CN118549384B - An airborne atmospheric methane leak remote sensing device - Google Patents

Abstract

The invention discloses an airborne atmospheric methane leakage telemetry device which comprises a laser module, a laser modulation module, a signal detection module, a signal frequency reduction module and a signal processing module, wherein the laser module is connected with the signal detection module; the laser module is configured to enable laser energy emitted by the laser to cover a target methane preset absorption peak; the laser modulation module is configured to perform high-frequency modulation on laser emitted by the laser, so that the laser emits three-color light beams, and the three-color light beams are emitted to the ground after power amplification and collimation. According to the airborne atmospheric methane leakage telemetry device, the scattered light radiation from an object or a hard target is used for replacing a detection method of specular reflection from a retro-reflector, so that the difficulty of device calibration is effectively reduced, interference caused by factors such as mechanical vibration and the like is reduced, and the carrier power and the measurement accuracy of phase information carried on an optical signal are improved by using an optical power amplifier.

Description

An airborne atmospheric methane leak remote sensing device

Technical Field

The invention relates to a methane detection device, in particular to an airborne atmospheric methane leakage remote sensing device.

Background Art

Atmospheric methane telemetry technology uses sensors such as lasers or infrared radiation to detect the degree of absorption of specific wavelengths of radiation by methane in the atmosphere, thereby determining the concentration of methane. This technology can be used in fields such as climate change monitoring, greenhouse gas control, natural resource exploration, and environmental pollution monitoring, providing important data support for scientific research and environmental protection. Most telemetry systems use direct laser absorption spectroscopy (DLAS) technology to detect small intensity changes on a large background of total transmitted laser intensity. Due to possible transmission changes in the telemetry configuration, the DLAS baseline is prone to significant fluctuations, which may be misunderstood as molecular absorption. In addition, the transmission of light in the atmospheric environment is affected by various factors, such as turbulence, obstructions, smoke particles, etc., making the echo light signal received by the receiver very weak and carrying various noises, which require various filtering algorithms to process.

Heterodyne phase-sensitive dispersion spectroscopy (HPSDS) technology is a phase-sensitive detection technology that has strong resistance to light intensity fluctuations and is immune to the intensity noise added by light during atmospheric transmission. At the same time, HPSDS technology is a differential technology that can suppress common-mode noise, such as phase noise caused by atmospheric turbulence. However, in traditional HPSDS systems, the co-transmission of multiple frequency-shifted waves will reduce the heterodyne gain in the photoelectric detection process. In addition, in traditional HPSDS telemetry systems, it is necessary to use mirror reflection of the retroreflector to collect optical signals, which greatly increases the difficulty of device calibration and is easily interfered by factors such as mechanical vibration, which is not conducive to installation in airborne environments such as drones or remote-controlled cars.

When light waves pass through particles, they will be scattered. The intensity distribution, polarization characteristics, and spectral characteristics of the scattered light are all related to the characteristics of the scatterer itself. By measuring the scattered light, a lot of information about the scatterer structure can be obtained, and the particle light scattering theory has been widely used in multiphase flow, combustion process, biomedicine and other fields. Collecting scattered light radiation from objects or hard targets can replace the mirror reflection from the retroreflector, but the scattered light radiation is very weak, much weaker than the echo light signal collected by the reflective lens, which will greatly limit the detection sensitivity in this low return light power environment.

Summary of the invention

In order to solve the above technical problems, the present invention provides an airborne atmospheric methane leakage remote sensing device.

In order to achieve the above object, the present invention adopts the following technical solutions:

The present invention provides an airborne atmospheric methane leakage remote sensing device, comprising a laser module, a laser modulation module, a signal detection module, a signal frequency reduction module and a signal processing module connected in sequence;

The laser module enables the laser emitted by the laser to cover the preset absorption peak of the target methane;

The laser modulation module is used to perform high-frequency modulation on the three-color laser emitted by the laser, and after power amplification and collimation of the light beam, the light beam is emitted toward the ground;

The signal detection module is used to convert the optical signal of the light beam scattered back from the ground into an electrical signal, generate a beat frequency signal through the square law characteristics of the photoelectric detector, and amplify and filter the signal;

The signal frequency reduction module is used to perform frequency reduction processing on the beat frequency signal collected by the signal detection module;

The signal processing module is used to demodulate and process the down-conversion signal processed by the signal down-conversion module. By processing the data, the absorption degree of wavelength radiation by methane in the atmosphere can be detected, and then the methane concentration can be determined.

