Methane monitoring system and method based on distributed fiber and lidar

Abstract

The present application relates to a kind of methane monitoring system and method based on distributed optical fiber and laser radar, the system includes system host, main optical fiber, multiple successively connected beam splitter and corresponding laser radar methane monitoring terminal.System host generates the modulation laser of methane characteristic absorption wavelength and is transmitted by main optical fiber, beam splitter is distributed to each terminal according to set proportion with laser.Light laser methane monitoring terminal actively emits laser to monitoring area and receives reflected signal, signal is returned to system host by original route and is demodulated, utilizes tunable semiconductor laser absorption spectroscopy technology to calculate methane concentration, and is positioned leakage position in combination with time-of-flight method.The present application significantly reduces wiring complexity by the topological design of single main optical fiber series connection beam splitting, supports the modular expansion of monitoring point;By active laser detection combined with spectral analysis technology, it has high sensitivity and anti-interference ability, suitable for coal mine, natural gas station and other large-scale dynamic monitoring scene.

Description

Technical Field

[0001] This invention relates to the field of gas monitoring technology, and in particular to a methane monitoring system and method based on distributed optical fiber and lidar. Background Technology

[0002] Methane, as a core component of coal mine gas and natural gas, is flammable and explosive. In industries such as coal mining and natural gas transmission and distribution, real-time and accurate monitoring of methane leaks is directly related to production safety and environmental risk prevention. Therefore, reliable monitoring of methane is of great significance for safe production and disaster prevention.

[0003] Most existing fiber optic methane monitoring devices employ point-to-point cabling structures, such as... Figure 1 As shown, the system mainly includes an optical transmitter, an optical receiver, an optical fiber splitter, and various optical transmission lines. Each monitoring terminal needs to be connected to the system host via an independent optical fiber link, forming a star or parallel physical connection topology. The system host connects to each monitoring terminal through independent optical fibers, distributes optical signals with the help of optical fiber splitters, outputs detection signals from the optical transmitter, and receives feedback signals from the optical receiver, ultimately realizing the monitoring of methane concentration at designated locations.

[0004] Traditional fiber optic methane monitoring devices using point-to-point cabling have the following problems: First, each monitoring terminal requires a separate fiber optic cable to the host, resulting in large-scale, complex fiber optic cabling, poor system scalability, and the need to re-lay fiber optic cables when adding new monitoring points, leading to a large workload. Second, this method is a passive monitoring system, relying on the natural diffusion of methane gas to a fixed sensor location to trigger an alarm, resulting in monitoring blind spots and response delays, making it difficult to achieve real-time, active, and full-coverage monitoring of methane distribution throughout the entire space. Summary of the Invention

[0005] In view of this, it is necessary to provide a methane monitoring system and method based on distributed optical fiber and lidar to solve the above-mentioned problems of the prior art.

[0006] To address the aforementioned problems, in a first aspect, embodiments of the present invention provide a methane monitoring system based on distributed optical fiber and lidar, comprising:

[0007] The system host is used to generate modulated laser with the characteristic absorption wavelength of methane and emit it to the main optical fiber, and to receive and demodulate the reflected light signal returned from the main optical fiber to obtain the methane concentration in the monitoring area.

[0008] The main optical fiber connects the system host to multiple beam splitters and is used to transmit modulated laser and reflected light signals.

[0009] Multiple beam splitters are connected in series on the main optical fiber to split the incident modulated laser into two paths according to a set ratio. One path is transmitted through the splitting fiber to the corresponding lidar methane monitoring terminal, and the other path is transmitted through the main optical fiber to the next beam splitter.

[0010] Multiple lidar methane monitoring terminals are connected to corresponding beam splitters via optical fibers. They are used to receive the modulated laser and actively transmit it to the monitoring area, receive the reflected light signal, and transmit it back to the corresponding beam splitter via optical fibers.

[0011] This invention connects multiple laser sensors through a series topology, reducing deployment costs and complexity, and solving the problems of spatial limitations, complex wiring, and difficult maintenance of traditional methane monitoring devices.

[0012] Preferably, the system host includes:

[0013] A laser source, connected to the main optical fiber, is used to generate modulated laser light with the characteristic absorption wavelength of methane.

[0014] The signal demodulator, connected to the main optical fiber, is used to receive the returned reflected light signal. It uses tunable semiconductor laser absorption spectroscopy to demodulate the reflected light signal and obtain the methane concentration in the monitored area.

[0015] Preferably, the lidar methane monitoring terminal includes:

[0016] The laser emitting component, connected to the fiber optic cable, is used to receive modulated laser light transmitted from the fiber optic cable and actively emit it into the monitoring area.

[0017] The laser receiving component, connected to the fiber optic cable, is used to receive the reflected light signal from the monitoring area and transmit it back to the corresponding beam splitter via the fiber optic cable.

[0018] A rotating base is used to support the laser emitting component and the laser receiving component, and to adjust the emission direction of the modulated laser to achieve spatial scanning of the monitoring area.

[0019] Preferably, the system host further includes:

[0020] The location processing unit, connected to the signal demodulator, is used to calculate the methane leak location based on the time-of-flight method, using the following formula:

[0021]

[0022] In the formula, d is the distance from the lidar methane monitoring terminal to the methane leak location, and c is the speed of light. This represents the time difference between the emission and reception of a laser pulse.

