comprises a NIR spectrum acquisition device and a LIBS spectrum acquisition device, wherein the NIR spectrum acquisition device comprises: a NIR light emitting unit 1, a first focusing lens 2, a beam splitter 3, a dichroic mirror 4, and a second focusing lens 5, and a third focusing lens 6 and a NIR spectrometer 8 arranged coaxially in sequence along a NIR light propagation path; the NIR spectrometer 8 is connected with a first signal acquisition optical fiber 7;

[0035] The NIR light propagation path I is: the NIR light beam emitted by the NIR light emitting unit 1 is vertically incident into the soil sample after passing through the first focusing lens 2, the beam splitter 3, the dichroic mirror 4, and the second focusing lens 5 in sequence, and generates a NIR spectrum signal; the third focusing lens 6 is arranged beside the beam splitter 3, and the generated NIR spectrum signal is propagated to the first signal acquisition optical fiber 7 after passing through the second focusing lens 5, the dichroic mirror 4, the beam splitter 3, and the third focusing lens 6 in sequence; the core end face of the first signal acquisition optical fiber 7 collects the NIR spectrum signal and then transmits it into the NIR spectrometer 8.

[0036] In the embodiment, the NIR light emitting unit 1 is a halogen tungsten lamp, the working wavelength of which is 360nm-2500nm; the NIR spectrometer adopts a two-stage refrigeration InGaAs detector, the number of pixel points of which is 512, and the working wavelength range is 900nm-2500nm; the first signal acquisition optical fiber 7 is a fiber cable with a core diameter of 400μm; in other preferred embodiments, the process parameters of the halogen tungsten lamp, the NIR spectrometer, and the first signal acquisition optical fiber 7 can also be freely selected according to the actual detection situation.

[0037] In the embodiment, the first focusing lens 2 is a non-spherical plano-convex lens made of calcium fluoride material, the working wavelength of which is 200nm-8000nm, and it is used to collimate the NIR light emitted by the halogen tungsten lamp into parallel light.

[0038] The beam splitter 3 is arranged in the propagation direction of the NIR light beam, and the mirror surface thereof forms a 45° angle with the NIR light beam incident therein; the beam splitter 3 can also divide the NIR light beam incident therein into a transmitted light beam and a reflected light beam, the reflected light beam is filtered by the beam splitter 3, and the transmitted light beam transmits through the beam splitter 3 to the dichroic mirror 4; the beam splitter 3 can also divide the NIR spectrum signal generated after the NIR light beam irradiates the soil sample (i.e., the second parallel light beam collimated by the second focusing lens 5) to obtain a reflected NIR spectrum reflection signal, and the optical axis of the reflected NIR spectrum reflection signal is perpendicular to the optical axis of the NIR light beam emitted by the halogen tungsten lamp; specifically, the beam splitter 3 is a non-polarized beam splitting cube, and the reflection and transmission ratio is 50:50; the main advantages of this beam splitter include non-polarization, uniform beam splitting, high precision, low reflection loss, and high laser damage threshold.

[0039] The aforementioned dichroic mirror 4 is arranged between the beam splitter 3 and the second focusing lens 5, the mirror surface of the dichroic mirror 4 is at an angle of 45° with the transmitted light beam, and the dichroic mirror 4 separates the near-infrared light beam (transmitted light beam) incident therein according to the wavelength, wherein the near-infrared light beam in the non-working wavelength range is reflected and filtered, and the near-infrared light beam in the working wavelength range is transmitted; specifically, the dichroic mirror 4 is a long-wave dichroic mirror, which has a reflectivity greater than 98% in the wavelength range of 350 nm to 900 nm, and a transmittance greater than 93% in the wavelength range of 900 nm to 2500 nm. The long-wave dichroic mirror can provide high reflectivity and transmittance for the specified wavelength range, ensuring efficient use of light energy, while achieving beam isolation in the required wavelength range.

