Soil respiration monitoring device and method based on tunable semiconductor laser absorption

Abstract

The invention relates to the technical field of soil respiration monitoring, and discloses a soil respiration monitoring device and method based on tunable semiconductor laser absorption.The device comprises a movable base which is hollow, the top of the base is fixedly connected with a top plate through a support, and a data controller is installed at the top of the base; and a plurality of breathing chambers are arranged between the base and the top plate. According to the soil respiration monitoring device and method based on tunable semiconductor laser absorption, the communication unit is arranged and used for controlling the detection end of the spectrum detection unit, so that the detection end of the spectrum detection unit is selectively connected with one respiration chamber or is sequentially connected with other respiration chambers; according to the soil respiration monitoring system, internal detection work of a single respiration chamber or internal detection work of multiple respiration chambers is formed, and the soil respiration monitoring accuracy can be further improved by calculating the average value of the internal detection data of the multiple respiration chambers.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of soil respiration monitoring, in particular to a soil respiration monitoring device and method based on tunable semiconductor laser absorption. BACKGROUND

[0002] Soil respiration refers to the process of organic carbon in soil being decomposed into carbon dioxide by microorganisms and roots and released into the atmosphere, and is an important part of the carbon cycle of terrestrial ecosystems. Accurate monitoring of soil respiration rate is of great significance for assessing ecosystem carbon budget, studying climate change and formulating carbon management policies.

[0003] Currently, soil respiration monitoring mainly uses a closed gas chamber measurement method. This method measures the change in carbon dioxide concentration in the gas chamber per unit time by covering a closed box on the soil surface, combines linear or exponential fitting models to calculate the carbon dioxide flux on the soil surface, and thus represents the soil respiration rate. However, this method has the following significant defects:

[0004] Concentration gradient decay problem: As the measurement time increases, the carbon dioxide concentration in the closed gas chamber gradually increases, resulting in a decrease in the carbon dioxide concentration gradient between the soil surface and the gas chamber, thus underestimating the actual soil respiration rate. This "concentration inhibition effect" limits the continuous monitoring ability of the closed gas chamber, making it difficult to achieve long-term and high-precision soil respiration observation.

[0005] Pressure disturbance error: During the placement of the gas chamber, improper operation or environmental changes may cause pressure differences inside and outside the gas chamber, thereby interfering with the gas exchange process between the soil and the atmosphere, and introducing significant errors. In addition, insufficient sealing of the gas chamber or uneven ground can exacerbate this problem.

[0006] Spatial heterogeneity limitation: Traditional methods usually use single-point measurement, which is difficult to reflect the spatial variability of soil respiration, and frequent replacement of measurement points will increase the labor cost and disturbance to the soil environment.

[0007] To solve the above problems, laser spectroscopy technology (such as tunable diode laser absorption spectroscopy technology, TDLAS) has been gradually applied to the field of trace gas monitoring due to its high sensitivity, high selectivity and non-contact measurement advantages. TDLAS technology analyzes the absorption characteristics of gas molecules to specific wavelength laser to achieve rapid and accurate measurement of carbon dioxide concentration. However, existing soil respiration monitoring devices based on TDLAS still have the following shortcomings:

[0008] Low system integration: Most devices are single-machine designs, lack multi-point synchronous monitoring capability, and are difficult to meet the needs of large-scale ecological research.

[0009] Lack of automation: The operation of air chamber lifting, point switching and other operations depends on manual intervention, which is low in efficiency and easy to introduce human error.

[0010] Poor environmental adaptability: Complex terrain (such as weeds, stones) will interfere with the adhesion of the air chamber to the soil, affecting the measurement accuracy.

[0011] Therefore, there is an urgent need for an integrated, automated and complex environment-adaptive soil respiration monitoring device to overcome the limitations of traditional methods and achieve high-precision, long-time and multi-point soil respiration monitoring. SUMMARY

[0012] (1) Technical problems solved

[0013] In view of the deficiencies of the prior art, the present application provides a soil respiration monitoring device and method based on tunable semiconductor laser absorption. By providing a communication unit, the detection end of the spectrum detection unit is controlled, so that the detection end of the spectrum detection unit is selectively connected to one of the respiration chambers, or sequentially connected to other respiration chambers, forming single respiration chamber internal detection work or multiple respiration chamber internal detection work. By calculating the average value of the detection data in multiple respiration chambers, the accuracy of soil respiration monitoring can be further improved. The problem of gradually decreasing carbon dioxide concentration gradient between soil surface and air chamber with increasing carbon dioxide concentration in the air chamber, which leads to underestimated measurement value, resulting in that the sealed air chamber cannot monitor soil respiration for a long time, and the pressure difference between the inside and outside of the air chamber when the air chamber is placed in the soil, thereby causing a large error in the calculation of soil carbon flux.

