CN118377030A - Gas detection method for laser radar and laser radar - Google Patents
Gas detection method for laser radar and laser radar Download PDFInfo
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
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Abstract
The invention discloses a gas detection method for a laser radar and the laser radar, relates to the field of the laser radar, and is used for solving the problem of interference caused by the influence of echo intensities caused by different wavelengths in the conventional method. The method comprises the following steps: emitting a first light beam with a first wavelength at the center, a second light beam with a second wavelength at the center and a third light beam with a third wavelength at the center to the atmosphere, wherein the first wavelength corresponds to the peak of an absorption spectrum of the gas to be detected, the second wavelength and the third wavelength are positioned at two sides of the peak of the absorption spectrum, echoes of the light beams are obtained, first narrow-band light with the first wavelength at the center, second narrow-band light with the second wavelength at the center and third narrow-band light with the third wavelength at the center are separated from the echoes, the intensity of the second narrow-band light and the intensity of the third narrow-band light are subjected to preset statistics to obtain statistical intensity, and the content of the gas to be detected is obtained by combining the intensity of the first narrow-band light. The invention can improve the accuracy of detecting the gas to be detected in the atmosphere.
Description
Technical Field
The invention relates to the field of laser radars, in particular to a gas detection method for a laser radar and the laser radar.
Background
In the detection of the atmospheric components, the principle of differential absorption is used for detection, namely, two laser pulses with similar wavelengths and great difference in the absorption rate of the gas to be detected are emitted to the atmosphere, the light wave attenuation caused by common aerosol and other components with similar wavelengths is basically the same, and the difference in the echo is caused by the absorption characteristics of the gas to be detected, so that the content of the gas to be detected is detected based on the detection.
The atmospheric component measurement is performed by using two lasers with similar wavelengths, and although the difference of the wavelengths is small, even though the absorption difference of the gas to be measured is not considered, the echo intensity difference is still caused by the difference of the wavelengths. In addition, because the content of the gas to be detected is generally low, the difference of echo intensities caused by absorption characteristics is small, and even if the difference of echo intensities caused by different wavelengths is small, obvious interference can be introduced.
Disclosure of Invention
The invention aims to provide a gas detection method for a laser radar and the laser radar, which can improve the accuracy of detecting gas to be detected in the atmosphere.
In order to achieve the above purpose, the present invention provides the following technical solutions:
a gas detection method for a lidar, comprising:
Emitting a first light beam with a first wavelength at the center, a second light beam with a second wavelength at the center and a third light beam with a third wavelength at the center to the atmosphere, wherein the first wavelength corresponds to the absorption line peak of the gas to be detected, and the second wavelength and the third wavelength are respectively positioned at two sides of the absorption line peak of the gas to be detected;
Acquiring echoes generated after the first light beam, the second light beam and the third light beam are transmitted to the atmosphere, separating first narrow-band light with a center wavelength of the first wavelength, second narrow-band light with a center wavelength of the second wavelength and third narrow-band light with a center wavelength of the third wavelength from the echoes, and detecting the intensity of the first narrow-band light, the intensity of the second narrow-band light and the intensity of the third narrow-band light respectively;
and carrying out preset statistics on the intensity of the second narrow-band light and the intensity of the third narrow-band light to obtain statistical intensity, and obtaining the content of the gas to be detected by combining the intensity of the first narrow-band light.
In some embodiments, the second wavelength is the same as the first wavelength.
In some embodiments, the intensity of the second light beam is the same as the intensity of the third light beam.
