Multi-component gas leakage detection method and system based on double near-infrared lasers

Abstract

The invention relates to the technical field of gas detection, in particular to a multi-component gas leakage detection method and system based on double near-infrared lasers. The method comprises the following steps: irradiating a to-be-detected area by adopting laser generation equipment; acquiring a detection image of the to-be-detected area by using image acquisition equipment; processing the detection image by adopting processing equipment to obtain detection data of the to-be-detected gas in the to-be-detected area; according to the invention, the first component gas and the second component gas of two components can be sequentially and alternately detected, so that the detection of a specific component gas can be realized only based on images of two times of detection, and the detection of the specific component gas can be realized only by switching the laser generation equipment once; the time window for detecting the single-component gas in multi-component gas detection is shortened, and the dynamic scene error can be effectively inhibited.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of gas detection, in particular to a multi-component gas leakage detection method and system based on double near-infrared lasers. BACKGROUND

[0002] At present, there are two categories of active detection and passive detection for single gas leakage detection imaging technology such as methane.

[0003] Active detection mostly uses a single-point laser-photo diode combination, which can only obtain integrated concentration of the light path and cannot be spatially positioned; active detection also includes a scanning laser radar based on a 1550nm DFB laser, and the methane concentration is detected and imaged by double-wavelength modulation and an APD detector, but is limited by the frame rate of the mechanical scanning architecture.

[0004] Passive detection mainly relies on mid-infrared thermal imaging technology, and its core defect is that the strong dependence of the mid-infrared band (3-5 μm) on temperature results in that when the temperature difference between the gas and the background is insufficient in a low-temperature environment (such as winter or an industrial cold area), the signal-to-noise ratio (SNR) of thermal imaging drops sharply, and the leakage area cannot be effectively identified; at the same time, due to the long-wavelength characteristics (λ=3-5 μm) of the mid-infrared, the diffraction limit is significantly degraded, resulting in generally low imaging resolution and increasing detection difficulty. SUMMARY

[0005] The present application provides a multi-component gas leakage detection method and system based on double near-infrared lasers, which can overcome some or some defects of the prior art.

[0006] The multi-component gas leakage detection method based on double near-infrared lasers according to the present application comprises, The laser generating device is used to irradiate the to-be-detected area; wherein the laser generating device is used to output first laser, second laser, third laser and fourth laser which are periodically switched in sequence, the first laser is obtained by coupling a laser with a first wavelength and a laser with a second wavelength, the second laser is obtained by coupling a laser with a third wavelength and a laser with a fourth wavelength, the third laser is obtained by coupling a laser with a fifth wavelength and a laser with a sixth wavelength, and the fourth laser is the same as the second laser; the to-be-detected gas at the to-be-detected area includes a first component gas and a second component gas, the first wavelength is an absorbable wavelength of the first component gas, the second wavelength is a non-absorbable wavelength of the second component gas, the third wavelength is a non-absorbable wavelength of the first component gas, the fourth wavelength is a non-absorbable wavelength of the second component gas, the fifth wavelength is a non-absorbable wavelength of the first component gas, and the sixth wavelength is an absorbable wavelength of the second component gas; The image acquisition device is used to acquire a detection image of the to-be-detected region; the detection image is a video image acquired in succession and having a frame sequence of a first image, a second image, a third image, and a fourth image; the first image, the second image, the third image, and the fourth image are reflection images acquired when the first laser, the second laser, the third laser, and the fourth laser irradiate the to-be-detected region, respectively; and the acquisition frame rate of the image acquisition device is consistent with the switching rate of the first laser, the second laser, the third laser, and the fourth laser. The processing device is used to process the detection image to acquire detection data of the to-be-detected gas of the to-be-detected region.

[0007] Preferably, the sum of the first wavelength and the second wavelength, the sum of the third wavelength and the fourth wavelength, and the sum of the fifth wavelength and the sixth wavelength are all equal.

[0008] Preferably, the laser generation device comprises two signal generators, two laser driver modules, a laser coupler, and a laser mirror group; the two signal generators are used to generate periodic first and second driving signals for driving the two laser driver modules, respectively; the first driving signal is used to drive the corresponding laser driver module to output laser having the first wavelength, laser having the third wavelength, and laser having the fifth wavelength in turn and periodically; the second driving signal is used to drive the corresponding laser driver module to output laser having the second wavelength, laser having the fourth wavelength, and laser having the sixth wavelength in turn and periodically; the laser coupler and the laser mirror group are used to couple the first laser, the second laser, the third laser, and the fourth laser and guide the coupled laser to the to-be-detected region, respectively.

[0009] Preferably, the laser mirror group comprises a laser collimating mirror, an adjustable lens sleeve, a lens sleeve, and an engineering diffuser arranged in turn.

[0010] Preferably, the processing of the detection image by the processing device comprises processing the detection image to acquire to-be-detected gas concentration data and a gas plume image; and the detection data of the to-be-detected gas comprises the to-be-detected gas concentration data and the gas plume image.

