A method and system for detecting atmospheric composition differential absorption laser imaging radar profiles

Abstract

The present invention belongs to the field of atmospheric environment monitoring and discloses a method and system for detecting atmospheric composition profiles using differential absorption laser imaging radar. The detection method comprises the following steps: Step S1: alternately emitting two laser beams with different central wavelengths toward the atmosphere to be measured; Step S2: receiving a light column image resulting from the interaction between the laser beams and the atmosphere to be measured, preloading a modulated speckle signal onto a spatial light modulator, modulating the light column image, and converting the modulated light signal into an electrical signal; Step S3: synchronously acquiring the electrical signal, converting the electrical signal into a digital signal, and combining the digital signal with the modulated speckle signal to restore the light column images corresponding to the two laser beams with different central wavelengths; Step S4: calculating the distance-resolved echo data corresponding to the two laser beams with different central wavelengths based on the relationship between the pixels of the restored light column image and the measured distance; and Step S5: inverting the concentration profile of the gas to be measured from the distance-resolved echo data corresponding to the two laser beams with different central wavelengths. The present invention has strong universal applicability.

Description

Technical Field

[0001] The present invention belongs to the technical field of atmospheric environment monitoring, and in particular relates to a method and system for detecting concentration profiles of atmospheric components using differential absorption laser imaging radar. Background Art

[0002] Since its introduction in 1966, differential absorption lidar (LAD) has been a research hotspot in the field of laser atmospheric sensing. Currently, it is widely used to profile atmospheric gases such as ozone, sulfur dioxide, nitrogen dioxide, and water vapor. Traditional pulsed differential absorption lidar systems require high-performance nanosecond pulsed light sources, resulting in bulky radar systems, high maintenance costs, and significant difficulty. This is particularly true for profiling gases such as methane and carbon dioxide, which absorb in the near-infrared band. The complex radar system structure makes it difficult to scale up and apply.

[0003] Some researchers have used continuous-wave laser sources combined with area-array CCD / CMOS sensors to detect atmospheric nitrogen dioxide and carbon dioxide profiles. However, for gases like methane and carbon dioxide, which have absorption characteristics in the near-infrared band, the 1.65 μm and 1.57 μm near-infrared bands are typically the most suitable for differential absorption profile detection. Due to limitations in manufacturing processes and other factors, high-resolution area-array CCD / CMOS sensors in these bands are difficult to manufacture, significantly limiting the detection performance of existing differential absorption lidars.

[0004] In order to overcome the shortcomings of existing technologies, it is now urgent to innovate and invent new atmospheric composition differential absorption laser imaging radar profile detection methods and systems. Summary of the Invention

[0005] In response to the above problems, the present invention discloses a method for detecting atmospheric composition differential absorption laser imaging radar profiles, the method comprising the following steps:

[0006] Step S1: alternately emitting two laser beams with different central wavelengths toward the atmosphere to be measured;

[0007] Step S2: receiving a light column image after the laser beam interacts with the atmosphere to be measured, preloading a modulated speckle signal on a spatial light modulator, modulating the light column image, and converting the modulated light signal into an electrical signal;

[0008] Step S3: synchronously collecting the electrical signals, converting the electrical signals into digital signals, and combining the digital signals with the modulated speckle signals to restore the light column images corresponding to the two laser beams with different central wavelengths;

[0009] Step S4: Calculating the distance-resolved echo data corresponding to the two laser beams with different central wavelengths based on the relationship between the restored light column image pixels and the measured distance;

[0010] Step S5: inverting the concentration profile of the gas to be measured from the distance-resolved echo data corresponding to the two beams of different central wavelengths.

[0011] Furthermore, the two central wavelengths of the laser beam are respectively located on the absorption peak and the absorption valley of the gas to be measured.

[0012] Furthermore, the calculation method for restoring the light column images corresponding to the two laser beams with different central wavelengths is as follows:

[0013]

[0014] in, Indicates the i The modulated speckle signal during the second modulation is The laser beam with the central wavelength i The digital signal corresponding to the acquisition time, L Indicates the amount of modulated speckle.