[0040] More specifically, the dichroic mirror 4 in the embodiment is used to filter out near-infrared light with a wavelength less than 900 nm, and to transmit near-infrared light with a wavelength of 900 nm to 2500 nm; it is also used to reflect pulsed laser light with a wavelength of 532 nm to change the direction of laser propagation; and it is also used to filter out stray light interference with a wavelength less than 900 nm, and to transmit near-infrared absorption spectrum signals with a wavelength of 900 nm to 2500 nm.

[0041] The aforementioned second focusing lens 5 is an aspherical plano-convex lens, with its horizontal surface facing the soil sample, for focusing the transmitted light beam to irradiate the soil sample, and for collimating the near-infrared spectrum signal into a second parallel light beam to enter the dichroic mirror 4; specifically, the second focusing lens 5 is also an aspherical plano-convex lens made of calcium fluoride, which has a high laser damage threshold, allowing it to withstand high-power laser irradiation, and has low dispersion, which helps to reduce chromatic aberration in the imaging process. The working wavelength range of the second focusing lens in the embodiment is 200 nm to 8000 nm, the diameter is selected to be 25.4 mm, and the focal length is selected to be 75 mm. In other embodiments, the diameter, focal length, and other parameters of the second focusing lens can also be customized according to actual needs.

[0042] The aforementioned NIR spectrometer 8 uses a two-stage cooled InGaAs detector, with a pixel count of 512 and a working wavelength range of 900 nm to 2500 nm. The NIR spectrometer 8 is also connected to a first signal acquisition optical fiber 7, which has a core diameter of 400 μm.

[0043] The LIBS spectrum acquisition device includes a pulsed laser 9, a fourth focusing lens 10, a fifth focusing lens 11, and a LIBS spectrometer 13 arranged in sequence along the pulsed laser propagation path. The LIBS spectrometer 13 is connected to a second signal acquisition optical fiber 12, and the core end face of the second signal acquisition optical fiber 12 is used to collect the plasma emission spectrum signal emitted by the fifth focusing lens 11.

[0044] The beam propagation path II of the pulsed laser is: the pulsed laser 9 is used for emitting pulsed laser, the pulsed laser is sequentially transmitted into the same position as the near-infrared light beam into the soil sample via the dichroic mirror 4 and the second focusing lens 5, and the plasma emission spectrum signal is generated; the plasma emission spectrum signal is sequentially transmitted to the second signal collection optical fiber 7 via the fourth focusing lens 10 and the fifth focusing lens 11, and is collected via the second signal collection optical fiber 7 and then transmitted to the LIBS spectrometer 13.

[0045] In the embodiment, the aforementioned pulsed laser 9 is a high-energy Nd:YAG nanosecond pulse Q-switched laser, and the laser wavelength is 532 nm; the aforementioned dichroic mirror 4 is at an angle of 45° with the propagation direction of the pulsed laser emitted by the pulsed laser 9, and is used for reflecting the pulsed laser into the second focusing lens 5 and focusing the pulsed laser via the second focusing lens 5 to generate the plasma emission spectrum signal into the soil sample.

[0046] In the embodiment, the fourth focusing lens 10 and the fifth focusing lens 11 are two aspheric plano-convex lenses coaxially arranged, and the plane mirrors of the two aspheric plano-convex lenses are arranged to face away from each other; the aforementioned fourth focusing lens 10 is used for collimating the plasma emission spectrum signal into the plasma parallel spectrum signal, and the aforementioned fifth focusing lens 11 is used for focusing the plasma parallel spectrum signal into the core end face of the second signal collection optical fiber 12.

[0047] Specifically, the fourth focusing lens 10 and the fifth focusing lens 11 in the embodiment are both aspheric plano-convex lenses made of calcium fluoride, the working wavelength is selected to be 200 nm-8000 nm, the diameter is selected to be 25.4 mm, and the focal length is selected to be 75 mm.