[0014] (2) Technical solutions

[0015] To achieve the above purpose, the present application provides the following technical solutions: a soil respiration monitoring device based on tunable semiconductor laser absorption, comprising a movable base, and the base is hollow, a top plate is fixedly connected to the top of the base through a support, a data controller is installed on the top of the base, a plurality of respiration chambers are arranged between the base and the top plate, and a plurality of through holes, extraction ports and circulation ports are arranged on the top of each respiration chamber.

[0016] A spectrum detection unit is arranged on the top of the top plate.

[0017] A communication unit is arranged on the bottom of the top plate for controlling the collection end and circulation end of the spectrum detection unit, and the communication unit is used to control the connection of the collection end and circulation end of the spectrum detection unit with the extraction port and circulation port of one of the respiration chambers, so as to form a detection work of the carbon dioxide in the different respiration chambers.

[0018] The base is provided with a lifting unit for lifting driving one or more breathing chambers.

[0019] Preferably, the communication unit comprises two connecting mouths and a transmission member for driving the two connecting mouths transversely and up and down;

[0020] The bottom end of each of the two connecting mouths is provided in a tapered shape, and the two connecting mouths are fixedly communicated with the collection end and the circulation end of the spectrum detection unit through telescopic hoses.

[0021] Preferably, the transmission member comprises a transmission block slidingly connected to the bottom of the top plate through a guide rail frame, both sides of the transmission block are connected with guide rods, and the bottom ends of the two guide rods are fixedly connected with the two connecting mouths respectively.

[0022] The bottom of the top plate is fixedly connected with a first motor, the output shaft of the first motor is fixedly connected with a first screw rod, and the first screw rod is internally screwed with the transmission block.

[0023] Preferably, the two guide rods are slidingly connected with the transmission block in an up-and-down sliding manner, each of the two connecting mouths is fixedly connected with a guide shaft frame, both sides of the bottom of the top plate are fixedly connected with guide frames, a plurality of V-shaped recesses are arranged on the two guide frames, and one end of each of the two guide shaft frames is in contact with the top of each of the two guide frames.

[0024] Preferably, the lifting unit comprises a driving member and two auxiliary members, the two auxiliary members are connected with the plurality of breathing chambers respectively, and the driving member is used for lifting driving one or more breathing chambers through the two auxiliary members.

[0025] The method of the soil respiration monitoring device based on tunable semiconductor laser absorption comprises the following steps:

[0026] S1, moving the integrated monitoring device to the area to be detected, according to the actual monitoring requirement, lifting driving one or more breathing chambers through the lifting unit, so that one or more breathing chambers are in contact with the ground, then connecting the detection end of the spectrum detection unit with one or other breathing chamber through the communication assembly, and performing monitoring work through the spectrum detection unit;

[0027] The spectrum detection unit is composed of a light source signal generating device, a CO2 concentration collecting device, and a data collecting and processing module.

[0028] S2, when the soil carbon flux online monitoring work is initiated, the CO2 concentration in the soil respiration chamber is the same as the CO2 concentration in the environment at this time, the initial concentration at this time is measured and recorded as C 标定 ;

[0029] S3, starting the light source signal generating device in the spectrum detection unit, and then based on the laser spectrum technology, combining the CO2 concentration collecting device to measure the peak value h of the second harmonic signal of the CO2 gas in the soil respiration cavity at the initial time 标定 ;

[0030] S4, continuously monitoring to obtain the measured peak value h of the second harmonic signal of the CO2 gas in the soil respiration cavity 实测 ;

[0031] S5, substituting the obtained data into the following calculation formula to obtain the measured CO2 concentration C 实测 , and the specific calculation formula is:

[0032]

[0033] Among them, F C is the soil CO2 flux; v is the total volume of the respiration chamber; P0 is the initial pressure measured by the instrument, R is the gas constant; S is the surface area of the collar; T0 is the initial temperature measured, is the initial change rate of the CO2 molar fraction.

[0034] Preferably, the light source signal generating device is composed of a DFB laser, a laser wavelength driving signal module, a power amplification module and a laser coupling module;

[0035] The DFB laser is used to generate laser of certain frequency, and the laser wavelength driving signal module is used to generate modulation current signal with uniform amplitude;

[0036] The power amplification module adopts a Ytterbium amplifier to amplify the laser power;

[0037] The laser coupling module is used to couple the output laser of the laser into the next optical fiber through the optical fiber and the flange.

[0038] Preferably, the CO2 concentration collecting device is composed of an optical path multiple reflection structure, an optical-electric signal conversion, an electric signal amplification and an electric signal transmission module; the optical path multiple reflection structure is used for collecting the CO2 concentration absorption spectrum signal.

[0039] Preferably, the data collection and processing module is composed of a signal receiving module, a CO2 concentration inversion module, a CO2 flux inversion module and a result output module.