[0011] Preferably, the processing device processes the first image and the second image to acquire detection data of the first component gas.

[0012] Preferably, the processing device processes the third image and the fourth image to acquire detection data of the second component gas.

[0013] Preferably, when the processing device processes the detection image, the processing comprises: constructing an input image set based on the detection image; the input image set is a video frame sequence of the detection image; Preprocessing is performed on each frame of image in the input image set; For any frame of image, based on the gray value of the any frame of image and the next frame of image, the gray value variation of each pixel point of the any frame of image is obtained, and a variation vector is constructed; For any frame of image, a threshold is determined based on the variation vector thereof, the gray value of the pixel point with the gray value variation lower than the determined threshold is set to 0, and the gray value of the pixel point with the gray value variation lower than the determined threshold is determined based on the variation vector; Postprocessing is performed on any frame of image, and an output image set is obtained and output.

[0014] The multi-component gas leakage detection system based on dual near-infrared lasers according to the present disclosure comprises a laser generating device, an image acquisition device, and a processing device, and the laser generating device, the image acquisition device, and the processing device are used to jointly implement any of the above-mentioned multi-component gas leakage detection methods based on dual near-infrared lasers.

[0015] Preferably, the laser generating device is used to output the first laser, the second laser, the third laser, and the fourth laser which are periodically switched in sequence, the first laser is obtained by coupling a laser with a first wavelength and a laser with a second wavelength, the second laser is obtained by coupling a laser with a third wavelength and a laser with a fourth wavelength, the third laser is obtained by coupling a laser with a fifth wavelength and a laser with a sixth wavelength, and the fourth laser is the same as the second laser.

[0016] The present disclosure has the following beneficial effects: The first component gas and the second component gas of the two components can be detected in sequence, so that the detection of a specific component gas can be realized based on the images obtained by the previous and subsequent detections, the detection of the specific component gas can be realized by switching the laser generating device only once, the time window for detecting a single component gas in multi-component gas detection is shortened, and dynamic scene errors can be effectively suppressed. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 A flowchart of a single-component gas leakage detection method according to the present disclosure; Figure 2 A deployment schematic diagram of a single-component gas leakage detection system according to the present disclosure; Figure 3 A first image obtained by a single-component gas leakage detection method according to the present disclosure in a specific example; Figure 4 A second image obtained by a single-component gas leakage detection method according to the present disclosure in a specific example; Figure 5A visualized image acquired by a single-component gas leakage detection method of the present disclosure in one embodiment; Figure 6 A wavelength timing diagram of a single-component gas leakage detection method of the present disclosure; Figure 7 A schematic diagram of a laser mirror set of a single-component gas leakage detection method of the present disclosure; Figure 8 A schematic diagram of a single-component gas leakage detection system of the present disclosure; Figure 9 A flowchart of a multi-component gas leakage detection method of the present disclosure; Figure 10 A schematic diagram of a multi-component gas leakage detection system of the present disclosure; Figure 11 A wavelength timing diagram of a multi-component gas leakage detection method of the present disclosure; Figure 12 A first image acquired by a multi-component gas leakage detection method of the present disclosure in one embodiment; Figure 13 A second image acquired by a multi-component gas leakage detection method of the present disclosure in one embodiment; Figure 14 A third image acquired by a multi-component gas leakage detection method of the present disclosure in one embodiment; Figure 15 Concentration data of methane gas at different locations and a visualized image at a detection area acquired by a multi-component gas leakage detection method of the present disclosure in one embodiment; Figure 16 Concentration data of hydrogen sulfide gas at different locations and a visualized image at a detection area acquired by a multi-component gas leakage detection method of the present disclosure in one embodiment; Figure 17 A flowchart of a gas detection method based on weak signal enhancement and time domain denoising of the present disclosure; Figure 18 A processing step diagram of a gas detection method based on weak signal enhancement and time domain denoising of the present disclosure in one embodiment; Figure 19 A flowchart of a gas detection system based on weak signal enhancement and time domain denoising of the present disclosure. DETAILED DESCRIPTION

[0018] For further understanding of the present disclosure, the present disclosure will be described in detail with reference to the embodiments. It should be understood that the embodiments are only used to explain the present disclosure but not to limit the present disclosure.

[0019] One of the purposes of the present disclosure is to propose a differential absorption imaging technology based on near-infrared (1.5-1.65 μm) active laser, which avoids thermal radiation interference and breaks through the diffraction limit by actively emitting a tunable laser source (line width <0.1 nm) combined with a high-resolution near-infrared camera; in addition, the dual-wavelength modulation technology (absorption peak λ0 and reference wavelength λ1 are alternately excited) is used to extract the differential absorption signal from the environmental background noise, realize high sensitivity recognition ability, and solve the temperature sensitivity and resolution bottleneck of existing mid-infrared technology.