Further, the laser module includes a function generator, a laser current controller, a distributed feedback laser and a laser temperature controller;

The function generator is connected to the laser current controller, and the function generator generates a low-frequency scanning signal to enable the distributed feedback laser to generate a laser that can cover the target methane absorption peak;

The laser current controller is connected to the distributed feedback laser, and the laser current controller is used to control the input current of the distributed feedback laser;

The laser temperature controller is connected to the distributed feedback laser, and is used to control the operating temperature of the distributed feedback laser.

Further, the laser modulation module includes an electro-optic modulator, a bias voltage module, a first amplifier, an optical power amplifier and a collimator;

The bias voltage module is connected to the electro-optic modulator, and the bias voltage module is used to apply a bias voltage to the electro-optic modulator;

The first amplifier is connected to the electro-optical modulator, and the first amplifier amplifies the received high-frequency modulation signal and then applies the high-frequency modulation signal to the electro-optical modulator;

The optical power amplifier is connected to the electro-optical modulator, and the optical power amplifier is used to amplify the power of the modulated optical signal;

The collimator collimates the laser beam, adjusts the divergence angle emitted into the free space, and emits the laser toward the ground.

Furthermore, the electro-optic modulator in the laser modulation module is used to externally modulate the laser emitted by the distributed feedback laser.

Further, the signal detection module includes a Newtonian telescope, a photoelectric detector, a second amplifier and a bandpass filter;

The Newton telescope gathers the light signal scattered back from the ground to the photoelectric detector;

The photoelectric detector is connected to the second amplifier, and the photoelectric detector is used to convert the light signal focused by the Newton telescope into an electrical signal, and to generate a beat frequency signal through interference using the square law characteristic of the photoelectric detector;

The second amplifier is used to amplify the beat frequency signal; the bandpass filter suppresses the noise signal outside the high-frequency modulation frequency band of the amplified beat frequency signal.

Furthermore, the Newton telescope in the signal detection module focuses the laser light emitted to the ground by the collimator in the laser modulation module and thus scattered back.

Further, the signal frequency reduction module includes a first radio frequency signal generator, a second radio frequency signal generator, a first power distributor, a second power distributor, a first mixer and a second mixer;

The first radio frequency signal generator is connected to the first power divider, and the radio frequency signal emitted by the first radio frequency signal generator is divided into a first radio frequency signal and a second radio frequency signal by the first power divider;

The second radio frequency signal generator is connected to the second power divider, and the radio frequency signal emitted by the second radio frequency signal generator is divided into a third radio frequency signal and a fourth radio frequency signal by the second power divider;

The second RF signal and the third RF signal enter the first mixer for frequency down-conversion, and the fourth RF signal and the beat frequency signal passing through the bandpass filter in the detection module enter the second mixer for frequency mixing;

The high-frequency modulation signal input by the first RF signal generator in the signal frequency reduction module to the first amplifier in the laser modulation module is the first RF signal.

Furthermore, the second mixer in the signal frequency reduction module is connected to the bandpass filter in the signal detection module, and the bandpass filter in the signal detection module transmits the amplified and filtered electrical signal to the second mixer in the signal frequency reduction module for frequency reduction processing.

Further, the signal processing module includes a lock-in amplifier, a data acquisition card and a data processing module;

The lock-in amplifier is connected to a data acquisition card, and the data acquisition card collects the signal demodulated by the lock-in amplifier;

The data acquisition card is connected to a data processing module, and the data processing module is used to process the data collected by the data acquisition card.

