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CN111829980B - Linear nonlinear correction detection system and method based on harmonic technology - Google Patents

Linear nonlinear correction detection system and method based on harmonic technology Download PDF

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CN111829980B
CN111829980B CN202010716706.3A CN202010716706A CN111829980B CN 111829980 B CN111829980 B CN 111829980B CN 202010716706 A CN202010716706 A CN 202010716706A CN 111829980 B CN111829980 B CN 111829980B
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CN111829980A (en
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唐七星
张玉钧
陈东
刘路
廖娟
王玉伟
何莹
郭楠
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Anhui Agricultural University AHAU
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Abstract

本发明公开了一种基于谐波技术的线型非线性修正的检测系统及方法，系统包括可调谐半导体激光器、激光器控制模块、信号发生器、参考光路与探测光路、相敏检测电路、数据处理器、显示模块等，并通过背景噪声消除，零线偏移修正，利用Hitran数据库拟合获取对应二次谐波的标准信号，随后根据最优准则进行自适应迭代拟合，使信号达到不对称性最小，得到线型不对称性修正后的信号。本发明能够有效降低零线偏移噪声的波动，线型不对称等影响，提高气体测量的准确性。

Figure 202010716706

The invention discloses a detection system and method for linear nonlinear correction based on harmonic technology. The system includes a tunable semiconductor laser, a laser control module, a signal generator, a reference optical path and a detection optical path, a phase-sensitive detection circuit, and a data processing circuit. The standard signal corresponding to the second harmonic is obtained by fitting the Hitran database, and then adaptive iterative fitting is performed according to the optimal criterion to make the signal asymmetrical is the smallest, and the signal after linear asymmetry correction is obtained. The invention can effectively reduce the fluctuation of the zero line offset noise, the influence of line asymmetry and the like, and improve the accuracy of gas measurement.

Figure 202010716706

Description

Linear nonlinear correction detection system and method based on harmonic technology
Technical Field
The invention relates to the field of environmental optics, in particular to a linear nonlinear correction detection system and method based on a harmonic technology, which are provided for nonlinear influence of a second harmonic signal.
Background
The laser spectrum technology utilizes the fingerprint characteristic of molecular spectrum to carry out quantitative analysis on the gas concentration, and is widely applied to gas detection. The wavelength modulation spectrum technology adopts a high-frequency detection signal, so that background noise can be effectively inhibited, and the detection sensitivity is improved. However, when the open space gas detection is performed by using the wavelength-modulated laser spectrum technology, the laser light intensity is inevitably interfered by the intensity modulation factor, the residual amplitude modulation of the laser and the uncontrollable environmental noise, so that the second harmonic spectrum signal is deformed and shifted, the nonlinearity of the spectrum line is enhanced, and the measurement accuracy is affected. Therefore, the nonlinear influence of spectral lines is effectively reduced, and the measurement accuracy is improved, so that the method has important research significance.
The existing research mainly solves the problem of light intensity modulation of second harmonic from the perspective of reducing RAM, but aims at the fact that the influence of nonlinear error in the actual measurement process is complex and various, and only by reducing the perspective of RAM, other influence factors still exist in a certain sense, and the influence of nonlinearity on a spectrum signal is not fundamentally solved.
Disclosure of Invention
In view of the defects of the prior art, the invention provides a linear nonlinear correction detection system and method based on a harmonic technology, and aims to solve the problem that the nonlinearity of a spectral line is enhanced and the measurement accuracy is influenced due to the deformation, the offset and the like of a second harmonic spectral signal in harmonic detection, so that the nonlinearity of the spectral line is eliminated and the measurement accuracy is improved.
