Lidar system for measuring atmospheric aerosols

Abstract

This application discloses a laser radar system for measuring atmospheric aerosols. The laser radar system for measuring atmospheric aerosols includes a light scattering receiving element disposed at the receiving end of a telescope in the laser radar system. The light scattering receiving element is an optical waveguide array having multiple optical waveguides with different light receiving surfaces in the light receiving direction. The light receiving surfaces have imaging receiving focal planes and fields of view corresponding to aerosol scattered light at different altitudes. The light scattering receiving element implemented in accordance with this application, when used in a laser radar system, allows laser radar signal beams scattered and returned at different distances to be focused at different focal planes and positions at the output end of the receiving telescope, allowing them to be effectively received, thereby obtaining complete atmospheric profile measurement data at different altitudes from low to high altitudes.

Description

[0001] This application is a divisional application of the patent application with the application date of November 11, 2021, application number 2021113333718, and invention name “Light scattering receiving element and its application in lidar system”. Technical Field

[0002] The present application relates to the field of laser radar technology, and more specifically, to a laser radar system for measuring atmospheric aerosols. Background Art

[0003] Atmospheric aerosols, the collective term for liquid and solid particles suspended in the atmosphere, primarily influence global climate and local air quality through direct and indirect effects. As a key parameter describing atmospheric conditions, aerosols influence short-term air quality, local meteorological variations, and long-term climate change. Therefore, real-time measurement of aerosol distribution is crucial. The primary sources of aerosols are dust and combustion emissions from human activities, with the vast majority concentrated within the boundary layer.

[0004] In related technologies, the measurement of atmospheric aerosols is achieved through lidar, which specifically uses a laser as the emission source, wherein the lidar signal beam is emitted vertically upward and is received by a receiver after being scattered by the aerosol. The interaction between the lidar signal beam and the air molecules and aerosol particles in the atmosphere is used to achieve the measurement of the optical and physical properties of the atmosphere, as well as active remote sensing detection of atmospheric meteorology (in addition to remote sensing measurements by lidar, it is mainly optical particle counters, nanoparticle spectrometers, etc., the disadvantage of which is that local sampling is required for detection), as well as measurement application scenarios including military and civilian activities such as flight.

[0005] However, a major effect in aerosol measurements is that they are subject to large temporal and spatial fluctuations, which makes predictions impossible and point measurements inadequate. Therefore, in applications where their effects can be crucial, it is often necessary to continuously monitor aerosols over the complete spatial domain of interest. For example, due to the important variations in altitude, the optical scattering properties of aerosols can be measured over as much altitude as possible within the cycle of one laser shot.

[0006] LiDAR has long been proposed for remote measurement of atmospheric parameters. However, due to the constraints of its optical structure, LiDAR technology itself has certain limitations in measuring aerosols. It cannot take into account the measurement needs of both long and short distances, especially the need to cover the entire airspace from an extremely short distance.

[0007] Existing lidar aerosol measurements include a variety of measurement schemes. For example, patent document All-fiber lidar aerosol detection device with patent application number 201410253958.1 discloses an all-fiber lidar aerosol detection device, which includes a signal transmission channel for emitting laser signals, a signal receiving channel for receiving the emitted laser signals and the echo signals generated by the laser signals emitted into the atmosphere, and a signal processing channel for converting the echo signals into electrical signals and analyzing and processing them. The signal transmission channel, signal receiving channel, and signal processing channel are all-fiber structures. The all-fiber structure can achieve signal detection of up to 20kHz and picowatt levels, improving temporal and spatial resolution.

[0008] The document with patent application number 202010828354.0 discloses an aerosol lidar system based on CCD lateral detection. It uses multiple cylindrical mirrors placed side by side at different heights to simultaneously receive atmospheric aerosol information at different height segments. Multiple cylindrical mirrors replace the traditional single lens. The CCD can detect multiple side-by-side light beams representing multiple height segments, thereby improving the spatial resolution of detection while ensuring the detection height range, while avoiding the reduction in accuracy caused by fisheye lens distortion at the bottom and upper layers.