[0023] Preferably, the system host further includes:

[0024] The methane concentration prediction unit, connected to the signal demodulator and the location processing unit, is used to receive time series data of methane concentration at the methane leak location within a given time period, and predict the methane concentration at the methane leak location at future times through a long short-term memory network.

[0025] Preferably, the system further includes:

[0026] Multiple tunable bandpass filters are connected in series on the fiber optic branch between the beam splitter and the lidar methane monitoring terminal. These filters are used to dynamically adjust the passband bandwidth according to the instructions of the system host, in order to filter the absorption spectrum of interfering gases and stray light of non-methane characteristic wavelengths.

[0027] Preferably, the system further includes:

[0028] The monitoring platform, connected to the system host, is used to receive and display the methane concentration and leak location in the monitored area. When the methane concentration exceeds a preset threshold, it issues an alarm signal and stores historical monitoring data for query and analysis.

[0029] Secondly, embodiments of the present invention provide a methane monitoring method based on distributed optical fiber and lidar, comprising:

[0030] The system host generates modulated laser light with the characteristic absorption wavelength of methane;

[0031] The modulated laser is transmitted through the main optical fiber to multiple beam splitters connected in series on the main optical fiber. Each beam splitter splits the incident modulated laser into two paths according to a set ratio. One path is transmitted through the split optical fiber to the corresponding lidar methane monitoring terminal, and the other path is transmitted through the main optical fiber to the next beam splitter.

[0032] Each lidar methane monitoring terminal receives the modulated laser and actively transmits it to the monitoring area. It receives the reflected light signal from the monitoring area and transmits it back to the corresponding beam splitter through the split optical fiber.

[0033] The reflected light signal is collected by a beam splitter and transmitted back to the system host via the main optical fiber. The system host demodulates the reflected light signal to obtain the methane concentration and methane leakage location in the monitoring area.

[0034] Preferably, the demodulation of the reflected light signal to obtain the methane concentration and methane leak location in the monitoring area includes:

[0035] The signal demodulator uses tunable semiconductor laser absorption spectroscopy to process the reflected light signal. By analyzing the intensity attenuation of the reflected light signal, the methane concentration in the monitoring area is calculated, and the location of the methane leak is calculated based on the time-of-flight method.

[0036] Preferably, the method further includes:

[0037] When a new monitoring point is needed, a beam splitter is added to the serial link of the main optical fiber, and the new lidar methane monitoring terminal is connected to the beam splitter through the split optical fiber.

[0038] The methane monitoring system and method based on distributed optical fiber and lidar provided by this invention have the following advantages compared with the prior art:

[0039] 1) This invention adopts a topology structure of multiple beam splitters and lidar methane monitoring terminals connected in series with a main optical fiber. Only one main optical fiber is needed to connect all terminals, which greatly reduces the complexity of the cabling project. When adding a new monitoring point, only beam splitters and terminals need to be added to the series link, without the need to re-lay a large number of optical fibers, thus solving the problems of poor scalability and large amount of engineering work in the existing technology.

[0040] 2) This invention utilizes a lidar methane monitoring terminal to actively emit modulated laser light into the monitoring area and receive reflected signals. Combined with TDLAS technology to analyze the light intensity attenuation caused by methane absorption, it achieves high-sensitivity concentration measurement at the ppm level. The time-of-flight (TOF) method is used to calculate the round-trip time difference of the light pulse, accurately locating the leak point.

[0041] 3) The lidar monitoring terminal of the present invention has no consumable sensing electronic components, and its theoretical lifespan is comparable to that of optical fiber, avoiding the high costs caused by frequent maintenance of existing technologies and reducing long-term operating costs. Attached Figure Description

[0042] Figure 1 This is a schematic diagram of the structure of a fiber optic methane monitoring device in the prior art;

[0043] Figure 2 A schematic diagram of the structure of a methane monitoring system based on distributed optical fiber and lidar provided in an embodiment of the present invention;

[0044] Figure 3 A structural block diagram of the system host provided in an embodiment of the present invention;

[0045] Figure 4 This is a schematic diagram of the time-domain signal of the methane monitoring system provided in an embodiment of the present invention;

[0046] Figure 5 A flowchart illustrating a methane monitoring method based on distributed optical fiber and lidar provided in an embodiment of the present invention.

[0047] In the attached diagram, 1: System host, 2: Transmitting main optical fiber, 3: Receiving main optical fiber, 4: LiDAR methane monitoring terminal, 5: Beam splitter. Detailed Implementation

[0048] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0049] The naming or numbering of steps in the embodiments of the present invention does not mean that the steps in the method flow must be executed in the time / logical order indicated by the naming or numbering. The execution order of the named or numbered process steps can be changed according to the technical purpose to be achieved, as long as the same or similar technical effect can be achieved.

[0050] Figure 2 A schematic diagram of the structure of a methane monitoring system based on distributed optical fiber and lidar provided in an embodiment of the present invention; see reference. Figure 2 The methane monitoring system based on distributed optical fiber and lidar provided by this invention includes:

[0051] System host 1 is used to generate modulated laser with the characteristic absorption wavelength of methane and emit it to the main optical fiber, and to receive and demodulate the reflected light signal returned from the main optical fiber to obtain the methane concentration in the monitoring area.