[0015] Furthermore, the inversion of the concentration profile of the gas to be measured from the distance-resolved echo data corresponding to two beams of different central wavelengths specifically includes the following steps:

[0016] Step S51: Measure a hard target object at a known distance to obtain an image of the hard target object. Based on the distance information of the hard target object from the measurement system and the pixel position information of the hard target object in the image, calibrate the relationship between the measurement system image pixels and the measurement distance.

[0017] Step S52: using the relationship between the calibrated measured distance and the image pixels, respectively calculating the distance-resolved echo data corresponding to the two beams with different central wavelengths in the measured image;

[0018] Step S53: applying a differential absorption algorithm to the two beams of distance-resolved echo data corresponding to different central wavelengths to invert and calculate the profile data of the gas to be measured.

[0019] Furthermore, the differential absorption algorithm is used to invert and calculate the profile data of the gas to be measured, and the calculation method is as follows:

[0020]

[0021] in, Indicates the obtained gas profile data to be measured, P(r, λ ON ) represents the distance-resolved data corresponding to the absorption peak wavelength, P(r, λ OFF ) represents the distance-resolved data corresponding to the absorption valley wavelength, It represents the absorption cross section of the gas to be measured at the absorption peak wavelength. It represents the absorption cross section of the gas to be measured at the absorption valley wavelength. r Indicates distance.

[0022] The present invention also discloses an atmospheric component differential absorption laser imaging radar profile detection system, the detection system comprising:

[0023] A laser, used for alternately emitting two laser beams with different central wavelengths into the atmosphere to be measured;

[0024] a receiving telescope for imaging a backscattered light column after the laser beam interacts with the atmosphere;

[0025] A spatial light modulator is used to preload a modulated speckle signal and modulate the light column image;

[0026] A photodetector, used to convert the modulated optical signal into an electrical signal;

[0027] A data acquisition card is used to convert the corresponding electrical signal into a digital signal;

[0028] A calculation control unit is used to calculate the light column images of lasers with different central wavelengths based on the digital signal and the modulated speckle signal, parse the distance-resolved data of the lasers with different central wavelengths based on the light column images, and invert and calculate the concentration profile of the gas to be measured based on the distance-resolved data of the lasers with different central wavelengths.

[0029] Furthermore, the plane where the receiving telescope is located, the plane where the spatial light modulator is located, and the optical axis of the laser beam emitted by the laser intersect, satisfying the Schaffner imaging principle.

[0030] Furthermore, the detection system further includes:

[0031] A beam expander, used to expand the laser beam emitted by the laser;

[0032] A converging lens, used to converge the modulated optical signal;

[0033] Narrowband filter, used to remove background stray light from the detection signal.

[0034] The present invention also discloses a computer-readable storage medium, which stores a computer program. After the computer program is run, the atmospheric differential absorption laser imaging radar profile detection method as described in any one of the above embodiments is executed.

[0035] The present invention also discloses a computer system including a processor and a storage medium, wherein a computer program is stored on the storage medium. The processor reads and runs the computer program from the storage medium to execute the atmospheric component differential absorption laser imaging radar profile detection method as described in any one of the above embodiments.

[0036] Beneficial effects

[0037] The atmospheric component differential absorption laser imaging radar echo signal of the present invention does not decay with the square of the distance, which reduces the system's requirements for the measurement dynamic range; the use of a high-resolution spatial light modulator can receive close-range atmospheric echo signals, greatly shortening the near-field detection blind spot, overcoming the problem of large close-range detection blind spots in traditional pulsed atmospheric laser radar technology; the spatial light modulator has high spatial resolution and low cost. A variety of spatial light modulators can be designed and processed for specific wavelengths, which can effectively solve the shortage of infrared array detectors in the prior art due to factors such as manufacturing processes. The atmospheric differential absorption laser imaging radar method of the present invention can be applied to the detection of gas profiles with absorption characteristics in the ultraviolet wavelength, visible wavelength, and infrared bands, and has strong universality.