[0040] (Three) beneficial effects

[0041] Compared with the prior art, the present application provides a soil respiration monitoring device and method based on tunable semiconductor laser absorption, which has the following beneficial effects:

[0042] The present application is used for controlling the detection end of the spectrum detection unit by the setting of the communication unit, so that the detection end of the spectrum detection unit is selectively connected with one of the breathing chambers or sequentially connected with other breathing chambers, forming single breathing chamber internal detection work or multiple breathing chamber internal detection work, and the accuracy of soil respiration monitoring can be further improved by calculating the average value of the detection data in multiple breathing chambers, solving the problems that as the carbon dioxide concentration in the gas chamber increases, the carbon dioxide concentration gradient between the soil surface and the gas chamber gradually decreases, the measured value is underestimated, the closed gas chamber cannot monitor soil respiration for a long time, and the pressure difference between the inside and outside of the gas chamber when the gas chamber is placed in the soil, thereby causing large errors in the calculation of soil carbon flux.

[0043] The present application can drive two auxiliary parts by the setting of the driving part, so that the two auxiliary parts drive one or more breathing chambers, and the lifting driving work of different number of breathing chambers is realized, meeting the monitoring work of different needs of the monitoring personnel and improving the adaptability of different position monitoring.

[0044] The present application can process the position to be monitored on the ground by the setting of the processing assembly, preventing the ground unevenness, weeds, stones and the like from interfering with the breathing chamber and thereby affecting the soil respiration monitoring effect; by elastically connecting the two toggle blocks at the two ends of the movable shaft, when the arc-shaped shovel plate is used for pre-processing the ground in transverse movement, the corresponding breathing chamber can be simultaneously moved downward to form soil respiration monitoring work, ensuring that the corresponding breathing chamber can automatically contact the processed ground after the ground is pre-processed, improving the orderliness of the ground pre-processing and the breathing chamber lowering operation, and when a small number of breathing chambers are used, the arc-shaped shovel plate can be used for local pre-processing work of the ground, further improving the functionality and practicability of the ground pre-processing. BRIEF DESCRIPTION OF DRAWINGS

[0045] Figure 1 It is a structural schematic view of the soil respiration monitoring device based on the tunable semiconductor laser absorption of the present application;

[0046] Figure 2 It is a rear view of the soil respiration monitoring device based on the tunable semiconductor laser absorption of the present application;

[0047] Figure 3 It is a structural schematic view of the base of the present application;

[0048] Figure 4 It is a combination schematic view of the communication unit and the plurality of breathing chambers of the present application;

[0049] Figure 5 It is a structural schematic view of the communication unit of the present application;

[0050] Figure 6 Partial schematic diagram of the communication unit of the present application;

[0051] Figure 7 Combined schematic diagram of several breathing chambers of the present application;

[0052] Figure 8 Structural top view of the base of the present application;

[0053] Figure 9 Structural schematic diagram of the processing assembly of the present application;

[0054] Figure 10 Structural schematic diagram of the spectral detection unit of the present application;

[0055] Figure 11 Schematic diagram of the data acquisition and processing flow of the present application;

[0056] Figure 12 Schematic diagram of the linear relationship between the carbon dioxide concentration value and the second harmonic signal peak value of the present application.

[0057] In the figure: 1, base; 2, top plate; 3, data controller; 4, breathing chamber; 5, spectral detection unit;

[0058] 6, communication unit; 61, connecting mouth; 62, guide rail frame; 63, transmission block; 64, guide rod; 65, first motor; 66, first lead screw; 67, guide shaft frame; 68, guide frame; 69, V-shaped recess;

[0059] 7, lifting unit; 71, second motor; 72, second lead screw; 73, sliding frame; 74, metal sliding block; 75, magnet block; 76, transmission frame; 77, sliding shaft; 78, push block;

[0060] 8, processing assembly; 81, guide frame; 82, movable shaft; 83, arc-shaped shovel plate; 84, telescopic column; 85, sliding block. DETAILED DESCRIPTION

[0061] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0062] Embodiment 1:

[0063] Refer to the accompanying drawings Figures 1-12, based on tunable semiconductor laser absorption soil respiration monitoring device, including the movable base 1, and the base 1 is hollow, the top of the base 1 is fixedly connected with the top plate 2 through the support, the top of the base 1 is provided with a data controller 3, the base 1 and the top plate 2 are provided with a plurality of breathing chambers 4, the top of the plurality of breathing chambers 4 is provided with a plurality of through holes, and the extraction port and the circulation port are arranged;

[0064] The data controller 3 adopts the control equipment in the prior art, is used for controlling the soil respiration monitoring device, and is internally integrated with a control module, a signal processing module and a wireless communication and display module; and the number of the breathing chambers 4 can be set according to actual conditions, and the more the number of the breathing chambers 4, the higher the accuracy after detection;

[0065] It should be noted that the top of the breathing chamber 4 is provided with a plurality of through holes, which can ensure that the carbon dioxide in the soil can be smoothly discharged from below, without affecting its diffusion;