[0020] As shown in Figure 1 and 2 The single-component gas leakage detection method based on near-infrared laser proposed by the present disclosure can include the following steps: A laser generating device is used to irradiate the detection area; wherein the laser generating device is used to alternately output first laser and second laser, the first laser has a first wavelength, and the second laser has a second wavelength; the first wavelength is the absorbable wavelength of the detected gas; the second wavelength is the non-absorbable wavelength of the detected gas; An image acquisition device is used to acquire a detection image of the detection area; wherein the detection image is a video image acquired continuously and adjacent frames are respectively first image and second image, the first image is a reflection image acquired when the first laser irradiates the detection area, and the second image is a reflection image acquired when the second laser irradiates the detection area; the acquisition frame rate of the image acquisition device is consistent with the alternating frequency of the first laser and the second laser; A processing device is used to process the detection image to obtain the detection data of the detected gas in the detection area.

[0021] Based on the above, the selective absorption of a single component gas to a specific waveband light can be used to generate a first laser with a wavelength that can be absorbed by the gas to be detected and a second laser with a wavelength that cannot be absorbed by the gas to be detected by a laser generating device; since the first laser is on the absorption spectrum of the gas to be detected, the gas to be detected will absorb the passing first laser, and the corresponding detection image can reflect the gas to be detected, specifically, the pixel value is positively correlated with the concentration of the gas to be detected; similarly, since the second laser is on the reflection spectrum of the gas to be detected, the gas to be detected will not absorb the passing second laser, and the corresponding detection image cannot reflect the gas to be detected, which can be preferably used as a background group image; by setting the acquisition frame rate of the image acquisition device to be consistent with the alternating frequency of the first laser and the second laser, the adjacent two frames of detection images that can and cannot reflect the gas to be detected can be obtained, and the detection image can be a continuous video image; then, the processing device can perform differential processing on the reflection image, thereby preferably realizing imaging of the gas plume of the gas to be detected.

[0022] It can be understood that the first wavelength and the second wavelength can be selected based on the type of the gas to be detected. For example, when the gas to be detected is methane, the first wavelength can be set to 1653.8 nm, and the second wavelength can be set to 1653 nm.

[0023] As shown in Figure 3 , the first image can reflect the gas to be detected.

[0024] As shown in Figure 4 , the second image cannot reflect the gas to be detected.

[0025] As shown in Figure 5 , based on the processing of the first image and the second image in the detection image, the detection data of the gas to be detected can be obtained.

[0026] As shown in Figure 6 , the laser generating device includes a signal generator, a laser driver module, and a laser mirror group. The signal generator is used to generate a periodically changing driving signal, the driving signal is used to drive the laser driver module to generate a periodically changing first laser and a second laser, and the laser mirror group is used to guide the first laser and the second laser to the detection area.

[0027] Based on the above, the wavelength and the change frequency of the first laser and the second laser can be set, so that the first laser and the second laser with a change frequency consistent with the frame rate of the image acquisition device can be generated, so that the continuous two frames of the image acquisition device correspond to different laser wavelengths, which is convenient for subsequent image processing, reduces the influence of background light changes, reduces the influence caused by camera shaking, and also improves the operation speed of the system.

[0028] Wherein, the laser driver module can include, for example, a distributed feedback laser diode (DFB-LD) with narrow linewidth (<0.1 nm) and wavelength tunable characteristics, so that the gas absorption peak can be accurately matched; the signal generator can realize the generation of the driving signal based on wavelength modulation means such as voltage tuning.

[0029] See Figure 7 The laser mirror group can include a laser collimating mirror, an adjustable lens sleeve, a lens sleeve, and an engineering diffuser arranged in sequence. Thus, the detection spot can be formed in a surface output manner at the to-be-detected area, effectively expanding the detection surface.

[0030] Wherein, the laser collimating mirror can adopt an aspherical lens with a focal length of 20 mm and a diameter of 25.4 mm, and the adjustable lens sleeve can select the SM1-20V model. The collimating mirror group composed of the laser collimating mirror and the adjustable lens sleeve can effectively collimate the point light source with a diameter of about 1 mm emitted by the laser driver module into a parallel light beam; the engineering diffuser can select the N-BK7 model, which has a diameter of 25.4 mm and a scattering angle of 20°, and can effectively realize wide-angle diffusion of the parallel light beam, thereby forming a surface output detection spot.

[0031] Wherein, the driving signal adopts a square wave signal, the high-level amplitude of the driving signal is used to drive the laser generating device to generate the first laser, and the low-level amplitude of the driving signal is used to drive the laser generating device to generate the second laser. Thus, the frequency and wavelength of the first laser and the second laser can be preferably controlled.

[0032] See Figure 8 In one specific embodiment of the present disclosure, the driving signal is used to simultaneously drive the image acquisition device to perform the acquisition action. Figure 8 Wherein, a represents the driving signal, b and d represent the laser driver module, c is the laser fiber generated by the laser driver module, e is the laser mirror group, and f is the image acquisition device (near-infrared camera).