Further, the lock-in amplifier in the signal processing module is connected to the first mixer in the signal frequency reduction module, and the frequency reduction signal output by the first mixer in the signal frequency reduction module is input into the lock-in amplifier in the signal processing module as a reference signal;

The lock-in amplifier in the signal processing module is connected to the second mixer in the signal frequency reduction module, and the frequency reduction signal output by the second mixer in the signal frequency reduction module is input into the lock-in amplifier in the signal processing module as a detection signal;

The phase-locked amplifier in the signal processing module compares the phase difference between the detection signal and the reference signal, and demodulates and outputs a phase signal.

In summary, the beneficial effects of the present invention are:

The airborne atmospheric methane leak remote sensing device of the present invention solves the technical problem of reduced heterodyne gain in the photoelectric detection process due to the common transmission of multiple frequency-shifted waves in the traditional heterodyne phase-sensitive dispersion spectroscopy system, and also solves the technical problem of high difficulty in device calibration and susceptibility to interference from factors such as mechanical vibration due to the use of a retroreflector in the traditional HPSDS telemetry system, as well as the technical problem of weak scattered light radiation signals limiting detection sensitivity caused by a detection method in which scattered light radiation from an object or hard target can replace the mirror reflection from the retroreflector.

The airborne atmospheric methane leakage remote sensing device of the present invention uses scattered light radiation from an object or hard target instead of the mirror reflection from the retroreflector, which can effectively reduce the difficulty of device calibration and reduce the interference of factors such as mechanical vibration, so that the device can be better used in airborne environments such as drones or remote-controlled cars. In addition, the device uses an optical power amplifier to increase the laser power, thereby increasing the carrier power, strengthening the intensity of the sidebands on both sides of the carrier generated by modulation, and increasing the heterodyne gain, thereby improving the measurement accuracy of the phase information carried on the optical signal, reducing the influence of noise, and further improving the signal-to-noise ratio of the system.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a schematic structural diagram of an airborne atmospheric methane leakage remote sensing device according to the present invention;

In the figure: 1. function generator; 2. laser current controller; 3. distributed feedback laser; 4. laser temperature controller; 5. electro-optic modulator; 6. bias voltage module; 7. first amplifier; 8. optical power amplifier; 9. collimator; 10. Newton telescope; 11. photodetector; 12. second amplifier; 13. bandpass filter; 14. first RF signal generator; 15. first power divider; 16. first mixer; 17. second power divider; 18. second RF signal generator; 19. second mixer; 20. phase-locked amplifier; 21. data acquisition card; 22. data processing module.

DETAILED DESCRIPTION

In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be described clearly and completely below. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

Please refer to Figure 1. The present invention provides an airborne atmospheric methane leakage remote sensing device, comprising a laser module, a laser modulation module, a signal detection module, a signal frequency reduction module and a signal processing module connected in sequence; the laser module enables the laser emitted by the laser to cover the preset absorption peak of the target methane; the laser modulation module is used to perform high-frequency modulation on the three-color laser emitted by the laser, and after power amplification and collimation of the light beam, the light beam is emitted to the ground; the signal detection module is used to convert the optical signal of the light beam scattered back from the ground into an electrical signal, generate a beat frequency signal through the square law characteristics of the photoelectric detector, and amplify and filter the signal; the signal frequency reduction module is used to perform frequency reduction processing on the beat frequency signal collected by the signal detection module; the signal processing module is used to demodulate and process the frequency reduction signal processed by the signal frequency reduction module, and by processing the data, the absorption degree of wavelength radiation by methane in the atmosphere can be detected, and then the methane concentration can be determined.

In one embodiment, the laser module includes a function generator 1, a laser current controller 2, a distributed feedback laser 3 and a laser temperature controller 4; the function generator 1 is connected to the laser current controller 2, and the function generator 1 generates a low-frequency scanning signal to enable the distributed feedback laser 3 to generate a laser covering the target methane absorption peak; the laser current controller 2 is connected to the distributed feedback laser 3, and the laser current controller 2 is used to control the input current of the distributed feedback laser 3; the laser temperature controller 4 is connected to the distributed feedback laser 3, and the laser temperature controller 4 is used to control the operating temperature of the distributed feedback laser 3.