[0066] Mainly to avoid when the breathing chamber 4 is in a closed air chamber, the carbon dioxide is not conducive to discharge from below; according to the concentration diffusion principle, when the concentration reaches a certain value, the carbon dioxide below cannot diffuse outward due to the excessive concentration accumulation above;

[0067] To ensure that the cavity is in full contact with the ground, the soil respiration cavity bottom surface and the soil contact part are provided with a pressure sensor and a current sensor;

[0068] Through the extraction port and the circulation port arranged at the top of the breathing chamber 4, since it is not measured at one time, a concentration change and a time change factor are needed, and the change rate can be understood by comparing the two, so as to facilitate the measurement of the circulating air flow;

[0069] After understanding the change rate, the carbon dioxide flux can be measured through the corresponding calculation formula;

[0070] Solve the problem that when the gas is not circulating, if the gas only flows to one side, its pressure will become larger and larger, and the larger the pressure, the more difficult the gas diffusion, so that the monitoring work cannot be formed.

[0071] The top of the top plate 2 is provided with a spectrum detection unit 5;

[0072] As shown in Figure 10 The spectrum detection unit 5 includes a pump, a flow controller, a pressure controller, a needle valve, a collimator, a long optical path gas absorption cell, a DFB laser, a photodetector, a data collector, a light source signal generating device, a PC and a driving and control unit;

[0073] The bottom of the top plate 2 is provided with a communication unit 6 for controlling the collection end and the circulation end of the spectrum detection unit 5, and the communication unit 6 is used to control the connection of the collection end and the circulation end of the spectrum detection unit 5 with the extraction port and the circulation port of one of the breathing chambers 4, so as to form the detection work of the carbon dioxide in the different breathing chambers 4;

[0074] Through the setting of the communication unit 6, the detection end of the spectrum detection unit 5 is controlled to be selectively connected with one of the breathing chambers 4 or sequentially connected with other breathing chambers 4, so as to form the detection work in a single breathing chamber 4 or the detection work in multiple breathing chambers 4, and the average value of the detection data in the multiple breathing chambers 4 can be calculated, so as to further improve the accuracy of the soil respiration monitoring.

[0075] The base 1 is provided with a lifting unit 7 for lifting driving one or more breathing chambers 4;

[0076] Through the setting of the lifting unit 7, one or more breathing chambers 4 are lifted and driven, so as to be in contact with the ground, to form soil respiration monitoring work at one or more positions, so as to improve the accuracy of the detection and reduce the error in the detection.

[0077] Referring to the accompanying drawings Figures 4 to 7 The communication unit 6 includes two connecting mouths 61 and a transmission member for driving the two connecting mouths 61 transversely and upward and downward;

[0078] Through the setting of the transmission member, the two connecting mouths 61 are driven transversely and upward and downward, so as to be communicated with the breathing chambers 4 at different positions, to form soil respiration monitoring work at different or multiple positions;

[0079] The bottom end of each of the two connecting mouths 61 is provided in a conical shape, and the two connecting mouths 61 are fixedly communicated with the collection end and the circulation end of the spectrum detection unit 5 through the flexible hoses;

[0080] Through the fixed communication of the two connecting mouths 61 with the collection end and the circulation end of the spectrum detection unit 5 through the flexible hoses, when the two connecting mouths 61 are communicated with the breathing chambers 4, the spectrum detection unit 5 can be communicated with the breathing chambers 4;

[0081] Through the conical shape of the bottom end of each of the two connecting mouths 61, the connecting mouths 61 can be better inserted into the inside of the extraction port and the circulation port, and the communication effect is improved.

[0082] Referring to the accompanying drawings Figures 4 to 7The transmission member includes a transmission block 63 slidably connected to the bottom of the top plate 2 through the guide rail frame 62, guide rods 64 connected to both sides of the transmission block 63, and the bottom ends of the two guide rods 64 fixedly connected with the two connecting mouths 61; the bottom of the top plate 2 is fixedly connected with a first motor 65, the output shaft of the first motor 65 is fixedly connected with a first lead screw 66, and the first lead screw 66 is threadedly connected with the inside of the transmission block 63;

[0083] The first motor 65 is connected with a power supply and a control switch outside, is a forward and reverse motor, is set in a connection mode and a coding mode of the prior art, is used to drive the first lead screw 66 to rotate, drives the transmission block 63 to move transversely through the rotation of the first lead screw 66, and then drives the two connecting mouths 61 to adjust the position, so that the two connecting mouths 61 are communicated with different positions of the respiration chamber 4, and the detection of soil respiration at different positions is formed.

[0084] Referring to the accompanying drawings Figures 4 to 7 The two guide rods 64 are slidably connected with the transmission block 63 in an up-down sliding manner, the two connecting mouths 61 are fixedly connected with guide shaft frames 67, the bottom of the top plate 2 is fixedly connected with guide frames 68, the two guide frames 68 are provided with a plurality of V-shaped recesses 69, and one end of each of the two guide shaft frames 67 is in contact with the top of each of the two guide frames 68.

