A gas concentration detection system with a relative path difference that reduces turbulence effects

Abstract

The application discloses a gas concentration detection system for reducing the influence of turbulence on the relative path difference, which comprises the following steps: a detection light beam on a first path is divided into a reflected light beam and a transmitted light beam through a semi-transparent half mirror; the single-pass length of the first path is L / 2, and the sum of the single-pass length of the first path and the length of a second path is 2L; first detection electrical signals and second detection electrical signals carrying highly correlated information are obtained; the absorption signal difference caused by the relative distance difference between the first detection electrical signals and the second detection electrical signals is used as an inversion object to effectively reduce the influence of turbulence; meanwhile, the characteristics of a triangular wave are combined, the first alignment signal and the second alignment signal are obtained through the signal after multi-peak fitting and are subjected to weighted processing to further reduce the influence of turbulence, so that the measurement stability and accuracy are ensured.

Description

Technical Field

[0001] The present invention relates to the field of environmental optics, and in particular to a gas concentration detection system which reduces the relative path difference affected by turbulence and aims at the linear deformation of gas absorption spectrum caused by turbulence during open space atmosphere detection. Background Art

[0002] When using laser absorption spectroscopy for atmospheric monitoring in open spaces, the transmitting and receiving beams are inevitably affected by atmospheric turbulence, resulting in the superposition of fluctuation noise in the received optical signal. Atmospheric turbulence, primarily through changes in the refractive index of atmospheric molecules, causes laser scintillation, leading to intensity fluctuations, phase fluctuations, beam expansion, beam drift, and image jitter, resulting in distortion of the gas absorption spectrum line shape. Therefore, effectively mitigating the effects of atmospheric turbulence on laser intensity fluctuations is a crucial research task.

[0003] Existing methods primarily include increasing the receiving aperture, increasing the scanning frequency, and using two-wavelength differential absorption technology. Increasing the receiving aperture area can mitigate the effects of turbulence on the laser signal, but this also requires consideration of factors such as equipment cost, size, and weight. Increasing the scanning frequency can render the existing power control module inoperable, requiring hardware modifications and increasing costs. Two-wavelength differential absorption technology typically uses two lasers, increasing the cost and difficulty of field experiments. Summary of the Invention

[0004] In view of the shortcomings of the existing technical methods, the present invention proposes a gas concentration detection system that reduces the relative path difference affected by turbulence, in order to effectively reduce the problems caused by atmospheric turbulence and ensure the accuracy of gas detection.

[0005] In order to achieve the above-mentioned object, the present invention adopts the following technical solutions:

[0006] The gas concentration detection system for reducing the relative path difference affected by turbulence of the present invention is characterized in that it includes: a main control module, a reference optical unit, a detection optical unit, a data processing unit, and a display module;

[0007] The main control module consists of a function generator, a temperature and current controller, a laser diode, and a fiber optic beam splitter;

[0008] The reference optical unit is composed of a second collimator, a reference gas cell, and a third photodetector;

[0009] The detection optical unit is composed of a telescope, a semi-transparent and semi-reflective mirror, and a cooperative reflector; wherein the telescope includes a first collimator, a first photodetector, and a second photodetector;

[0010] The function generator provides a triangular wave scanning signal and transmits it to the temperature current controller. The temperature current controller controls the current and temperature of the laser diode to tune the laser diode to produce a laser beam with a stable laser wavelength and transmits it to the optical fiber beam splitter, so that the optical fiber beam splitter splits the laser beam into a detection beam and a reference beam.

[0011] The detection beam is sent to the telescope and is collimated by the first collimator and then emitted into space, thereby forming a first path and reaching the semi-transparent and semi-reflective mirror, so that the semi-transparent and semi-reflective mirror divides the beam on the first path into a reflected beam and a transmitted beam;

[0012] The reflected light beam returns along the first path and is received by the first photodetector, thereby converting the optical signal on the first path into a first detection electrical signal; after the transmitted light beam is transmitted and reaches the cooperative reflector, it forms a second path and finally reaches the second photodetector, thereby converting the optical signal on the second path into a second detection electrical signal, wherein the one-way length of the first path is L / 2, and the sum of the one-way length of the first path and the length of the second path is 2L;

[0013] The reference beam is emitted into the reference gas pool after passing through the second collimator and reaches the third photodetector, thereby converting the optical signal of the reference beam into a reference signal;

[0014] The first detection electrical signal, the second detection electrical signal and the reference signal are respectively transmitted to the data processing unit for concentration inversion, and the inversion result is finally displayed on the display module.