[0052] The main optical fiber connects the system host 1 to multiple beam splitters 5 and is used to transmit modulated laser and reflected light signals. The main optical fiber includes a transmitting main optical fiber 2 for transmitting modulated laser and a receiving main optical fiber 3 for transmitting reflected light signals;

[0053] Multiple beam splitters 5 are connected in series on the main optical fiber to split the incident modulated laser into two paths according to a set ratio. One path is transmitted to the corresponding lidar methane monitoring terminal through the split optical fiber, and the other path is transmitted to the next beam splitter through the main optical fiber.

[0054] Multiple lidar methane monitoring terminals 4 are connected to corresponding beam splitters 5 via optical fibers, respectively, for receiving the modulated laser and actively transmitting it to the monitoring area, receiving the reflected light signal, and transmitting it back to the corresponding beam splitter via optical fibers.

[0055] Understandably, traditional point-based monitoring systems suffer from problems such as large detection blind spots, long response delays, and complex wiring, making it difficult to meet the needs of real-time monitoring in large spaces. Therefore, this invention proposes a solution based on distributed optical fibers and lidar, reducing deployment costs and complexity, and solving the spatial limitations and complex wiring problems of traditional methane monitoring devices.

[0056] Specifically, the system host 1, as the control and processing core of the monitoring system, generates modulated laser light with the characteristic absorption wavelength of methane and transmits it outward through the main transmitting fiber 2. Simultaneously, the system host 1 receives the reflected light signals returned through the receiving main fiber 3 and demodulates these signals to obtain the concentration information of methane gas within the monitoring area. The modulated laser light with the characteristic absorption wavelength of methane refers to a modulated laser light with a wavelength in the specific absorption band of methane molecules. Methane molecules have a fixed absorption peak for near-infrared light of a specific wavelength. When this wavelength of laser light irradiates methane, some of the light energy is absorbed by the methane, thus the reflected light signal carries the methane concentration information.

[0057] The main optical fiber serves as the physical channel for optical signal transmission, connecting the system host 1 with multiple fiber optic beam splitters 5. The transmitting main optical fiber 2 is responsible for transmitting the modulated laser from the system host 1 to each fiber optic beam splitter 5, while the receiving main optical fiber 3 is responsible for transmitting the reflected optical signal from the fiber optic beam splitter 5 back to the system host 1.

[0058] Multiple fiber optic beam splitters 5 are connected in series on the main optical fiber to form a chain topology. Each fiber optic beam splitter 5 splits the incident modulated laser into two paths according to a preset optical power ratio: one path is transmitted through the split fiber to the corresponding lidar methane monitoring terminal 4 to provide a detection light source for the terminal; the other path continues to be transmitted through the main optical fiber to the next fiber optic beam splitter 5, ensuring that the optical signal can be transmitted sequentially to each subsequent monitoring node.

[0059] Multiple lidar methane monitoring terminals 4 are connected to corresponding fiber optic beam splitters 5 via fiber optic branches. These terminals are responsible for receiving modulated laser light transmitted from the fiber optic branches and actively emitting laser beams into the monitoring area. Simultaneously, the terminals also receive optical signals reflected from the monitoring area and transmit these reflected signals back to the corresponding fiber optic beam splitters 5 via the fiber optic branches, ultimately returning them to the system host 1 via the main receiving fiber optic branch 3 for processing.

[0060] The specific working process of the methane monitoring system based on distributed optical fiber and lidar is as follows:

[0061] The system host 1 generates modulated laser light with the characteristic absorption wavelength of methane. The modulated laser light is transmitted through the main transmitting fiber 2 to the first fiber beam splitter 5. The first fiber beam splitter 5 splits the laser light into two paths according to a set ratio. One path is transmitted through the splitting fiber to the corresponding lidar methane monitoring terminal 4, and the other path is transmitted through the main transmitting fiber 2 to the next fiber beam splitter 5, and so on, until all fiber beam splitters 5 have completed the splitting and all lidar methane monitoring terminals 4 have received the modulated laser light. Each lidar methane monitoring terminal 4 actively emits modulated laser light into the monitoring area. During the propagation of the laser light in the monitoring area, if methane gas is present, part of the laser light is absorbed by methane. When the laser light encounters an object in the monitoring area, it is reflected to form a reflected light signal. This signal carries the methane absorption characteristics and is received by the lidar methane monitoring terminal 4. The lidar methane monitoring terminal 4 transmits the reflected light signal back to the corresponding fiber beam splitter 5 through the splitting fiber. The fiber beam splitter 5 summarizes the reflected light signal to the receiving main fiber 3. All reflected light signals are transmitted back to the system host 1 through the receiving main fiber 3. The system host 1 demodulates the reflected light signals and finally obtains the methane concentration in the monitoring area.

[0062] This invention employs a topology that connects multiple beam splitters and lidar methane monitoring terminals in series via a main optical fiber. Only a single trunk fiber is needed to connect all terminals, significantly reducing the complexity of cabling. When adding new monitoring points, only beam splitters and terminals need to be added to the series link, eliminating the need for extensive new fiber optic cabling. This solves the problems of poor scalability and large engineering workload associated with existing technologies. The lidar monitoring terminal of this invention has no consumable sensing electronic components, and its theoretical lifespan is comparable to that of optical fibers, avoiding the high costs associated with frequent maintenance in existing technologies and reducing long-term operating costs.

