Scanning type multi-view-field aerosol laser radar

Abstract

The invention discloses a scanning type multi-view-field aerosol laser radar. The laser radar comprises a laser, an optical transmitting module, an optical receiving module and an acquisition processing and control module, the optical transmitting module comprises a beam expanding mirror and a laser reflecting mirror; the optical receiving module comprises a Kepler transmission type structure, a rotating wheel disc device arranged on an image space focal plane of the Kepler transmission type structure, a polarization beam splitting cube and a coupling lens; wherein the rotating wheel disc device comprises a rotating wheel disc and a rotating motor, the rotating wheel disc is driven by the rotating motor to adjust the field angle of the Kepler transmission-type structure, a single scattering dominant signal is received at a small field angle, and inversion of the backward scattering efficiency is facilitated; multiple scattering signals are received in a large view field, inversion of a forward scattering phase function is facilitated, and the detection precision of the multi-view-field laser radar is improved.

Description

Technical Field

[0001] The present invention relates to an aerosol laser radar in the technical field of laser radars, and in particular to a scanning multi-field-of-view aerosol laser radar. Background Art

[0002] Aerosol and cloud microphysical parameters (such as extinction coefficient, effective radius, and number concentration) are core parameters for studying atmospheric pollution, cloud microphysical processes, and climate change. The limitations of traditional single-field-of-view (SFOV) lidar systems are mainly reflected in their reliance on a single scattering signal to infer backscattering and extinction coefficients in the atmosphere. However, such an approach often brings uncertainty and requires the use of additional assumptions or models to obtain more accurate results.

[0003] Multiple field of view (MFOV) lidar systems, which collect data from multiple fields of view, have been developed to address these limitations of traditional systems. By simultaneously capturing signals from different fields of view, MFOV lidar can obtain more independent data, thereby improving the inversion accuracy of aerosol and cloud properties.

[0004] Most commercial aerosol radars are single-field-of-view systems, and MFOV radar systems have not yet been commercialized. The main bottlenecks are the high hardware complexity and insufficient algorithm robustness. Summary of the invention

[0005] In order to improve the detection sensitivity of a multi-field-of-view laser radar, the present invention provides a scanning multi-field-of-view aerosol laser radar.

[0006] The present invention is implemented by the following technical scheme: a scanning multi-field-of-view aerosol laser radar, the laser radar comprises a laser, an optical transmitting module, an optical receiving module and an acquisition processing and control module; the laser, the optical transmitting module, the optical receiving module and the acquisition processing and control module are sequentially connected through optical fibers, the optical transmitting module comprises a beam expander and a laser reflector; the beam expander and the laser reflector are sequentially connected through optical fibers; An optical receiving module, the optical receiving module comprising a Kepler transmission structure, a rotating wheel device arranged on the image side focal plane of the Kepler transmission structure, a polarization beam splitter cube and a coupling lens; the Kepler transmission structure, the polarization beam splitter cube and the coupling lens are sequentially connected through an optical fiber; Wherein, the rotating wheel device includes a rotating wheel and a rotating motor, and the rotating wheel is driven by the rotating motor to adjust the field of view angle of the Kepler transmission structure.

[0007] As a further improvement of the above solution, a plurality of pinhole apertures with different apertures are evenly distributed on the circumference of the rotating wheel. The rotating wheel is driven by the rotating motor so that each pinhole aperture is aligned with the focal position of the Kepler transmission structure in turn.

[0008] As a further improvement of the above solution, the rotating motor is electrically connected to the acquisition processing and control module; the rotating wheel device also includes a feedback controller and a limit photoelectric sensor.

[0009] As a further improvement of the above solution, the optical receiving module also includes a narrow-band filter.

[0010] As a further improvement of the above solution, the acquisition processing and control module includes a horizontal polarization signal detector, a vertical polarization signal detector and an acquisition card; the acquisition card is electrically connected to the horizontal polarization signal detector and the vertical polarization signal detector respectively.

[0011] As a further improvement of the above solution, the horizontal polarization signal detector and the vertical polarization signal detector are both PMT single-photon detectors.