[0015] The gas concentration detection system for reducing relative path difference due to turbulence influence of the present invention is also characterized in that the data processing unit performs concentration inversion according to the following steps:

[0016] Step 1. Record the first detection electrical signal {y d1 (m)|m=1,2,…,n,n+1,…,2n}, the second detection electrical signal {y d2 (m)|m=1,2,…,n,n+1,…,2n}, where m is the sequence position; y d1 (m) represents the first detection electrical signal at the mth position; y d2 (m) represents the second detection electrical signal at the mth position; 2n represents the maximum value range of m;

[0017] Step 2. Use formula (1) to obtain the detection signal {y d0 (m)|m=1, 2,…,n,n+1,…,2n};

[0018] yd0 (m) = y d2 (m) - y d1 (m) (1)

[0019] In formula (1), y d0 (m) represents the detection signal of the mth position with reduced turbulence effect;

[0020] Step 3. Select the background signal of the 3-section non-absorption region in the detection signal {y d0 (m) | m = 1, 2, …, n, n+1, …, 2n} with reduced turbulence effect to constitute a background baseline signal, and fit the background baseline signal by using formula (2) to obtain the fitted background baseline signal {y0(m) | m = 1, 2, …, n, n+1, …, 2n};

[0021] y0(m) = a0 + a1m + a2m 2 +a3m 3 (2)

[0022] In formula (2), a0, a1, a2, and a3 are four fitting coefficients, and y0(m) represents the fitted background baseline signal of the mth position;

[0023] Step 4. Obtain the signal {y(m) | m = 1, 2, …, n, n+1, …, 2n} with reduced background baseline by using formula (3);

[0024] y(m) = y d0 (m) - y0(m) (3)

[0025] In formula (3), y(m) represents the signal of the mth position with reduced background baseline;

[0026] Step 5. Set the window length as l, slide the window successively, and fit the signal {y(m) | m = 1, 2, …, n, n+1, …, 2n} with reduced background baseline in the window to obtain the preprocessed signal {y'(m) | m = 1, 2, …, n, n+1, …, 2n}; wherein y'(m) represents the preprocessed signal of the mth position;

[0027] Step 6. Perform multi-peak voigt fitting on the preprocessed signal {y'(m) | m = 1, 2, …, n, n+1, …, 2n} to obtain the multi-peak fitted signal {y'(m) | m = 1, 2, …, n, n+1, …, 2n}; wherein y'(m) represents the multi-peak fitted signal of the mth position; v v (m) represents the multi-peak fitted signal of the mth position;

[0028] Step 7. Take the multi-peak fitted signal {y'(m) | m = 1, 2, …, n, n+1, …, 2n} to obtain the signal {y'(m) | m = 1, 2, …, n, n+1, …, 2n} with reduced background baseline and turbulence effect; v ​(m)|m=1,2,…,n,n+1,…,2n}, and obtain the first signal {y v1 (l)|l=1, 2, ..., n}, where l is the sequence position, y v1 (1) represents the first signal at the lth position;

[0029] Take the signal {y′ v (m)|m=1,2,…,n,n+1,…,2n}, and obtain the second signal {y v2 |l=1,2,…,n},where y v2 (1) represents the second signal at the lth position;

[0030] Step 8. Use the offset algorithm to v1 (l)|l=1, 2, ..., n} and the second signal {y v2 |l=1,2,…,n} perform peak alignment and obtain the first alignment signal {y′ v1 (l)|l=1, 2, ..., n} and the second alignment signal {y′ v2 (l)|l=1,2,…,n};where y′ v1 (l) represents the first alignment signal at the lth position, y′ v2 (1) represents the second alignment signal at the lth position;

[0031] Step 9. Use formula (4) to get the weighted signal

[0032]

[0033] In formula (4), is the weighted signal at the lth position, σ l1 is the standard deviation of the first alignment signal at position l, is the standard deviation of the arithmetic mean of the first alignment signal, σ l2 is the standard deviation of the second alignment signal at position l, is the standard deviation of the arithmetic mean of the second alignment signal, p1 and p2 are respectively the standard deviation of the arithmetic mean of the first alignment signal {y v1 (l)|l=1, 2, ..., n}, the second alignment signal {y′ v1 (l)|l=1, 2, ..., n} weight;

[0034] Step 10. The weighted signal Integrate to obtain the relative integral area S;

[0035] Step 11. According to the process of step 1 to step 10, the reference signal is processed to obtain the standard gas integral area S r , thus according to S r , invert S to obtain the gas concentration in space.