[0063] Figure 3 The structural block diagram of the system host provided in the embodiment of the present invention is shown below. Figure 3 In some embodiments of this application, the system host 1 includes:

[0064] The laser source 101 is connected to the main optical fiber and is used to generate modulated laser light with the characteristic absorption wavelength of methane.

[0065] The signal demodulator 102 is connected to the main optical fiber and is used to receive the returned reflected light signal. It uses tunable semiconductor laser absorption spectroscopy technology to demodulate the reflected light signal and obtain the methane concentration in the monitoring area.

[0066] Reference Figure 2 and Figure 3 The system host 1 includes a laser source 101 and a signal demodulator 102. The laser source is directly connected to the main optical fiber and can generate modulated laser light that targets the characteristic absorption wavelength of methane. This laser source is precisely designed to stably output laser light with a wavelength of 1653 nm, which corresponds precisely to the characteristic absorption spectral line of methane molecules in the near-infrared region.

[0067] The signal demodulator is also connected to the main optical fiber and is responsible for receiving the reflected light signal returned from the monitoring area. This instrument uses Tunable Semiconductor Laser Absorption Spectroscopy (TDLAS) for signal demodulation, which is the core technology for achieving high-precision gas concentration measurement. The principle of TDLAS technology is: utilizing the wavelength-tunable characteristic of a tunable semiconductor laser, the laser wavelength is scanned past the absorption peak of methane; by measuring the change in light intensity after the laser is absorbed by methane, combined with wavelength-modulated harmonic detection methods (such as second harmonic detection), DC interference from dust and stray light is suppressed, thereby accurately calculating the methane concentration. The intensity of the reflected light signal attenuates due to absorption by methane molecules. According to Beer-Lambert's law, the light intensity attenuation is related to the gas concentration.

[0068]

[0069] In the formula, I is the incident light intensity, and I is the reflected light intensity. For methane at wavelength The absorption coefficient at the given location, where C represents the gas concentration and L represents the absorption path length.

[0070] By measuring the degree of light intensity attenuation at a specific absorption spectral line, and combining this with the known absorption coefficient and optical path length, the concentration of methane gas can be accurately calculated.

[0071] In practical applications, the system can employ wavelength modulation spectroscopy to further improve measurement sensitivity and anti-interference capabilities by detecting second harmonic signals. This method can effectively suppress optical noise and background interference, achieving high-precision measurements at the ppm level.

[0072] This invention utilizes a lidar methane monitoring terminal to actively emit modulated laser light into the monitoring area and receive reflected signals. By combining this with TDLAS technology to analyze the light intensity attenuation caused by methane absorption, it achieves high-sensitivity concentration measurement at the ppm level.

[0073] In some embodiments of this application, the lidar methane monitoring terminal includes:

[0074] The laser emitting component, connected to the fiber optic cable, is used to receive modulated laser light transmitted from the fiber optic cable and actively emit it into the monitoring area.

[0075] The laser receiving component, connected to the fiber optic cable, is used to receive the reflected light signal from the monitoring area and transmit it back to the corresponding beam splitter via the fiber optic cable.

[0076] A rotating base is used to support the laser emitting component and the laser receiving component, and to adjust the emission direction of the modulated laser to achieve spatial scanning of the monitoring area.

[0077] Understandably, traditional methane monitoring systems mostly use fixed-point sensors, relying on natural gas diffusion to trigger alarms, resulting in monitoring blind spots and response delays. In this invention, the lidar methane monitoring terminal actively emits lasers and dynamically adjusts the scanning direction to achieve full-coverage spatial detection of the monitoring area, eliminating blind spots. Combined with a rotating base, it allows for flexible rotation of the transmitting and receiving components, improving monitoring efficiency and spatial resolution, and meeting the real-time monitoring needs of large-area, complex scenarios.

[0078] Specifically, the laser emitting component is connected to the system's main fiber optic network via a branch fiber and is responsible for receiving modulated laser light transmitted from the system host. After collimating and expanding the received modulated laser light, it is actively emitted into the monitoring area. This active emission mechanism breaks through the limitations of traditional passive sensors, enabling the active detection of methane gas in the laser path and achieving a fundamental shift from waiting for gas diffusion to active searching.

[0079] The laser receiving component is also connected to the system via a fiber optic splitter, and its core function is to capture the reflected light signal returning from the monitoring area. This component employs a high-sensitivity photodetector, capable of effectively receiving the weak reflected signal after absorption by methane gas. The received light signal is efficiently injected into the fiber optic splitter through a precise optical coupling system, and then transmitted back to the main system for in-depth analysis via a beam splitter. This process ensures the complete transmission of gas absorption information, providing a reliable data foundation for subsequent accurate concentration calculations.

[0080] The rotating base, serving as the support and movement mechanism for the terminal, carries the entire laser emitting and receiving components. Driven by a precision stepper motor, the base enables accurate angle control and continuous rotation. Through programmed control, the base can rotate the laser emitting and receiving components 360 degrees, adjusting the emission direction of the modulated laser and achieving three-dimensional spatial scanning of the monitoring area. This scanning mechanism allows a single terminal to cover a larger monitoring range, forming a fan-shaped or spherical monitoring network, significantly improving spatial coverage.