[0038] Other features and advantages of the present invention will be described in the following description, and in part will become apparent from the description, or will be understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained by the structures pointed out in the description, claims and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following is a brief introduction to the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0040] Figure 1 A flowchart of a method for detecting atmospheric component differential absorption laser imaging radar profiles according to an embodiment of the present invention is shown;

[0041] Figure 2 A flow chart showing the inversion of the concentration profile of the gas to be measured from two beams of distance-resolved echo data corresponding to different central wavelengths according to an embodiment of the present invention is shown;

[0042] Figure 3 A schematic structural diagram of an atmospheric composition differential absorption laser imaging radar profile detection system according to an embodiment of the present invention is shown. DETAILED DESCRIPTION

[0043] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only 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 making creative efforts shall fall within the scope of protection of the present invention.

[0044] like Figure 1 As shown, the present invention discloses a method for detecting atmospheric component differential absorption laser imaging radar profiles, the profile detection method comprising the following steps:

[0045] Step S1: alternately emitting two laser beams with different central wavelengths toward the atmosphere to be measured;

[0046] Step S2: receiving a light column image after the laser beam interacts with the atmosphere to be measured, preloading a modulated speckle signal on a spatial light modulator, modulating the light column image, and converting the modulated light signal into an electrical signal;

[0047] Step S3: synchronously collecting the electrical signals, converting the electrical signals into digital signals, and combining the digital signals with the modulated speckle signals to restore the light column images corresponding to the two laser beams with different central wavelengths;

[0048] Step S4: Calculating the distance-resolved echo data corresponding to the two laser beams with different central wavelengths based on the relationship between the restored light column image pixels and the measured distance;

[0049] Step S5: inverting the concentration profile of the gas to be measured from the distance-resolved echo data corresponding to the two beams of different central wavelengths.

[0050] For example, a laser is used to alternately emit laser beams of different central wavelengths into the atmosphere. Alternating emission refers to sequentially emitting two laser beams of different central wavelengths in a predetermined cycle. In this embodiment, the laser can be a conventional Nd:YAG-pumped optical parametric oscillator / amplifier or a pulsed laser light source pumped by a dye laser, or a continuous-wave semiconductor laser, fiber laser, or the like. When used to detect different atmospheric components, the corresponding laser wavelength pairs are different.

[0051] For example, when detecting the atmospheric carbon dioxide profile, the central wavelength of the laser beam is located at the absorption peak and absorption valley of carbon dioxide. The carbon dioxide absorption peak wavelength is denoted as λ ON , the wavelength λ ON It can be 1572.335nm, and the absorption valley wavelength of carbon dioxide is recorded as λ OFF, the corresponding laser wavelength can be 1572.18nm. Assuming that a measurement cycle is 1 second, the laser emits λ in one emission cycle. ON The time is 0.5 seconds, the laser emits λ OFF The laser periodically switches the emitted laser beam for a period of 0.5 seconds.

[0052] After the emitted laser beam interacts with the atmosphere, the gas to be measured reacts with λ ON The absorption of λ is strong. OFF The absorption of the two laser beams is weak, while other atmospheric components have roughly the same effect on the two laser beams. Therefore, the concentration of the gas being measured is inverted by detecting the difference in the backscattered signals of the two laser beams. Furthermore, the duration of each cycle can be reduced to improve measurement accuracy. The smaller the interval between the two laser beams, the smaller the difference in the effect of atmospheric aerosols or other interfering gases on the two wavelengths of laser light. During data inversion, the influence of other factors can be offset.

[0053] After the laser beam is emitted into the atmosphere, it interacts with other substances in the atmosphere, such as the gas to be measured and aerosols, to generate a scattered signal. A receiving telescope forms an image of the backscattered light column, and a spatial light modulator receives the light column image. The spatial light modulator is preloaded with a modulated speckle signal and modulates the light column image. The modulated light column image is then photoelectrically converted by a photodetector without spatial resolution to generate an electrical signal. Simultaneously with the modulation, a data acquisition card synchronously acquires the electrical signal and converts it into a digital signal. The digital signal and the modulated speckle signal are combined to restore the light column images corresponding to the two laser beams with different central wavelengths. The modulated speckle signal refers to the speckle signal preloaded on the spatial light modulator, which modulates the light column image.