[0009] The document with patent application number 202010553916.5 discloses a rotational Raman spectroscopic system and spectroscopic method for atmospheric aerosol detection. It transmits the atmospheric echo signal received by the telescope in the lidar through optical fiber and optical fiber flange, and emits it as collimated light after passing through the collimator, filtering out the light beam below 950nm, and then separating the signal in the light beam through a grating, a long-focal-length lens and a holed reflector to achieve independent and precise detection of aerosols in the near-infrared 1064nm band.

[0010] U.S. Patent Document No. US5239352 discloses providing an improved backscattering lidar that overcomes the above difficulties by measuring multiple scattering contributions in addition to conventional lidar technology. This additional information can then be used to resolve the uncertainties described previously. Any backscattered signal at a field of view that is larger than the laser beam divergence is due to multiple scattering. Therefore, the additional information obtained by simultaneously measuring the backscattering of several fields of view can be used to determine the multiple scattering contributions to the received signal. This is achieved by using a multi-element radiation detector having radiation receiving elements (including four concentric silicon detectors (PIN photodiodes)) located in separate parts of the focal plane of the lidar's receiving optics to distinguish the received backscattered radiation between several fields of view.

[0011] However, the aforementioned prior art solutions still present unresolved issues: First, the use of CCD imaging to address multi-range altitude measurements introduces inherent uncertainty in aerosol inversion due to the varying scattering angles of aerosols captured by the CCD pixels, necessitating complex calculations and multiple measurements. Second, the spatial distribution of multiple optoelectronic components imposes certain spatial constraints and is primarily used to calculate the backscattered signal from multiple scattering events. (The scattering cross section of Mie scattering varies with scattering angle, and the biggest drawback of the Schaffner radar is its assumption for low-altitude echoes: the variation of the scattering cross section with angle is negligible. This assumption is unreasonable for complex aerosols.) Summary of the Invention

[0012] Although the measurement methods in the existing technology can measure atmospheric aerosols, since aerosols are distributed at different atmospheric altitudes, the scattered laser radar signals returned have different focusing positions and cannot be fully received by the receiver at the same time. It is often necessary to adjust the position of the receiver to receive the laser radar signal beams scattered at different altitudes through multiple measurements.

[0013] The present application proposes a light scattering receiving element, which is used in a laser radar system for measuring atmospheric aerosols. The light scattering receiving element is arranged at the telescope receiving end of the laser radar system. The light scattering receiving element is an optical waveguide array. The optical waveguide array has multiple optical waveguides with different light receiving surfaces in the light receiving direction. The light receiving surfaces have imaging receiving focal planes and fields of view corresponding to aerosol scattered light at different heights.

[0014] Furthermore, the optical waveguide array has a plurality of optical waveguides with light receiving surfaces corresponding to different laser wavelengths in the direction array corresponding to the aerosol scattered light at the same height.

[0015] Furthermore, the optical waveguide array is a modular package adapted to the shape of the receiving end of the telescope.

[0016] Furthermore, the optical waveguide array is configured to correspond to a single wavelength laser.

[0017] Furthermore, the light received by the optical waveguide array is transmitted through an optical fiber component.

[0018] The present application also discloses a laser radar system for measuring atmospheric aerosols, wherein the laser radar system includes a laser transmitting component, a receiving component, and a main control component;

[0019] The laser emission assembly includes a laser and a reflector, wherein the reflector is arranged opposite to the laser to reflect the laser radar signal beam emitted by the laser into the atmosphere;

[0020] The receiving assembly includes a telescope, an optical fiber fixture, multiple optical fibers, and a spectrometer. The telescope is used to receive the laser radar signal beam after atmospheric scattering, and the output end of the telescope is used to inject the received laser radar signal beam into the multiple optical fibers inserted in the optical fiber fixture. The top end face of the optical fiber fixture is inclined, and the multiple optical fibers are evenly spaced and inserted in the optical fiber fixture. Each optical fiber passes through the optical fiber fixture, and the top ends of the multiple optical fibers are arranged in a trapezoidal shape in the vertical direction so that the top ends of the multiple optical fibers are sequentially located at the focal plane of the telescope corresponding to different height distances. The bottom end of each optical fiber is connected to the spectrometer.

[0021] The main control is electrically connected to the spectrometer to perform data analysis and processing on the laser radar signal beam.