In some embodiments, the first wavelength is λ 0, the second wavelength is λ 0 -mΔλ, and the third wavelength is λ 0 +nΔλ;
Carrying out preset statistics on the intensity of the second narrow-band light and the intensity of the third narrow-band light to obtain statistical intensity, and combining the intensity of the first narrow-band light to obtain the content of the gas to be detected comprises the following steps:
The intensities of the first narrowband light, the second narrowband light and the third narrowband light are P a1、Pa2 and P a3 in sequence, and the intensities of the first narrowband light, the second narrowband light and the third narrowband light are P b1、Pb2 and P b3 in sequence, corresponding to the distance L a, corresponding to the distance L b;
The following relationship exists:
；
；
Wherein, Gamma <1, alpha represents the concentration of the gas to be measured on the path from the distance L a to the distance L b, epsilon represents the absorption characteristic parameter of the gas to be measured on the light with the first wavelength, and A is a constant;
the method is obtained according to the following relation: 。
A lidar for gas detection, comprising:
The first light source is used for emitting a first light beam with a first wavelength at the center to the atmosphere, wherein the first wavelength corresponds to the peak of an absorption spectrum line of the gas to be detected;
A second light source for emitting a second light beam having a second wavelength at a center wavelength toward the atmosphere;
the third light source is used for emitting a third light beam with a third wavelength at the center wavelength to the atmosphere, and the second wavelength and the third wavelength are respectively positioned at two sides of an absorption spectrum crest of the gas to be detected;
a telescopic optical system for acquiring echoes generated after the first light beam, the second light beam and the third light beam are transmitted to the atmosphere;
The light receiving and detecting assembly is used for separating first narrow-band light with the center wavelength of the first wavelength, second narrow-band light with the center wavelength of the second wavelength and third narrow-band light with the center wavelength of the third wavelength from the echo, and detecting the intensity of the first narrow-band light, the intensity of the second narrow-band light and the intensity of the third narrow-band light respectively;
and the control component is used for carrying out preset statistics on the intensity of the second narrow-band light and the intensity of the third narrow-band light to obtain statistical intensity, and combining the intensity of the first narrow-band light to obtain the content of the gas to be detected.
In some embodiments, the distance between the optical axis of the first light source and the optical axis of the telescopic optical system, the distance between the optical axis of the second light source and the optical axis of the telescopic optical system, and the distance between the optical axis of the third light source and the optical axis of the telescopic optical system are all identical.
In some embodiments, the second wavelength is less than the first wavelength, the third wavelength is greater than the first wavelength, the light receiving and detecting assembly comprises:
The first light-splitting element is used for reflecting light with a first boundary wavelength or less and transmitting light with a wavelength greater than the first boundary wavelength, the first boundary wavelength is between the second wavelength and the first wavelength, and an echo acquired by the telescopic optical system is incident to the first light-splitting element;
The second light splitting element is arranged on a transmission light path of the first light splitting element and is used for reflecting light with a second boundary wavelength or less and transmitting light with a wavelength larger than the second boundary wavelength, and the second boundary wavelength is between the first wavelength and the third wavelength;
The second narrow-band filter element is arranged on the reflection light path of the first light-splitting element and is used for enabling the reflection light of the first light-splitting element to penetrate through the second narrow-band filter element and then enter the second photoelectric detector, and the center wavelength of the second narrow-band filter element is the second wavelength;
The first narrow-band filter element is arranged on a reflection light path of the second light-splitting element and is used for enabling the reflection light of the second light-splitting element to penetrate through the first narrow-band filter element and then enter the first photoelectric detector, and the center wavelength of the first narrow-band filter element is the first wavelength;
The third narrow-band filter element is arranged on the transmission light path of the second light-splitting element and is used for enabling the transmission light of the second light-splitting element to penetrate through the third narrow-band filter element and then enter the third photoelectric detector, and the center wavelength of the third narrow-band filter element is the third wavelength.
In some embodiments, a first focusing element is disposed between the first narrowband filter element and the first photodetector, the first focusing element configured to focus outgoing light from the first narrowband filter element to the first photodetector;
a second converging element is arranged between the second narrow-band filter element and the second photoelectric detector, and the second converging element is used for converging the emergent light of the second narrow-band filter element to the second photoelectric detector;
A third converging element is arranged between the third narrow-band filter element and the third photodetector, and the third converging element is used for converging the emergent light of the third narrow-band filter element to the third photodetector.
In some embodiments, an aperture stop is disposed between the telescopic optical system and the light receiving and detecting assembly.
In some embodiments, a collimation assembly is disposed between the telescopic optical system and the light receiving and detecting assembly, and the collimation assembly is used for collimating the echo light beam from the telescopic optical system, so that the collimated echo light beam is incident to the light receiving and detecting assembly.