[0085] The two guide shaft frames 67 are fixedly connected with the two connecting mouths 61, and the two guide shaft frames 67 are in contact with the top of each of the two guide frames 68, so that when the two connecting mouths 61 are driven by the transmission block 63 to move transversely, the two guide shaft frames 67 can move on the top of the two guide frames 68.

[0086] When the guide shaft frame 67 moves to the V-shaped recess 69 area, the guide shaft frame 67 and the connecting mouth 61 can automatically communicate with the extraction port and the circulation port of the respiration chamber 4 through the gravity of the guide shaft frame 67 and the connecting mouth 61, so as to form the soil respiration monitoring work, and have the functions of transverse and lifting connection.

[0087] With the continuous movement of the transmission block 63, the spectral detection unit 5 can be controlled to communicate with different respiration chambers 4, so as to form the monitoring work of carbon dioxide in the different respiration chambers 4, and then the detection conditions in the multiple respiration chambers 4 can be collected by the staff to determine the accuracy of the soil respiration monitoring.

[0088] Referring to the accompanying drawings Figures 10 to 12 The method for monitoring soil respiration based on tunable semiconductor laser absorption includes the following steps:

[0089] S1, the integrated monitoring device is moved to the area to be detected, according to the actual monitoring requirements, one or more of the breathing chambers 4 are driven by the lifting unit 7 to make contact with the ground, and the detection end of the spectrum detection unit 5 is communicated with one or other of the breathing chambers 4 through the communication assembly 6, and the spectrum detection unit 5 is used for monitoring work;

[0090] The spectrum detection unit 5 is composed of a light source signal generating device, a CO2 concentration collecting device and a data collecting and processing module.

[0091] S2, the initial online monitoring of the soil carbon flux, at this time, the CO2 concentration in the soil breathing chamber 4 is the same as that in the environment, the initial concentration is measured and recorded as C 标定 ;

[0092] S3, the light source signal generating device in the spectrum detection unit 5 is started, and then based on the laser spectrum technology, the peak value h 标定 of the second harmonic signal of the CO2 gas in the soil breathing chamber at the initial time is measured by the CO2 concentration collecting device.

[0093] S4, continuous monitoring, the peak value h 实测 of the measured second harmonic signal of the CO2 gas in the soil breathing chamber is obtained.

[0094] S5, the obtained data is substituted into the following calculation formula to obtain the measured CO2 concentration C 实测 , and the specific calculation formula is:

[0095]

[0096] Among them, F C is the soil CO2 flux; v is the total volume of the breathing chamber; P0 is the initial pressure measured by the instrument, R is the gas constant; S is the surface area of the collar; T0 is the initial temperature measured, is the initial change rate of CO2 molar fraction.

[0097] Preferably, the light source signal generating device is composed of a DFB laser, a laser wavelength driving signal module, a power amplification module and a laser coupling module.

[0098] The DFB laser is used to generate laser with certain frequency, and the laser wavelength driving signal module is used to generate modulation current signal with uniform amplitude.

[0099] The power amplification module adopts a Ytterbium amplifier to amplify the laser power.

[0100] The laser coupling module is used to couple the output laser of the laser into the next optical fiber through the optical fiber and the flange.

[0101] The CO2 concentration collecting device is composed of a light path multiple reflection structure, a photoelectric signal conversion, an electric signal amplification and an electric signal transmission module; the light path multiple reflection structure is used for collecting CO2 concentration absorption spectrum signals.

[0102] The data collecting and processing module is composed of a signal receiving module, a CO2 concentration inversion module, a CO2 flux inversion module and a result output module.

[0103] Embodiment: A sampling period T is specifically set, and the CO2 concentration, temperature, humidity and pressure data change amount in the sampling period T are measured and recorded; the obtained CO2 concentration change amount is multiplied by the time change amount T to calculate the CO2 emission flux in the sampling period T; the obtained CO2 concentration change data is subjected to correlation analysis with the temperature data, pressure data and time data to obtain the change relationship of the CO2 flux with the temperature, pressure and time.

[0104] The peak value of the measured second harmonic signal is in a proportional relationship with the gas concentration, so the concentration of the measured gas can be directly inverted according to the processed second harmonic signal amplitude. The second harmonic signal of the standard gas is measured, the least square linear fitting is performed on the measured second harmonic signal of the measured gas to obtain a fitting coefficient, and the concentration of the measured gas is calculated according to the fitting curve. As shown in the formula (2), wherein x is the second harmonic peak value, and y is the CO2 concentration value. Figure 12

[0105] The data collection and processing process is as follows: first, the original spectrum data is obtained, accumulated and averaged, the background signal and large errors are removed, and then normalized processing is performed; then the demodulation reference signal frequency is set to be twice the frequency of the scanning sawtooth signal, the signal is detected by the quadrature vector phase-locked amplifier for second harmonic detection, and the second harmonic signal is extracted; then the least square method is used for fitting, and the standard second harmonic of the above known concentration gas and the measured second harmonic signal of the measured gas are compared to obtain the gas concentration.