It can be understood that the distributed feedback laser 3 is driven by the laser current controller 2 and the laser temperature controller 4 , and the low-frequency scanning signal is generated by the function generator 1 .

In one embodiment, the laser modulation module includes an electro-optic modulator 5, a bias voltage module 6, a first amplifier 7, an optical power amplifier 8 and a collimator 9; the bias voltage module 6 is connected to the electro-optic modulator 5, and the bias voltage module 6 is used to apply a bias voltage to the electro-optic modulator 5; the first amplifier 7 is connected to the electro-optic modulator 5, and the first amplifier 7 is used to amplify the received high-frequency modulation signal, and then apply the high-frequency modulation signal to the electro-optic modulator 5; the optical power amplifier 8 is connected to the electro-optic modulator 5, and the optical power amplifier 8 is used to amplify the power of the modulated optical signal; the collimator 9 collimates the laser beam, adjusts the divergence angle emitted into the free space, and then emits the laser to the ground.

It can be understood that the electro-optic modulator 5 in the laser modulation module is driven by the bias voltage module 6 and the high-frequency modulation signal transmitted from the first amplifier 7 to externally modulate the laser emitted by the distributed feedback laser 3 .

In one embodiment, the signal detection module includes a Newtonian telescope 10, a photodetector 11, a second amplifier 12 and a bandpass filter 13; the Newtonian telescope 10 is used to converge the light signal scattered back from the ground to the photodetector 11; the photodetector 11 is used to convert the light signal converged by the Newtonian telescope 10 into an electrical signal, which is beneficial to the square law characteristics of the photodetector 11 and generates a beat frequency signal through interference; the second amplifier 12 is used to amplify the beat frequency signal; the bandpass filter 13 is used to suppress the noise signal outside the high-frequency modulation frequency band of the amplified beat frequency signal.

It can be understood that the Newton telescope 10 in the signal detection module focuses the laser light emitted to the ground by the collimator 9 in the laser modulation module and thus scattered back.

In one embodiment, the signal frequency reduction module includes a first RF signal generator 14, a second RF signal generator 18, a first power divider 15, a second power divider 17, a first mixer 16 and a second mixer 19; the first RF signal generator 14 is connected to the first power divider 15, and the RF signal emitted by the first RF signal generator 14 is divided into a first RF signal and a second RF signal through the first power divider 15; the second RF signal generator 18 is connected to the second power divider 17, and the RF signal emitted by the second RF signal generator 18 is divided into a third RF signal and a fourth RF signal through the second power divider 17; wherein the second RF signal and the third RF signal enter the first mixer 16 for frequency reduction, and the fourth RF signal and the beat frequency signal passing through the bandpass filter 13 in the detection module enter the second mixer 19 for mixing; the high-frequency modulation signal input by the first RF signal generator 14 in the signal frequency reduction module to the first amplifier 7 in the laser modulation module is the first RF signal.

The second mixer 19 in the signal frequency reduction module is connected to the bandpass filter 13 in the signal detection module. The bandpass filter 13 in the signal detection module transmits the amplified and filtered electrical signal to the second mixer 19 in the signal frequency reduction module for frequency reduction processing.

In one embodiment, the signal processing module includes a phase-locked amplifier 20, a data acquisition card 21 and a data processing module 22; the phase-locked amplifier 20 is connected to the data acquisition card 21, and the data acquisition card 21 is used to collect the signal demodulated by the phase-locked amplifier 20; the data acquisition card 21 is connected to the data processing module 22, and the data processing module 22 is used to process the data collected by the data acquisition card 21.

