CN112799099A - Near-infrared all-fiber water vapor differential absorption laser radar - Google Patents
Near-infrared all-fiber water vapor differential absorption laser radar Download PDFInfo
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Abstract
The invention discloses a near-infrared all-fiber water vapor differential absorption laser radar, and belongs to the technical field of laser radars. The near-infrared all-fiber water vapor differential absorption laser radar comprises: the device comprises a laser light source for outputting on-band continuous laser and off-band continuous laser, an optical switch, a pulse generator, an optical amplifier, an optical transceiver telescope, a filter, a detector, an acquisition card and a data processing module. The laser light source adopts the near-infrared long wave band with the wavelength range of 1100-2526 nm as the measurement wave band for water vapor differential absorption, and compared with the common near-infrared short wave, the molecular Rayleigh signal can be ignored, so that the water vapor inversion precision is improved, and the inversion algorithm is simplified. The invention realizes wavelength division multiplexing by adopting the optical switch, realizes the simultaneous detection of on-band and off-band signals, simplifies the system structure and saves the system cost.
Description
Technical Field
The invention relates to the technical field of water vapor laser radars, in particular to a near-infrared all-fiber water vapor differential absorption laser radar.
Background
Water vapor is the only substance in the earth's atmosphere where a phase change occurs and plays an important role in many atmospheric physical and chemical processes. In the troposphere, water vapor affects the formation of aerosols and clouds and exchanges heat with the environment through phase changes. Water vapor has a plurality of absorption bands in an infrared band, so that the water vapor is the most important greenhouse gas in the atmosphere, and the positive and negative feedback effects of the water vapor have great influence on temperature change and contribute to about 60 percent of greenhouse effect.
The current detection modes of atmospheric water vapor comprise sampling detection and remote sensing detection, and the remote sensing detection comprises passive remote sensing and active remote sensing. The passive remote sensing detection mode comprises a microwave water vapor radiometer, a GPS-based detection, a Fourier infrared spectrometer and an infrared hyperspectral atmosphere detector. Two main types of active remote sensing detection are raman lidar and differential absorption lidar. Compared with a passive remote sensing technology, the Raman laser radar can obtain a water vapor profile with high space-time resolution, but the Raman scattering cross section is small, so that the radar needs a high-power laser and a large-caliber telescope, the detection performance of the radar in the daytime is greatly reduced, and in addition, in order to obtain correct water vapor concentration data, the system needs to be calibrated by system constants.
In comparison, the differential absorption lidar is the most effective remote sensing means for detecting the water vapor profile at present, and the basic principle is as follows: emitting two beams of laser with closely spaced wavelengths to atmosphere, one beam of laser having a wavelength of lambdaonThe other laser beam has a wavelength of lambdaoffWhich is located outside the moisture absorption line and is substantially not absorbed or weakly absorbed by moisture. Because the wavelength interval of the two laser beams is very close (usually on the order of nanometers), other gas substances in the atmosphere and the transmitting and receiving systems thereof can be considered to have basically the same influence on the two laser beams, so that the echo signals of the two laser beams can be utilized to eliminate the interference difference, and the water vapor concentration can be inverted.
However, the inventors of the present invention have studied and found that: at present, the water vapor differential absorption laser radar mainly works in the wavelength bands of 720nm, 815nm and 935nm (near infrared short wave band). In these bands, the influence of the rayleigh scattering of molecules is large and cannot be ignored, so that not only the mie scattering of aerosol but also the rayleigh scattering of molecules need to be considered during the detection of water vapor by the laser radar in the band, and the corresponding data inversion is very complex. In addition, the existing water vapor differential absorption laser radar system is large in size, loose and not compact in structure and high in cost.
Disclosure of Invention
The invention aims to provide a near-infrared all-fiber water vapor differential absorption laser radar which has the advantages of all-fiber integration, stable system, compact receiving light path structure and high measurement precision.