[0106] Measurement principle

[0107] The CO2 flux calculation method specifically includes the following contents:

[0108] The gas detection based on the TDLAS technology is mainly based on the Lambert-Beer law. The wavelength modulation technology is adopted, and a suitable absorption spectrum is selected to measure the CO concentration.

[0109] The expression of the Lambert-Beer law is shown in the formula (3).

[0110] I(t)=I0exp[-a(v)CL] (3)

[0111] ​In the formula: I(t) is the light intensity after gas absorption; I0 is the light intensity without gas absorption; a(v) represents the absorption cross section of the gas at frequency v; C is the concentration of the gas to be measured; and L is the optical path of the absorption cell.

[0112] The absorbance A at frequency v is shown in formula (4).

[0113] A = ln [I0 / I(t)] (4)

[0114] The high-frequency modulation is performed by injecting a high-frequency sinusoidal wave into the laser, and the instantaneous frequency v(t) of the diode laser is shown in formula (5).

[0115] v(t) = v0 + σ v cos(2πft) (5)

[0116] In the formula: v0 is the center frequency of the diode laser; σ v is the modulation amplitude of the frequency; f is the frequency of the sinusoidal wave; and t is the time.

[0117] Substituting formula (5) into formula (4) can calculate the Fourier expansion series as:

[0118]

[0119] The n-th harmonic signal component A n can be obtained by a phase-locked amplifier.

[0120] exp{-σ[v0+σ v cos(2πft)]CL}·cos(2nπft)d(2πft) (7)

[0121] In an ideal case, I0 is independent of v(t), so there is no amplitude modulation. Formula (5) is rewritten, and when the absorption a(v)CL is much less than 1, formula (8) is established.

[0122]

[0123] According to the Taylor series expansion, formula (9) can be obtained.

[0124]

[0125] As can be seen from formula (9), the n-th harmonic component is proportional to the concentration of the gas to be measured, and the harmonic component can be used to inverse the gas concentration. In actual calculation, considering the symmetry and amplitude of the harmonic, the second harmonic is often selected to use the ratio method to inverse the concentration.

[0126] After the CO concentration is obtained by inversion, the ratio of the concentration change amount to the time difference is the change rate of the CO concentration. The flux can be calculated after formula (10) is brought in.

[0127]

[0128] In the formula, F C is the soil CO2 flux we want to calculate. v is the total volume of the chamber, including the chamber volume and the collar volume, P0 is the initial pressure measured by the instrument, R is the gas constant. S is the surface area of the collar. T0 is the initial temperature we measured, is the initial change rate of the CO2 mole fraction.

[0129] Example 2: Based on Example 1, the difference is that;

[0130] Referring to the accompanying Figure 5 and Figures 7 to 9 , the lifting unit 7 includes a driving member and two auxiliary members, the two auxiliary members are connected with a plurality of breathing chambers 4 respectively, and the driving member is used for lifting driving one or more breathing chambers 4 through the two auxiliary members; the driving member includes a second motor 71 fixed on the top of the base 1, a second screw rod 72 fixedly connected with the output shaft of the second motor 71, and a threaded block threadedly connected with the outer surface of the second screw rod 72, and two triangular-shaped push blocks 78 elastically connected with the driving end of the threaded block;

[0131] The second motor 71 is connected with the power supply and the control switch outside, is a forward and reverse motor, is set in the connection mode and the coding mode in the prior art, is used for driving the second screw rod 72 to rotate forward and backward, and through the rotation of the second screw rod 72, the two push blocks 78 can be driven to move horizontally, and then the auxiliary member can be driven, so that the lifting work of one or more breathing chambers 4 is formed;

[0132] The auxiliary member includes a plurality of sliding frames 73 fixed on the bottom of the top plate 2 through mounting frames, a metal sliding block 74 slidably connected in the plurality of sliding frames 73, and a magnet block 75 fixedly connected with the inner top of the plurality of sliding frames 73 and used for magnetically attracting the metal sliding block 74, and a transmission frame 76 rotatably connected with one end of the plurality of metal sliding blocks 74;

[0133] Through the setting of the sliding frame 73, the smoothness of the up-down movement of the metal sliding block 74 is improved, through the fan-shaped movement of the transmission frame 76, the metal sliding block 74 can be driven to move up and down, and then the breathing chamber 4 is driven to move up and down, the magnet block 75 is fixedly connected with the inner top of the sliding frame 73, and is used for magnetically attracting the metal sliding block 74, so as to ensure the stability of the breathing chamber 4 after being contracted upward;

[0134] The inner side of the base 1 is provided with a transverse sliding groove, the bottom of each transmission frame 76 is fixedly connected with a sliding shaft 77, and one end of each sliding shaft 77 is movably connected inside the transverse sliding groove.

