Lidar system to measure atmospheric carbon dioxide and methane column concentrations

Abstract

A laser radar system for measuring atmospheric carbon dioxide and methane column concentrations includes a 1572nm seed laser, a 1645nm seed laser, a 1572nm laser frequency locking module, a 1645nm laser frequency locking module, a dual-wavelength dual-pulse laser (1572 and 1645nm), an integrating sphere, a collimator, a photoelectric detection module, a data acquisition and processing module, a transmitting beam expander, a visual axis monitoring module, a relay optical module, an optical receiving telescope, a spectroscope 1, a spectroscope 2, and a spectroscope 3; the photoelectric detection module includes a spectroscope 4, a narrowband filter 1, a 1572nm detection optical unit, a 1572nm detector, a narrowband filter 2, a 1645nm detection optical unit, and a 1645nm detector. The present invention utilizes a set of lasers that simultaneously output dual-wavelength dual-pulse lasers, adopts seed injection technology and high-precision frequency stabilization technology, obtains laser pulse output with high frequency stability, and adopts a path integral differential absorption method to implement all-day high-precision detection of the main greenhouse gases in the atmosphere, carbon dioxide and methane.

Description

Technical Field

[0001] The invention belongs to laser radar, in particular to a laser radar system for measuring atmospheric carbon dioxide and methane column concentrations. Background Art

[0002] Since the Industrial Revolution, human activities have caused the concentration of greenhouse gases such as carbon dioxide and methane in the atmosphere to rise rapidly, which has had an immeasurable impact on global climate change. Therefore, high-precision monitoring of the concentrations of carbon dioxide and methane in the atmosphere is an indispensable means to study the greenhouse effect and formulate relevant measures.

[0003] At present, there are two main methods for detecting greenhouse gases: active and passive. Passive detection is mature and can invert information on multiple gases at the same time, but passive detection relies on the reflection of sunlight, cannot achieve nighttime detection and full-latitude detection, and is easily interfered by clouds and aerosols. Active lidar detection methods can make up for the shortcomings of passive methods. The path-integrated differential absorption (IPDA) method uses two laser beams with similar wavelengths to be emitted in a short period of time, thereby eliminating the influence of other factors on the path, and can achieve high-precision detection at all times of the day and at all latitudes.

[0004] In recent years, carbon dioxide differential absorption lidar technology has flourished, but it is often concentrated in ground-based detection and low-altitude detection. The main reason is that long-distance, high-precision gas detection places higher requirements on the system, such as high energy and high frequency stability of the laser emission system, and high sensitivity of the detector. Lidars that achieve long-distance detection often rely on long-term signal accumulation to improve the signal-to-noise ratio, and are not suitable for high-speed satellite platforms. Therefore, lidars that can achieve long-distance detection on airborne and satellite platforms are more expensive, but they can only measure the concentration of one gas, which greatly limits their application space. In the development of fossil fuels and other links, portable methane detection devices have been widely used, but such devices have low sensitivity and are not suitable for long-distance, large-scale detection in the atmosphere.

[0005] Path-integrated differential absorption (IPDA) technology is a key technology that is applicable to both methane and carbon dioxide. It can not only achieve high-precision detection throughout the day, but also can be applied to various ground-based, vehicle-mounted, airborne, and satellite-based platforms. However, there is currently no IPDA lidar that can detect both gases at the same time. Summary of the invention

[0006] The purpose of the present invention is to overcome the problem that the laser radar system can only measure a single gas, and to overcome the problems of small application range, short detection distance and long integration time of traditional detection equipment. A laser radar system for measuring the concentration of atmospheric carbon dioxide and methane columns is proposed. The system can be used for ground-based, vehicle-mounted, airborne and satellite-mounted platforms, and can realize the synchronous measurement of atmospheric carbon dioxide and methane concentrations in different coverage ranges, and has the ability of high-precision measurement over a large range throughout the day.