[0081] In actual deployment, multiple lidar methane monitoring terminals are connected in series via a beam splitter, with each terminal responsible for scanning and monitoring a specific area. The collaborative work between the terminals forms a comprehensive spatial monitoring network. When a terminal detects an abnormal methane concentration, the system can immediately pinpoint the leak location and activate the early warning mechanism.

[0082] In this embodiment, the lidar methane monitoring terminal achieves full spatial coverage and dynamic tracking of the monitoring area through active laser emission and rotational scanning technology, eliminating the blind spot problem of traditional fixed-point sensors. The rotating base supports multi-angle adjustment to adapt to complex scene requirements, improving monitoring flexibility and response speed.

[0083] In some embodiments of this application, the system host 1 further includes:

[0084] The location processing unit 103, connected to the signal demodulator, is used to calculate the methane leak location based on the time-of-flight method, using the following formula:

[0085]

[0086] In the formula, d is the distance from the lidar methane monitoring terminal to the methane leak location, and c is the speed of light. This represents the time difference between the emission and reception of a laser pulse.

[0087] Traditional methane monitoring systems typically only detect whether methane concentration exceeds the standard, making it difficult to quickly pinpoint the leak source, resulting in low emergency response efficiency. Therefore, this invention integrates time-of-flight ranging technology into a positioning processing unit, combined with pre-set fiber optic length data, to achieve precise spatial location of the methane leak. By calculating the straight-line distance from the terminal to the leak point using the round-trip time difference of optical pulses, and combining this with a distributed terminal layout, the leak coordinates can be quickly located, improving the efficiency of disaster early warning and response.

[0088] Specifically, when the positioning processing unit is working, it first calls the pre-stored fiber optic length data between each lidar methane monitoring terminal and the system host. This data was measured and entered during system installation based on the actual wiring, and is used to determine the fixed spatial position of each terminal. Subsequently, positioning is carried out based on the time-of-flight method: the laser source of the system host emits a laser pulse, which is transmitted through the main fiber, beam splitter, and branch fiber to the corresponding lidar methane monitoring terminal. The terminal then emits the laser pulse toward the monitoring area. If there is a methane leak in the monitoring area, the laser pulse will interact with the leaking gas and be reflected, forming a reflected light signal carrying the leak information. This reflected light signal is transmitted back to the system host along the original path.

[0089] The positioning processing unit captures the emission time of the laser pulse and the reception time of the reflected light signal in real time, and calculates the time difference between the two. Substitute into the formula The distance 'd' from the current lidar methane monitoring terminal to the methane leak location is calculated. Finally, combined with pre-stored terminal fixed spatial location data, the specific spatial location of the methane leak can be determined through spatial coordinate conversion, achieving precise positioning.

[0090] This embodiment achieves precise spatial location of methane leak points using the time-of-flight method, solving the problem that traditional monitoring systems can only alarm but not locate. Combined with preset fiber length data, a complete spatial coordinate system is established, enabling rapid determination of the specific location of the leak point. High-precision time measurement ensures the reliability of the location, providing accurate location information for emergency response and significantly improving the practicality and safety of the methane monitoring system.

[0091] In some embodiments of this application, reference is made to Figure 3 The system host 1 also includes:

[0092] The methane concentration prediction unit 104 is connected to the signal demodulator and the positioning processing unit. It is used to receive the time series data of methane concentration at the methane leak location within a given time period and predict the methane concentration at the methane leak location at a future time through a long short-term memory network.

[0093] Traditional methane monitoring systems can only output the current methane concentration in real time and cannot predict the concentration change trend at the leak location. When the methane concentration rises rapidly, it is difficult for staff to formulate emergency strategies in a timely manner (such as personnel evacuation and leak sealing), which can easily lead to the expansion of the leak area due to delayed response, or even cause safety accidents such as explosions and poisoning.

[0094] Therefore, this embodiment of the invention designs a methane concentration prediction unit, which relies on a long short-term memory network (LSTM) to analyze the concentration time series data of a specific leak location, predicts the concentration at future moments in advance, provides data support for proactive prevention and control in high-risk scenarios, and enhances the system's proactive prevention and control capabilities.

[0095] Specifically, the methane concentration prediction unit establishes connections with both the signal demodulator and the location processing unit: the signal demodulator transmits real-time methane concentration data from each monitoring point, and the location processing unit transmits data on the identified methane leak locations; the data from both are linked via timestamps to ensure that the prediction unit can accurately obtain the concentration data of a specific methane leak location within a given time period. For example, if the past hour is selected as the given time period, and data is collected at 10-second intervals, 360 concentration data points are generated, forming a time series of methane concentration data for that leak location.

[0096] Long Short-Term Memory (LSTM) networks, through their gating mechanisms of forget gates, input gates, and output gates, can effectively handle long-term dependencies in time-series data, avoiding the gradient vanishing problem that occurs in traditional neural networks when processing long sequences. For the dynamic characteristics of methane concentration changes over time (e.g., a slow increase in concentration at the initial stage of a leak, followed by a rapid increase after the crack expands), LSTM can retain key historical concentration information, such as the rate of increase and fluctuation patterns, providing a reliable basis for prediction.