[0033] Wherein, the processing performed by the processing device on the detection image can include processing the detection image, obtaining the to-be-detected gas concentration data and the gas plume image; wherein the detection data of the to-be-detected gas includes the to-be-detected gas concentration data and the gas plume image.

[0034] Based on the above, the concentration data of the to-be-detected gas at different positions and the visualized image of the to-be-detected gas at the to-be-detected area can be obtained.

[0035] Wherein, obtaining the to-be-detected gas concentration data includes the following steps, aligning the first image and the second image of the continuous frames at the pixel level; obtain the concentration information at each pixel point of the detection image; wherein, for any pixel point with pixel coordinates (x, y) in the detection image, the concentration C(x, y) is, ; wherein, is the absorption coefficient of the to-be-detected gas to the first laser, is the optical path at the point with pixel coordinates (x, y), is the pixel value of the point with pixel coordinates (x, y) at the first image, is the pixel value of the point with pixel coordinates (x, y) at the second image.

[0036] Wherein, the processing of the gas plume image can be obtained based on the difference processing of the first image and the second image of the continuous frames.

[0037] In addition, based on the single-component gas leakage detection method based on the near-infrared laser proposed in the disclosure, the disclosure further proposes a single-component gas leakage detection system based on a near-infrared laser, which includes a laser generating device, an image acquisition device and a processing device, and the laser generating device, the image acquisition device and the processing device are used to jointly implement the single-component gas leakage detection method based on the near-infrared laser of the disclosure.

[0038] Based on the above-mentioned scheme of the disclosure, in view of the temperature influence, the methane gas absorption waveband of near-infrared can be selected to avoid the interference of temperature on the result; in view of the resolution, the image acquisition device of the near-infrared waveband with higher resolution can be selected; in view of the imaging, the laser and the near-infrared camera can be matched to realize the quantitative analysis of the gas and the imaging of the gas at the same time; in view of the speed, the matching laser lens group can be used to make the laser output in one plane instead of one point through the engineering beam expander, and the gas area can be imaged at one time without scanning.

[0039] Considering that the single-component gas leakage detection method and system disclosed above have the following disadvantages, 1. The type of to-be-detected gas is limited, and only one type of to-be-detected gas can be detected; for example, in the natural gas leakage detection scene, due to the limitation of the tuning range of the distributed feedback laser diode, which is only 2 nm, the absorption peaks of methane (CH4) and hydrogen sulfide (H2S) are located at 1653.8 nm and 1578 nm, respectively, which is far beyond the tuning range of a single distributed feedback laser diode, and the synchronous detection of multi-component gas cannot be realized; therefore, when multiple-component gas needs to be detected, an independent laser needs to be configured for each gas, which is difficult to meet the multi-parameter monitoring demand in the industrial scene; 2、Signal generator based on timing signal (square wave signal) timing spectroscopy, and then drive to produce different wavelengths of laser; This will lead to the existence of light intensity-wavelength coupling interference, light intensity-wavelength coupling interference refers to, the driving current of the distributed feedback laser diode simultaneously modulates the output wavelength and the optical power, resulting in significant differences in laser intensity between the reference wavelength and the absorption wavelength, the baseline drift introduced by light intensity fluctuation cannot be eliminated by simple difference, especially in low concentration (<10 ppm·m) detection, the system noise is significantly amplified; Although three wavelength switching can be used to complete single gas detection, but this will lead to the extension of the data acquisition time window (typical period > 30 ms), during which the change of environmental light, target displacement or gas plume shape will introduce additional errors, reduce the detection reliability.

[0040] In order to achieve the goals of reducing the number of switches, suppressing environmental interference, increasing the ability to detect multiple gases and scalability, the present disclosure also proposes a multi-component gas leakage detection method and system based on double near-infrared lasers.

[0041] As shown in Figure 9 The multi-component gas leakage detection method based on double near-infrared lasers proposed by the present disclosure comprises, The laser generating device is used to output the first laser, the second laser, the third laser and the fourth laser which are periodically switched in turn, the first laser is obtained by coupling the laser with the first wavelength and the laser with the second wavelength, the second laser is obtained by coupling the laser with the third wavelength and the laser with the fourth wavelength, the third laser is obtained by coupling the laser with the fifth wavelength and the laser with the sixth wavelength, and the fourth laser is consistent with the second laser; The gas to be detected in the detection area includes the first component gas and the second component gas, the first wavelength is the absorbable wavelength of the first component gas, the second wavelength is the non-absorbable wavelength of the second component gas, the third wavelength is the non-absorbable wavelength of the first component gas, the fourth wavelength is the non-absorbable wavelength of the second component gas, the fifth wavelength is the non-absorbable wavelength of the first component gas, and the sixth wavelength is the absorbable wavelength of the second component gas; The image acquisition device is used to acquire the detection image of the detection area; wherein the detection image is a video image acquired continuously and having a frame sequence of the first image, the second image, the third image and the fourth image, the first image, the second image, the third image and the fourth image are respectively the reflection images acquired when the first laser, the second laser, the third laser and the fourth laser irradiate the detection area, and the acquisition frame rate of the image acquisition device is consistent with the switching rate of the first laser, the second laser, the third laser and the fourth laser; The processing device is used to process the detection image to obtain the detection data of the gas to be detected in the detection area.