[0048] The LIBS-NIR dual-spectrum integrated system for soil component detection provided in the embodiment further comprises a sample displacement platform 14 and a digital signal generator 16, the digital signal generator 16 is electrically connected with the sample displacement platform 14, and is used for controlling the sample displacement platform 14 to move to adjust the soil sample carried on the sample displacement platform 14, and the digital signal generator 16 is also connected with the halogen tungsten lamp, the pulsed laser 9, the NIR spectrometer 8 and the LIBS spectrometer 13 respectively, and is used for controlling the emission of the near-infrared light and the pulsed laser and the collection of the near-infrared spectrum signal and the plasma emission spectrum signal; preferably, the system further comprises a data analysis unit 15, the data analysis unit 15 is a computer, and the computer is used for reading the near-infrared spectrum signal collected by the NIR spectrometer 8 and the plasma emission spectrum signal collected by the LIBS spectrometer 13 respectively, and performing subsequent data fusion analysis and outputting the soil component detection result.

[0049] The person skilled in the art should know that the digital signal generator 16 used in the embodiment is further improved in precision and stability of the control signal by adjusting the frequency, amplitude, phase and waveform through the control circuit.

[0050] Compared with the prior art, the highly integrated coaxial light path design ensures the consistency of the sample position when collecting the LIBS spectrum and the NIR spectrum; the present application ingeniously integrates the NIR spectrum system and the LIBS system into one by designing the pulsed laser and the near-infrared light beam to share one set of focusing light path system; in addition, the dichroic mirror is used to filter and separate the near-infrared light beam according to the working wavelength, so as to ensure that the two sets of spectrum systems do not interfere with each other during the collection process, further improve the collection efficiency and consistency of the dual-spectrum data, and ensure the reliability of the subsequent fused spectrum analysis.

[0051] Embodiment 2

[0052] The present embodiment provides a method for soil component detection using the LIBS-NIR dual-spectrum integrated system for soil component detection as any one of the preceding embodiments, as shown in the figure, the method comprises the following steps: Figure 2

[0053] S1 determines the soil test index and collects soil samples with a certain concentration gradient; 2g of soil sample is weighed and pressed into a sheet as a standard soil sample; the near-infrared light emitting unit 1 is controlled to emit a near-infrared light beam, which is sequentially incident into the soil sample through the first focusing lens 2, the beam splitter 3, the dichroic mirror 4 and the second focusing lens 5 and generates a near-infrared spectrum signal; the NIR spectrometer 8 is controlled to collect the near-infrared spectrum signal which is sequentially emitted through the second focusing lens 5, the dichroic mirror 4, the beam splitter 3 and the third focusing lens 6;

[0054] Specifically, the near-infrared light beam is collimated into parallel light by the first focusing lens 2; the beam splitter 3 divides the parallel light into a transmitted light beam and a reflected light beam, wherein the reflected light beam is filtered and the transmitted light beam is transmitted; the dichroic mirror 4 separates the near-infrared light beam according to the wavelength, wherein the near-infrared light beam in the non-working wavelength range is reflected and filtered, and the near-infrared light beam in the working wavelength range is transmitted, and finally the transmitted near-infrared light beam is focused by the second focusing lens 5 to irradiate the sample to generate a near-infrared spectrum signal.

[0055] S2 controls the pulsed laser 9 to emit a pulsed laser, which is sequentially incident into the same position as the near-infrared light beam in step S1 into the soil sample through the dichroic mirror 4 and the second focusing lens 5, and generates a plasma emission spectrum signal; the LIBS spectrometer 13 is controlled to collect the plasma emission spectrum signal which is sequentially emitted through the fourth focusing lens 10 and the fifth focusing lens 11;

[0056] ​Specifically, the pulsed laser is reflected by the dichroic mirror 4 into the second focusing lens 5, and the light path of the pulsed laser between the dichroic mirror 4 and the second focusing lens 5 coincides with the light path of the near-infrared light beam between the dichroic mirror 4 and the second focusing lens 5 at the same time of collection, so that the focusing focal point of the pulsed laser irradiated to the surface of the soil sample coincides with the focusing focal point of the near-infrared light beam; the generated plasma emission spectrum signal is collimated into parallel light after entering the fourth focusing lens 10, and the parallel light signal is focused by the fifth focusing lens 11 and then collected by the core end face of the second signal collection optical fiber 12 and transmitted to the LIBS spectrometer.