[0135] By providing a transverse sliding groove on the inner side of the base 1, one end of the sliding shaft 77 can be inserted into the transverse sliding groove for limiting movement, which improves the subsequent fan-shaped movement of the transmission frame 76 and forms the downward driving of the breathing chamber 4.

[0136] In specific operation, through the transverse movement of the triangular-shaped actuating block 78, when it moves to contact the other end of the sliding shaft 77, the sliding shaft 77 can be extruded and driven by the continuous movement of the actuating block 78, so that the transmission frame 76 moves obliquely, and in turn drives the metal sliding block 74 to move downward, and in turn drives the breathing chamber 4 to move downward to contact the ground, forming soil respiration monitoring work.

[0137] And with the continuous movement of the actuating block 78, since the breathing chamber 4 moves downward to the extreme position, the actuating block 78 cannot indirectly drive the metal sliding block 74 to move downward, and the actuating block 78 is elastically installed, so that the actuating block 78 gradually loses contact with the sliding shaft 77, forming the downward driving work of the second breathing chamber 4.

[0138] Conversely, when the breathing chamber 4 is upwardly reset, the reverse movement of the actuating block 78 can form the reset work of the breathing chamber 4.

[0139] Embodiment 3: Different from embodiment 1 is that

[0140] Referring to the accompanying drawings Figure 8 And Figure 9 The bottom of the base 1 is provided with a processing assembly 8 for processing the detection area, the processing assembly 8 includes two guide frames 81 fixed to the bottom of the base 1, the initial end of the two guide frames 81 is upwardly inclined, an activity shaft 82 is movably connected between the interiors of the two guide frames 81, the bottom of the activity shaft 82 is fixedly connected with an arc-shaped shovel plate 83, the top of the activity shaft 82 is fixedly connected with two telescopic columns 84, the outer surfaces of the two telescopic columns 84 are movably sleeved with sliding blocks 85, and the two sliding blocks 85 are slidably connected inside the base 1 in a transverse horizontal sliding manner;

[0141] Through the transverse driving of the two sliding blocks 85, the activity shaft 82 can be driven to move transversely through the two telescopic columns 84, and in turn the arc-shaped shovel plate 83 can be driven to move transversely, so that the to-be-monitored position of the ground can be pretreated through the transverse movement of the arc-shaped shovel plate 83.

[0142] The two ends of the movable shaft 82 are movably arranged inside the two guide frames 81, and the initial ends of the two guide frames 81 are upwardly inclined, so that the movable shaft 82 can slightly move downward before driving the arc-shaped shovel plate 83 to move laterally, and then the arc-shaped shovel plate 83 is inserted into the soil, and the lateral movement of the arc-shaped shovel plate 83 can pre-treat the ground to be monitored;

[0143] One of the sliding blocks 85 is fixedly connected with the threaded block, and the two push blocks 78 are elastically connected at the two ends of the movable shaft 82, respectively;

[0144] The lateral movement of the threaded block in the lifting unit 7 can drive the lateral movement of the sliding block 85, and then the lateral movement of the movable shaft 82 and the arc-shaped shovel plate 83, so as to pre-treat the ground, effectively utilize the driving force of the lifting unit 7, and improve the energy saving and environmental protection of the equipment;

[0145] The two push blocks 78 are elastically connected at the two ends of the movable shaft 82, respectively, so that when the arc-shaped shovel plate 83 moves laterally to pre-treat the ground, the corresponding breathing chamber 4 can move downward synchronously, so as to monitor the soil respiration, ensure that the corresponding breathing chamber 4 can automatically contact the treated ground after the ground is pre-treated, improve the orderliness of the ground pre-treatment and the lowering operation of the breathing chamber 4, and when a small number of breathing chambers 4 are used, the arc-shaped shovel plate 83 can pre-treat the ground locally, further improving the functionality and practicality of the ground pre-treatment.

[0146] Finally, it should be noted that: the above is only the preferred embodiment of the present application, and is not used to limit the present application, although the present application has been described in detail with reference to the foregoing embodiments, for those skilled in the art, the technical solutions recorded in the foregoing embodiments can be modified, or some technical features can be replaced, any modification, equivalent replacement, improvement, etc. within the spirit and principles of the present application, should be included in the protection scope of the present application.

Claims

1. A soil respiration monitoring device based on tunable semiconductor laser absorption, comprising a movable base (1), wherein the base (1) is hollow, a top plate (2) is fixedly connected to the top of the base (1) by a bracket, and a data controller (3) is installed on the top of the base (1), characterized in that: The base (1) and the top plate (2) are provided with a plurality of breathing chambers (4), the top of each of the plurality of breathing chambers (4) is provided with a plurality of through holes, an extraction port and a circulation port; The top of the top plate (2) is provided with a spectrum detection unit (5); The bottom of the top plate (2) is provided with a communication unit (6) for controlling the collection end and the circulation end of the spectrum detection unit (5), the communication unit (6) is used for connecting and controlling the collection end and the circulation end of the spectrum detection unit (5) and the extraction port and the circulation port of one of the breathing chambers (4), forming a detection work of the carbon dioxide inside different breathing chambers (4); The base (1) is provided with a lifting unit (7) for lifting driving one or more breathing chambers (4).

