CN115480265A - Atmospheric methane detection method with high dynamic range, methane radar and computer terminal - Google Patents
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Abstract
The invention relates to an atmospheric methane detection method with a high dynamic range, a methane radar and a computer terminal. The detection method measures a methane concentration in a target region of the atmosphere based on a result of atmospheric detection in the target region. The atmospheric detection result is that a differential signal formed by a first laser beam and a second laser beam is transmitted to a corresponding echo signal generated in a target area, the wavelength of the first laser beam is positioned on a methane absorption line, and the wavelength of the second laser beam is positioned outside the methane absorption line. The detection method also determines whether the methane concentration is greater than a preset upper methane concentration limit. And when the methane concentration is greater than the upper limit of the methane concentration, the measurement range of the methane concentration is increased. And under the increased measuring range, the methane concentration in the target area is measured again. The atmospheric methane detection method has the advantage of large dynamic range, and effectively improves the detection capability of the methane radar to a large concentration area.
Description
Technical Field
The invention relates to the technical field of methane monitoring, in particular to an atmospheric methane detection method with a high dynamic range, a methane radar adopting the detection method and a computer terminal applying the detection method.
Background
In the aspect of environmental protection, methane is used as the second greenhouse gas, and the greenhouse effect per molecule of methane is 72 times that of carbon dioxide, so that the emission of methane needs to be monitored, and currently, methane radar is mostly adopted to monitor the emission of methane. In addition, in the aspect of life and production, the methane radar has the advantage of large detection range, can acquire concentration information of any region in the detection range, and plays a role in danger prevention and leakage source searching which are difficult to replace.
The existing methane radar measurement technology mainly has two categories.
One is a path integral methane radar, which irradiates a hard target far away by laser, and measures the whole optical density of methane on the whole path by using a differential absorption method according to a reflected signal of the hard target.
The second is a distance resolution type coherent methane radar, laser emits to the atmosphere, a single mode receives a back reflection signal of aerosol in the atmosphere, the back reflection signal interferes with local oscillation light after frequency shift, and the methane absorption rate in different distance gates is obtained by measuring the frequency spectrum power of interference signals under different time delays, so that the distance resolution type methane detection is realized. Compared with a path integral type methane radar, although the measuring distance of the method is shorter, the precision is relatively lower, the distance resolution can be realized, and the positioning of the precision of dozens of meters can be realized for the leakage source, so that the method is more practical in the aspects of large-scale safety early warning and searching for the leakage source.
However, the above two methods have problems of low light sensitivity and small dynamic range. In terms of sensitivity, the conventional photodetector needs nw-level optical signals to respond, and has strong thermal noise. In terms of dynamic range, the measurement threshold of a range-resolved methane radar is about 5000ppm · m, but when the methane path concentration greatly exceeds the measurement threshold, for example, 50000ppm · m, the signal photon count is greatly reduced due to too strong absorption, and is much lower than the noise photon count, at which point the radar cannot identify the true magnitude of the methane concentration. Particularly, the explosion point of methane in the air is 5% to 16%, and the original methane radar cannot distinguish whether the methane concentration in the air reaches the explosion point. In addition, in terms of finding a source of leakage, the location capability of the methane radar will be greatly reduced when the methane concentration in a large area exceeds the dynamic range.
Disclosure of Invention
Based on this, the invention provides an atmospheric methane detection method with a high dynamic range, a methane radar and a computer terminal, aiming at the technical problem that the detection capability of the methane radar to a large concentration area is limited due to the fact that the dynamic range of the methane laser radar in the prior art is small.
The invention discloses an atmospheric methane detection method with a high dynamic range, which comprises the following steps:
methane concentration in a target region of the atmosphere is measured based on atmospheric detection in the target region. The atmospheric detection result is a corresponding echo signal generated when a differential signal formed by a first laser beam and a second laser beam is transmitted to a target area, the wavelength of the first laser beam is located on a methane absorption line, and the wavelength of the second laser beam is located outside the methane absorption line.
The detection method further comprises the following steps:
and judging whether the methane concentration is greater than a preset upper limit of the methane concentration.
And when the methane concentration is greater than the upper limit of the methane concentration, the measurement range of the methane concentration is increased.