[0054] Furthermore, because there is a deterministic relationship between the image pixels and the detection distance, the measured distance can be determined based on the image pixel position, and the size of the image pixel value can be used to determine the size of the distance-resolved echo signal. The measured distance is the distance between the atmosphere to be measured and the measurement device. Based on this deterministic relationship, the distance-resolved echo data of the corresponding wavelength can be parsed, and the concentration profile of the gas to be measured can be calculated based on the distance-resolved echo data of two laser beams with different central wavelengths.

[0055] Furthermore, the calculation method for restoring the corresponding light column images of two laser beams with different central wavelengths is as follows:

[0056]

[0057] in, Indicates the i The modulated speckle signal during the second modulation is The laser beam with the central wavelength i The digital signal corresponding to the acquisition time, L Indicates the amount of modulated speckle.

[0058] For example, the central wavelength of a laser beam is located at the absorption peak of the gas to be measured, which is denoted as λ ON The central wavelength of the other laser beam is located on the absorption valley of the gas to be measured, denoted as λ OFF .

[0059] According to the above formula, the light column image corresponding to the absorption peak wavelength can be expressed as:

[0060]

[0061] The light column image corresponding to the absorption valley wavelength can be expressed as:

[0062]

[0063] Further, such as Figure 2 As shown, the inversion of the concentration profile of the gas to be measured from the distance-resolved echo data corresponding to two beams of different central wavelengths specifically includes the following steps:

[0064] Step S51: Measure a hard target object at a known distance to obtain an image of the hard target object. Based on the distance information of the hard target object from the measurement system and the pixel position information of the hard target object in the image, calibrate the relationship between the measurement system image pixels and the measurement distance.

[0065] Step S52: using the relationship between the calibrated measured distance and the image pixels, respectively calculating the distance-resolved echo data corresponding to the two beams with different central wavelengths in the measured image;

[0066] Step S53: applying a differential absorption algorithm to the two beams of distance-resolved echo data corresponding to different central wavelengths to invert and calculate the profile data of the gas to be measured.

[0067] Specifically, after the measurement system parameters are determined, there is a specific relationship between the measured distance and the image pixels. In order to determine the relationship between the measured distance and the pixels, a hard target object with a known distance can be imaged. According to the principle of geometric imaging, the position information of the fixed object in the image pixel is calculated, and the relationship between the image pixel and the measured distance is calibrated. The distance-resolved echo data corresponding to different central wavelengths can be obtained from the relationship between the calibrated light column image pixels and the measured distance and the size of the image pixel value. For example, the distance-resolved data obtained by image analysis corresponding to the absorption peak wavelength is P(r,λ ON ), the distance resolution data obtained by analyzing the image corresponding to the absorption valley wavelength is P(r,λ OFF ).

[0068] Furthermore, according to the differential absorption principle, the distance-resolved data is P(r,λ OFF ) and the distance-resolved data is P(r,λ ON ) can be used to inversely calculate the profile of the gas to be measured. The specific calculation method is as follows:

[0069]

[0070] in, Indicates the obtained gas profile data to be measured, P(r, λ ON ) represents the distance-resolved data corresponding to the absorption peak wavelength, P(r, λ OFF ) represents the distance-resolved data corresponding to the absorption valley wavelength, It represents the absorption cross section of the gas to be measured at the absorption peak wavelength. It represents the absorption cross section of the gas to be measured at the absorption valley wavelength. r Indicates distance.