The technical scheme for solving the problems is as follows:
the invention relates to a detection system for linear nonlinear correction based on harmonic technology, which is characterized by comprising the following steps: the device comprises a laser, a control unit, an optical unit and a data processing unit;
the laser and control unit consists of a tunable semiconductor laser, a laser control module and a signal generator;
the laser control module controls the temperature and the current of the tunable semiconductor laser to enable the tunable semiconductor laser to output wavelength near a target absorption spectral line;
the sawtooth scanning signal and the high-frequency sinusoidal signal generated by the signal generator are superposed on the tunable semiconductor laser, so that the output wavelength of the tunable semiconductor laser is scanned and modulated, and a modulated light beam is obtained;
the optical unit consists of a transceiver telescope, a reference light path and a detection light path;
the modulation light beam is divided into reference light and detection light, and the reference light path receives the reference light, converts the reference light into a reference electric signal and transmits the reference electric signal to the data processing unit;
the detection light path receives the detection light, enters the open space through the transceiver telescope, telemeters the atmosphere, converts the atmosphere into a detection electric signal and transmits the detection electric signal to the data processing unit;
the data processing unit consists of a phase-sensitive detection circuit, a data processor and a display module;
the phase-sensitive detection circuit performs harmonic signal detection on the reference electric signal in the ith measurement period to obtain a second harmonic spectrum signal of the reference light path in the ith measurement period or a second harmonic background signal of the reference light path without absorption in the ith measurement period;
the phase-sensitive detection circuit performs harmonic signal detection on the detection electric signal in the ith measurement period to obtain a second harmonic spectrum signal of the detection optical path in the ith measurement period;
and carrying out nonlinear correction on the second harmonic spectrum signal or the second harmonic background signal of the reference light path and the second harmonic spectrum signal of the detection light path in the ith measurement period by the data processor, and then carrying out online concentration inversion, so as to obtain an inversion result in the ith measurement period and sending the inversion result to the display module for display.
The invention relates to a detection method of linear nonlinear correction based on harmonic technology, which is characterized by comprising the following steps:
step 1, acquiring a second harmonic spectrum signal D under the ith measurement periodi(n) second harmonic background signal B without absorption with reference light path in ith measurement periodi(n) and correcting the background noise by using the formula (1) to obtain a spectrum signal D after correcting the background noise in the ith measurement periodi’(n)；
D′i(n)＝Di(n)-Bi(n) n＝0,1,2...N (1)
In the formula (1), i represents a corresponding measurement period, N is a signal corresponding sequence position, and N is a maximum value obtained by the N;
step 2, selecting a spectral signal D under the i-1 th measurement periodi-1' (n) m signals of the side lobe non-absorption region on the right side to the spectral signal D at the ith measurement periodi' (n) m signals of left side lobe non-absorption region, and spectral signal D at i-th measurement periodi' (n) m signals of the side lobe non-absorption region on the right side to the spectral signal D after background noise correction in the (i + 1) th measurement periodi+1' (n) m signals of the unabsorbed region of the left side lobe; and m is more than or equal to 0 and less than or equal to N;
polynomial fitting is carried out on the selected non-absorption area signals by using the formula (2) to obtain zero line offset noise signals Z under the ith measurement periodi(n’)；
Zi(n')＝a0+a1n'+a2n'2 n'＝0,1,2...N+2m (2)
In the formula (2), a0，a1，a2Is a fitting coefficient, and n' is a sequence position corresponding to the fitting signal;
step 3, zero line offset noise signal Z is obtained by using formula (3)i(n') intercepting to obtain the intercepted zero line offset noise signal Zi’(n’)：
Figure BDA0002598458760000031
In the formula (3), in the formula (1), pi-1、pi、pi+1Respectively are unequal precision weights, n 'of the ith-1 measurement period, the ith measurement period and the (i + 1) th measurement period'maxIs the maximum value obtained by n ', and n'max＝N+2m；
Step 4, the spectrum signal D after the background noise is corrected by using the formula (4)i' (n) correcting to obtain zero line offset noise corrected probeMeasuring spectral signal Di”(n)；
D″i(n)＝D′i(n)-Z′i(n+m) n＝0,1,2…N (4)
Acquiring a second harmonic spectrum signal R under the ith measurement periodi(n) according to the method of the steps 1 to 4, carrying out measurement on the second harmonic spectrum signal R under the ith measurement period of the reference light pathi(n) obtaining a reference spectrum signal R after zero line offset noise correctioni”(n)；
Step 5, acquiring relevant parameters from a Hitran database to be used for solving a second order differential of the Gaussian line type, and substituting the obtained differential result into an expression of a second harmonic component so as to obtain a standard signal of a second harmonic;
the optimal criterion for the adaptive fit is set using equation (5):
Figure BDA0002598458760000032
in the formula (5), IminlRepresenting the left trough intensity, I, of the second harmonic lineminrRepresenting the intensity of the right trough of the second harmonic line, IminmRepresents the average of the intensities at the two troughs of the second harmonic line,
Figure BDA0002598458760000033
representing the theoretical left and right side lobe widths, Λ, respectivelyl、ΛrThe left side lobe width and the right side lobe width of a second harmonic spectral line are represented respectively, and xi and epsilon are respectively a peak-valley asymmetric threshold and a side lobe threshold;
according to the optimal criterion, the reference spectrum signal R after the zero line offset noise is corrected by using the standard signali"(n) and the detection spectral signal Di"(n) performing adaptive iterative fitting to obtain a reference signal XR after linear asymmetry correction in the ith measurement periodi"(n) with the detection signal XDi”(n)；
Step 6, according to the known reference light path concentration, the reference signal XR is correctedi"(n) with the detection signal XDiAnd (n) inverting the concentration of the gas to be measured, thereby obtaining an inversion result in the ith measurement period.