The purpose of the invention is realized by the following technical scheme: a near-infrared all-fiber water vapor differential absorption laser radar comprises: the device comprises a laser light source, an optical switch, a pulse generator, an optical amplifier, an optical transceiving telescope, a filter, a detector, a collection card and a data processing module; the laser light source, the optical switch, the pulse generator, the optical amplifier, the optical transceiver telescope, the filter and the detector are sequentially connected by adopting optical fibers, and the detector, the acquisition card and the data processing module are sequentially connected;
the laser light source is used for generating on-band continuous laser and off-band continuous laser, and the laser wavelength generated by the laser light source is 1100-2526 nm; the center wavelength of the on-waveband continuous laser is lambdaonWhich is located on a certain absorption peak of the water vapor spectrum; the center wavelength of the off-band continuous laser is lambdaoffLocated outside the water vapor absorption line; the on-band continuous laser and the off-band continuous laser enter a pulse generator to be modulated into pulse light in a time-sharing manner after passing through an optical switch; the pulse light is amplified by the optical amplifier and then is transmitted to the atmosphere through the optical transceiver telescope, and the atmosphere echo signal is received through the optical transceiver telescope; the signal output by the optical transceiver telescope is detected by the detector after passing through the optical filter, the detected electric signal is collected by the collecting card, and the collected signal is processed by the data processing module.
Further, the pulse generator may be an acousto-optic modulator or an electro-optic modulator.
Further, the optical transceiver telescope comprises a transmitting telescope and a receiving telescope; the pulse light is amplified by the optical amplifier and then transmitted to the atmosphere through the transmitting telescope of the optical transceiver telescope, and the atmosphere echo signal is received by the receiving telescope of the optical transceiver telescope.
Furthermore, the lenses of the transmitting telescope and the receiving telescope are connected in the direction of the mirror surface, the transmitting telescope and the receiving telescope form an 8-shaped structure, both the transmitting telescope and the receiving telescope comprise a notch, and the transmitting telescope and the receiving telescope are connected through respective notches.
Further, the wavelength generated by the laser light source is preferably in the 1.5 micron band.
The technical scheme provided by the invention can show that the invention has the advantages that:
1. the laser light source adopts the near-infrared long wave band as the measurement band of water vapor differential absorption, and compared with the common near-infrared short wave, the molecular Rayleigh signal can be ignored, thereby improving the water vapor inversion precision and simplifying the inversion algorithm.
2. Wavelength division multiplexing is achieved by using optical switches. Originally, two sets of optical systems are needed for two light sources, and only a single amplifier, a single telescope, a single detector and a single acquisition card are adopted by applying an optical switch, so that on-band and off-band signals are simultaneously detected, the system structure is simplified, and the system cost is saved. And compared with a plurality of amplifiers and a differential laser radar system with a plurality of detectors, the differential laser radar system avoids the difference caused by inconsistent response of different detectors, different detection performances and the like along with different temperature fields, and improves the detection precision.
3. In 1.5 micron optical communication wave band, the response time of optical fiber device is quick, for example, two laser beams lambda can be realized by high-speed device optical switchonAnd λoffThe fast switching of the on channel and the off channel can be realized, and the detection efficiency is greatly improved.
4. In the near-infrared long-wave band, a full-optical-fiber integration method can be adopted, so that the system stability is improved.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings needed to be used in the description of the embodiments are briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on the drawings without creative efforts.
Fig. 1 is a block diagram of a structure of a near-infrared all-fiber water vapor differential absorption laser radar according to an embodiment of the present invention;
fig. 2 is a timing diagram of the near-infrared all-fiber moisture differential absorption lidar according to an embodiment of the present invention.
Fig. 3 is a water vapor absorption curve of the near-infrared all-fiber water vapor differential absorption laser radar according to the embodiment of the present invention, which is measured at a wavelength of 1.5 μm.
In the figure, 1 is a laser light source, 11 is an on wave band continuous laser, 11 is a 12 is an off wave band continuous laser, 2 is an optical switch, 3 is a pulse generator, 4 is an optical amplifier, 5 is an optical transceiver telescope, 6 is a filter, 7 is a detector, 8 is an acquisition card, and 9 is a data processing module.
Detailed Description
The technical solutions in the embodiments of the present invention are clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiment 1 is only a part of the embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments of the present invention without making any creative effort, shall fall within the protection scope of the present invention.