[0012] As a further improvement of the above solution, the optical emission module also includes a power monitoring module, and the power monitoring module includes a laser beam sampling mirror and a power monitor; the power monitoring module is connected to the laser through an optical fiber.

[0013] As a further improvement of the above solution, the laser radar includes a scanning platform, which is used to carry the laser, the optical transmitting module, the optical receiving module and the acquisition processing and control module.

[0014] The multi-field-of-view aerosol laser radar of the present invention has the following beneficial effects: In the present application, a laser, an optical transmitting module, an optical receiving module, and an acquisition processing and control module are connected in sequence through optical fibers; the optical receiving module includes a Kepler transmission structure, a rotating wheel device arranged on the image focal plane of the Kepler transmission structure, a polarization beam splitter cube, and a coupling lens; wherein the rotating wheel device includes a rotating wheel and a rotating motor, and the rotating wheel is driven by the rotating motor to adjust the field of view angle of the Kepler transmission structure, and a small field of view angle receives a single scattering dominant signal, which is conducive to accurately inverting the backscattering efficiency; a large field of view receives multiple scattering signals, which is conducive to accurately inverting the forward scattering phase function, thereby improving the detection accuracy of a multi-field-of-view aerosol lidar. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 The figure is a structural block diagram of a multi-field-of-view aerosol lidar according to an embodiment of the present invention.

[0016] The figure numbers are as follows: objective lens 1, eyepiece 2, narrow-band filter 3, polarization beam splitter cube 4, first coupling lens 5, second coupling lens 6, rotating wheel 7, rotating motor 8, horizontal polarization signal detector 9, vertical polarization signal detector 10, laser 11, beam expander 12, first laser reflector 13, second laser reflector 14, laser beam sampling mirror 15, power monitor 16 and scanning gimbal 17. DETAILED DESCRIPTION

[0017] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0018] See also Figure 1 In an embodiment of the present application, a specific structure of a scanning multi-field-of-view aerosol lidar is proposed, which includes a laser, an optical transmitting module, an optical receiving module, and an acquisition processing and control module; the laser, the optical transmitting module, the optical receiving module, and the acquisition processing and control module are connected in sequence through optical fibers.

[0019] The laser 11 is a YAG micro-pulse laser, which is used to generate detection laser.

[0020] The optical transmitting module includes a beam expander 12, a first laser reflecting mirror 13, and a second laser reflecting mirror 14; the beam expander 12 is a 20x beam expander with a compressed divergence angle of <0.1 mrad to ensure that the laser beam diameter of the detection laser matches the field of view of the telescope; the first laser reflecting mirror 13 and the second laser reflecting mirror 14 are used to reflect the collimated laser beam of the detection laser and are installed on an adjustable adjustment frame to facilitate adjustment of the parallelism of the transmitting and receiving optical axes.

[0021] The optical receiving module includes a Kepler transmission structure, a rotating wheel device arranged on the image side focal plane of the Kepler transmission structure, a polarization beam splitting cube 4, a first coupling lens 5 and a second coupling lens 6; the Kepler transmission structure, the polarization beam splitting cube 4 and the first coupling lens 5 are connected in sequence through optical fibers; the Kepler transmission structure, the polarization beam splitting cube 4 and the second coupling lens 6 are also connected in sequence through optical fibers; wherein, the Kepler transmission structure includes an objective lens 1 and an eyepiece 2, the rotating wheel device is arranged on the image side focal plane of the Kepler transmission structure, the rotating wheel device includes a rotating wheel 7 and a rotating motor 8, and the rotating wheel 7 is driven by the rotating motor 8 to adjust the field of view angle of the Kepler transmission structure.

[0022] In one embodiment of the application, the optical receiving module further includes a narrowband filter 3 for filtering out stray light in other bands and background light.

[0023] In one embodiment of the application, the acquisition processing and control module includes a horizontal polarization signal detector, a vertical polarization signal detector and an acquisition card; the acquisition card is electrically connected to the horizontal polarization signal detector and the vertical polarization signal detector respectively.