[0097] Historical methane concentration time series data is input into an LSTM network. Temporal features are extracted through multi-layer stacking, and finally, the predicted methane concentration for future times is output via a fully connected layer. The methane concentration prediction expression based on the LSTM network is:

[0098]

[0099] In the formula, Indicates the future The methane concentration value at time t. This is the weight matrix of the fully connected layer. Let t be the hidden state of the LSTM network at time t. This is the bias term for the fully connected layer. The prediction step size represents the number of time points to predict backwards from the current time t.

[0100] In actual prediction, the system first receives real-time methane concentration data transmitted from a signal demodulator and constructs a time series sample. Then, the time series sample is input into a trained LSTM model, which outputs a concentration prediction curve for the next 5-30 minutes to the monitoring platform. Finally, if the monitoring platform determines that the predicted methane concentration at a future time exceeds a preset threshold, it triggers an alarm in advance and pushes emergency response suggestions.

[0101] In this embodiment, the methane concentration prediction unit utilizes a Long Short-Term Memory (LSTM) network to deeply mine historical concentration time-series data and establish an LSTM-based methane concentration prediction model, achieving accurate prediction of future concentration trends. This technical solution overcomes the passive response shortcomings of traditional monitoring systems, providing forward-looking early warning capabilities and advancing emergency response time by several minutes to tens of minutes. Combined with spatial positioning information, it can predict leakage evolution paths, optimize evacuation and disposal strategies, and improve the safety risk prevention and control level in scenarios such as coal mines and natural gas stations.

[0102] In some embodiments of this application, the methane monitoring system based on distributed optical fiber and lidar further includes:

[0103] Multiple tunable bandpass filters are connected in series on the fiber optic branch between the beam splitter and the lidar methane monitoring terminal. These filters are used to dynamically adjust the passband bandwidth according to the instructions of the system host, in order to filter the absorption spectrum of interfering gases and stray light of non-methane characteristic wavelengths.

[0104] Understandably, in complex industrial environments such as coal mines and natural gas pipelines, in addition to methane, there are various interfering gases such as water vapor and carbon dioxide. The absorption spectra of these gases may overlap with the characteristic absorption peak of methane, causing the measured value to deviate from the true concentration. At the same time, stray light and non-characteristic wavelength light in the environment can also interfere with signal detection, reducing the system's signal-to-noise ratio and measurement accuracy.

[0105] Therefore, this invention designs multiple tunable bandpass filters to precisely filter interference by dynamically adjusting the bandwidth, ensuring the purity of the methane characteristic signal. The number of tunable bandpass filters is consistent with the number of lidar methane monitoring terminals and beam splitters. Each tunable bandpass filter is connected in series on the fiber optic branch between the corresponding beam splitter and the lidar methane monitoring terminal, forming a "beam splitter". Tunable bandpass filter Fiber optic The optical signal transmission link of the "LiDAR methane monitoring terminal".

[0106] The input of each tunable bandpass filter is fixedly connected to the fiber optic output port of the corresponding beam splitter, and the output is connected to the optical signal input port of the corresponding lidar methane monitoring terminal. This ensures that the modulated laser beam split by the beam splitter must pass through the filter before entering the terminal. The tunable bandpass filter has a built-in control module that communicates with the system host via wired or wireless means, receiving adjustment commands from the host in real time. The system host analyzes the spectral characteristics of interfering gases in the reflected light signal using a signal demodulator (e.g., when a NO absorption peak is detected), and combines this with stray light intensity data fed back from the lidar methane monitoring terminal to generate bandwidth adjustment commands.

[0107] The tunable bandpass filter dynamically adjusts its passband bandwidth according to instructions: when the concentration of interfering gas is high or stray light is strong, the passband bandwidth is narrowed to 1652.5nm-1653.5nm, allowing only the characteristic wavelength of methane laser light to pass through; when the interference is weak, the bandwidth is widened to 1652nm-1654nm, improving the transmission efficiency of optical signals. Through this dynamic adjustment, the absorption spectrum of interfering gases and stray light of non-methane characteristic wavelengths are effectively filtered, ensuring that the modulated laser light entering the lidar methane monitoring terminal, as well as the reflected light signal returned from the terminal to the beam splitter, are dominated by the characteristic wavelength of methane.

[0108] In some embodiments of this application, the methane monitoring system based on distributed optical fiber and lidar further includes:

[0109] The monitoring platform, connected to the system host, is used to receive and display the methane concentration and leak location in the monitored area. When the methane concentration exceeds a preset threshold, it issues an alarm signal and stores historical monitoring data for query and analysis.

[0110] Specifically, the monitoring platform and the system host establish a stable connection via wired (e.g., Ethernet) or wireless (e.g., 4G / 5G) methods to ensure that the monitoring data collected by the system host can be transmitted to the monitoring platform in real time. The monitoring platform receives two types of core data transmitted from the system host in real time: first, the methane concentration data of the monitoring area calculated by the signal demodulator; and second, the methane leak location data determined by the location processing unit. The platform presents this data in a visual form, such as a zoning chart divided by the monitoring area and leak location markers overlaid on an electronic map (associated with the corresponding terminal number, clearly showing the spatial distribution of leak points), making it convenient for staff to intuitively grasp the overall monitoring situation.