According to the technical scheme, the gas detection method for the laser radar and the laser radar provided by the invention emit the first light beam with the first wavelength, the second light beam with the second wavelength and the third light beam with the third wavelength to the atmosphere, wherein the first wavelength corresponds to the absorption line peak of the gas to be detected, and the second wavelength and the third wavelength are respectively positioned at two sides of the absorption line peak of the gas to be detected; and acquiring echoes generated after the first light beam, the second light beam and the third light beam are transmitted to the atmosphere, separating first narrow-band light with a first wavelength, second narrow-band light with a second wavelength and third narrow-band light with a third wavelength from the echoes, respectively detecting the intensity of the first narrow-band light, the intensity of the second narrow-band light and the intensity of the third narrow-band light, carrying out preset statistics on the intensity of the second narrow-band light and the intensity of the third narrow-band light to obtain statistical intensity, and combining the intensity of the first narrow-band light to obtain the content of the gas to be detected. The invention has the advantages that the statistical intensity is obtained by carrying out preset statistics on the intensity of the second narrow-band light and the intensity of the third narrow-band light, the influence of the echo intensity introduced by different wavelengths can be weakened, the interference on the echo intensity difference generated by the absorption characteristic of the gas to be detected is reduced, and the accuracy of detecting the gas to be detected in the atmosphere is improved.
Drawings
In order to more clearly illustrate the embodiments of the invention or the technical solutions in the prior art, the drawings that are required in the embodiments or the description of the prior art will be briefly described, it being obvious that the drawings in the following description are only some embodiments of the invention, and that other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
FIG. 1 is a flow chart of a gas detection method for a lidar according to an embodiment of the present invention;
FIG. 2 is a schematic diagram showing an absorption spectrum of a gas to be measured in a gas detection method for a laser radar according to an embodiment of the present invention;
fig. 3 is a schematic diagram of a lidar for gas detection according to an embodiment of the present invention.
Reference numerals in the drawings of the specification include:
101-first light source, 102-second light source, 103-third light source, 104-telescopic optical system, 105-aperture stop, 106-collimation component, 107-first light-splitting element, 108-second light-splitting element, 109-second narrow-band filter element, 110-second convergence element, 111-second photodetector, 112-first narrow-band filter element, 113-first convergence element, 114-first photodetector, 115-third narrow-band filter element, 116-third convergence element, 117-third photodetector, 118-data acquisition board, 119-industrial personal computer.
Detailed Description
In order to make the technical solution of the present invention better understood by those skilled in the art, the technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention, and it is apparent that the described embodiments are only some embodiments of the present invention, not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the present invention without making any inventive effort, shall fall within the scope of the present invention.
Referring to fig. 1, fig. 1 is a flowchart of a gas detection method for a laser radar according to an embodiment, and as shown in the drawing, the gas detection method for a laser radar includes the following steps:
S11: emitting a first light beam with a first wavelength at the center, a second light beam with a second wavelength at the center and a third light beam with a third wavelength at the center to the atmosphere, wherein the first wavelength corresponds to the absorption line peak of the gas to be detected, and the second wavelength and the third wavelength are respectively positioned at two sides of the absorption line peak of the gas to be detected;
S12: acquiring echoes generated after the first light beam, the second light beam and the third light beam are transmitted to the atmosphere, separating first narrow-band light with a center wavelength of the first wavelength, second narrow-band light with a center wavelength of the second wavelength and third narrow-band light with a center wavelength of the third wavelength from the echoes, and detecting the intensity of the first narrow-band light, the intensity of the second narrow-band light and the intensity of the third narrow-band light respectively;
S13: and carrying out preset statistics on the intensity of the second narrow-band light and the intensity of the third narrow-band light to obtain statistical intensity, and obtaining the content of the gas to be detected by combining the intensity of the first narrow-band light.
The first wavelength corresponds to the absorption line wave crest of the gas to be detected, the second wavelength and the third wavelength are respectively positioned at two sides of the absorption line wave crest of the gas to be detected, the second wavelength is smaller than/larger than the first wavelength, and the third wavelength is larger than/smaller than the first wavelength.
And each light beam is transmitted to the atmosphere to generate back scattered light, and the back scattered light generated after each light beam is transmitted to the atmosphere is acquired, namely the echo is acquired. The first narrowband light may be considered to be an echo after the first light beam is transmitted to the atmosphere, the second narrowband light may be an echo after the second light beam is transmitted to the atmosphere, and the third narrowband light may be an echo after the third light beam is transmitted to the atmosphere. Further, the content of the gas to be measured is obtained by combining the intensity of the first narrow-band light, the intensity of the second narrow-band light, and the intensity of the third narrow-band light.