As shown in fig. 1, the present invention provides a near-infrared all-fiber moisture differential absorption lidar, which includes: the device comprises a laser light source 1, an optical switch 2, a pulse generator 3, an optical amplifier 4, an optical transceiving telescope 5, a filter 6, a detector 7, an acquisition card 8 and a data processing module 9; the laser light source 1 is sequentially connected with the optical switch 2, the pulse generator 3, the optical amplifier 4, the optical transceiving telescope 5, the filter 6 and the detector 7 by optical fibers, and the detector 7 is sequentially connected with the acquisition card 8 and the data processing module 9;
the laser source 1 is used for generating on-waveband continuous laser 11 and off-waveband continuous laser 12, and the laser wavelength generated by the laser source 1 is 1100-2526 nm; the central wavelength of the on-band continuous laser 11 is lambdaonWhich is located on a certain absorption peak of the water vapor spectrum; the off band is continuously excitedThe light 12 has a central wavelength λoffLocated outside the water vapor absorption line; the on-waveband continuous laser 11 and the off-waveband continuous laser 12 are switched by the optical switch 2 and enter the pulse generator 3 in a time-sharing manner to be modulated into pulse light; the pulse light is amplified by the optical amplifier 4 and then transmitted to the atmosphere through the optical transceiver telescope 5, and the atmosphere echo signal is received through the optical transceiver telescope 5; the signal output by the optical transceiver telescope 5 is detected by the detector 7 after passing through the optical filter 6, the detected electric signal is collected by the collecting card 8, and the collected signal is processed by the data processing module 9.
Specifically, the optical transceiver telescope 5 comprises a transmitting telescope and a receiving telescope; the pulse light is amplified by the optical amplifier 4 and then transmitted to the atmosphere through the transmitting telescope of the optical transceiver telescope 5, and the atmosphere echo signal is received by the receiving telescope of the optical transceiver telescope 5. The signal output by the optical transceiver telescope 5 is detected by the detector 7 after the sun and the atmospheric background noise are filtered by the optical filter 6, the detected electric signal is collected by the collecting card 8, and the collected signal is inverted after data processing by the data processing module 9 to obtain the atmospheric water vapor profile.
The data processing module 9 can be a computer, a single chip, an FPGA, or other processor with an operation function.
The lenses of the transmitting telescope and the receiving telescope are connected in the direction of the mirror surface, and the transmitting telescope and the receiving telescope form an 8-shaped structure. Specifically, the transmitting telescope and the receiving telescope both comprise a notch, and the transmitting telescope and the receiving telescope are connected through respective notches. The design can enable the receiving telescope to receive signals in each distance transmitted by the laser radar, so that the measuring blind area of the laser radar is eliminated.
In one embodiment, the optical transceiver telescope 5 comprises a telescope and an optical circulator, the pulse light is amplified by the optical amplifier 4, then is output to the telescope through a transceiver multiplexing end of the circulator and is transmitted to the atmosphere through the telescope, and an atmosphere echo signal is received by the telescope and then is output through an output end of the circulator.
The laser light source 1 of the present invention generates a laser wavelength of 1100 to 2526 nm. Water vapor absorption lines exist in many regions of the infrared spectral region. The existing differential water vapor absorption laser radar mainly works in the wave bands of 720nm, 815nm and 935 nm. Prior to this application, it was generally believed that the most suitable wavelengths for differential absorption lidar were approximately 730, 820, and 930 nm. In these bands, the interference with other gases is minimal, both the laser and the sensitive detector 7 are present, and the band covers a wide line intensity. However, the inventors of the present invention have found that the band has problems in that: in these bands, the lidar must consider not only the mie scattering of the aerosol but also the rayleigh scattering of the molecules, which makes the whole vapor inversion algorithm more complex. The meter scattering is proportional to the minus first power of the wavelength and the rayleigh scattering is proportional to the minus fourth power of the wavelength. Thus, the longer the wavelength, the faster the rayleigh scattered signal decays, and the less rayleigh scattering is affected.
Taking the near infrared band of 1550nm as an example, because the rayleigh scattering signal is proportional to the minus fourth power of the wavelength, when the 1550nm band is used for measurement, the rayleigh signal is 21 times weaker than the 720nm band, 13 times weaker than the 815nm band, and 7.5 times weaker than the 935nm band. Therefore, the influence of Rayleigh signals of atmospheric molecules can be effectively reduced by adopting the near-infrared band detection with longer wavelength. In addition, the detection mechanism of the laser radar is micro-pulse, and the Rayleigh scattering signals of atmospheric molecules can be ignored, so that the accuracy of inverting atmospheric water vapor components is improved. Specifically, when data processing is carried out, the Rayleigh scattering signals of atmospheric molecules can be ignored, so that the algorithm can be greatly simplified, and the inversion speed and accuracy of atmospheric water vapor components can be improved.
Furthermore, in a near-infrared long-wave band, a full-fiber integration method can be adopted, so that the system stability is improved, and the near-infrared short waves (namely the existing 720nm, 815nm and 935nm bands) cannot realize full-fiber integration, so that the system is huge and not compact.