[0042] Based on the above, the first component gas and the second component gas of the two components can be detected in turn, so that the detection of a specific component gas can be realized based on the images of the previous and next two detections, and the detection of a specific component gas can be realized by switching the laser generating device only once, which shortens the time window for detecting a single component gas in multi-component gas detection and can effectively suppress dynamic scene errors.

[0043] In combination Figure 10 As shown in the scheme, the laser generating device includes two signal generators, two laser driver modules, a laser coupler, and a laser mirror group. The two signal generators are used to generate periodic first and second driving signals for driving the two laser driver modules, respectively. The first driving signal is used to drive the corresponding laser driver module to output laser with a first wavelength, laser with a third wavelength, and laser with a fifth wavelength in turn and periodically. The second driving signal is used to drive the corresponding laser driver module to output laser with a second wavelength, laser with a fourth wavelength, and laser with a sixth wavelength in turn and periodically. The laser coupler and the laser mirror group are used to couple the first, second, third, and fourth lasers and guide the coupled laser to the detection area.

[0044] Based on the above, the double-laser parallel modulation technology can be used to make the two lasers emit light at the same time and be coupled into a beam of light output through a fiber coupler, which can better realize the detection of multi-component gas. This can expand the wavelength coverage range to two independent wavebands (such as 1.58 μm and 1.65 μm), realize the synchronous detection of multi-component mixed gas (such as CH4 and H2S mixed gas) by a single system, and break through the limitation of spectral matching. At the same time, the optical interface of the laser can be designed in a modular way, so that the detection of new component gas categories can be realized by only replacing different laser driver modules, without the need to reconfigure the optical path or algorithm framework, and has good expandability.

[0045] wherein, Figure 10 In the above, f represents a laser coupler. The laser coupler can use a fiber combiner to couple the dual-wavelength laser into a single multimode optical fiber (core diameter 50 μm, NA=0.22).

[0046] As shown in Figure 11 , the disclosure takes CH4 and H2S mixed gas as an example for illustration, At t0, one of the laser driving modules (laser A) outputs at a wavelength of 1653.8 nm (first wavelength, strong methane absorption peak), and the other laser driving module (laser B) outputs at a wavelength of 1577.2 nm (second wavelength, hydrogen sulfide non-absorption region); at this time, the image acquisition device synchronously acquires a first image (methane absorption image, both the first wavelength and the second wavelength are far away from the hydrogen sulfide absorption peak, and hydrogen sulfide does not absorb); At t1, one of the laser driving modules (laser A) outputs at a wavelength of 1653.4 nm (third wavelength, methane absorption coefficient non-absorption region with a 90% drop), and the other laser driving module (laser B) outputs at a wavelength of 1577.6 nm (fourth wavelength, hydrogen sulfide non-absorption region); at this time, the image acquisition device synchronously acquires a second image (no gas absorption image, which is a reference background image, and is used to eliminate common-mode noise caused by environmental reflectivity differences and laser power fluctuations); At t2, one of the laser driving modules (laser A) outputs at a wavelength of 1653.0 nm (fifth wavelength, methane complete non-absorption region), and the other laser driving module (laser B) outputs at a wavelength of 1578.0 nm (sixth wavelength, hydrogen sulfide absorption peak); at this time, the image acquisition device synchronously acquires a third image (hydrogen sulfide absorption image, both the first wavelength and the second wavelength are far away from the methane absorption peak, and methane does not absorb); At the end time, one of the laser driving modules (laser A) outputs at a wavelength of 1653.4 nm (third wavelength, methane absorption coefficient non-absorption region with a 90% drop), and the other laser driving module (laser B) outputs at a wavelength of 1577.6 nm (fourth wavelength, hydrogen sulfide non-absorption region); at this time, the image acquisition device synchronously acquires a fourth image (same as the second image).

[0047] See Figure 12 The first image obtained at t0; the methane gas can be reflected in the first image.

[0048] See Figure 13 The second image obtained at t1; the background information can be reflected in the second image.

[0049] See Figure 14 The third image obtained at t2; the hydrogen sulfide gas can be reflected in the third image.

[0050] See Figure 15 The processing device can process the first image and the second image based on, for example, the above method, so as to obtain the concentration data of the methane gas at different positions and the visualization image of the methane gas in the detection area.

[0051] SeeFigure 16 The processing device can obtain the concentration data of hydrogen sulfide gas at different positions and the visualized image at the region to be detected by processing the third image and the fourth image based on the above method.