[0022] Furthermore, the top end surface of the optical fiber fixing member is a plurality of steps with decreasing heights in the vertical direction, the plurality of optical fibers correspond to the plurality of steps one by one, and each optical fiber is inserted into the corresponding step.

[0023] Furthermore, the number of the steps is not less than 2.

[0024] Furthermore, the number of optical fiber bundles and the cross-sectional area of ​​the optical fiber bundles in each step surface increase sequentially from high to low in the vertical direction.

[0025] In general, the above technical solutions conceived by the present invention have the following advantages compared with the prior art:

[0026] Beneficial effects:

[0027] (1) When measuring atmospheric aerosols, the lidar system provided by this application can still be effectively received even if the lidar signal beams scattered and returned at different distances are focused on different focal planes and positions at the output end of the receiving telescope due to different distances and non-coaxiality, thereby obtaining complete atmospheric profile measurement data at different altitudes from low altitude to high altitude;

[0028] (2) The laser radar system provided by this application is not only applicable to single-wavelength laser emission, but also to the application and measurement of multi-wavelength laser radar systems;

[0029] (3) The lidar system provided in this application is applicable not only to elastic scattering (Mie scattering, Rayleigh scattering), but also to the application and measurement of Raman scattering and high spectral resolution lidar systems;

[0030] (4) The light scattering receiving element provided in the present application is preferably an optical fiber component, and the production process is relatively simple, and has good compatibility with the optical system of the existing laser radar system. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0032] Figure 1 1 is a schematic structural diagram of a laser radar system for measuring atmospheric aerosols provided by an embodiment of the present invention;

[0033] Figure 2 Schematic diagram of the structure of an optical fiber bundling fixture provided by an embodiment of the present invention;

[0034] Figure 3 It is a top view of an optical fiber bundling fixture provided by an embodiment of the present invention.

[0035] The symbols in the figure mean the following:

[0036] 1. Laser emitting assembly; 11. Laser; 12. Reflector; 2. Receiving assembly; 21. Telescope; 211. Pinhole; 22. Fiber bundle fixture; 222. Step surface; 23. Fiber bundle; 24. Spectrum splitter; 3. Main control unit. DETAILED DESCRIPTION

[0037] The technical solutions in the embodiments of the present application will be described clearly and completely below in conjunction with the drawings in the embodiments of the present application.

[0038] The terms "first," "second," "third," and the like in the specification and claims of this application and the accompanying drawings are used to distinguish between different objects, not to describe a particular order. Furthermore, the terms "including," "having," and any variations thereof, are intended to cover non-exclusive inclusions. For example, a process, method, system, product, or apparatus comprising a series of steps or elements is not limited to the listed steps or elements, but may optionally include steps or elements not listed, or may optionally include other steps or elements inherent to the process, method, product, or apparatus.

[0039] This application first proposes a light scattering receiving element, which is used in a laser radar system for measuring atmospheric aerosols. The light scattering receiving element is arranged at the telescope receiving end of the laser radar system. The light scattering receiving element is an optical waveguide array. The optical waveguide array has multiple optical waveguides with different light receiving surfaces in the light receiving direction. The light receiving surface has an imaging receiving focal plane and field of view corresponding to aerosol scattered light at different heights.

[0040] As described above, the focal plane positions corresponding to aerosol scattered light imaging at different heights are different, and the sizes of the imaging are also different, so a single receiving device cannot effectively receive, process and analyze the corresponding imaging information.

[0041] Exemplarily, the optical waveguide array is a modular package adapted to the shape of the receiving end of the telescope 21 .

[0042] Furthermore, the optical waveguide is preferably an optical fiber.

[0043] The optical waveguide array also has optical waveguides with light receiving surfaces corresponding to different laser wavelengths in the direction corresponding to the aerosol scattered light at the same height.

[0044] Taking into account the use of this device in a multi-wavelength state, it has better adaptability to multiple wavelengths. When multi-wavelength is used, the scattering effect of the wavelength is reduced. At the same height, multiple optical waveguide arrays are also set to receive more information.