And under the increased measuring range, the methane concentration in the target area is measured again.
As a further improvement of the scheme, the wavelength of the first laser beam is tuned by controlling the seed light current value of the first laser generating the first laser beam, so that the measuring range of the methane concentration is improved.
As a further improvement of the above scheme, the method for controlling the seed light current value of the first laser comprises:
(1) Obtaining a second count n in a farthest range gate of a first laser 0 。
(2) Obtain the first time in the current time periodWavelength average second count a of a first laser beam within a target range gate of a laser 0 。
(3) Real-time second count a within the Collection target Range Gate t 。
(4) When a is t <2n 0 And controlling the seed photocurrent value of the first laser to gradually decrease until a t Reaches 0.5a 0 The tuning is stopped.
As a further improvement of the above solution, the methane absorption line is calibrated in the following way:
the wavelength of the first laser is scanned in advance between a preset wavelength range, and the power, the wavelength and the methane absorption cross section under each tuning current are calibrated. When the system enters a working mode, a power monitoring module and a methane absorption pool which are arranged in the methane radar are respectively utilized to measure the transmitting power and the methane absorption cross section under the current tuning current in real time, normalization processing is carried out on the differential absorption signal according to pre-calibrated data, and the methane concentration in a target area is calculated.
As a further improvement of the above scheme, the preset wavelength range is between 1600nm and 1700nm, and the width is 0.1nm-1nm.
As a further improvement of the above scheme, the preset upper limit of the methane concentration is 50000ppm m.
The invention also discloses a high dynamic range methane radar which comprises a controller, wherein the controller adopts any one of the high dynamic range atmospheric methane detection methods.
As a further improvement of the above solution, the methane radar further includes: and a filter.
The filter is used for filtering the echo signal and transmitting the echo signal to the controller.
As a further improvement of the above solution, the methane radar further includes: laser module, detector, acousto-optic modulator, beam splitter and programmable digital circuit.
A laser module including a first laser and a second laser for generating a first laser beam and a second laser beam, respectively.
And the detector is used for generating an atmosphere detection result according to the echo signal. The detector adopts a coherent balance detector.
And the acousto-optic modulator is used for shifting the frequency of the pulse light of the first laser and the second laser.
And the beam splitter is used for carrying out interference of the echo signal and the local oscillator light.
And the programmable digital circuit is used for carrying out digital acquisition and fast Fourier transform processing on the analog signal of the coherent balance detector.
The invention also discloses a computer terminal which comprises a memory, a processor and a computer program which is stored on the memory and can run on the processor, wherein the processor executes the program to realize any one of the steps of the atmospheric methane detection method with high dynamic range.
Compared with the prior art, the technical scheme disclosed by the invention has the following beneficial effects:
1. this atmosphere methane detection method utilizes algorithm optimization when discerning the high concentration region, and tune the best detection wavelength with hardware, make the radar system can the intelligent increase range when methane concentration exceedes the range, improve the dynamic range of measurement, can make the radar system carry out more accurate explosion early warning on the one hand, on the other hand can be under the condition that large area concentration exceeds standard, improve the positioning accuracy to the source, and then make the methane radar have more superior performance in the aspect of production life safety and pipeline leakage detection, the detectability of methane radar to the large concentration region has been promoted.
3. The methane radar and the computer terminal can use the atmospheric methane detection method to detect atmospheric methane, and the beneficial effects of the methane radar and the computer terminal are the same as those of the atmospheric methane detection method, and are not repeated herein.
Drawings
FIG. 1 is a system block diagram of a high dynamic range methane radar in example 1 of the present invention;
FIG. 2 is a graph showing the absorption cross section of methane molecule as a function of wave number in example 1 of the present invention;
fig. 3 is a flowchart of a method for controlling a seed photocurrent value of the first laser in embodiment 1 of the present invention;
FIG. 4 is a flow chart of a method for atmospheric methane detection in example 3 of the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
It will be understood that when an element is referred to as being "mounted on" another element, it can be directly on the other element or intervening elements may also be present. When a component is referred to as being "disposed on" another component, it can be directly on the other component or intervening components may also be present. When an element is referred to as being "secured to" another element, it can be directly secured to the other element or intervening elements may also be present.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the term "or/and" includes any and all combinations of one or more of the associated listed items.