According to the gas detection method for the laser radar, the statistical intensity is obtained by carrying out preset statistics on the intensity of the second narrow-band light and the intensity of the third narrow-band light, so that the influence of echo intensity caused by different wavelengths can be weakened, the interference on the echo intensity difference generated by the absorption characteristic of the gas to be detected is reduced, and the accuracy of detecting the gas to be detected in the atmosphere is improved.
The atmosphere contains an aerosol and a gas, and light emitted to the atmosphere is scattered and absorbed, and back-scattering means scattering in a direction opposite to the emission direction of the light. The backscattering cross section refers to the ratio of the backscattering wave power to the incident wave power density.
The backscattering cross section of an atmospheric aerosol can be expressed as:
。
for atmospheric aerosols, the following relationship holds: 。
Where β A denotes the backscattering coefficient of the aerosol, α A denotes the extinction coefficient of the aerosol, k denotes the extinction backscattering ratio (also called lidar ratio), and the magnitude of k varies over a large range depending on the type and concentration of the aerosol. Beta 0 (z) represents the backscattering coefficient of the aerosol for wavelength lambda 0.
The backscattering cross section of atmospheric gas can be expressed as:
。
The following relationship holds for atmospheric gases: 。
According to the above formula, the backscattering cross section of the aerosol and the atmospheric gas shows a uniform change rule along with the change of wavelength, and the extinction coefficient of the aerosol and the atmospheric gas also shows a uniform change rule along with the change of wavelength, and the backscattering cross section and the extinction coefficient become smaller along with the increase of wavelength. Considering that the difference of the working wavelengths is small under the condition of differential absorption, that is, the wavelength difference of the first wavelength, the second wavelength and the third wavelength is small, the corresponding backscattering section change can be regarded as a relatively linear change rule, and the corresponding extinction coefficient change can be regarded as a relatively linear change rule.
Therefore, the absorption rate detection at the peak of the absorption spectrum of the gas to be detected is performed by using the first wavelength, the non-absorption detection of the gas to be detected is performed by using the second wavelength and the third wavelength, namely, the detection of the atmospheric back scattering and the non-absorption spectrum of the gas to be detected is performed by using the second wavelength and the third wavelength, the echo intensity difference introduced by the wavelength difference can be neutralized by the echo intensity statistical processing of the echo intensity of the second wavelength and the echo intensity of the third wavelength, and the difference of the atmospheric echo intensity with the first wavelength can be considered to be caused only by the absorption of the gas to be detected, and the change of the atmospheric extinction and the back scattering introduced by the wavelength difference is completely removed, so that the accurate concentration of the gas to be detected is obtained.
The wavelength difference of the second wavelength and the first wavelength may be different from or the same as the wavelength difference of the third wavelength and the first wavelength. In order to improve measurement accuracy, the wavelength difference between the second wavelength and the first wavelength and the wavelength difference between the third wavelength and the first wavelength are 20 nm or less, typically about ten or more nm. In some embodiments, the first wavelength is λ 0, the second wavelength is λ 0 -mΔλ, the third wavelength is λ 0 +nΔλ, and may be m=n, such as m=n=1, i.e., the second wavelength is λ 0 - Δλ, and the third wavelength is λ 0 +Δλ. Referring to fig. 2, fig. 2 is a schematic diagram of an absorption line of a gas to be measured in a gas detection method for a laser radar according to an embodiment, where a first wavelength λ 0 corresponds to a peak of the absorption line of the gas to be measured, a second wavelength λ 0 - Δλ and a third wavelength λ 0 +Δλ are located on two sides of the peak of the absorption line respectively.
The intensity of the second light beam is the same or substantially the same as the intensity of the third light beam. In some embodiments, the intensity of the second beam is the same as the intensity of the third beam, and if the difference in the intensities of the two beams is large, the correction effect of the subsequent echo addition may not match well. For example, the combined measurement of two echoes makes an average correction for the intensity introduced by the wavelength difference. If there is a significant difference in the two beam intensities, the corrective effect of the subsequent echo addition may not match well. Meanwhile, the difference coefficients m and n of the above wavelengths cannot be too large.