[0007] The technical solution of the present invention is as follows:

[0008] A laser radar system for measuring atmospheric carbon dioxide and methane column concentrations, characterized in that it includes: a 1572nm seed laser, a 1645nm seed laser, a 1572nm laser frequency locking module, a 1645nm laser frequency locking module, a dual-wavelength dual-pulse laser (1572 and 1645nm), an integrating sphere, a collimator, a photoelectric detection module, a data acquisition and processing module, a transmitting beam expander, a visual axis monitoring module, a relay optical module, an optical receiving telescope, a spectroscope 1, a spectroscope 2, and a spectroscope 3; the photoelectric detection module includes a spectroscope 4, a narrowband filter 1, a 1572nm detection optical unit, a 1572nm detector, a narrowband filter 2, a 1645nm detection optical unit, and a 1645nm detector. The positional relationship of the above components is as follows:

[0009] The output ports of the 1572nm seed laser, 1645nm seed laser, 1572nm laser frequency stabilization module and 1645nm laser frequency stabilization module are connected to the input port of the dual-wavelength dual-pulse laser. The 1572nm and 1645nm light beams emitted by the dual-wavelength dual-pulse laser are divided into two paths through the spectroscope one: one path enters the photoelectric detection module through the integrating sphere and the collimator, and the other path is further divided into two paths through the spectroscope two: one path enters the visual axis monitoring module, and the other path is emitted into the atmosphere through the transmitting beam expander. The light signal of this light beam after being reflected by hard targets such as the ground or clouds is divided into two paths through the spectroscope three after the echo signal of the optical receiving telescope: one path enters the visual axis monitoring module, and the other path enters the photoelectric detection module through the relay optical module. The output end of the photoelectric detection module is connected to the input end of the data acquisition and processing module.

[0010] The light beam passing through the integrating sphere and the collimating mirror enters the photoelectric detection module and is incident on the beam splitter four. The beam splitter four reflects the 1572nm light to the narrowband filter one and the 1572nm detection optical unit and is incident on the 1572nm detector. At the same time, the 1645nm light is transmitted through the beam splitter four into the narrowband filter two and the 1645nm detection optical unit and is incident on the 1645nm detector; the echo signal reflected by the hard target enters the photoelectric detection module after passing through the optical receiving telescope, the beam splitter three and the relay optical module, and is incident on the beam splitter four. The beam splitter four transmits the 1572nm light in the echo signal and enters the narrowband filter one and the 1572nm detection optical unit and is incident on the 1572nm detector. At the same time, the 1645nm light is reflected through the beam splitter four to the narrowband filter two and the 1645nm detection optical unit and is incident on the 1645nm detector.

[0011] The 1572nm laser frequency locking module and the 1645nm laser frequency locking module are both connected to the input port of the dual-wavelength dual-pulse laser to stabilize the center frequency of the two-wavelength output lasers, especially the frequency stability of the online pulses.

[0012] The relay optical module is mainly used to convert the convergent light received by the optical receiving telescope into parallel light, and filter out stray light with a pinhole aperture.

[0013] The photoelectric detection module comprises narrowband filter 1 and narrowband filter 2, which are used to filter the influence of solar background noise and stray light and improve the signal-to-noise ratio.

[0014] The visual axis monitoring module includes a spectroscopic module and a CCD, which are used to monitor the angle between the transmitting and receiving optical axes to ensure the parallelism of the transmitting and receiving optical axes.

[0015] The advantages of the present invention are:

[0016] 1. The laser radar system of the present invention adopts an active detection method. The dual-wavelength dual-pulse laser can output 1572nm and 1645nm online and offline lasers simultaneously and independently. It does not rely on the reflected light of the sun and can detect all day long. In addition, there are corresponding narrow-band filters in front of the detection modules of the two wavelengths, which can filter out the influence of solar background noise and stray light and improve the detection accuracy.

[0017] 2. The laser radar system of the present invention not only provides an effective detection method for atmospheric methane concentration with high precision and large range, but also realizes integration with the carbon dioxide detection system, which can measure the two most important greenhouse gases at the same time and better meet the monitoring needs of controlling the greenhouse effect.

[0018] 3. The laser radar system of the present invention is applicable to all ground-based, vehicle-mounted, airborne and satellite-mounted platforms. It can be used for monitoring the emissions of local carbon sources and methane sources, as well as for overall monitoring of atmospheric carbon dioxide and methane concentrations on a global scale.

[0019] 4. The laser radar system of the present invention sets a reference optical path for normalizing the energy of the emitted light beam during inversion calculation, which can reduce the requirements for laser energy stability.

[0020] 5. The laser radar system designed in the present invention can measure the column concentrations of carbon dioxide and methane simultaneously. Since there is a small amount of carbon dioxide absorption interference in the absorption spectrum of methane, the system can use the synchronously measured carbon dioxide differential absorption optical density to correct the methane differential absorption optical density. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 The figure is a block diagram of the overall structure of the laser radar system device for measuring atmospheric carbon dioxide and methane column concentrations according to the present invention.