[0036] Compared with the existing technology, the beneficial effects of the present invention are embodied in:

[0037] 1. The present invention uses a semi-transparent and semi-reflective mirror to split the light beam into a reflected first detection beam and a transmitted second detection beam, thereby obtaining two signals carrying highly correlated information, thereby improving the quality of the absorption signal generated by the relative distance difference and providing the possibility for accurate gas inversion;

[0038] 2. The present invention uses the absorption signal difference generated by the relative distance difference between the first detection electrical signal and the second detection electrical signal as the inversion object, effectively reducing the influence of turbulence, thereby improving the accuracy of open optical path measurement;

[0039] 3. The present invention utilizes the characteristics of the triangular wave and obtains the first alignment signal and the second alignment signal through the signal after multi-peak fitting, and performs weighted processing to further reduce the influence of turbulence and ensure measurement stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 A schematic diagram of a gas concentration detection system for reducing relative path difference influenced by turbulence according to the present invention;

[0041] Figure 2 Flowchart of concentration inversion of the data processing unit of the present invention. DETAILED DESCRIPTION

[0042] In this embodiment, see Figure 1 A gas concentration detection system for reducing the relative path difference affected by turbulence is composed of a main control module, a reference optical unit, a detection optical unit, a data processing unit 13, and a display module 14. It includes: a function generator 1, a temperature and current controller 2, a laser diode 3, a fiber optic splitter 4, a first collimator 5, a semi-transparent and semi-reflective mirror 6, a first photodetector 7, a cooperative reflector 8, a second photodetector 9, a second collimator 10, a reference gas cell 11, a third photodetector 12, a data processing unit 13, a display module 14, a first path 15, and a second path 16.

[0043] The main control module consists of a function generator 1, a temperature and current controller 2, a laser diode 3, and a fiber beam splitter 4. The reference optical unit consists of a second collimator 10, a reference gas cell 11, and a third photodetector 12. The detection optical unit consists of a telescope, a semi-transparent and semi-reflective mirror 6, and a cooperative reflector 8. The telescope includes a first collimator 5, a first photodetector 7, and a second photodetector 9.

[0044] Function generator 1 provides a triangular wave scanning signal and transmits it to temperature and current controller 2. By controlling the current and temperature of laser diode 3, a laser beam with a stable laser wavelength is tuned and then split into a detection beam and a reference beam by fiber optic beam splitter 4.

[0045] The detection beam is sent to the telescope and collimated by the first collimator 5 before being emitted into space, thereby forming a first path 15 and reaching the semi-transparent half-reflective mirror 6, which then splits the beam on the first path 15 into a reflected beam and a transmitted beam.

[0046] The reflected light beam returns along the first path 15 and is received by the first photodetector 7, thereby converting the optical signal on the first path 15 into a first detection electrical signal. After the transmitted light beam reaches the cooperative reflector 8, it forms a second path 16 and finally reaches the second photodetector 9, thereby converting the optical signal on the second path 16 into a second detection electrical signal. The one-way length of the first path 15 is L / 2, and the sum of the one-way length of the first path 15 and the length of the second path 16 is 2L.

[0047] The reference beam passes through the second collimator 10 and is emitted into the reference gas pool 11 and reaches the third photodetector 12, thereby converting the optical signal of the reference beam into a reference signal;

[0048] The first detection electrical signal, the second detection electrical signal and the reference signal are respectively transmitted to the data processing unit 13 for concentration inversion, and the inversion result is finally displayed on the display module 14 .

[0049] The effective optical path of the first detection electrical signal is L, and the effective optical path of the second detection electrical signal is 2L; the information carried by the two signals is highly correlated; although the gas concentration in the open space remains unchanged, the difference in effective optical path leads to greater absorption of the second detection electrical signal, thereby making it possible to utilize the absorption signal generated by the relative distance difference for gas inversion; at the same time, using a triangular wave scanning signal, two absorptions can be obtained within one cycle.