Example 1
Referring to fig. 1, the present embodiment provides a high dynamic range methane radar, including: the laser module, the telescope module single photon detector and the controller can also comprise an optical fiber link, a time sequence control module, an optical switch module and a filter.
The laser module includes a first laser and a second laser. The first laser is used to generate a first laser beam having a wavelength on the methane absorption line. The second laser is used for generating a second laser beam with the wavelength outside the methane absorption line. In this embodiment, the first laser and the second laser may be named as lasers of two wavelengths, on and off. The light exiting the system is switched between two wavelengths, on and off.
The telescope module is used for transmitting a pair of differential signals formed by the first laser beam and the second laser beam according to a preset control time sequence to a target area of the atmosphere and receiving corresponding echo signals, and the echo signals can be transmitted to the detector after being filtered by the filter.
The detector may be operable to generate a detection result from the received echo signal. In this embodiment, the detector may be an indium gallium arsenic single photon detector, so that the radar obtains higher detection sensitivity, and compared with a conventional photomultiplier and a coherent detector, the required number of echo photons is less, so that a longer distance can be detected, or the requirements on the laser power and the telescope aperture are reduced.
The methane radar system can use an infrared single-photon detector, and because the existing distance resolution methane radar using a classical detector usually needs an echo signal in a picowatt level, which corresponds to nearly ten million photons, and a single-photon scheme only needs to detect hundreds of signal photons to obtain methane concentration information of a target space, the requirement on the echo signal is far lower than that of a traditional detector even if the detection efficiency of the single-photon detector at a position of 1.65 mu m is about 6 percent. The method not only greatly improves the detection distance and the sensitivity of the radar system, but also reduces the requirements on the laser power and the aperture of the telescope and reduces the cost.
The controller is used for primarily tracing the source of methane leakage in the target area according to the detection result, and judging whether the absorption amount of the first laser beam in the target area reaches a measurement threshold value or not in real time according to an echo signal formed by the first laser, so as to judge whether the methane concentration in the target area is greater than a preset upper limit of the methane concentration or not, and when the methane concentration is greater than the upper limit, the controller is also used for improving the measurement range of the methane concentration. In this example, the measurement accuracy of the methane radar was 5000ppm · m; the measurement threshold triggering the dynamic range adjustment is 50000ppm · m.
Referring to fig. 2, in the scanning mode, the on-laser wavelength is locked on the top of the methane R6 absorption peak, and at this time, the methane absorption cross section is about 1.6E-20cm ^ 2/molecule, the distance resolution is set to be 30m, when the methane concentration reaches 150ppm · m, the optical density of methane with the length of 30m is 0.18, the echo signal will be attenuated by about 30% in this interval, considering the data of 2km measurement distance, the estimated effective count is 110/s, the daytime background noise is about 20/s, and after 1s accumulation, 10 SNR can be obtained, at this time, 30% absorption reaches the measurement threshold, and can be identified by the radar, and the radar performs preliminary warning on the area.
When the methane concentration in the region is far beyond the measurement threshold, for example 10 times the measurement threshold, the signal photons are absorbed to only 3 photons/s, which is far below the background noise, and the true methane concentration cannot be obtained in the original system, i.e. it is not possible to distinguish whether the methane concentration is 1500ppm · m or 15000ppm · m or higher.
Referring to fig. 3, when the absorption amount reaches the measurement threshold, the target region is identified as a high concentration region, and the first laser is controlled to tune, thereby increasing the measurement range of the methane concentration. The aforementioned software system will work as follows:
(1) Obtaining a second count n in a farthest range gate of a first laser 0 And serves as a background noise determination value.
(2) Obtaining the wavelength average second count a of the first laser beam within a target range within a current time period 0 As a total count determination value.
(3) Real-time second count a within the Collection target Range Gate t 。
(4) The relationship of the real-time second count to the background noise decision value and the total count decision value is analyzed. Wherein when a t <2n 0 Triggering the range switching judgment, and controlling the seed photocurrent value of the first laser to gradually decrease until a t Reaches 0.5a 0 The tuning is stopped and the tuning current value at that time is recorded.
The optical fiber link is used for transmitting the laser generated by the laser module to the telescope module and transmitting the echo signal received by the telescope module to the detector.