[0057] S3 changes the position of the soil sample irradiated by the light beam and repeats steps S1 and S2 to obtain near-infrared spectrum signals and plasma emission spectrum signals at different positions of the soil sample.

[0058] Specifically, the translation of the sample displacement platform is controlled by the digital signal generator 16, so as to change the position of the soil sample carried thereon, so that the position irradiated by the near-infrared light and the pulsed laser on the soil sample is different each time.

[0059] S4 analyzes and processes a plurality of groups of near-infrared spectrum signals and plasma emission spectrum signals to determine the components of the soil sample; specifically, the preprocessed LIBS spectrum (plasma emission spectrum signal) and NIR spectrum (near-infrared spectrum signal) are respectively input into the corresponding branches of the double-branch convolutional neural network, the model is trained in combination with the true content of the soil test index, a quantitative prediction model is established, and the prediction result of the soil component is obtained by using the prediction model.

[0060] Those skilled in the art can easily understand that the above description is only a preferred embodiment of the present application, and is not intended to limit the present application, and any modification, equivalent replacement and improvement made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A LIBS-NIR dual-spectroscopy integrated system for soil composition detection, characterized in that, The system comprises a near-infrared spectrum acquisition unit and a LIBS spectrum acquisition unit; The near-infrared spectrum acquisition unit comprises a near-infrared light emitting unit (1), a first focusing lens (2), a beam splitter (3), a dichroic mirror (4), a second focusing lens (5), a third focusing lens (6) and a NIR spectrometer (8) arranged coaxially along the propagation path of the near-infrared light beam in sequence; the near-infrared light beam emitted by the near-infrared light emitting unit (1) is sequentially transmitted through the first focusing lens (2), the beam splitter (3), the dichroic mirror (4) and the second focusing lens (5) and then is incident into the soil sample, and a near-infrared spectrum signal is generated; the third focusing lens (6) is arranged beside the beam splitter (3), and the near-infrared spectrum signal is sequentially transmitted through the second focusing lens (5), the dichroic mirror (4), the beam splitter (3) and the third focusing lens (6) and then is transmitted to the NIR spectrometer (8); The LIBS spectrum acquisition unit comprises a pulsed laser (9), a fourth focusing lens (10), a fifth focusing lens (11) and a LIBS spectrometer (13) arranged along the propagation path of the pulsed laser in sequence; the pulsed laser (9) is used for emitting a pulsed laser, the pulsed laser is sequentially transmitted through the dichroic mirror (4) and the second focusing lens (5) and then is incident into the same position of the soil sample irradiated by the near-infrared light beam, and a plasma emission spectrum signal is generated, the plasma emission spectrum signal is sequentially transmitted through the fourth focusing lens (10) and the fifth focusing lens (11) and then is transmitted to the LIBS spectrometer (13).

2. The LIBS-NIR dual-spectroscopy integrated system for soil composition detection according to claim 1, wherein, The first focusing lens (2) is a non-spherical plano-convex lens, which is used for collimating the near-infrared light beam into a first parallel light beam; the mirror surface of the beam splitter (3) forms a 45° angle with the propagation direction of the first parallel light beam, and the beam splitter (3) is used for dividing the first parallel light beam into a transmitted light beam and a reflected light beam.