In a preferred embodiment, the laser light source 1 generates a wavelength preferably in the 1.5 micron band. In the 1.5 micron wave band, except that the influence of atmospheric molecule Rayleigh signals can be ignored, the optical communication device is stable and reliable due to the high-speed development and maturity of the optical communication device, and the safety coefficient of human eyes in the 1.5 micron wave band is high, so that the optical communication device can be operated in places with dense human mouths, such as cities, airports, meteorological stations and the like, and can realize miniaturization, convenience and human eye safety detection. In the prior art, the near infrared wave short wave band widely used for water vapor measurement cannot realize all-fiber integration, and the system is huge and not compact.
When the laser light source 1 is in a 1.5-micron waveband, the optical amplifier 4 is an erbium-doped fiber amplifier (EDFA).
It should be noted that the 1.5 micron wavelength band mentioned in the present invention includes a plurality of fine wavelengths between 1.5 microns and 1.6 microns, for example, 1.55 microns, and is not specific to the 1.5 micron wavelength alone. Fig. 3 is a water vapor absorption curve of the near-infrared all-fiber water vapor differential absorption laser radar according to the embodiment of the present invention, which is measured at a wavelength of 1.5 μm. In the figure, the curve depressed downward represents the water vapor absorption line, and as shown in fig. 3, the water vapor transmission rate is significantly reduced in the 1.552 micron wavelength band, and a significant water vapor absorption peak exists.
In one embodiment, the laser source 1 may be a narrow-band laser, or may be a broad-spectrum laser, preferably a single-mode narrow-band laser, which may improve the detection sensitivity.
In an alternative embodiment, the laser source 1 may be a broad spectrum laser capable of outputting multiple target wavelengths, reducing system cost.
The optical switch 2 is used for switching the laser in the on wave band and the laser in the off wave band in the time domain, so that the wavelength division multiplexing technology is applied to the water vapor differential absorption laser radar. Originally, two sets of optical systems are needed for two light sources, and only a single amplifier, a single telescope, a single detector 7 and a single acquisition card 8 are adopted by applying an optical switch 2, so that on-band and off-band signals are simultaneously detected, the system structure is simplified, and the system cost is saved.
More importantly, the laser wavelength is preferably 1.5 micron wave band, and the rising time of the optical switch 2 in the wave band can reach hundred nanoseconds, so that the switching speed of the on-band laser and the off-band laser is in KHz order, the fast switching detection of an on channel and an off channel can be realized, and the detection efficiency is greatly improved. Within microsecond order, the difference between the signals of the on wave band and the off wave band caused by atmospheric change is negligible, thereby improving the detection accuracy. And the switching time of the on wavelength and the off wavelength of the laser radars in other wave bands is in the order of seconds or even minutes. The atmosphere changes constantly, and the stability of the atmosphere irradiated at the same time cannot be ensured at all by the long switching time, so that the timeliness and the accuracy of the measurement result cannot be ensured. Therefore, the timeliness of the measurement result of the 1.5-micron wave band is higher than that of other wave band laser radars by more than 9 orders of magnitude, the switching time of the on wave band and the off wave band can be almost ignored, and the accuracy and the stability of the measurement result can be effectively ensured.
In addition, the optimized 1.5-micron wave band can further improve the system stability and achieve the safety of human eyes, so that the water vapor differential absorption laser radar has the advantages of stability, miniaturization and safety of human eyes. And compared with a plurality of amplifiers and a differential laser radar system with a plurality of detectors, the differential laser radar system avoids the difference caused by inconsistent response of different detectors, different detection performances along with different temperature fields and the like, and improves the detection precision.
The pulse generator 3 may be an acousto-optic modulator or an electro-optic modulator. In one embodiment, an acousto-optic modulator is preferred, which can generate a pulsed signal with a high extinction ratio.
The detector 7 is preferably a single-photon detector 7 and comprises a superconducting nanowire single-photon detector 7, an indium gallium arsenic single-photon detector 7 and a frequency up-conversion single-photon detector 7. In order to meet the requirement of miniaturization, the detector 7 is preferably an indium gallium arsenic single photon detector 7, and the detector has the advantages of low cost, miniaturization, small size and the like.
In another embodiment, to improve the detection signal-to-noise ratio, the detector 7 is a superconducting nanowire single photon detector 7, which is currently the best detecting single photon detector 7.