[0022] In the figure: 1-1572nm seed laser, 2-1645nm seed laser, 3-1572nm laser frequency locking module, 4-1645nm laser frequency locking module, 5-dual-wavelength dual-pulse laser, 6-integrating sphere, 7-collimator, 8-photoelectric detection module, 9-data acquisition and processing module, 10-transmitting beam expander, 11-line of sight monitoring module, 12-relay optical module, 13-optical receiving telescope, 14-beam splitter one, 15-beam splitter two, 16-beam splitter three.

[0023] Figure 2 It is a structural block diagram of the photoelectric detection module of the present invention.

[0024] In the figure: 8-1—beam splitter four, 8-2—narrow band filter one, 8-3—1572nm detection optical unit, 8-4—1572nm detector, 8-5—narrow band filter two, 8-6—1645nm detection optical unit, 8-7—1645nm detector. DETAILED DESCRIPTION

[0025] The present invention is further described below in conjunction with examples and drawings, but the protection scope of the present invention should not be limited thereto.

[0026] See also Figure 1 , Figure 1 The overall structural block diagram of the laser radar system for measuring atmospheric carbon dioxide and methane column concentrations of the present invention is as follows: Figure 1As shown, the laser radar system device for measuring atmospheric carbon dioxide and methane column concentrations of the present invention includes a 1572nm seed laser 1, a 1645nm seed laser 2, a 1572nm laser frequency locking module 3, a 1645nm laser frequency locking module 4, a dual-wavelength dual-pulse laser (1572 and 1645nm) 5, an integrating sphere 6, a collimator 7, a photoelectric detection module 8, a data acquisition and processing module 9, a transmitting beam expander 10, a visual axis monitoring module 11, a relay optical module 12, an optical receiving telescope 13, a spectroscope 1 14, a spectroscope 2 15 and a spectroscope 3 16; Figure 2 is a structural block diagram of the photoelectric detection module 8 of the present invention, such as Figure 2 As shown, the photoelectric detection module 8 includes a spectroscope 4 8-1, a narrowband filter 1 8-2, a 1572nm detection optical unit 8-3, a 1572nm detector 8-4, a narrowband filter 2 8-5, a 1645nm detection optical unit 8-6 and a 1645nm detector 8-7. The positional relationship of the above components is as follows:

[0027] The output ports of the 1572nm seed laser 1, the 1645nm seed laser 2, the 1572nm laser frequency stabilization module 3, and the 1645nm laser frequency stabilization module 4 are connected to the input port of the dual-wavelength dual-pulse laser 5. The 1572nm and 1645nm light beams emitted by the dual-wavelength dual-pulse laser 5 are divided into two paths through the spectroscope 1 14: one path enters the photoelectric detection module 8 through the integrating sphere 6 and the collimator 7, and the other path is further divided into two paths through the spectroscope 2 15: one path enters the visual axis monitoring module 11, and the other path is emitted into the atmosphere through the transmitting beam expander 10. The echo light signal of this light beam after being reflected by hard targets such as the ground or clouds enters the laser radar system through the optical receiving telescope 13. The echo signal is divided into two paths through the spectroscope 3 16, one path enters the visual axis monitoring module 11, and the other path enters the photoelectric detection module 8 through the relay optical module 12. The output end of the photoelectric detection module 8 is connected to the input end of the data acquisition and processing module 9.

[0028] In the photoelectric detection module 8, the light beam passes through the integrating sphere 6 and the collimating mirror 7 and enters the photoelectric detection module 8, and is incident on the spectroscope 4 8-1. The spectroscope 4 8-1 reflects the 1572nm light to the narrowband filter 1 8-2 and the 1572nm detection optical unit 8-3 and is incident on the 1572nm detector 8-4. At the same time, the 1645nm light is transmitted through the spectroscope 4 8-1 into the narrowband filter 2 8-5 and the 1645nm detection optical unit 8-6 and is incident on the 1645nm detector 8-7. The echo signal reflected by the hard target The light of 1645nm passes through the optical receiving telescope 13, the spectroscope three 16 and the relay optical module 12, and then enters the photoelectric detection module 8, and is incident on the spectroscope four 8-1. The spectroscope four 8-1 transmits the 1572nm light in the echo signal and then enters the narrowband filter one 8-2 and the 1572nm detection optical unit 8-3, and is incident on the 1572nm detector 8-4. At the same time, the light of 1645nm is reflected by the spectroscope four 8-1 to the narrowband filter two 8-5 and the 1645nm detection optical unit 8-6, and is incident on the 1645nm detector 8-7.