Compared with the prior art, the invention has the beneficial effects that:
1. according to the invention, through a 'black box' mode, on the basis of not changing a hardware structure system and not increasing the complexity of hardware, a linear nonlinear correction method is provided for processing, so that nonlinear influence is eliminated, and the measurement accuracy is improved.
2. The invention eliminates the spectrum signal D after the background noise correction by correcting the zero line offset and processing according to unequal precision and weighti' (n) zero line offset noise reduces the offset effect of the second harmonic.
3. According to the invention, the optimal criterion is set, and self-adaptive iterative fitting is carried out, so that the asymmetry of the signal is minimized, and the nonlinear influence is eliminated.
Drawings
FIG. 1 is a schematic diagram of a linear nonlinear correction detection system based on harmonic techniques of the present invention;
FIG. 2 is a flow chart of a non-linear modified detection method of the present invention;
FIG. 3 is a diagram of a standard second harmonic in the prior art;
FIG. 4 is a verification chart before and after correction of the method of the present invention;
reference numbers in the figures: 1. a tunable semiconductor laser; 2. a laser control module; 3. a signal generator; 4. a beam splitter; 5. a collimator of the reference light path; 6. a standard gas reference cell; 7. an InGaAs photodetector in the reference optical path; 8. a collimator that detects the light path; 9. a transceiver telescope; 10. a corner mirror; 11. an InGaAs photodetector for detecting the optical path; 12. a phase sensitive detection circuit; 13. a data processor; 14. and a display module.
Detailed Description
In this embodiment, referring to fig. 1, a linear nonlinear correction detection system based on a harmonic technique includes a laser, a control unit, an optical unit, and a data processing unit;
the laser and control unit consists of a tunable semiconductor laser 1, a laser control module 2 and a signal generator 3; the optical unit consists of a transceiver telescope 9, a reference light path and a detection light path; the data processing unit consists of a phase-sensitive detection circuit 12, a data processor 13 and a display module 14;
the tunable semiconductor laser 1 is used as a detection light source, and the temperature and the current are changed through the laser control module 2, so that the output wavelength of the tunable semiconductor laser 1 is changed; enabling the tunable semiconductor laser 1 to output wavelength near a target absorption spectral line;
the tunable semiconductor laser 1 scans and modulates the output wavelength under the combined action of a sawtooth scanning signal generated by the signal generator 3 and a high-frequency sinusoidal signal, so as to obtain a modulated light beam; the modulated light beam is divided into reference light and detection light by a beam splitter 4, the reference light is collimated by a collimator 5 of a reference light path, and then is subjected to photoelectric conversion by an InGaAs photoelectric detector 7 of the reference light path through a standard gas reference cell 6 to obtain a reference electric signal; the detection light is collimated by a collimator 8 of a detection light path, then is emitted by a transceiver telescope 9, is telemetered to atmosphere through an open space, returns by a corner reflector 10, and is subjected to photoelectric conversion by an InGaAs photoelectric detector 11 of the detection light path to obtain a detection electric signal; both signals are sent to a data processing unit, and harmonic signal detection is carried out by a phase sensitive detection circuit 12;
the phase-sensitive detection circuit performs harmonic signal detection on the reference electric signal in the ith measurement period to obtain a second harmonic spectrum signal of the reference light path in the ith measurement period or a second harmonic background signal of the reference light path without absorption in the ith measurement period; the phase-sensitive detection circuit performs harmonic signal detection on the detection electric signal in the ith measurement period to obtain a second harmonic spectrum signal of the detection optical path in the ith measurement period;
the data processor 13 performs nonlinear correction on the second harmonic spectrum signal or the second harmonic background signal of the reference light path in the ith measurement period and the second harmonic spectrum signal of the detection light path in the ith measurement period, and then performs online concentration inversion, so as to obtain an inversion result in the ith measurement period and send the inversion result to the display module 14 for display.