Fig. 2 is a timing diagram of the near-infrared all-fiber moisture differential absorption lidar according to an embodiment of the present invention. As shown in fig. 2, the laser light source outputs two continuous optical signals; optical switch willonAnd λoffThe laser with wavelength is switched to enter a pulse generator, the modulated pulse enters an optical amplifier for amplification in a time-sharing manner, and after the amplified pulse is emitted to the atmosphere, lambda isonThe attenuation ratio lambda of the wavelength laser due to water vapor absorptionoffThe laser of wavelength decays fast, and the water profile is inverted through a differential absorption algorithm.
The technical scheme provided by the invention can show that the invention has the advantages that:
1. the laser light source adopts the near-infrared long wave band with the wavelength range of 1100-2526 nm as the measurement wave band for water vapor differential absorption, and compared with the common near-infrared short wave, the molecular Rayleigh signal can be ignored, so that the water vapor inversion precision is improved, and the inversion algorithm is simplified.
2. Wavelength division multiplexing is achieved by using optical switches. Originally, two sets of optical systems are needed for two light sources, and only a single amplifier, a single telescope, a single detector and a single acquisition card are adopted by applying an optical switch, so that on-band and off-band signals are simultaneously detected, the system structure is simplified, and the system cost is saved. And compared with a plurality of amplifiers and a differential laser radar system with a plurality of detectors, the differential laser radar system avoids the difference caused by inconsistent response of different detectors, different detection performances and the like along with different temperature fields, and improves the detection precision.
3. In 1.5 micron optical communication wave band, the response time of optical fiber device is quick, for example, two laser beams lambda can be realized by high-speed device optical switchonAnd λoffThe fast switching of the on channel and the off channel can be realized, and the detection efficiency is greatly improved. And the switching time of the on wavelength and the off wavelength of the laser radars in other wave bands is in the order of seconds or even minutes. The atmosphere changes constantly, and the stability of the atmosphere irradiated at the same time cannot be ensured at all by the long switching time, so that the timeliness and the accuracy of the measurement result cannot be ensured. Therefore, the timeliness of the measurement result of the 1.5-micron wave band is higher than that of other wave band laser radars by more than 9 orders of magnitude, the switching time of the on wave band and the off wave band can be almost ignored, and the on wave band and the off wave band can be measuredThe accuracy and the stability of the measuring result are effectively ensured.
4. In the near-infrared long-wave band selected by the invention, the near-infrared all-fiber water vapor differential absorption laser radar adopts all-fiber integration, so that the system stability is improved.
The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are included in the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.
Claims (4)
1. The utility model provides a near-infrared all-fiber water vapour differential absorption lidar which characterized in that includes: the device comprises a laser light source, an optical switch, a pulse generator, an optical amplifier, an optical transceiving telescope, a filter, a detector, a collection card and a data processing module; the laser light source, the optical switch, the pulse generator, the optical amplifier, the optical transceiver telescope, the filter and the detector are sequentially connected by adopting optical fibers, and the detector, the acquisition card and the data processing module are sequentially connected;
the laser light source is used for generating on-band continuous laser and off-band continuous laser, and the laser wavelength generated by the laser light source is 1100-2526 nm; the center wavelength of the on-waveband continuous laser is lambdaonWhich is located on a certain absorption peak of the water vapor spectrum; the center wavelength of the off-band continuous laser is lambdaoffLocated outside the water vapor absorption line; the on-band continuous laser and the off-band continuous laser enter a pulse generator to be modulated into pulse light in a time-sharing manner after passing through an optical switch; the pulse light is amplified by the optical amplifier and then is transmitted to the atmosphere through the optical transceiver telescope, and the atmosphere echo signal is received through the optical transceiver telescope; the signal output by the optical transceiver telescope is detected by the detector after passing through the optical filter, the detected electric signal is collected by the collecting card, and the collected signal is processed by the data processing module.
2. The near-infrared all-fiber moisture differential absorption lidar according to claim 1, wherein the pulse generator is an acousto-optic modulator or an electro-optic modulator.
3. The near-infrared all-fiber moisture differential absorption lidar of claim 1, wherein the optical transceiver telescope comprises a transmitting telescope and a receiving telescope; the pulse light is amplified by the optical amplifier and then transmitted to the atmosphere through the transmitting telescope of the optical transceiver telescope, and the atmosphere echo signal is received by the receiving telescope of the optical transceiver telescope.
4. The near-infrared all-fiber water vapor differential absorption lidar according to claim 1, wherein the lenses of the transmitting telescope and the receiving telescope are connected in the direction of the mirror surface, the transmitting telescope and the receiving telescope form an 8-shaped structure, both the transmitting telescope and the receiving telescope comprise a notch, and the transmitting telescope and the receiving telescope are connected through the respective notches.
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