[0045] According to the concept of this application, any optical waveguide design that can receive reflection information of aerosols at different spatial heights within a certain field of view can achieve the collection of scattered imaging light. The following embodiments are described using a preferred embodiment of an optical fiber.

[0046] Figure 1 FIG. 1 is a schematic structural diagram of a laser radar system for measuring atmospheric aerosols provided by an embodiment of the present invention. Figure 1 As shown, the laser radar system includes a laser emitting component 1, a receiving component 2 and a main control component 3.

[0047] The laser emitting assembly 1 includes a laser 11 and a reflector 12. The reflector 12 is arranged opposite to the laser 11 to reflect the laser radar signal beam emitted by the laser 11 into the atmosphere.

[0048] The receiving component 2 includes a telescope 21, a fiber optic bundle fixture 22, multiple fiber optic bundles 23 and a spectrometer 24. The telescope 21 is used to receive the laser radar signal beam after atmospheric scattering, and the output end of the telescope 21 is used to input the received laser radar signal beam into the multiple fiber optic bundles 23 inserted on the fiber optic bundle fixture 22. The multiple fiber optic bundles 23 are evenly spaced and inserted in the fiber optic bundle fixture 22. Each fiber optic bundle 23 passes through the fiber optic bundle fixture 22, and the top ends of the multiple fiber optic bundles 23 are arranged in a trapezoidal shape in the vertical direction, so that the top ends of the multiple fiber optic bundles 23 are located in sequence at the focal plane of the telescope 21 corresponding to different height distances, and the bottom end of each fiber optic bundle 23 is connected to the spectrometer 24.

[0049] The main control 3 is electrically connected to the optical splitter 24 to perform data analysis and processing on the laser radar signal beam.

[0050] That is to say, when measuring aerosols, the laser radar system provided by the present invention can ensure that the laser radar signal beams scattered and returned at different heights can be received by the optical fiber bundles 23 at different heights when passing through the optical fiber bundle fixture 22, and transmitted together to the spectrometer 24. Finally, the scattered signals received by the spectrometer 24 are analyzed and processed by the main control unit 3 to obtain measurement data of aerosols at different heights.

[0051] It should be noted that the top end surface of the optical fiber bundling fixture 22 can be in different forms such as a flat surface or an inclined surface. This article takes a stepped flat end surface as an example.

[0052] It is easy to understand that since the positions of the real images of the scattered light corresponding to the aerosols at different altitudes in the atmosphere are different, the scattered light is received by the optical fiber bundles 23 at different altitudes.

[0053] It should be noted that the emission and reception of the laser radar signal beam adopt a non-coaxial layout, that is, the emission optical axis of the laser radar signal beam and the optical axis of the telescope 21 are two parallel lines separated by a distance.

[0054] In this embodiment, the main control 3 includes a signal acquisition module and a computer. The signal acquisition module is used to collect signal data received by the spectrometer 24 and transmit the signal data to the computer for data analysis. The signal acquisition module can be a photoelectric detector.

[0055] Figure 2 Schematic diagram of the structure of an optical fiber bundle fixing member provided by an embodiment of the present invention. Figure 2 As shown, in another embodiment of the present invention, the top end face of the optical fiber bundle fixing member 22 is a plurality of step surfaces 222 whose heights decrease successively in the vertical direction, and the plurality of optical fiber bundles 23 correspond one to one with the plurality of step surfaces 222, and each optical fiber bundle 23 is inserted into the corresponding step surface 222.

[0056] Exemplarily, the top surface of the fiber bundle fixture 22 is formed into a trapezoidal shape by a plurality of stepped surfaces 222, with each stepped surface 222 decreasing in height from left to right. The fiber bundles 23 are inserted into each stepped surface 222 of the fiber bundle fixture 22 at intervals, with each stepped surface 222 corresponding to a fiber bundle 23. The top end of each fiber bundle 23 penetrates each stepped surface 222 to receive the LiDAR signal beams scattered by aerosols from different heights. The bottom end of each fiber bundle 23 is electrically connected to a beam splitter 24, which performs optical splitting processing on the scattered LiDAR signal beams of different wavelengths.

[0057] In this embodiment, the number of the stepped surfaces 222 is not less than two.

[0058] In other embodiments of the present disclosure, the number of the stepped surfaces 222 may also be 3 or 4, and the present disclosure is not limited thereto.