[0111] The monitoring platform has multiple preset methane concentration thresholds, such as daily monitoring values, early warning thresholds, and danger thresholds, set according to industrial safety standards. When the received real-time methane concentration data exceeds the preset threshold, the platform immediately triggers a local audible and visual alarm, and simultaneously sends alarm information to on-site personnel via SMS, mobile app push notifications, etc. The information clearly indicates the monitoring area exceeding the threshold, the current concentration value, and the corresponding leak location, guiding personnel to quickly locate and handle the situation.

[0112] The monitoring platform is equipped with a database that continuously stores historical monitoring data, including monitoring time, methane concentration at each terminal, leak location records, and alarm trigger time and type. Staff can use the platform's interface to query historical data by time range and monitoring area. The platform can also automatically generate concentration change trend charts and alarm statistics reports to help staff analyze the time patterns and high-frequency areas of methane leaks, providing data support for subsequent optimization of monitoring points and the development of targeted prevention and control measures.

[0113] In this embodiment, a centralized and visualized management system for methane monitoring data is implemented through a monitoring platform. This allows staff to monitor the concentration and location of leaks in multiple areas in real time without needing to visit the system host on-site, thus improving monitoring efficiency. A real-time alarm mechanism for exceeding thresholds ensures that leak events can be detected and handled promptly, enhancing the level of intelligent safety management in production.

[0114] Figure 4 This is a schematic diagram of the time-domain signal of the methane monitoring system provided in an embodiment of the present invention. Figure 4 This diagram illustrates the operating data and performance of the monitoring system of this invention under multi-channel, long-term time-series conditions. The horizontal axis represents time (in seconds, ranging from 0 to 600 seconds), corresponding to the system's continuous monitoring duration; the vertical axis represents signal amplitude. The diagram compiles the time-domain signal curves of a total of 120 monitoring channels (corresponding to different lidar methane monitoring terminals or their scanning zones). The system continuously acquires reflected light signals through each independent monitoring channel and records the changes in signal intensity over time. The points in the diagram where abnormal fluctuations in signal amplitude occur correspond to the moments when methane is detected by the corresponding terminal.

[0115] Figure 5 A flowchart of a methane monitoring method based on distributed optical fiber and lidar provided for embodiments of the present invention is shown below. Figure 5 The method includes at least:

[0116] Step S1: The system host generates modulated laser light with the characteristic absorption wavelength of methane;

[0117] Step S2: The modulated laser is transmitted through the main optical fiber to multiple beam splitters connected in series on the main optical fiber. Each beam splitter splits the incident modulated laser into two paths according to a set ratio. One path is transmitted through the splitting optical fiber to the corresponding lidar methane monitoring terminal, and the other path is transmitted through the main optical fiber to the next beam splitter.

[0118] Step S3: Each lidar methane monitoring terminal receives the modulated laser and actively transmits it to the monitoring area, receives the reflected light signal from the monitoring area and transmits it back to the corresponding beam splitter through the splitting fiber;

[0119] In step S4, the reflected light signal is collected by the beam splitter and transmitted back to the system host through the main optical fiber. The system host demodulates the reflected light signal to obtain the methane concentration and methane leakage location in the monitoring area.

[0120] The signal demodulator uses tunable semiconductor laser absorption spectroscopy to process the reflected light signal. By analyzing the intensity attenuation of the reflected light signal, the methane concentration in the monitoring area is calculated, and the location of the methane leak is calculated based on the time-of-flight method.

[0121] The methane monitoring method provided by the present invention is executed by the methane monitoring system based on distributed optical fiber and lidar provided in the foregoing embodiments. The methane monitoring system based on distributed optical fiber and lidar has been described in detail in the foregoing embodiments, and the methane monitoring method will not be described again in this embodiment.

[0122] In some embodiments of this application, the methane monitoring method based on distributed optical fiber and lidar further includes:

[0123] When a new monitoring point is needed, a beam splitter is added to the serial link of the main optical fiber, and the new lidar methane monitoring terminal is connected to the beam splitter through the split optical fiber.

[0124] It should be noted that the monitoring point architecture of traditional methane monitoring systems is mostly fixed. If new monitoring points are needed, it is often necessary to re-lay the entire fiber optic link, resulting in a large amount of engineering work, high costs, and disruption to normal production during construction.

[0125] To address this issue, this invention utilizes a main fiber chain topology and a modular design of beam splitters to enable flexible expansion of monitoring points. New terminals only require the insertion of a beam splitter into the main fiber cascade link and connection via branch fibers, avoiding backbone network reconstruction. This meets the needs of dynamic adjustment of monitoring range in scenarios such as coal mines and natural gas stations, reducing expansion costs and implementation complexity.

[0126] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Unless otherwise expressly specified and limited, the terms "installed," "connected," or "linked" should be interpreted broadly, for example, as a fixed connection, a detachable connection, or an integral connection; a mechanical connection or an electrical connection; a direct connection or an indirect connection via an intermediate medium; or a connection within two components. Those skilled in the art will understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0127] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the appended claims.