Referring to fig. 2, in this embodiment, a detection method for linear nonlinear correction based on a harmonic technique is performed according to the following steps:
step 1, acquiring a second harmonic spectrum signal D under the ith measurement periodi(n) second harmonic background signal B without absorption with reference light path in ith measurement periodi(n) and correcting the background noise by using the formula (1) to obtain a spectrum signal D after correcting the background noise in the ith measurement periodi’(n)；
D′i(n)＝Di(n)-Bi(n) n＝0,1,2...N (1)
In the formula (1), i represents a corresponding measurement period, N is a signal corresponding sequence position, and N is a maximum value obtained by the N;
step 2, selecting a spectral signal D under the i-1 th measurement periodi-1' (n) m signals of the side lobe non-absorption region on the right side to the spectral signal D at the ith measurement periodi' (n) m signals of left side lobe non-absorption region, and spectral signal D at i-th measurement periodi' (n) m signals of the side lobe non-absorption region on the right side to the spectral signal D after background noise correction in the (i + 1) th measurement periodi+1' (n) m signals of the unabsorbed region of the left side lobe; and m is more than or equal to 0 and less than or equal to N;
polynomial fitting is carried out on the selected non-absorption area signals by using the formula (2) to obtain zero line offset noise signals Z under the ith measurement periodi(n’)；
Zi(n')＝a0+a1n'+a2n'2 n'＝0,1,2...N+2m (2)
In the formula (2), a0，a1，a2Is a fitting coefficient, and n' is a sequence position corresponding to the fitting signal;
step 3, zero line offset noise signal Z is obtained by using formula (3)i(n') intercepting to obtain the intercepted zero line offset noise signal Zi’(n’)：
Figure BDA0002598458760000051
In the formula (3), in the formula (1), pi-1、pi、pi+1Respectively are unequal precision weights, n 'of the ith-1 measurement period, the ith measurement period and the (i + 1) th measurement period'maxIs the maximum value obtained by n ', and n'max＝N+2m；
Step 4, the spectrum signal D after the background noise is corrected by using the formula (4)i' (n) correcting to obtain a detection spectrum signal D after correcting zero line offset noisei”(n)；
D″i(n)＝D′i(n)-Z′i(n+m) n＝0,1,2…N (4)
Acquiring a second harmonic spectrum signal R under the ith measurement periodi(n), correcting zero line offset noise according to the method of the steps 1 to 4 to obtain a reference spectrum signal R after correcting the zero line offset noisei”(n)；
Step 5, acquiring relevant parameters from a Hitran database to be used for solving a second order differential of the Gaussian line type, and substituting the obtained differential result into an expression of a second harmonic component, so as to obtain a standard signal of a second harmonic, wherein the expression is shown in figure 3;
the optimal criterion for the adaptive fit is set using equation (5):
Figure BDA0002598458760000061
in the formula (5), IminlRepresenting the left trough intensity, I, of the second harmonic lineminrRepresenting the intensity of the right trough of the second harmonic line, IminmRepresents the average of the intensities at the two troughs of the second harmonic line,
Figure BDA0002598458760000062
representing the theoretical left and right side lobe widths, Λ, respectivelyl、ΛrRespectively represent the left side lobe width and the right side lobe width of a second harmonic spectral line, and xi and epsilon are respectively asymmetric peak-valleyA threshold and a sidelobe threshold;
according to the optimal criterion, the reference spectrum signal R after the zero line offset noise is corrected by using the standard signali"(n) and the detection spectral signal Di"(n) performing adaptive iterative fitting to obtain a reference signal XR after linear asymmetry correction in the ith measurement periodi"(n) with the detection signal XDi”(n)；
Step 6, according to the known reference light path concentration, the reference signal XR is correctedi"(n) with the detection signal XDiAnd (n) inverting the concentration of the gas to be measured, thereby obtaining an inversion result in the ith measurement period.