[0071] As an example, the detection method of this embodiment is used to detect the atmospheric carbon dioxide profile. First, two laser beams with different central wavelengths are alternately emitted into the atmosphere. The central wavelength of one laser beam lies at a strong carbon dioxide absorption line, while the central wavelength of the other laser beam lies at a carbon dioxide absorption valley. After the laser beams interact with atmospheric components, including carbon dioxide, a receiving telescope forms an image of the resulting backscattered light beam. A spatial light modulator receives the imaged light beam image, modulates the light beam image, and converts the modulated light signal into an electrical signal. A data acquisition card synchronously acquires the electrical signal and then converts it into a digital signal. Light beam images of laser beams with different central wavelengths are restored based on the digital signal and the modulated speckle signal. Image pixels are calibrated against the detection distance to obtain a specific relationship between the image pixels and the detection distance. Distance-resolved echo data for laser beams with different central wavelengths are analyzed based on this specific relationship and the restored measured light beam images. The atmospheric carbon dioxide concentration profile is calculated based on the distance-resolved echo data for the laser beams with central wavelengths located at the carbon dioxide absorption peak and the laser beams with central wavelengths located at the carbon dioxide absorption valley, according to the differential absorption principle.

[0072] like Figure 3 As shown, in another embodiment of the present invention, an atmospheric component differential absorption laser imaging radar profile detection system is also disclosed, and the detection system includes:

[0073] A laser, used for alternately emitting two laser beams with different central wavelengths into the atmosphere to be measured;

[0074] a receiving telescope for imaging a backscattered light column after the laser beam interacts with the atmosphere;

[0075] A spatial light modulator, configured to modulate the imaged light column;

[0076] A photodetector, used to convert the modulated optical signal into an electrical signal;

[0077] A data acquisition card is used to convert the corresponding electrical signal into a digital signal;

[0078] A calculation control unit is used to calculate the light column images of lasers with different central wavelengths based on the digital signal and the modulated speckle signal, parse the distance-resolved data of the lasers with different central wavelengths based on the light column images, and invert and calculate the concentration profile of the gas to be measured based on the distance-resolved data of the lasers with different central wavelengths.

[0079] Furthermore, the detection system also includes a beam expander, which is used to expand the laser light emitted by the laser, compress the divergence angle of the emitted laser light, and increase the detection distance.

[0080] Furthermore, the detection system also includes a converging lens, which is used to converge the modulated optical signal.

[0081] Furthermore, the detection system also includes a narrowband filter, which is used to subtract stray background light from the modulated optical signal.

[0082] Furthermore, the plane where the receiving telescope is located, the plane where the spatial light modulator is located, and the optical axis of the laser beam emitted by the laser intersect, satisfying the Schaffner imaging principle.

[0083] Satisfying the Schaffner imaging principle allows the detection system to have a theoretically infinite depth of field, enabling clear images of objects within a wide range. For example, the spatial light modulator can be a digital micromirror device. When the three conditions satisfy the Schaffner imaging principle, the image of the light beam formed by the receiving telescope can be clearly presented on the image plane of the digital micromirror device.

[0084] In another embodiment of the present invention, a computer-readable storage medium is disclosed. The medium stores a computer program. When the computer program is run, the atmospheric differential absorption laser imaging radar profile detection method described in any one of the above embodiments is executed.

[0085] In another embodiment of the present invention, a computer system is disclosed, including a processor and a storage medium, wherein a computer program is stored on the storage medium. The processor reads and runs the computer program from the storage medium to execute the atmospheric component differential absorption laser imaging radar profile detection method described in any one of the above embodiments.

[0086] Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein; and these modifications or replacements 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 method for detecting atmospheric component differential absorption laser imaging radar profiles, characterized in that: The profile detection method comprises the following steps: Step S1: alternately emitting two laser beams with different central wavelengths toward the atmosphere to be measured; Step S2: receiving a light column image after the laser beam interacts with the atmosphere to be measured, preloading a modulated speckle signal on a spatial light modulator, modulating the light column image, and converting the modulated light signal into an electrical signal; Step S3: synchronously collecting the electrical signals, converting the electrical signals into digital signals, and combining the digital signals with the modulated speckle signals to restore the light column images corresponding to the two laser beams with different central wavelengths; Step S4: Calculating the distance-resolved echo data corresponding to the two laser beams with different central wavelengths based on the relationship between the restored light column image pixels and the measured distance; Step S5: inverting the concentration profile of the gas to be measured from the distance-resolved echo data corresponding to the two beams of different central wavelengths.