[0052] In addition, in the multi-component gas leakage detection method of the present disclosure, in order to eliminate the detection difference caused by light intensity fluctuation, improve the signal-to-noise ratio (SNR) of low-concentration detection, and reduce the lower limit of small-dose gas detection, the sum of the driving currents of the two signal generators is kept constant. Based on this, at any moment, the first laser, the second laser, the third laser, and the fourth laser can all maintain a constant light intensity. Through the light intensity balancing design of the dual laser, the light intensity fluctuation can be better suppressed.

[0053] Specifically, the output light intensity (I) of the laser is linearly related to the driving current (i), and the wavelength tuning of the signal generator is realized by current fine tuning. Therefore, only the sum of the first wavelength and the second wavelength, the sum of the third wavelength and the fourth wavelength, and the sum of the fifth wavelength and the sixth wavelength need to be designed to be equal, so as to realize the light intensity balancing design of the dual laser.

[0054] Based on the above design, in the image processing stage, the light intensity fluctuation can be offset through differential processing, and the residual noise is only contributed by the gas absorption signal.

[0055] In the scheme of the present disclosure, the non-overlapping wavelength pairs (such as methane 1653.8 nm and hydrogen sulfide 1578.0 nm) can be designed based on the accurate matching of gas absorption lines using the HITRAN database to avoid spectral crosstalk. Through independent modulation of the dual laser, quantitative imaging of multiple gases (CH4, H2S) is completed in a single detection cycle, which expands the limitations of traditional single-gas detection.

[0056] Meanwhile, the present disclosure also proposes a multi-component gas leakage detection system based on dual near-infrared lasers, which includes a laser generating device, an image collecting device, and a processing device.

[0057] In addition, considering that when there is a small flow of gas leakage, the change vector of the gas in the image is similar to the background change, it is difficult to accurately segment the gas region, resulting in a high false detection and missed detection rate. That is, when the processing device processes the detection image by image difference or fixed threshold method, it is based on the static background assumption, which causes a large amount of non-uniform noise in the processed image due to changes in the light spot, changes in the surrounding environment, etc. At the same time, the current processing method also has defects such as lack of weak signal enhancement mechanism for small flow gas, poor processing effect on complex noise (such as randomly occurring single-frame noise), etc., which will affect the detection accuracy of the processing device when processing the detection image.

[0058] Based on the above, another purpose of the present disclosure is to provide a gas detection method and system based on weak signal enhancement and time domain denoising.

[0059] See Figure 17 In the process of processing the detection image by the processing device, based on the gas detection method based on weak signal enhancement and time domain denoising of the present disclosure, the following steps can be performed, Based on the detection image, an input image set is constructed, which is a video frame sequence of the detection image; Pretreatment is performed on each frame image in the input image set; For any frame image, based on the gray value of the any frame image and the next frame image, the gray value change amount of each pixel point of the any frame image is obtained, and a change vector is constructed; For any frame image, a threshold is determined based on its change vector, and the gray value of the pixel point with a gray value change amount lower than the determined threshold is set to 0, and the gray value of the pixel point with a gray value change amount lower than the determined threshold is determined based on the change vector; Post-processing is performed on any frame image to obtain an output image set and output.

[0060] Based on the above, the deficiency of the prior art can be overcome, and the weak signal can be enhanced. By using the change vector analysis method, the feature saliency of small flow gas in the image can be effectively improved, and accurate segmentation can be facilitated. Through pretreatment and post-treatment, a multi-stage noise suppression process can be designed, and through the comprehensive use of various filters and time domain filters described later, effective processing of different types of noise can be realized, and the signal-to-noise ratio of the detection result can be improved. It can realize a fully automated gas detection process, reduce manual intervention, improve detection efficiency and accuracy, and is suitable for gas leakage detection under various environmental conditions.

[0061] Among them, bilateral filtering can be used to pretreat each frame image in the input image set. Based on this, by setting appropriate filtering parameters, the edge information between the gas and the background can be retained while removing the image noise, providing a clear and accurate image basis for subsequent change vector analysis.

[0062] In one specific embodiment of the present disclosure, the diameter of the filter of the bilateral filter can be set to 9, the spatial distance parameter can be set to 75, and the color difference range parameter can be set to 75.

[0063] Wherein, in the calculation of the gray value variation, the current frame image and the next frame image can be first converted to the RGB color space, the gray value variation is obtained based on the square root of the sum of squares of the difference of the three image channel values of the current frame image and the next frame image in the RGB color space, and the gray value variations at all pixel points jointly constitute the change vector. Based on this, the gray difference value can be calculated pixel by pixel, and the change vector amplitude can be obtained by taking the square root of the sum of squares of the gray difference, so as to highlight the area with obvious changes in the image, i.e. the potential gas leakage area.

[0064] Wherein, the calculation formula of the gray value variation can be ; Wherein, represents the gray difference value of the pixel point with pixel coordinates (x, y), , and respectively represent the R, G and B three image channel values corresponding to the i-th frame image. , and respectively represent the R, G and B three image channel values corresponding to the i+1-th frame image.