[0050] See also Figure 2 In this embodiment, the concentration inversion of the data processing unit is performed according to the following steps:

[0051] Step 1. Record the first detection electrical signal {y d1(m)|m=1,2,…,n,n+1,…,2n},the second detection electrical signal {y d2 (m)|m=1, 2, ..., n, n+1, ..., 2n}, where m is the sequence position; y d1 (m) represents the first detection electrical signal at the mth position; y d2 (m) represents the second detection electrical signal at the mth position; 2n represents the maximum value range of m.

[0052] Step 2. Use formula (1) to obtain the detection signal {y d0 (m)|m=1, 2,…,n,n+1,…,2n};

[0053] y d0 (m) = y d2 (m)-y d1 (m) (1)

[0054] In formula (1), y d0 (m) represents the detection signal at the mth position with reduced turbulence influence.

[0055] Step 3. Select the detection signal that reduces the influence of turbulence {y d0 The background baseline signal is composed of the background signals of the three non-absorption regions in {y0(m)|m=1, 2, ..., n, n+1, ..., 2n}. The background baseline signal is fitted using formula (2) to obtain the fitted background baseline signal {y0(m)|m=1, 2, ..., n, n+1, ..., 2n}.

[0056] y0(m)=a0+a1m+a2m 2 +a3m 3 (2)

[0057] In formula (2), a0, a1, a2, and a3 are four fitting coefficients, and y0(m) represents the background baseline signal after fitting at the mth position.

[0058] Step 4. Use equation (3) to obtain the background baseline-reduced signal {y(m)|m=1, 2, ..., n, n+1, ..., 2n};

[0059] y(m)=y d0 (m)-y0(m) (3)

[0060] In formula (3), y(m) represents the signal at the m-th position after reducing the background baseline.

[0061] Step 5. Set the window length as l, slide the window successively and fit the reduced background baseline signal {y(m) | m = 1, 2, …, n, n+1, …, 2n} in the window to obtain the pre-processed signal {y'(m) | m = 1, 2, …, n, n+1, …, 2n}; wherein y'(m) represents the pre-processed signal at the mth position.

[0062] Step 6. Perform multi-peak Voigt fitting on the pre-processed signal {y'(m) | m = 1, 2, …, n, n+1, …, 2n} to obtain the multi-peak fitted signal {y'(m) | m = 1, 2, …, n, n+1, …, 2n}; wherein y'(m) represents the multi-peak fitted signal at the mth position. v v (m) represents the multi-peak fitted signal at the mth position.

[0063] Step 7. Take the first n signals in the multi-peak fitted signal {y'(m) | m = 1, 2, …, n, n+1, …, 2n} to obtain the first signal {y(l) | l = 1, 2, …, n}; wherein l is the sequence position, y(l) represents the first signal at the lth position. v v1 (l) represents the first signal at the lth position. v1

[0064] Take the last n signals in the multi-peak fitted signal {y'(m) | m = 1, 2, …, n, n+1, …, 2n} to obtain the second signal {y(l) | l = 1, 2, …, n}; wherein y(l) represents the second signal at the lth position. v v2 (l) represents the second signal at the lth position. v2

[0065] Step 8. Perform peak alignment on the first signal {y(l) | l = 1, 2, …, n} and the second signal {y(l) | l = 1, 2, …, n} by using the shift algorithm to obtain the first aligned signal {y'(l) | l = 1, 2, …, n} and the second aligned signal {y'(l) | l = 1, 2, …, n}, respectively; wherein y'(l) represents the first aligned signal at the lth position, y'(l) represents the second aligned signal at the lth position. v1 v2 v1 v2 v1 v2 (l) represents the first aligned signal at the lth position, y'(l) represents the second aligned signal at the lth position.

[0066] Step 9. Obtain the weighted signal y'(l) by using formula (4)

[0067]

[0068] In formula (4), ​​​​​​​​​​is the weighted signal at the lth position, σ l1 is the standard deviation of the first alignment signal at position l, is the standard deviation of the arithmetic mean of the first alignment signal, σ l2 is the standard deviation of the second alignment signal at position l, is the standard deviation of the arithmetic mean of the second alignment signal, p1 and p2 are the standard deviation of the arithmetic mean of the first alignment signal {y v1 (l)|l=1, 2, ..., n}, the second alignment signal {y′ v1 (l)|l=1, 2, ..., n} weight.

[0069] Step 10. Weighted signal Integrate to obtain the relative integral area S;

[0070] Step 11. Process the reference signal according to the process of steps 1 to 10 to obtain the standard gas integral area S r , thus according to S r , invert S to obtain the gas concentration in space.