In some embodiments, the first wavelength is λ 0, the second wavelength is λ 0 -mΔλ, and the third wavelength is λ 0 +nΔλ; carrying out preset statistics on the intensity of the second narrow-band light and the intensity of the third narrow-band light to obtain statistical intensity, and combining the intensity of the first narrow-band light to obtain the content of the gas to be detected comprises the following steps:
The intensities of the first narrowband light, the second narrowband light and the third narrowband light are P a1、Pa2 and P a3 in sequence, and the intensities of the first narrowband light, the second narrowband light and the third narrowband light are P b1、Pb2 and P b3 in sequence, corresponding to the distance L a, corresponding to the distance L b;
The following relationship exists:
；
；
Wherein, Gamma <1, alpha represents the concentration of the gas to be measured on the path from the distance L a to the distance L b, epsilon represents the absorption characteristic parameter of the gas to be measured on the light with the first wavelength, and A is a constant;
the method is obtained according to the following relation: 。
The intensities of the first, second, and third narrowband lights are P a1、Pa2 and P a3, respectively, in order, corresponding to the distance L a, and the distance is increased to L b, and the intensities of the first, second, and third narrowband lights are P b1、Pb2 and P b3, respectively. If the content of the differential absorption characteristic gas, i.e. the gas to be measured, in the whole path from the distance L a to the distance L b is zero, the echoes of different wavelengths in the path from the distance L a to the distance L b are not affected by absorption and only show consistent atmospheric ordinary attenuation characteristics, then:
。
In order to improve the measurement accuracy as much as possible, under the condition that the energy of the emitted pulse of each light beam and the efficiency of each subsequent channel are basically consistent, A is basically 1, the transmission is expressed as the transmission through the paths from L a to L b, the energy attenuation of the two non-absorption wavelength echo waves is consistent with the energy attenuation of the absorption wavelength, only the difference of the system constant A exists, and A is basically 1.
If there is a gas to be measured in the path from the distance L a to the distance L b, and the absorption characteristic gas with the concentration α is uniformly distributed on the path from the distance L a to the distance L b, then:
；
。
If m=n=1, then there are:
，，。
the present embodiment also provides a lidar for gas detection, including:
The first light source is used for emitting a first light beam with a first wavelength at the center to the atmosphere, wherein the first wavelength corresponds to the peak of an absorption spectrum line of the gas to be detected;
A second light source for emitting a second light beam having a second wavelength at a center wavelength toward the atmosphere;
the third light source is used for emitting a third light beam with a third wavelength at the center wavelength to the atmosphere, and the second wavelength and the third wavelength are respectively positioned at two sides of an absorption spectrum crest of the gas to be detected;
a telescopic optical system for acquiring echoes generated after the first light beam, the second light beam and the third light beam are transmitted to the atmosphere;
The light receiving and detecting assembly is used for separating first narrow-band light with the center wavelength of the first wavelength, second narrow-band light with the center wavelength of the second wavelength and third narrow-band light with the center wavelength of the third wavelength from the echo, and detecting the intensity of the first narrow-band light, the intensity of the second narrow-band light and the intensity of the third narrow-band light respectively;
and the control component is used for carrying out preset statistics on the intensity of the second narrow-band light and the intensity of the third narrow-band light to obtain statistical intensity, and combining the intensity of the first narrow-band light to obtain the content of the gas to be detected.
The laser radar of the embodiment obtains the statistical intensity by carrying out preset statistics on the intensity of the second narrow-band light and the intensity of the third narrow-band light, can weaken the influence of echo intensity caused by different wavelengths, and reduces the interference on the difference of echo intensities generated by the absorption characteristics of the gas to be detected, thereby improving the accuracy of detecting the gas to be detected in the atmosphere.
The distance between the optical axis of the first light source and the optical axis of the telescopic optical system, the distance between the optical axis of the second light source and the optical axis of the telescopic optical system and the distance between the optical axis of the third light source and the optical axis of the telescopic optical system are all consistent, so that the distances between the emergent beam center of the first light source and the optical axis of the telescopic optical system, the distances between the emergent beam center of the second light source and the optical axis of the telescopic optical system and the distances between the emergent beam center of the third light source and the optical axis of the telescopic optical system are kept consistent, and the receiving efficiency space correction coefficients of different wavelengths can be ensured to be consistent. The first light source, the second light source and the third light source can respectively adopt lasers, and the first light source, the second light source and the third light source can be controlled to emit laser pulses simultaneously in actual detection.
In the present embodiment, the structure of the telescopic optical system is not limited, and includes, but is not limited to, a convex mirror, a concave mirror, or a lens. The telescopic optical system may also be referred to as a telescope.