[0059] For example, the laser radar signal beam a is a light signal scattered and returned by aerosol at an altitude of 500 meters. After passing through the telescope 21, the laser radar signal beam a is received by the optical fiber bundle 23 in one step surface 222. The laser radar signal beam b is a light signal scattered and returned by aerosol at an altitude of 200 meters. After passing through the telescope 21, the laser radar signal beam b is received by the optical fiber bundle 23 in another step surface 222.

[0060] That is to say, the laser radar signal beams scattered and returned at different heights can all be received by the optical fiber bundles 23 at different heights when passing through the optical fiber bundle fixture 22, and transmitted together to the spectrometer 24. Finally, the main control 3 performs data analysis and processing on the scattered signals received by the spectrometer 24, so as to obtain the measurement data of aerosols at different heights through a single measurement, thereby avoiding the problem of multiple measurements.

[0061] It should be noted that in this embodiment, the width of each step surface 222 of the fiber bundle fixing member 22 in the horizontal direction is slightly larger than the diameter of the fiber bundle 23, so as to prevent the scattered laser radar signal beam from being scattered by the step surface 222 and unable to be received by the fiber bundle 23.

[0062] It should be noted that in addition to the stepped position of the optical fiber bundle relative to the receiving imaging focal plane in the height direction, there is also a certain design for the imaging receiving field of view at different heights. The corresponding height area with a larger imaging spot has a larger designed field of view.

[0063] It should be noted that the specific step surface height parameters or the corresponding field of view size range of the waveguide arrays for receiving light at different heights designed in accordance with the present application can be obtained by using the design and calculation method of geometric optics through parameters such as the focal length of the telescope, the lateral distance from the laser beam to the telescope optical axis, and the laser divergence angle, thereby obtaining the parameter calculations regarding the height, lateral deviation, and field of view size of the fiber bundle. Based on the concept of the present application, the above is a known optical calculation method.

[0064] In this embodiment, the laser radar signal beam emitted by the laser 11 is a multi-wavelength laser radar signal.

[0065] For example, the wavelength of the laser radar signal beam may be 355 mm, 532 mm, or 1064 mm.

[0066] Figure 3 FIG. 1 is a top view of an optical fiber bundle fixing member provided by an embodiment of the present invention, as shown in FIG. Figure 3As shown, in this embodiment, the number of optical fiber bundles 23 in each step surface 222 and the cross-sectional area of ​​the optical fiber bundle 23 increase from high to low in the vertical direction (the lower the step surface 222, the greater the number of optical fiber bundles 23 and the larger the cross-sectional area of ​​the optical fiber bundle 23), and the number of optical fiber bundles 23 in the step surface 222 on the left is always 1.

[0067] It is easy to understand that laser radar signal beams of different wavelengths are emitted parallel to each other (not coaxially), and there is a certain horizontal deviation when they are scattered by aerosols at the same height and imaged by telescope 21 to fiber bundle fixture 22. Therefore, by arranging multiple fiber bundles 23 on the same stepped surface 222, scattered beams of different wavelengths can be received. In other words, the laser radar system provided by the present invention is applicable not only to single-wavelength laser radars, but also to multi-wavelength laser radars.

[0068] For example, the stepped surface 222 on the left is equipped with one optical fiber bundle 23, which corresponds to a single-wavelength laser radar, and the cross-sectional area of ​​the optical fiber bundle 23 is relatively small; while the stepped surface 222 on the right is equipped with three optical fiber bundles 23, which corresponds to a three-wavelength laser radar, and the cross-sectional area of ​​the optical fiber bundle 23 is relatively large. The present invention is not limited to this. In these embodiments, in order to adapt to the different sizes of scattered light imaging at different heights, the optical fiber bundle fields of view at the three stepped surfaces are arranged from small to large, that is, Figure 3 The corresponding fiber bundle field sizes are small, medium, and large from left to right. Figure 3 The same size does not necessarily mean that the field of view designs are the same size.

[0069] It should be noted that the first fiber bundle 23 on the leftmost end is on the optical axis of the telescope 21, and the remaining fiber bundles 23 are all outside the optical axis of the telescope 21 and correspond to real image positions corresponding to different distances from far to near.