Claims

1. A gas concentration detection system for reducing relative path difference due to turbulence, characterized in that: include: Main control module, reference optical unit, detection optical unit, data processing unit (13), display module (14); The main control module is composed of a function generator (1), a temperature current controller (2), a laser diode (3), and an optical fiber beam splitter (4); The reference optical unit is composed of a second collimator (10), a reference gas cell (11), and a third photodetector (12); The detection optical unit is composed of a telescope, a semi-transparent and semi-reflective mirror (6), and a cooperative reflective mirror (8); wherein the telescope includes a first collimator (5), a first photodetector (7), and a second photodetector (9); The function generator (1) provides a triangular wave scanning signal and transmits it to the temperature current controller (2). The temperature current controller (2) controls the current and temperature of the laser diode (3) so that the laser diode (3) tunes a laser beam with a stable laser wavelength and transmits it to the optical fiber beam splitter (4). The optical fiber beam splitter (4) then splits the laser beam into a detection beam and a reference beam. The detection beam is sent to the telescope and is collimated by the first collimator (5) and then emitted into space, thereby forming a first path (15) and reaching the semi-transparent and semi-reflective mirror (6), so that the semi-transparent and semi-reflective mirror (6) divides the light beam on the first path (15) into a reflected light beam and a transmitted light beam; The reflected light beam returns along the first path (15) and is received by the first photodetector (7), thereby converting the light signal on the first path (15) into a first detection electrical signal; after the transmitted light beam reaches the cooperative reflector (8), it forms a second path (16) and finally reaches the second photodetector (9), thereby converting the light signal on the second path (16) into a second detection electrical signal, wherein the one-way length of the first path (15) is L / 2, and the sum of the one-way length of the first path (15) and the length of the second path (16) is 2L; The reference beam is emitted into the reference gas pool (11) after passing through the second collimator (10) and reaches the third photodetector (12), thereby converting the optical signal of the reference beam into a reference signal; The first detection electrical signal, the second detection electrical signal and the reference signal are respectively transmitted to the data processing unit (13) for concentration inversion, and the inversion result is finally displayed on the display module (14). The data processing unit (13) performs concentration inversion according to the following steps: Step 1. Record the first detection electrical signal , the second detection electrical signal , where m is the sequence position; represents the first detection electrical signal at the m-th position; represents the second detection electrical signal at the mth position; 2n represents the maximum value range of m; Step 2. Use equation (1) to obtain the detection signal with reduced turbulence effect ; (1) In formula (1), Represents the detection signal of reducing turbulence effect at the mth position; Step 3. Select the detection signal that reduces the influence of turbulence The background signals of the three non-absorption areas in the image are used to form the background baseline signal, and the background baseline signal is fitted using formula (2) to obtain the fitted background baseline signal ; (2) In formula (2), are the four fitting coefficients, represents the fitted background baseline signal at the mth position; Step 4. Use formula (3) to obtain the signal after reducing the background baseline ; (3) In formula (3), represents the signal at the mth position after subtracting the background baseline; Step 5. Set the window length to l, slide the window in sequence and calculate the signal after reducing the background baseline in the window. Perform fitting to obtain the preprocessed signal ;in, represents the preprocessed signal at the mth position; Step 6. Preprocess the signal Perform multi-peak voigt fitting to obtain the signal after multi-peak fitting ;in, Represents the signal after multi-peak fitting at the mth position; Step 7. Take the signal after the multi-peak fitting The first n signals in the , where l is the sequence position, Indicates the first signal at the lth position; Take the signal after the multi-peak fitting The last n signals in the , get the second signal ,in, Indicates the second signal at the lth position; Step 8. Use the offset algorithm to and the second signal Perform peak alignment to obtain the first alignment signal and the second alignment signal ;in, represents the first alignment signal at the lth position, Indicates a second alignment signal at the lth position; Step 9. Use formula (4) to get the weighted signal ; (4) In formula (4), is the weighted signal at the lth position, is the standard deviation of the first alignment signal at position l, is the standard deviation of the arithmetic mean of the first alignment signal, is the standard deviation of the second alignment signal at position l, is the standard deviation of the arithmetic mean of the second alignment signal, 、 The first alignment signal , second alignment signal The weight of Step 10. Integrate to obtain the relative integral area S; Step 11. Process the reference signal according to the process of steps 1 to 10 to obtain the standard gas integrated area S r , thus according to S r , invert S to obtain the gas concentration in space.

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