In some embodiments, the second wavelength is less than the first wavelength, the third wavelength is greater than the first wavelength, and the light receiving and detecting assembly may include:
The first light-splitting element is used for reflecting light with a first boundary wavelength or less and transmitting light with a wavelength greater than the first boundary wavelength, the first boundary wavelength is between the second wavelength and the first wavelength, and an echo acquired by the telescopic optical system is incident to the first light-splitting element;
The second light splitting element is arranged on a transmission light path of the first light splitting element and is used for reflecting light with a second boundary wavelength or less and transmitting light with a wavelength larger than the second boundary wavelength, and the second boundary wavelength is between the first wavelength and the third wavelength;
The second narrow-band filter element is arranged on the reflection light path of the first light-splitting element and is used for enabling the reflection light of the first light-splitting element to penetrate through the second narrow-band filter element and then enter the second photoelectric detector, and the center wavelength of the second narrow-band filter element is the second wavelength;
The first narrow-band filter element is arranged on a reflection light path of the second light-splitting element and is used for enabling the reflection light of the second light-splitting element to penetrate through the first narrow-band filter element and then enter the first photoelectric detector, and the center wavelength of the first narrow-band filter element is the first wavelength;
The third narrow-band filter element is arranged on the transmission light path of the second light-splitting element and is used for enabling the transmission light of the second light-splitting element to penetrate through the third narrow-band filter element and then enter the third photoelectric detector, and the center wavelength of the third narrow-band filter element is the third wavelength.
Referring to fig. 3 for an exemplary embodiment, fig. 3 is a schematic diagram of a lidar for gas detection, where the lidar includes a first light source 101, a second light source 102, a third light source 103, and a telescopic optical system 104, where the first light source 101, the second light source 102, and the third light source 103 emit light beams to the atmosphere, and the telescopic optical system 104 acquires echoes generated after the first light beam, the second light beam, and the third light beam are transmitted to the atmosphere.
The first wavelength is lambda 0, the second wavelength is lambda 0 -mDeltalambda, and the third wavelength is lambda 0 +nDeltalambda. The echo beam obtained by the telescopic optical system 104 is incident on the first spectroscopic element 107, and the first spectroscopic element 107 reflects light of a first boundary wavelength or less, so that light of a first boundary wavelength or more is transmitted, and the first boundary wavelength is between λ 0 -mΔλ and λ 0. The reflected light from the first spectroscopic element 107 is transmitted through the second narrowband filter element 109 and then enters the second photodetector 111, and the second narrowband filter element 109 has a passband with a center wavelength of the second wavelength, that is, the second narrowband light having the center wavelength of the second wavelength is separated by the first spectroscopic element 107 and the second narrowband filter element 109.
The transmitted light of the first spectroscopic element 107 is incident on the second spectroscopic element 108, and the second spectroscopic element 108 reflects light of the second boundary wavelength or less, so that light of the second boundary wavelength or more is transmitted, and the second boundary wavelength is between λ 0 and λ 0 +nΔλ. The reflected light from the second light splitting element 108 is transmitted through the first narrowband filter element 112 and then enters the first photodetector 114, and the passband center wavelength of the first narrowband filter element 112 is the first wavelength, that is, the first narrowband light having the center wavelength of the first wavelength is separated by the first light splitting element 107, the second light splitting element 108 and the first narrowband filter element 112.
The transmitted light of the second spectroscopic element 108 is transmitted through the third narrowband filter element 115 and then enters the third photodetector 117, and the center wavelength of the passband of the third narrowband filter element 115 is the third wavelength, that is, the third narrowband light whose center wavelength is the third wavelength is separated by the first spectroscopic element 107, the second spectroscopic element 108, and the third narrowband filter element 115.
The first spectroscopic element 107 and the second spectroscopic element 108 have long-wavelength characteristics, and the first spectroscopic element 107 may be a spectroscopic sheet, and the second spectroscopic element 108 may be a spectroscopic sheet. The first narrowband filter element 112 may be a filter, the second narrowband filter element 109 may be a filter, and the third narrowband filter element 115 may be a filter.
In some embodiments, a first focusing element 113 is disposed between the first narrowband filter element 112 and the first photodetector 114, where the first focusing element 113 is configured to focus the outgoing light of the first narrowband filter element 112 to the first photodetector 114; a second converging element 110 is arranged between the second narrow band filter element 109 and the second photodetector 111, the second converging element 110 being configured to converge the outgoing light of the second narrow band filter element 109 to the second photodetector 111; a third converging element 116 is arranged between the third narrowband filter element 115 and the third photodetector 117, the third converging element 116 being configured to converge the outgoing light of the third narrowband filter element 115 to the third photodetector 117. The first converging element 113 may employ, but is not limited to, a focusing lens, the second converging element 110 may employ, but is not limited to, a focusing lens, and the third converging element 116 may employ, but is not limited to, a focusing lens.