[0065] Wherein, for any frame image, the 97th percentile of its change vector can be taken as the threshold value. Based on this, the determination and screening of the adaptive threshold value can be realized by calculating the change vector amplitude of the adjacent frame images, the preliminary gas region screening can be realized by classifying the pixel points below the threshold value as background or noise, and most irrelevant change information can be removed; the weak signal of small flow gas leakage can be effectively highlighted; compared with the method of fixed threshold segmentation, the weak signal change in different scenes can be adapted, and the gas region can also be accurately segmented when the change vector of small flow gas is similar to the background change, and the missed detection is not easy to occur.

[0066] Wherein, in the determination of the gray value of the pixel point with the gray value variation below the determined threshold value, the gray value variation above the determined threshold value is linearly mapped to the interval [0, 255], and the mapped value is taken as the gray value of the corresponding pixel point. Based on this, each frame image can be converted to a gray image, which is convenient for subsequent processing and visual display, so that the gas region is intuitively presented in the form of gray change.

[0067] The post-processing of any frame image includes, in sequence, cluster segmentation, median filtering, non-local mean denoising, and time domain filtering. Based on this, various image processing techniques such as bilateral filtering, median filtering, non-local mean denoising, and DBSCAN clustering algorithm can be comprehensively used, in a specific order and parameter setting, to remove noise interference in the image step by step, while accurately segmenting the gas region, and the entire process cooperates to significantly improve the accuracy and robustness of gas detection. The median filtering can effectively suppress salt and pepper noise and smooth the image edges. The non-local mean denoising can effectively target Gaussian noise, removing noise while preserving the details of the gas region. The time domain filtering can use time series information to filter out random noise that only appears in a single frame, making the detection result more stable.

[0068] The cluster segmentation can be implemented based on the DBSCAN clustering segmentation algorithm or the K-means clustering algorithm. Taking the DBSCAN clustering segmentation algorithm as an example, the field radius can be set to 10, and the minimum sample number can be set to 10. The cluster processing is performed on the pixel points with non-zero gray values in each frame image, the high-density connected pixel points are clustered into a region, the continuous gas region is extracted, and the gray values of the non-continuous pixel points are set to 0. Based on this, the scattered noise points can be effectively removed, and the gas cluster can be distinguished from the background or other interference objects.

[0069] Specifically, the DBSCAN clustering algorithm is a density-based spatial clustering algorithm, which can divide high-density regions into clusters as gas reserves, and low-density regions are considered as noise and removed.

[0070] In the median filtering, the kernel size can be set to 3x3. The remaining isolated noise points in the image can be effectively removed by median filtering, the boundaries of the gas region are smoothed, the detection result is further optimized, and the outline of the gas region is more clear and complete.

[0071] The non-local mean denoising can set the denoising intensity parameter h=10, the template window size to 5x5, and the search window size to 11x11. Based on this, the details of the gas region can be preserved while removing random noise and improving image quality.

[0072] In the time domain filtering, the number of gray values that are non-zero in the images of a set number of frames (for example, 7 frames) before the current frame for any pixel point in the current frame image is counted, and the gray value of the corresponding pixel point is set to 0 when the number is lower than a set threshold number of times (for example, 4 times). Based on this, the number of times each pixel point changes within a time window can be counted, only those regions that change continuously in enough frames are retained, and accidental and transient noise interference is filtered out, enhancing the stability and reliability of the detection result.

[0073] The present disclosure provides a gas detection method based on weak signal enhancement and time domain denoising. Figure 18 The present disclosure provides a gas detection method based on weak signal enhancement and time domain denoising.

[0074] The present disclosure provides a gas detection method based on weak signal enhancement and time domain denoising. Figure 19 The present disclosure also provides a gas detection system based on weak signal enhancement and time domain denoising, which comprises, An image acquisition module is configured to acquire detection images. It can be understood that the image acquisition module can comprise the laser generating device and the image acquisition device described above. A preprocessing and change detection module is configured to preprocess each frame of image in the input image set and to construct a change vector. A weak signal extraction module is configured to determine the gray value of any frame of image based on the change vector and to perform clustering segmentation. A multi-stage denoising module is configured to perform median filtering, non-local mean denoising and time domain filtering.

[0075] It can be easily understood that, based on one or more embodiments provided by the present application, other embodiments can be obtained by combining, splitting, recombining, etc. of the embodiments of the present application, and these embodiments do not exceed the protection scope of the present application.

[0076] The above describes the present application and its embodiments in a schematic manner, and the description is not restrictive. The embodiments shown are only part of the embodiments of the present application, and the actual structure is not limited thereto. Therefore, if a person skilled in the art is inspired by the present application, without departing from the spirit of the present application, similar structural modes and embodiments can be designed without creative design, and all of them should belong to the protection scope of the present application.