[0029] The following is a specific device used in an example:

[0030] The optical receiving telescope 13 is a telescope system with the receiving and optical axes parallel; the visual axis monitoring module 11 is composed of a spectroscopic module and a CCD; the data acquisition and processing module 9 includes an acquisition card and a data preprocessing module; the 1572nm detector 8-4 and the 1645nm detector 8-7 are APD detectors.

[0031] The specific process of the laser radar system for measuring atmospheric carbon dioxide and methane column concentrations implemented by the present invention is:

[0032] The online and offline lasers of 1572nm and 1645nm output by the dual-wavelength dual-pulse laser 5 pass through the integrating sphere 6 and the collimating mirror 7 and enter the photoelectric detection module 8, wherein the laser of 1572nm band passes through the beam splitter 4 8-1, the narrowband filter 1 8-2, and the 1572nm detection optical unit 8-3 and enters the 1572nm detector 8-4 as the energy monitoring signal to obtain the energy E1. on0 and E1 off0 The 1645nm laser passes through the spectroscope 8-1, narrowband filter 8-5, 1645nm detection optical unit 8-6, and then enters the 1645nm detector 8-7 as an energy detection signal to obtain energy E2. on0 and E2 off0Another route of the hard target reflected echo signal is received by the optical receiving telescope 13 and enters the photoelectric detection module 8. After passing through the spectroscope 8-1, it enters the 1572nm and 1645nm two-way detection modules respectively, and obtains the 1572nm line and offline echo signal energy E1 carrying atmospheric information. on and E1 off And 1645nm online and offline echo signal energy E2 on and E2 off , from which the differential optical depth of carbon dioxide can be obtained Differential Optical Depth of Methane The differential optical thickness is accumulated and averaged in multiple groups according to the signal-to-noise ratio requirements. The number of accumulated averages is determined by the horizontal resolution and the pulse repetition frequency. According to the IPDA method, the concentration of the carbon dioxide column on the laser path is expressed as The methane column concentration is expressed as Where IWF1 is the integral of the weight function of carbon dioxide along the path, and IWF2 is the integral of the weight function of methane along the path. IWF1 and IWF2 can be calculated based on wavelength, atmospheric auxiliary parameters and measurement path.

[0033] Experiments show that the present invention has the following advantages:

[0034] 1. The laser radar system of the present invention adopts an active detection method. The dual-wavelength dual-pulse laser can output 1572nm and 1645nm online and offline lasers simultaneously and independently. It does not rely on the reflected light of the sun and can detect all day long. In addition, there are corresponding narrow-band filters in front of the detection modules of the two wavelengths, which can filter out the influence of solar background noise and stray light and improve the detection accuracy.

[0035] 2. The laser radar system of the present invention not only provides an effective detection method for atmospheric methane concentration with high precision and large range, but also realizes integration with the carbon dioxide detection system, which can measure the two most important greenhouse gases at the same time and better meet the monitoring needs of controlling the greenhouse effect.

[0036] 3. The laser radar system of the present invention is applicable to all ground-based, vehicle-mounted, airborne and satellite-mounted platforms. It can be used for monitoring the emissions of local carbon sources and methane sources, as well as for overall monitoring of atmospheric carbon dioxide and methane concentrations on a global scale.

[0037] 4. The laser radar system of the present invention sets a reference optical path for normalizing the energy of the emitted light beam during inversion calculation, which can reduce the requirements for laser energy stability.

[0038] 5. The laser radar system designed in the present invention can measure the column concentrations of carbon dioxide and methane simultaneously. Since there is a small amount of carbon dioxide absorption interference in the absorption spectrum of methane, the system can use the synchronously measured carbon dioxide differential absorption optical density to correct the methane differential absorption optical density.