[0070] Exemplarily, the optical fiber bundling fixture 22 is arranged opposite to the small hole 211 of the telescope 21 , and the optical fiber bundling fixture 22 is located below the small hole 211 .

[0071] In this embodiment, the beam splitter 24 includes one or more of a convex lens, a filter, and a reflector.

[0072] For example, the laser 11 is a Nd:YAG laser, which can achieve multi-wavelength emission. The telescope 21 is a Cassegrain telescope with an aperture of 400 mm and a focal length of 2000 mm.

[0073] In other embodiments of the present invention, as a replacement and improvement for the commonly used optical fiber bundle 23 components, the optical fiber bundle 23 is mainly changed into a stepped surface 222 type optical waveguide device and a bundled stepped surface 222 type photoelectric detection unit (the expansion of the implementation method is to realize the coupled transmission of light reception, which requires further improvement of the design of the optical waveguide, such as other waveguide elements made of the same material waveguide as the optical fiber bundle 23, or even directly using a photoelectric detection unit).

[0074] In addition, in this embodiment, by adding a polarization component filtering component before the light scattering receiving element at the receiving end and considering the selection of polarization sensing components in the design of the optical waveguide device, more measurement results can be obtained by utilizing the characteristics of optical polarization.

[0075] The following is a brief description of the working principle of this lidar system:

[0076] First, a laser 11 emits a LiDAR signal beam. After being totally reflected by a reflector 12, the LiDAR signal beam enters the atmosphere, interacts with aerosols at different altitudes, and is scattered. The scattered LiDAR signal beams at different altitudes are then received by a telescope 21 and directed into the corresponding fiber bundle 23. Finally, they are transmitted to a beam splitter 24, where the returned LiDAR signal beams of different wavelengths are split and processed. The scattered signals received by the beam splitter 24 are then analyzed and processed by the main control unit 3, resulting in aerosol measurement data at different altitudes.

[0077] It will be easily understood by those skilled in the art that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A laser radar system for measuring atmospheric aerosols, characterized in that: The laser radar system comprises a laser emitting component (1), a receiving component (2) and a main control component (3); The laser emitting assembly (1) comprises a laser (11) and a reflector (12), wherein the reflector (12) is arranged opposite to the laser (11) to reflect the laser beam emitted by the laser (11) into the atmosphere; The receiving assembly (2) includes a telescope (21), an optical fiber bundle fixture (22), a plurality of optical fiber bundles (23) and a spectrometer (24), wherein the telescope (21) is used to receive a laser beam scattered by the atmosphere, and the output end of the telescope (21) is used to inject the received laser radar signal beam into the plurality of optical fiber bundles (23) inserted on the optical fiber bundle fixture (22), the plurality of optical fiber bundles (23) are inserted in the optical fiber bundle fixture (22) at even intervals, each optical fiber bundle (23) passes through the optical fiber bundle fixture (22), and the top ends of the plurality of optical fiber bundles (23) are arranged in a trapezoidal shape in the vertical direction, so that the top ends of the plurality of optical fiber bundles (23) are sequentially located at focal planes of the telescope (21) corresponding to different height distances, and the bottom end of each optical fiber bundle (23) is connected to the spectrometer (24); The main control (3) is electrically connected to the optical splitter (24) to perform data analysis and processing on the laser radar signal beam.

2. The laser radar system for measuring atmospheric aerosols according to claim 1, characterized in that: The top end surface of the optical fiber bundle fixing member (22) is a plurality of stepped surfaces (222) whose heights decrease in sequence in the vertical direction; the plurality of optical fiber bundles (23) correspond to the plurality of stepped surfaces (222) one by one, and each optical fiber bundle (23) is inserted into the corresponding stepped surface (222).

3. The laser radar system for measuring atmospheric aerosols according to claim 2, characterized in that: The number of the stepped surfaces (222) is not less than 2.

4. The laser radar system for measuring atmospheric aerosols according to claim 2, characterized in that: The number of the optical fiber bundles (23) and the cross-sectional area of ​​the optical fiber bundles (23) in each step surface (222) increase sequentially from high to low in the vertical direction.

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