Claims

1. A method for multi-component gas leak detection based on dual near-infrared lasers, characterized in that, The application relates to a laser detection device and a laser detection method. The laser detection device comprises a laser generation device, an image acquisition device and a processing device. The laser generation device is used for irradiating a to-be-detected area; wherein the laser generation device is used for outputting first laser, second laser, third laser and fourth laser which are periodically switched in sequence, the first laser is obtained by coupling first laser with second laser, the second laser is obtained by coupling third laser with fourth laser, the third laser is obtained by coupling fifth laser with sixth laser, and the fourth laser is the same as the second laser; the to-be-detected gas at the to-be-detected area comprises first component gas and second component gas, the first wavelength is the absorbable wavelength of the first component gas, the second wavelength is the non-absorbable wavelength of the second component gas, the third wavelength is the non-absorbable wavelength of the first component gas, the fourth wavelength is the non-absorbable wavelength of the second component gas, the fifth wavelength is the non-absorbable wavelength of the first component gas, and the sixth wavelength is the absorbable wavelength of the second component gas. The image acquisition device is used for acquiring a detection image of the to-be-detected area; wherein the detection image is a video image which is continuously acquired and has a frame sequence of first image, second image, third image and fourth image, the first image, the second image, the third image and the fourth image are reflection images which are acquired when the first laser, the second laser, the third laser and the fourth laser irradiate the to-be-detected area respectively, and the acquisition frame rate of the image acquisition device is consistent with the switching rate of the first laser, the second laser, the third laser and the fourth laser.

2. The dual near-infrared laser based multi-component gas leak detection method of claim 1, wherein, The processing device is used for processing the detection image and acquiring detection data of the to-be-detected gas of the to-be-detected area.

3. The dual near-infrared laser based multi-component gas leak detection method of claim 1, wherein, The sum of the first wavelength and the second wavelength, the sum of the third wavelength and the fourth wavelength and the sum of the fifth wavelength and the sixth wavelength are all equal.

4. The dual near-infrared laser based multi-component gas leak detection method of claim 3, wherein, The laser generation device comprises two signal generators, two laser driver modules, a laser coupler and a laser mirror group; the two signal generators are used for generating first driving signal and second driving signal which are periodically changed and are used for driving the two laser driver modules respectively; the first driving signal is used for driving the corresponding laser driver module to output laser with the first wavelength, laser with the third wavelength and laser with the fifth wavelength which are periodically switched in sequence, the second driving signal is used for driving the corresponding laser driver module to output laser with the second wavelength, laser with the fourth wavelength and laser with the sixth wavelength which are periodically switched in sequence; the laser coupler and the laser mirror group are used for coupling the first laser, the second laser, the third laser and the fourth laser respectively and guiding the coupled laser to the to-be-detected area.

5. The dual near-infrared laser based multi-component gas leak detection method of claim 1, wherein, The laser mirror group comprises laser collimating mirrors, an adjustable lens sleeve, a lens sleeve and an engineering diffuser which are arranged in sequence.

6. The dual near-infrared laser based multi-component gas leak detection method of claim 5, wherein, The processing device processes the detection image, acquires to-be-detected gas concentration data and gas plume images; wherein the detection data of the to-be-detected gas comprises the to-be-detected gas concentration data and the gas plume images.

7. The dual near-infrared laser based multi-component gas leak detection method of claim 5, wherein, The processing device processes the first image and the second image, and acquires detection data of the first component gas. The processing device processes the third image and the fourth image, and acquires detection data of the second component gas.

8. The dual near-infrared laser based multi-component gas leak detection method of claim 5, wherein, When the processing device processes the detection image, comprising, constructing an input image set based on the detection image, the input image set being a video frame sequence of the detection image; preprocessing each frame image in the input image set; for any frame image, obtaining a gray value variation quantity at each pixel point of the any frame image based on the gray values of the any frame image and a next frame image, and constructing a variation vector; for any frame image, determining a threshold based on the variation vector thereof, setting the gray value of a pixel point with a gray value variation quantity lower than the determined threshold to 0, and determining the gray value of a pixel point with a gray value variation quantity lower than the determined threshold based on the variation vector; postprocessing any frame image, obtaining an output image set and outputting.

9. A multi-component gas leak detection system based on dual near infrared lasers, characterized in that: The laser generating device, the image collecting device and the processing device are used to jointly implement any one of the above-mentioned multi-component gas leakage detection methods based on dual near-infrared lasers.

10. The dual near-infrared laser based multi-component gas leak detection system of claim 9, wherein, The laser generating device is used to output first laser, second laser, third laser and fourth laser which are periodically switched in sequence, the first laser is obtained by coupling a laser with a first wavelength and a laser with a second wavelength, the second laser is obtained by coupling a laser with a third wavelength and a laser with a fourth wavelength, the third laser is obtained by coupling a laser with a fifth wavelength and a laser with a sixth wavelength, and the fourth laser is the same as the second laser.

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