[0128] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A methane monitoring system based on distributed optical fiber and lidar, characterized in that, include: The system host is used to generate modulated laser with the characteristic absorption wavelength of methane and emit it to the main optical fiber, and to receive and demodulate the reflected light signal returned from the main optical fiber to obtain the methane concentration in the monitoring area. The main optical fiber connects the system host to multiple beam splitters and is used to transmit modulated laser and reflected light signals. Multiple beam splitters are connected in series on the main optical fiber to split the incident modulated laser into two paths according to a set ratio. One path is transmitted through the splitting fiber to the corresponding lidar methane monitoring terminal, and the other path is transmitted through the main optical fiber to the next beam splitter. Multiple lidar methane monitoring terminals are connected to corresponding beam splitters via optical fibers, respectively, to receive the modulated laser and actively transmit it to the monitoring area, receive the reflected light signal, and transmit it back to the corresponding beam splitter via optical fibers. The lidar methane monitoring terminal includes: A laser emitting component, connected to a split optical fiber, is used to receive modulated laser transmitted from the split optical fiber and actively emit it to the monitoring area; a laser receiving component, connected to a split optical fiber, is used to receive reflected light signals from the monitoring area and transmit them back to the corresponding beam splitter through the split optical fiber; a rotating base is used to support the laser emitting component and the laser receiving component, and to adjust the emission direction of the modulated laser to achieve spatial scanning of the monitoring area. The system host includes: A laser source, connected to the main optical fiber, is used to generate modulated laser light with the characteristic absorption wavelength of methane. The signal demodulator, connected to the main optical fiber, is used to receive the returned reflected light signal. It uses tunable semiconductor laser absorption spectroscopy technology to demodulate the reflected light signal and obtain the methane concentration in the monitoring area. The system also includes multiple tunable bandpass filters. The number of the multiple tunable bandpass filters is the same as the number of the lidar methane monitoring terminal and the beam splitter. Each tunable bandpass filter is connected in series on the fiber optic branch between the corresponding beam splitter and the corresponding lidar methane monitoring terminal. The input of each tunable bandpass filter is connected to the fiber output port of the corresponding beam splitter, and the output is connected to the optical signal input port of the corresponding lidar methane monitoring terminal. The tunable bandpass filter has a built-in control module, which is connected to the system host in communication. The system host analyzes the spectral characteristics of interfering gases in the reflected light signal using a signal demodulator, and generates a bandwidth adjustment command by combining the stray light intensity data fed back by the lidar methane monitoring terminal. The tunable bandpass filter dynamically adjusts the passband bandwidth according to the bandwidth adjustment command to filter the absorption spectrum of interfering gases and stray light of non-methane characteristic wavelengths, so that the modulated laser entering the lidar methane monitoring terminal and the reflected light signal returned from the lidar methane monitoring terminal to the beam splitter are both dominated by methane characteristic wavelengths. The location processing unit, connected to the signal demodulator, is used to calculate the methane leak location based on the time-of-flight method, using the following formula: ； In the formula, d is the distance from the lidar methane monitoring terminal to the methane leak location, c is the speed of light, and Δt represents the time difference between the laser pulse emission and reception.

2. The methane monitoring system based on distributed optical fiber and lidar according to claim 1, characterized in that, The system host also includes: The methane concentration prediction unit, connected to the signal demodulator and the location processing unit, is used to receive time series data of methane concentration at the methane leak location within a given time period, and predict the methane concentration at the methane leak location at future times through a long short-term memory network.

3. The methane monitoring system based on distributed optical fiber and lidar according to claim 1, characterized in that, The system also includes: The monitoring platform, connected to the system host, is used to receive and display the methane concentration and leak location in the monitored area. When the methane concentration exceeds a preset threshold, it issues an alarm signal and stores historical monitoring data for query and analysis.

4. A methane monitoring method based on the methane monitoring system based on distributed optical fiber and lidar as described in any one of claims 1-3, characterized in that, include: The system host generates modulated laser light with the characteristic absorption wavelength of methane; The modulated laser is transmitted through the main optical fiber to multiple beam splitters connected in series on the main optical fiber. Each beam splitter splits the incident modulated laser into two paths according to a set ratio. One path is transmitted through the split optical fiber to the corresponding lidar methane monitoring terminal, and the other path is transmitted through the main optical fiber to the next beam splitter. Each lidar methane monitoring terminal receives the modulated laser and actively transmits it to the monitoring area. It receives the reflected light signal from the monitoring area and transmits it back to the corresponding beam splitter through the split optical fiber. The reflected light signal is collected by a beam splitter and transmitted back to the system host via the main optical fiber. The system host demodulates the reflected light signal to obtain the methane concentration and methane leakage location in the monitoring area.

5. The methane monitoring method based on distributed optical fiber and lidar according to claim 4, characterized in that, The demodulation of the reflected light signal to obtain the methane concentration and methane leak location in the monitoring area includes: The signal demodulator uses tunable semiconductor laser absorption spectroscopy to process the reflected light signal. By analyzing the intensity attenuation of the reflected light signal, the methane concentration in the monitoring area is calculated, and the location of the methane leak is calculated based on the time-of-flight method.

6. The methane monitoring method based on distributed optical fiber and lidar according to claim 4, characterized in that, Also includes: When a new monitoring point is needed, a beam splitter is added to the serial link of the main optical fiber, and the new lidar methane monitoring terminal is connected to the beam splitter through the split optical fiber.

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