2. The tunable semiconductor laser absorption based soil respiration monitoring device of claim 1, wherein: The communication unit (6) includes two connecting mouths (61) and a transmission member for transversely and vertically driving the two connecting mouths (61); The bottom end of each of the two connecting mouths (61) is provided in a tapered shape, and the two connecting mouths (61) are fixedly communicated with the collection end and the circulation end of the spectrum detection unit (5) through a flexible hose.

3. The tunable semiconductor laser absorption based soil respiration monitoring device of claim 2, wherein: The transmission member includes a transmission block (63) slidably connected to the bottom of the top plate (2) through a guide rail frame (62), both sides of the transmission block (63) are connected with guide rods (64), and the bottom ends of the two guide rods (64) are fixedly connected with the two connecting mouths (61), respectively. The bottom of the top plate (2) is fixedly connected with a first motor (65), the output shaft of the first motor (65) is fixedly connected with a first lead screw (66), and the first lead screw (66) is threadedly connected with the inside of the transmission block (63).

4. The tunable semiconductor laser absorption based soil respiration monitoring device of claim 3, wherein: Both of the guide rods (64) are slidably connected with the transmission block (63) in an up-down sliding manner, both of the connecting mouths (61) are fixedly connected with guide shaft frames (67), both sides of the bottom of the top plate (2) are fixedly connected with guide frames (68), a plurality of V-shaped recesses (69) are arranged on the two guide frames (68), and one end of each of the two guide shaft frames (67) is in contact with the top of each of the two guide frames (68).

5. The tunable semiconductor laser absorption based soil respiration monitoring device of claim 1, wherein: The lifting unit (7) includes a driving member and two auxiliary members, the two auxiliary members are connected with the plurality of breathing chambers (4), respectively, and the driving member is used for lifting driving one or more breathing chambers (4) through the two auxiliary members.

6. The method of soil respiration monitoring based on tunable semiconductor laser absorption according to any one of claims 1-5, wherein, The method comprises the following steps: S1, moving the integrated monitoring device to the detection area, according to the actual monitoring requirement, lifting driving one or more breathing chambers (4) through the lifting unit (7), so that one or more breathing chambers (4) are in contact with the ground, then connecting the detection end of the spectrum detection unit (5) with one or other breathing chambers (4) through the communication assembly (6), and monitoring through the spectrum detection unit (5); The spectrum detection unit (5) is composed of a light source signal generating device, a CO2 concentration collecting device and a data collecting and processing module; S2, the initial concentration of the soil carbon flux online monitoring work, at this time the soil respiration chamber (4) in the CO2 concentration and the CO2 concentration in the environment is the same, the initial concentration is measured at this time, marked as C 标定 ; S3, start the light source signal generating device in the spectrum detection unit (5), and then based on the laser spectrum technology, combined with the CO2 concentration collecting device to measure the peak value h of the second harmonic signal of the CO2 gas in the soil respiration cavity at the initial time 标定 ; S4, continuously monitoring, obtaining the measured peak value h of the second harmonic signal of the CO2 gas in the soil respiration cavity 实测 ; S5, the obtained data into the following calculation formula, the measured CO2 concentration C 实测 , the specific calculation formula is: Among them, F C ρ is the soil CO2 flux; v is the total volume of the respiration chamber; P0 is the initial pressure measured by the instrument; R is the gas constant; S is the surface area of ​​the bottom of the respiration chamber; T0 is the measured initial temperature. The initial rate of change of CO2 mole fraction.

7. The method of claim 6, wherein the soil respiration monitoring device is based on tunable semiconductor laser absorption. The light source signal generating device is composed of a DFB laser, a laser wavelength driving signal module, a power amplification module and a laser coupling module; The DFB laser is used to generate laser of certain frequency, and a laser wavelength driving signal module is used to generate a modulation current signal with uniform amplitude; The power amplification module adopts a rare earth element amplifier to amplify laser power; The laser coupling module is used to couple the output laser of the laser through an optical fiber and a flange into the next optical fiber.

8. The method of claim 6, wherein the soil respiration monitoring device is based on tunable semiconductor laser absorption. The CO2 concentration acquisition device is composed of an optical path multiple reflection structure, an optical-electrical signal conversion module, an electrical signal amplification module and an electrical signal transmission module; the optical path multiple reflection structure is used for collecting CO2 concentration absorption spectrum signals.

9. The method of claim 6, wherein the soil respiration monitoring device is based on tunable semiconductor laser absorption. The data acquisition and processing module is composed of a signal receiving module, a CO2 concentration inversion module, a CO2 flux inversion module and a result output module.

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