Specifically, the phase-locked amplifier 20 in the signal processing module is connected to the first mixer 16 in the signal frequency reduction module, and the frequency reduction signal output by the first mixer 16 in the signal frequency reduction module is input into the phase-locked amplifier 20 in the signal processing module as a reference signal; the phase-locked amplifier 20 in the signal processing module is connected to the second mixer 19 in the signal frequency reduction module, and the frequency reduction signal output by the second mixer 19 in the signal frequency reduction module is input into the phase-locked amplifier 20 in the signal processing module as a detection signal; the phase-locked amplifier 20 in the signal processing module compares the detection signal with the reference signal. The phase difference of the signal is demodulated and the output phase signal is output. The airborne atmospheric methane leak remote sensing device of the present invention solves the technical problem of reduced heterodyne gain in the photoelectric detection process due to the common transmission of multiple frequency-shifted waves in the traditional heterodyne phase-sensitive dispersion spectroscopy system, and also solves the technical problem of high difficulty in device calibration and susceptibility to interference from factors such as mechanical vibration due to the use of retroreflectors in the traditional HPSDS telemetry system, as well as the technical problem of weak scattered light radiation signals limiting detection sensitivity caused by the detection method that uses scattered light radiation from objects or hard targets to replace the mirror reflection from the retroreflector.

The airborne atmospheric methane leakage remote sensing device of the present invention uses scattered light radiation from an object or hard target instead of the mirror reflection from the retroreflector, which can effectively reduce the difficulty of device calibration and reduce the interference of factors such as mechanical vibration, so that the device can be better used in airborne environments such as drones or remote-controlled cars. In addition, the device uses an optical power amplifier to increase the laser power, thereby increasing the carrier power, strengthening the intensity of the sidebands on both sides of the carrier generated by modulation, and increasing the heterodyne gain, thereby improving the measurement accuracy of the phase information carried on the optical signal, reducing the influence of noise, and further improving the signal-to-noise ratio of the system.

Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the essence and scope of the technical solution of the present invention.

Claims (7)

1. The airborne atmospheric methane leakage telemetry device is characterized by comprising a laser module, a laser modulation module, a signal detection module, a signal frequency reduction module and a signal processing module which are connected in sequence;

The laser module enables laser energy emitted by the laser to cover a target methane preset absorption peak;

The laser modulation module is used for carrying out high-frequency modulation on three-color laser emitted by the laser, and emitting the light beam to the ground after carrying out power amplification and collimation on the light beam;

The signal detection module comprises a Newton telescope (10), a photoelectric detector (11), a second amplifier (12) and a band-pass filter (13);

The signal detection module is used for converting an optical signal of a light beam scattered back from the ground into an electric signal, generating a beat frequency signal through square law characteristics of the photoelectric detector, and then amplifying and filtering the signal;

the signal down-conversion module is used for down-converting the beat frequency signals acquired by the signal detection module;

the signal processing module is used for demodulating and data processing the down-conversion signals processed by the signal down-conversion module, and the absorption degree of methane in the atmosphere to wavelength radiation can be detected by processing the data so as to further determine the methane concentration; the laser module comprises a function generator (1), a laser current controller (2), a distributed feedback laser (3) and a laser temperature controller (4);

The function generator (1) is connected with the laser current controller (2), and the function generator (1) generates a low-frequency scanning signal to enable the distributed feedback laser (3) to generate laser capable of covering a target methane absorption peak;

The laser current controller (2) is connected with the distributed feedback laser (3), and the laser current controller (2) is used for controlling the input current of the distributed feedback laser (3);

the laser temperature controller (4) is connected with the distributed feedback laser (3), and the laser temperature controller (4) is used for controlling the working temperature of the distributed feedback laser (3); the laser modulation module comprises an electro-optic modulator (5), a bias voltage module (6), a first amplifier (7), an optical power amplifier (8) and a collimator (9);

the bias voltage module (6) is connected with the electro-optic modulator (5), and the bias voltage module (6) is used for applying bias voltage to the electro-optic modulator (5);