In order to verify the effect of the method, the established atmosphere detection system for harmonic detection is used for carrying out experiments, the scanning frequency is set to be 100Hz, the modulation frequency is 50kHz, simulation verification experiments are carried out, a 20m multiple reflection cell is placed on a detection light path in the experiments, and methane with the fixed concentration of 27ppm is measured. The result graphs before and after correction by using the method of the invention are shown in figure 4, the zero line offset detail after correction is inhibited, and the line type asymmetry is eliminated. Therefore, the method provided by the invention can effectively reduce the cost requirement, simultaneously can eliminate the nonlinear influence in harmonic detection, and improves the accuracy of measurement.

Claims (1)

1.一种基于谐波技术的线型非线性修正的检测方法，其特征是按如下步骤进行：1. a detection method based on the linear nonlinear correction of harmonic technology is characterized in that carrying out as follows: 步骤1.获取第i个测量周期下的二次谐波光谱信号Di(n)与参考光路在第i个测量周期下无吸收情况的二次谐波背景信号Bi(n)，并利用式(1)进行背景噪声修正，得到第i个测量周期下的背景噪声修正后的光谱信号Di’(n)；Step 1. Obtain the second harmonic spectral signal D i (n) under the ith measurement period and the second harmonic background signal B i (n) of the reference optical path without absorption under the ith measurement period, and use Formula (1) is used to correct the background noise, and the spectral signal D i '(n) after the background noise correction under the i-th measurement period is obtained; D′i(n)＝Di(n)-Bi(n) n＝0,1,2...N (1)D' i (n)=D i (n)-B i (n) n=0,1,2...N (1) 式(1)中，i表示对应的测量周期，n为信号对应序列位置，N为所述n所取得的最大值；In formula (1), i represents the corresponding measurement period, n is the sequence position corresponding to the signal, and N is the maximum value obtained by the n; 步骤2.选取第i-1个测量周期下的光谱信号Di-1’(n)的右侧旁瓣无吸收区的m个信号到第i个测量周期下的光谱信号Di’(n)的左侧旁瓣无吸收区的m个信号，以及第i个测量周期下的光谱信号Di’(n)的右侧旁瓣无吸收区的m个信号到第i+1个测量周期下的背景噪声修正后的光谱信号Di+1’(n)的左侧旁瓣的无吸收区的m个信号；且0≤m≤N；Step 2. Select m signals from the right side lobe non-absorbing region of the spectral signal D i-1 '(n) under the i-1th measurement period to the spectral signal D i '(n under the i-th measurement period ) and the m signals of the left side lobe non-absorbing region of the i-th measurement period, and the m signals of the right side-lobe non-absorbing region of the spectral signal D i '(n) under the i-th measurement period to the i+1-th measurement period m signals in the non-absorbing region of the left side lobe of the spectral signal D i+1 '(n) after the background noise correction under the background noise; and 0≤m≤N; 利用式(2)对所选取的无吸收区域信号进行多项式拟合，得到第i个测量周期下零线偏移噪声信号Zi(n’)；Use formula (2) to perform polynomial fitting on the selected non-absorbing area signal, and obtain the zero-line offset noise signal Z i (n') under the i-th measurement period; Zi(n')＝a0+a1n'+a2n'2 n'＝0,1,2...N+2m (2)Z i (n')=a 0 +a 1 n'+a 2 n' 2 n'=0,1,2...N+2m (2) 式(2)中，a0，a1，a2为拟合系数，n’为拟合信号对应序列位置；In formula (2), a 0 , a 1 , and a 2 are the fitting coefficients, and n' is the sequence position corresponding to the fitting signal; 步骤3.利用式(3)对零线偏移噪声信号Zi(n’)进行截取，获取截取后的零线偏移噪声信号Zi’(n’)：Step 3. Use equation (3) to intercept the zero-line offset noise signal Z i (n'), and obtain the intercepted zero-line offset noise signal Z i '(n'):
Figure FDA0003059031710000011