The time sequence control module is used for uniformly controlling the laser module, the telescope module, the detector and the controller to ensure that all parts work orderly.
The optical switch module is used for switching between the first laser and the second laser according to an instruction sent by the controller, and further communication between one of the lasers and the telescope module is achieved.
In the embodiment, the wavelength of the on laser is positioned on a methane absorption line, the wavelength of the off laser is positioned outside the methane absorption line, the light emitted by the system is continuously switched between the on wavelength and the off wavelength, and the laser is transmitted into the telescope through the optical fiber link and is emitted into the atmosphere; the telescope receives the echo signal and transmits the echo signal to the detector through the optical fiber chain wheel, and the detection result of the detector can be input into the software processing system to primarily trace the source of the methane leakage; after the high-concentration area is identified, the controller tunes the laser to the position with lower methane absorption rate, improves the measurement range of the methane concentration and further measures the high-concentration area. Therefore, the methane radar can obtain a larger methane detection dynamic range, when the on wavelength is positioned at a methane absorption peak, the methane radar carries out large-range scanning, after a high-concentration area is detected, an appropriate measuring range can be selected by utilizing an algorithm, the first laser is tuned to a corresponding position in an absorption spectral line, and the high-concentration area is further detected.
The method of implementation in the calibration of the absorption line can be carried out in the following manner.
The wavelength of the first laser is scanned in advance between a preset wavelength range 1645.55nm and 1645.37nm, and the power, the wavelength and the methane absorption cross section under each tuning current are calibrated in advance. When the system enters a working mode, a power monitoring module and a methane absorption pool which are arranged in the radar are respectively utilized to measure the transmitting power and the methane absorption cross section under the current tuning current in real time, normalization processing is carried out on the differential absorption signal according to pre-calibrated data, and the methane concentration in a target area is calculated. Of course, in other embodiments, the predetermined wavelength range may be set in other ranges as long as the predetermined wavelength range is between 1600nm and 1700nm and the width is 0.1nm-1nm.
Therefore, the radar can measure under different wavelengths, the traditional methane radar uses fixed wavelengths, and the wavelength of the laser can be changed through a built-in calibration absorption cell and an algorithm, so that the methane concentration can be measured under different wavelengths.
Example 2
This example provides a high dynamic range methane radar which differs from the radar of example 1 in that the single photon detector of the high dynamic range methane radar of example 1 is replaced with a coherent balance detector. Wherein, this methane radar still includes: acousto-optic modulators, beam splitters, and programmable digital circuits (FPGAs).
The acousto-optic modulator is used for frequency shifting pulse light of the first laser and the second laser. The beam splitter is used for interfering the echo signal and the local oscillation light. The programmable digital circuit is used for carrying out digital acquisition and fast Fourier transform processing on the analog signal of the coherent balance detector. In this embodiment, the coherent balance detector still ensures the advantage of using wavelength tuning to expand the measurement range.
Example 3
Referring to fig. 4, the present embodiment provides an atmospheric methane detection method, which can be applied to the methane radar with high dynamic range in embodiment 1 for detection. The detection method may include the steps of:
s1, calibrating a methane absorption line, wherein a method for calibrating the absorption line is described in embodiment 1 and is not described in detail herein.
And S2, transmitting a differential signal formed by the first laser beam and the second laser beam to a target area according to the calibrated methane absorption line, and receiving a corresponding echo signal.
And S3, generating a detection result according to the echo signal.
And S4, measuring the methane concentration in the target area according to the detection result, judging whether the methane concentration is greater than a preset methane concentration upper limit or not in real time, and executing S5 when the methane concentration is greater than the methane concentration upper limit.
And S5, improving the measurement range of the methane concentration, and re-measuring the methane concentration in the target area under the improved measurement range. The method for increasing the measurement range of the methane concentration can adopt the method in the embodiment 1, and the details are not repeated herein.
Example 4
The present embodiments provide a computer terminal comprising a memory, a processor, and a computer program stored on the memory and executable on the processor.
The computer terminal may be a smart phone, a tablet computer, a notebook computer, a desktop computer, a rack server, a blade server, a tower server or a cabinet server (including an independent server or a server cluster composed of a plurality of servers) capable of executing programs, and the like.