In some embodiments, an aperture stop 105 is disposed between the telescopic optical system 104 and the light receiving and detecting assembly, and the aperture stop 105 can limit the background light intensity in the acquired echo beam. The telescopic optical system 104 is used to acquire an echo and focus the echo beam, and an aperture stop 105 may be provided at the focal point of the telescopic optical system 104.
In some embodiments, a collimation assembly 106 is disposed between the telescopic optical system 104 and the light receiving and detecting assembly, and the collimation assembly 106 is configured to collimate the echo beam from the telescopic optical system 104, so that the collimated echo beam is incident on the light receiving and detecting assembly. The collimation assembly 106 may include, but is not limited to, a collimation lens.
In some embodiments, the light receiving and detecting assembly may further include a data collecting board 118, where the data collecting board 118 is connected to the first photodetector 114, the second photodetector 111 and the third photodetector 117, and the electrical signals converted by the photodetectors are transmitted to the data collecting board 118, converted into three digital signals, and further transmitted to the industrial personal computer 119 for measuring the corresponding gas content. The control components may include, but are not limited to, an industrial personal computer 119.
The industrial personal computer 119 sends working instructions to each light source, and the data acquisition board 118 transmits three synchronous trigger signals to the three light sources, controls the three light sources to synchronously emit pulse lasers and synchronously acquires echo signals. The intensities of lambda 0 -delta lambda wavelength and lambda 0 +delta lambda wavelength are the same, the two beams of echo signals are averaged to be used as non-absorption light, and the non-absorption light is calculated with lambda 0 wavelength echo at the peak value of the absorption line of the component of the gas to be detected, so that the inversion of the atmospheric content of the corresponding gas to be detected is completed.
The gas detection method for the laser radar and the laser radar provided by the invention are described in detail. The principles and embodiments of the present invention have been described herein with reference to specific examples, the description of which is intended only to facilitate an understanding of the method of the present invention and its core ideas. It should be noted that it will be apparent to those skilled in the art that various modifications and adaptations of the invention can be made without departing from the principles of the invention and these modifications and adaptations are intended to be within the scope of the invention as defined in the following claims.
Claims (10)
1. A gas detection method for a lidar, comprising:
Emitting a first light beam with a first wavelength at the center, a second light beam with a second wavelength at the center and a third light beam with a third wavelength at the center to the atmosphere, wherein the first wavelength corresponds to the absorption line peak of the gas to be detected, and the second wavelength and the third wavelength are respectively positioned at two sides of the absorption line peak of the gas to be detected;
Acquiring echoes generated after the first light beam, the second light beam and the third light beam are transmitted to the atmosphere, separating first narrow-band light with a center wavelength of the first wavelength, second narrow-band light with a center wavelength of the second wavelength and third narrow-band light with a center wavelength of the third wavelength from the echoes, and detecting the intensity of the first narrow-band light, the intensity of the second narrow-band light and the intensity of the third narrow-band light respectively;
and carrying out preset statistics on the intensity of the second narrow-band light and the intensity of the third narrow-band light to obtain statistical intensity, and obtaining the content of the gas to be detected by combining the intensity of the first narrow-band light.
2. The gas detection method for a lidar according to claim 1, wherein a wavelength difference between the second wavelength and the first wavelength is the same as a wavelength difference between the third wavelength and the first wavelength.
3. The gas detection method for a lidar according to claim 2, wherein the intensity of the second beam is the same as the intensity of the third beam.