2. The atmospheric composition differential absorption laser imaging radar profile detection method according to claim 1, characterized in that: The two central wavelengths of the laser beam are respectively located on the absorption peak and the absorption valley of the gas to be measured.

3. The atmospheric component differential absorption laser imaging radar profile detection method according to any one of claims 1 to 2, characterized in that: The calculation method for restoring the beam images corresponding to two laser beams with different central wavelengths is as follows: ， in, Indicates the i The modulated speckle signal during the second modulation is The laser beam with the central wavelength i The digital signal corresponding to the acquisition time, L Indicates the amount of modulated speckle.

4. The atmospheric composition differential absorption laser imaging radar profile detection method according to claim 1, characterized in that: The inversion of the concentration profile of the gas to be measured from the distance-resolved echo data corresponding to two beams of different central wavelengths specifically includes the following steps: Step S51: Measure a hard target object at a known distance to obtain an image of the hard target object. Based on the distance information of the hard target object from the measurement system and the pixel position information of the hard target object in the image, calibrate the relationship between the measurement system image pixels and the measurement distance. Step S52: using the relationship between the calibrated measured distance and the image pixels, respectively calculating the distance-resolved echo data corresponding to the two beams with different central wavelengths in the measured image; Step S53: applying a differential absorption algorithm to the two beams of distance-resolved echo data corresponding to different central wavelengths to invert and calculate the profile data of the gas to be measured.

5. The atmospheric composition differential absorption laser imaging radar profile detection method according to claim 4, characterized in that: The differential absorption algorithm is used to invert and calculate the profile data of the gas to be measured. The calculation method is as follows: ， in, Indicates the obtained gas profile data to be measured, P(r, λ ON ) represents the distance-resolved data corresponding to the absorption peak wavelength, P(r, λ OFF ) represents the distance-resolved data corresponding to the absorption valley wavelength, It represents the absorption cross section of the gas to be measured at the absorption peak wavelength. It represents the absorption cross section of the gas to be measured at the absorption valley wavelength. r Indicates distance.

6. An atmospheric composition differential absorption laser imaging radar profile detection system, characterized in that: The detection system comprises: A laser, used for alternately emitting two laser beams with different central wavelengths into the atmosphere to be measured; a receiving telescope for imaging a backscattered light column after the laser beam interacts with the atmosphere; A spatial light modulator is used to preload a modulated speckle signal and modulate the light column image; A photodetector, used to convert the modulated optical signal into an electrical signal; A data acquisition card is used to convert the corresponding electrical signal into a digital signal; A calculation control unit is used to calculate the light column images of lasers with different central wavelengths based on the digital signal and the modulated speckle signal, parse the distance-resolved data of the lasers with different central wavelengths based on the light column images, and invert and calculate the concentration profile of the gas to be measured based on the distance-resolved data of the lasers with different central wavelengths.

7. The atmospheric composition differential absorption laser imaging radar profile detection system according to claim 6, characterized in that: The plane where the receiving telescope is located, the plane where the spatial light modulator is located, and the optical axis of the laser light beam emitted by the laser intersect, satisfying the Schaffner imaging principle.

8. The atmospheric composition differential absorption laser imaging radar profile detection system according to claim 6, characterized in that: The detection system further includes: A beam expander, used to expand the laser beam emitted by the laser; A converging lens, used to converge the optical signal modulated by the spatial light modulator; Narrowband filter, used to remove background stray light from the detection signal.

9. A computer-readable storage medium, characterized in that The medium stores a computer program, and after the computer program is run, the atmospheric component differential absorption laser imaging radar profile detection method according to any one of claims 1 to 5 is executed.

10. A computer system, characterized in that: The method comprises a processor and a storage medium, wherein a computer program is stored on the storage medium, and the processor reads and runs the computer program from the storage medium to execute the atmospheric component differential absorption laser imaging radar profile detection method according to any one of claims 1 to 5.

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