The processor may be a Central Processing Unit (CPU), controller, microcontroller, microprocessor, or other data Processing chip in some embodiments. The processor is typically used to control the overall operation of the computer device. In this embodiment, the processor is configured to execute the program code stored in the memory or process data. The steps of the atmospheric methane detection method with a high dynamic range in embodiment 3 can be realized when the processor executes the program, and further, the analysis of the methane concentration in the target area in the atmosphere is completed.
All possible combinations of the technical features of the above embodiments may not be described for the sake of brevity, but should be considered as within the scope of the present disclosure as long as there is no contradiction between the combinations of the technical features.
The above-mentioned embodiments only express several embodiments of the present invention, and the description thereof is specific and detailed, but not to be construed as limiting the scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present invention should be subject to the appended claims.
Claims (10)
1. A high dynamic range atmospheric methane detection method comprises the following steps:
measuring a methane concentration in a target region of the atmosphere based on atmospheric detection in the target region; the atmospheric detection result is a corresponding echo signal generated when a differential signal formed by a first laser beam and a second laser beam is transmitted into the target area, wherein the wavelength of the first laser beam is located on a methane absorption line, and the wavelength of the second laser beam is located outside the methane absorption line;
characterized in that the detection method further comprises the following steps:
judging whether the methane concentration is greater than a preset upper limit of methane concentration;
when the methane concentration is greater than the upper limit of the methane concentration, the measurement range of the methane concentration is increased;
at the increased measurement range, re-measuring the methane concentration in the target area.
2. The high dynamic range atmospheric methane detection method of claim 1 wherein the wavelength of said first laser beam is tuned by controlling the seed photocurrent value of a first laser generating said first laser beam to increase the measurement range of methane concentration.
3. The high dynamic range atmospheric methane detection method according to claim 2, wherein the control method of the seed photocurrent value of said first laser is:
(1) Obtaining a second count n within a farthest distance gate of the first laser 0 ；
(2) Obtaining a wavelength average second count a of a first laser beam within a target range of the first laser within a current time period 0 ；
(3) Collecting real-time within the target range gateSecond count a t ；
(4) When a is t <2n 0 And controlling the seed photocurrent value of the first laser to gradually decrease until a t Reaches 0.5a 0 The tuning is stopped.
4. A high dynamic range atmospheric methane detection method according to claim 2, characterized by calibrating the methane absorption line in the following way:
scanning the wavelength of the first laser within a preset wavelength range in advance, and calibrating the power, the wavelength and the methane absorption cross section under each tuning current; when the system enters a working mode, a power monitoring module and a methane absorption pool which are arranged in a methane radar are respectively utilized to measure the transmitting power and the methane absorption cross section under the current tuning current in real time, normalization processing is carried out on the differential absorption signals according to pre-calibrated data, and the methane concentration in a target area is calculated.
5. A high dynamic range atmospheric methane detection method according to claim 4, characterized in that said predetermined wavelength range is between 1600nm and 1700nm, and the width is 0.1nm-1nm.
6. The high dynamic range atmospheric methane detection method of claim 1 wherein the preset upper methane concentration limit is 50000 ppm-m.
7. A high dynamic range methane radar comprising a controller, wherein the controller employs the high dynamic range atmospheric methane detection method of any one of claims 1 to 6.
8. The high dynamic range methane radar of claim 7, further comprising:
and the filter is used for filtering the echo signal and transmitting the echo signal to the controller.
9. The high dynamic range methane radar of claim 7, further comprising:
a laser module comprising a first laser and a second laser for generating the first laser beam and the second laser beam, respectively;
a detector for generating the atmospheric detection result from the echo signal; the detector adopts a coherent balance detector;
an acousto-optic modulator for frequency shifting the pulsed light of the first and second lasers;
the beam splitter is used for carrying out interference between the echo signal and local oscillation light; and
and the programmable digital circuit is used for carrying out digital acquisition and fast Fourier transform processing on the analog signal of the coherent balance detector.
10. A computer terminal comprising a memory, a processor and a computer program stored on the memory and executable on the processor, characterized in that the processor when executing the program implements the steps of the high dynamic range atmospheric methane detection method according to any one of claims 1 to 6.
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