4. The gas detection method for a lidar according to claim 1, wherein the first wavelength is λ 0, the second wavelength is λ 0 -mΔλ, and the third wavelength is λ 0 +nΔλ;
Carrying out preset statistics on the intensity of the second narrow-band light and the intensity of the third narrow-band light to obtain statistical intensity, and combining the intensity of the first narrow-band light to obtain the content of the gas to be detected comprises the following steps:
The intensities of the first narrowband light, the second narrowband light and the third narrowband light are P a1、Pa2 and P a3 in sequence, and the intensities of the first narrowband light, the second narrowband light and the third narrowband light are P b1、Pb2 and P b3 in sequence, corresponding to the distance L a, corresponding to the distance L b;
The following relationship exists:
；
；
Wherein, Gamma <1, alpha represents the concentration of the gas to be measured on the path from the distance L a to the distance L b, epsilon represents the absorption characteristic parameter of the gas to be measured on the light with the first wavelength, and A is a constant;
the method is obtained according to the following relation: 。
5. A lidar for gas detection, comprising:
The first light source is used for emitting a first light beam with a first wavelength at the center to the atmosphere, wherein the first wavelength corresponds to the peak of an absorption spectrum line of the gas to be detected;
A second light source for emitting a second light beam having a second wavelength at a center wavelength toward the atmosphere;
the third light source is used for emitting a third light beam with a third wavelength at the center wavelength to the atmosphere, and the second wavelength and the third wavelength are respectively positioned at two sides of an absorption spectrum crest of the gas to be detected;
a telescopic optical system for acquiring echoes generated after the first light beam, the second light beam and the third light beam are transmitted to the atmosphere;
The light receiving and detecting assembly is used for separating first narrow-band light with the center wavelength of the first wavelength, second narrow-band light with the center wavelength of the second wavelength and third narrow-band light with the center wavelength of the third wavelength from the echo, and detecting the intensity of the first narrow-band light, the intensity of the second narrow-band light and the intensity of the third narrow-band light respectively;
and the control component is used for carrying out preset statistics on the intensity of the second narrow-band light and the intensity of the third narrow-band light to obtain statistical intensity, and combining the intensity of the first narrow-band light to obtain the content of the gas to be detected.
6. The lidar for gas detection according to claim 5, wherein a distance between an optical axis of the first light source and an optical axis of the telescopic optical system, a distance between an optical axis of the second light source and an optical axis of the telescopic optical system, and a distance between an optical axis of the third light source and an optical axis of the telescopic optical system are all identical.
7. The lidar for gas detection of claim 5, wherein the second wavelength is smaller than the first wavelength, the third wavelength is larger than the first wavelength, and the light-receiving and detecting assembly comprises:
The first light-splitting element is used for reflecting light with a first boundary wavelength or less and transmitting light with a wavelength greater than the first boundary wavelength, the first boundary wavelength is between the second wavelength and the first wavelength, and an echo acquired by the telescopic optical system is incident to the first light-splitting element;
The second light splitting element is arranged on a transmission light path of the first light splitting element and is used for reflecting light with a second boundary wavelength or less and transmitting light with a wavelength larger than the second boundary wavelength, and the second boundary wavelength is between the first wavelength and the third wavelength;
The second narrow-band filter element is arranged on the reflection light path of the first light-splitting element and is used for enabling the reflection light of the first light-splitting element to penetrate through the second narrow-band filter element and then enter the second photoelectric detector, and the center wavelength of the second narrow-band filter element is the second wavelength;
The first narrow-band filter element is arranged on a reflection light path of the second light-splitting element and is used for enabling the reflection light of the second light-splitting element to penetrate through the first narrow-band filter element and then enter the first photoelectric detector, and the center wavelength of the first narrow-band filter element is the first wavelength;
The third narrow-band filter element is arranged on the transmission light path of the second light-splitting element and is used for enabling the transmission light of the second light-splitting element to penetrate through the third narrow-band filter element and then enter the third photoelectric detector, and the center wavelength of the third narrow-band filter element is the third wavelength.
8. The lidar for gas detection according to claim 7, wherein a first condensing element for condensing outgoing light of the first narrowband filter element to the first photodetector is provided between the first narrowband filter element and the first photodetector;
a second converging element is arranged between the second narrow-band filter element and the second photoelectric detector, and the second converging element is used for converging the emergent light of the second narrow-band filter element to the second photoelectric detector;
A third converging element is arranged between the third narrow-band filter element and the third photodetector, and the third converging element is used for converging the emergent light of the third narrow-band filter element to the third photodetector.
9. The lidar for gas detection according to claim 5, wherein a small aperture stop is provided between the telescopic optical system and the light receiving and detecting assembly.
10. The lidar for gas detection according to claim 5, wherein a collimating unit for collimating the echo beam from the telescopic optical system and making the collimated echo beam incident on the light receiving and detecting unit is provided between the telescopic optical system and the light receiving and detecting unit.
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