Figure FDA0003059031710000011
 式(3)中，式(1)中，pi-1、pi、pi+1分别为第i-1个测量周期、第i个测量周期与第i+1个测量周期的不等精度权重，n’max为所述n'所取得的最大值，且n’max＝N+2m；In formula (3), in formula (1), p i-1 , p i , and p i+1 are the inequalities of the i-1th measurement period, the i-th measurement period and the i+1th measurement period, respectively. Accuracy weight, n' max is the maximum value obtained by the n', and n' max =N+2m; 步骤4.利用式(4)对所述背景噪声修正后的光谱信号Di’(n)进行修正，得到零线偏移噪声修正后的探测光谱信号Di”(n)；Step 4. Use formula (4) to correct the spectral signal D i '(n) after the background noise correction, and obtain the detection spectral signal D i "(n) after the zero line offset noise correction; D″i(n)＝D′i(n)-Z′i(n+m) n＝0,1,2…N (4)D″ i (n)=D′ i (n)-Z′ i (n+m) n=0,1,2...N (4) 获取第i个测量周期下的二次谐波光谱信号Ri(n)，按照步骤1-步骤4的方法对所述参考光路的第i个测量周期下的二次谐波光谱信号Ri(n)进行零线偏移噪声修正后得到零线偏移噪声修正后的参考光谱信号Ri”(n)；Obtain the second harmonic spectral signal R i (n) under the i-th measurement period, and perform the second harmonic spectral signal R i ( n) After the zero-line offset noise correction is performed, the reference spectral signal R i ″(n) after the zero-line offset noise correction is obtained; 步骤5.从Hitran数据库获取相关参数用于对高斯线型求取二阶微分，得到微分结果带入二次谐波分量的表达式，从而获得二次谐波的标准信号；Step 5. Obtain the relevant parameters from the Hitran database for obtaining the second-order differential of the Gaussian line shape, and obtain the expression of the second-order harmonic component brought into the differential result, thereby obtaining the standard signal of the second-order harmonic; 利用式(5)设置自适应拟合的最优准则：Use formula (5) to set the optimal criterion of adaptive fitting:
Figure FDA0003059031710000021
Figure FDA0003059031710000021
 式(5)中，Iminl代表二次谐波谱线左侧波谷强度，Iminr代表二次谐波谱线右侧波谷强度，Iminm代表二次谐波谱线两个波谷处的强度平均值，
Figure FDA0003059031710000022
分别代表理论左侧与右侧旁瓣宽度，Λl、Λr分别代表二次谐波谱线左侧与右侧旁瓣宽度，ξ、ε分别为峰谷不对称阈值与旁瓣阈值；In formula (5), I minl represents the trough intensity on the left side of the second harmonic spectrum line, I minr represents the trough intensity on the right side of the second harmonic spectrum line, and I minm represents the average intensity of the two troughs of the second harmonic spectrum line. value,
Figure FDA0003059031710000022
represent the theoretical left and right side lobe widths, respectively, Λ l and Λ r represent the left and right side lobe widths of the second harmonic spectrum, respectively, ξ and ε are the peak-valley asymmetry threshold and the side lobe threshold, respectively; 根据所述最优准则，利用所述标准信号对零线偏移噪声修正后的参考光谱信号Ri”(n)和探测光谱信号Di”(n)进行自适应迭代拟合，从而得到第i个测量周期下的线型不对称性修正后的参考信号XRi”(n)与探测信号XDi”(n)；According to the optimal criterion, use the standard signal to perform adaptive iterative fitting on the reference spectral signal R i ″(n) and the detection spectral signal D i ″(n) after the zero-line offset noise correction, so as to obtain the first Linear asymmetry corrected reference signal XR i ″(n) and detection signal XD i ″(n) under i measurement periods; 步骤6.根据已知的参考光路浓度，从而对所述参考信号XRi”(n)与探测信号XDi”(n)进行待测气体浓度反演，从而得到第i个测量周期下的反演结果。Step 6. According to the known reference optical path concentration, inversion of the concentration of the gas to be measured is performed on the reference signal XR i "(n) and the detection signal XD i "(n), thereby obtaining the inversion under the i-th measurement cycle. performance result.
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