Claims

1. A laser radar system for measuring atmospheric carbon dioxide and methane column concentrations, characterized in that: The system comprises a 1572nm seed laser (1), a 1645nm seed laser (2), a 1572nm laser frequency locking module (3), a 1645nm laser frequency locking module (4), a dual-wavelength dual-pulse laser (5), an integrating sphere (6), a collimator (7), a photoelectric detection module (8), a data acquisition and processing module (9), a transmitting beam expander (10), a visual axis monitoring module (11), a relay optical module (12), an optical receiving telescope (13), a spectroscope 1 (14), a spectroscope 2 (15) and a spectroscope 3 (16); the photoelectric detection module (8) comprises a spectroscope 4 (8-1), a narrowband filter 1 (8-2), a 1572nm detection optical unit (8-3), a 1572nm detector (8-4), a narrowband filter 2 (8-5), a 1645nm detection optical unit (8-6) and a 1645nm detector (8-7); the positional relationship of the above components is as follows: The output ports of the 1572nm seed laser (1), the 1645nm seed laser (2), the 1572nm laser frequency locking module (3), and the 1645nm laser frequency locking module (4) are connected to the input port of the dual-wavelength dual-pulse laser (5). The 1572nm and 1645nm light beams emitted by the dual-wavelength dual-pulse laser (5) are divided into two paths through the first beam splitter (14); one path enters the photoelectric detection module (8) through the integrating sphere (6) and the collimating mirror (7), and the other path is further divided into two paths through the second beam splitter (15). Path: one path enters the visual axis monitoring module (11), and the other path is emitted into the atmosphere through the transmitting beam expander (10). The optical signal of this light beam after being reflected by hard targets such as the ground or clouds enters the laser radar receiving system through the optical receiving telescope (13). The echo signal is divided into two paths through the spectroscope three (16): one path enters the visual axis monitoring module (11), and the other path enters the photoelectric detection module (8) through the relay optical module (12). The output end of the photoelectric detection module (8) is connected to the input end of the data acquisition and processing module (9); The light beam passing through the integrating sphere (6) and the collimating mirror (7) enters the photoelectric detection module (8) and is incident on the beam splitter 4 (8-1). The beam splitter 4 (8-1) reflects the 1572nm light to the narrowband filter 1 (8-2) and the 1572nm detection optical unit (8-3) and is incident on the 1572nm detector (8-4). At the same time, the beam splitter 4 (8-1) transmits the 1645nm light into the narrowband filter 2 (8-5) and the 1645nm detection optical unit (8-6) and is incident on the 1645nm detector (8-7). At the same time, the echo signal reflected by the hard target is transmitted through the optical The light passes through the receiving telescope (13), the spectroscope three (16) and the relay optical module (12) and then enters the photoelectric detection module (8) and is incident on the spectroscope four (8-1). The spectroscope four (8-1) transmits the 1572nm light in the echo signal and then enters the narrowband filter one (8-2) and the 1572nm detection optical unit (8-3) and is incident on the 1572nm detector (8-4). Meanwhile, the 1645nm light is reflected by the spectroscope four (8-1) to the narrowband filter two (8-5) and the 1645nm detection optical unit (8-6) and is incident on the 1645nm detector (8-7).

2. The laser radar system for measuring atmospheric carbon dioxide and methane column concentration according to claim 1, characterized in that: The dual-wavelength dual-pulse laser (5) can simultaneously output lasers of two wavelengths, 1572nm and 1645nm, and the 1572nm seed laser (1) and the 1645nm seed laser (2) can achieve online and offline fast switching. The seed injection technology ensures that the laser can achieve high-energy and narrow pulse width output in both bands. The dual pulses output in the 1572nm and 1645nm bands correspond to the online and offline wavelengths of carbon dioxide and methane detection respectively.

3. The laser radar system for measuring atmospheric carbon dioxide and methane column concentration according to claim 1, characterized in that: The dual-wavelength dual-pulse laser (5) is controlled by a 1572nm laser frequency locking module (3) and a 1645nm laser frequency locking module (4), ensuring that the 1572nm and 1645nm output pulse lights both maintain stable frequencies and are locked in the online and offline bands, respectively.

4. The laser radar system for measuring atmospheric carbon dioxide and methane column concentration according to claim 1, characterized in that: The photoelectric detection module (8) comprises a narrowband filter 1 (8-2) and a narrowband filter 2 (8-5), which are used to filter the influence of solar background noise and stray light and improve the signal-to-noise ratio.

5. The laser radar system for measuring atmospheric carbon dioxide and methane column concentrations according to claim 1, characterized in that: In the 1645nm band of methane detection, the online laser is located in the absorption slot produced by the two absorption lines, which greatly reduces the requirements for the stability of the emitted laser frequency.

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