The first amplifier (7) is connected with the electro-optical modulator (5), and the first amplifier (7) amplifies the received high-frequency modulation signal and then applies the high-frequency modulation signal to the electro-optical modulator (5);

The optical power amplifier (8) is connected with the electro-optical modulator (5), and the optical power amplifier (8) is used for amplifying the power of the modulated optical signal;

The collimator (9) collimates the laser beam, adjusts the divergence angle emitted to the free space and emits the laser to the ground;

The signal down-conversion module comprises a first radio frequency signal generator (14), a second radio frequency signal generator (18), a first power distributor (15), a second power distributor (17), a first mixer (16) and a second mixer (19);

The first radio frequency signal generator (14) is connected with the first power distributor (15), and radio frequency signals sent by the first radio frequency signal generator (14) are divided into first radio frequency signals and second radio frequency signals through the first power distributor (15);

The second radio frequency signal generator (18) is connected with the second power distributor (17), and radio frequency signals sent by the second radio frequency signal generator (18) are divided into third radio frequency signals and fourth radio frequency signals through the second power distributor (17);

the second radio frequency signal and the third radio frequency signal enter the first mixer (16) to be subjected to frequency reduction, and the fourth radio frequency signal and the beat frequency signal passing through the band-pass filter (13) in the signal detection module enter the second mixer (19) to be subjected to frequency reduction;

the high-frequency modulation signal input to the first amplifier (7) in the laser modulation module by the first radio-frequency signal generator (14) in the signal down-conversion module is the first radio-frequency signal.

2. The on-board atmospheric methane leakage telemetry device according to claim 1, characterized in that the electro-optical modulator (5) in the laser modulation module is used for external modulation of the laser light emitted by the distributed feedback laser (3).

3. The on-board atmospheric methane leakage telemetry device according to claim 2, characterized in that the newtonian telescope (10) converges the optical signals scattered back from the ground to the photodetector (11);

The photoelectric detector (11) is connected with the second amplifier (12), the photoelectric detector (11) is used for converting the optical signals collected by the Newton telescope (10) into electric signals, and beat frequency signals are generated through interference by utilizing square law characteristics of the photoelectric detector;

The second amplifier (12) is used for amplifying the beat frequency signal; the band-pass filter (13) suppresses noise signals outside the high-frequency modulation frequency band from the amplified beat signal.

4. An airborne atmospheric methane leakage telemetry device according to claim 3, characterized in that the newton telescope (10) in the signal detection module focuses the laser light scattered back by the collimator (9) in the laser modulation module to the ground.

5. The airborne atmospheric methane leakage telemetry device according to claim 4, wherein the second mixer (19) in the signal down conversion module is connected to the band pass filter (13) in the signal detection module, the band pass filter (13) in the signal detection module transmitting the amplified and filtered electrical signal to the second mixer (19) in the signal down conversion module for down conversion.

6. The airborne atmospheric methane leakage telemetry device of claim 5, wherein the signal processing module comprises a lock-in amplifier (20), a data acquisition card (21), and a data processing module (22);

the phase-locked amplifier (20) is connected with the data acquisition card (21), and the data acquisition card (21) acquires signals demodulated by the phase-locked amplifier (20);

The data acquisition card (21) is connected with the data processing module (22), and the data processing module (22) is used for processing the data acquired by the data acquisition card (21).

7. The airborne atmospheric methane leakage telemetry device according to claim 6, wherein the lock-in amplifier (20) in the signal processing module is connected to the first mixer (16) in the signal down-conversion module, and a down-converted signal output by the first mixer (16) in the signal down-conversion module is input as a reference signal to the lock-in amplifier (20) in the signal processing module;

The phase-locked amplifier (20) in the signal processing module is connected with the second mixer (19) in the signal down-conversion module, and a down-conversion signal output by the second mixer (19) in the signal down-conversion module is input into the phase-locked amplifier (20) in the signal processing module as a detection signal;

the phase-locked amplifier (20) in the signal processing module compares the phase difference between the detection signal and the reference signal, and demodulates and outputs a phase signal.