3. The LIBS-NIR dual-spectroscopy integrated system for soil composition detection according to claim 2, wherein, The second focusing lens (5) is a non-spherical plano-convex lens, the horizontal surface of which faces the soil sample, which is used for focusing the transmitted light beam and irradiating the soil sample, and is also used for collimating the near-infrared spectrum signal into a second parallel light beam and then transmitting the second parallel light beam into the dichroic mirror (4); preferably, the second parallel light beam is reflected into the beam splitter (3) through the dichroic mirror (4), and the optical axis of the reflected near-infrared spectrum signal is perpendicular to the optical axis of the near-infrared light beam.

4. The LIBS-NIR dual spectroscopy integrated system for soil composition detection according to claim 1, wherein, The mirror surface of the dichroic mirror (4) forms a 45° angle with the propagation direction of the near-infrared light beam, and forms a 90° angle with the mirror surface of the beam splitter (3), the dichroic mirror (4) is used for filtering the near-infrared light beam and the near-infrared spectrum signal in the non-working wave band, and is also used for changing the propagation direction of the pulsed laser so that the pulsed laser is incident into the second focusing lens (5).

5. The LIBS-NIR dual spectroscopy integrated system for soil composition detection according to claim 1, wherein, The dichroic mirror (4) forms a 45° angle with the propagation direction of the pulsed laser emitted by the pulsed laser (9), which is used for reflecting the pulsed laser into the second focusing lens (5) and then focusing the pulsed laser through the second focusing lens (5) and then incident into the soil sample.

6. The LIBS-NIR dual spectroscopy integrated system for soil composition detection of claim 1, wherein, The dichroic mirror (4) is a long-wave dichroic mirror.

7. The LIBS-NIR dual spectroscopy integrated system for soil composition detection according to claim 1, wherein, The beam splitter (3) is a non-polarized beam splitting cube.

8. The LIBS-NIR dual spectroscopy integrated system for soil composition detection of claim 1, wherein, The fourth focusing lens (10) and the fifth focusing lens (11) are two aspheric plano-convex lenses arranged coaxially, and the plane mirrors of the two are arranged away from each other.

9. The LIBS-NIR dual spectroscopy integrated system for soil composition detection according to claim 1, wherein, The system further comprises a sample displacement platform (14) and a digital signal generator (16) for controlling the movement of the sample displacement platform (14), the emission of the near-infrared light and the pulsed laser, and the collection of the near-infrared spectral signal and the plasma emission spectral signal, respectively; preferably, the system further comprises a data analysis unit (15) for reading and analyzing the near-infrared spectral signal collected by the NIR spectrometer (8) and the plasma emission spectral signal collected by the LIBS spectrometer (13), respectively.

10. A method for soil composition detection using the LIBS-NIR dual-spectroscopy integrated system according to any one of claims 1-9, characterized in that, The method comprises the following steps: S1 controlling the near-infrared light emission unit (1) to emit a near-infrared light beam, the near-infrared light beam being sequentially incident into the soil sample via the first focusing lens (2), the beam splitter (3), the dichroic mirror (4) and the second focusing lens (5) and generating a near-infrared spectral signal; controlling the NIR spectrometer (8) to collect the near-infrared spectral signal sequentially emitted via the second focusing lens (5), the dichroic mirror (4), the beam splitter (3) and the third focusing lens (6); S2 controlling the pulsed laser (9) to emit a pulsed laser, the pulsed laser being sequentially incident into the same position in the soil sample as the near-infrared light beam in step S1 via the dichroic mirror (4) and the second focusing lens (5) and generating a plasma emission spectral signal; controlling the LIBS spectrometer (13) to collect the plasma emission spectral signal sequentially emitted via the fourth focusing lens (10) and the fifth focusing lens (11); S3 changing the position of the soil sample irradiated by the light beam and repeating steps S1 and S2 to obtain the near-infrared spectral signal and the plasma emission spectral signal at different positions of the soil sample; S4 analyzing and processing the near-infrared spectral signal and the plasma emission spectral signal of multiple groups of soil samples and predicting the composition of the soil sample.

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