[0024] Specifically, the Kepler transmission structure collects the echo signal of the detection laser after it is reflected by the atmosphere, and after collimating the echo signal, it passes through a narrowband filter 3 to filter out stray light and background light in other bands, and the polarization beam splitter cube 4 divides the echo signal into two parts with different polarization components. The horizontal polarization signal is coupled to the horizontal polarization signal detector 9 through the first coupling lens 5, and the vertical polarization signal is coupled to the vertical polarization signal detector 10 through the second coupling lens 6; wherein, the horizontal polarization echo signal and the vertical polarization echo signal generate corresponding electrical signals after photoelectric conversion, which are collected by the acquisition card and subsequently processed and analyzed by the digital processor.

[0025] Specifically, the digital processor processing analysis process includes: First, when the field of view of the Kepler transmission structure is a small field of view, the single scattering signal equation of the received single scattering signal is: in, For height The single scattering signal intensity at is the laser emission power; is the system constant; is the extinction coefficient; is the backscattering cross section; is the backscattering efficiency.

[0026] When the field of view of the Kepler transmission structure is a large field of view, the multiple scattering signal equation of the received multiple scattering signal is: in, The field of view interval The multiple scattering signal intensity; is the forward scattering phase function; For height The extinction coefficient at .

[0027] It can be understood that the single scattering signal is not affected by multiple scattering and is suitable for accurately inverting the extinction coefficient and backscattering efficiency of the atmosphere; the difference between multiple scattering signals can accurately invert the forward phase function, and finally the particle size distribution of the atmosphere can be accurately inverted based on the extinction coefficient, backscattering efficiency and forward phase function.

[0028] The laser, optical transmitting module, optical receiving module and acquisition processing and control module in the embodiment of the present application are connected in sequence through optical fibers; the optical receiving module includes a Kepler transmission structure, a rotating wheel device arranged on the image focal plane of the Kepler transmission structure, a polarization beam splitter cube and a coupling lens; wherein the rotating wheel device includes a rotating wheel and a rotating motor, and the rotating wheel is driven by the rotating motor to adjust the field of view of the Kepler transmission structure, wherein when the field of view of the Kepler transmission structure is a small field of view, a single scattering signal is received; when the field of view of the Kepler transmission structure is a large field of view, multiple scattering signals are received; and the single scattering signal is not affected by multiple scattering, and is suitable for accurately inverting the extinction coefficient and backscattering efficiency of the atmosphere, so the small field of view is used to separate the single scattering, and the large field of view inverts the forward phase function through the difference between the multiple scattering signals, and accurately inverts the particle size distribution of the atmosphere according to the extinction coefficient, the backscattering efficiency and the forward phase function.

[0029] Please continue reading Figure 1 In one embodiment of the application, a plurality of small hole apertures with different apertures are evenly distributed on the circumference of the rotating wheel 7. The rotating wheel 7 is driven by the rotating motor 8 so that each small hole aperture is aligned with the focal position of the Kepler transmission structure in turn; illustratively, six stainless steel small hole apertures are evenly distributed on the circumference of the rotating wheel 7, and the apertures are different, corresponding to the full angles of the field of view of 0.5mrad, 1mrad, 4mrad, 8mrad, 16mrad, and 32mrad, respectively.

[0030] Among them, the rotating motor 8 is electrically connected to the acquisition processing and control module; the rotating wheel device also includes a feedback controller and a limit photoelectric sensor; a stepper motor and a Hall sensor with encoder feedback are used to achieve a smaller hole positioning error.

[0031] Specifically, after the detection laser pulse is emitted, it is incident on the atmosphere and interacts with aerosol particles, cloud droplets, etc., and multiple scattering occurs to form echo signals. The echo signals include single echo signals and multiple scattered echo signals. The echo signals are collected by the optical receiving module, among which the single scattered signal is mainly received by a small field of view (0.5~1mrad), and the multiple scattered signals are received by other larger fields of view (4~32mrad). The PMT single-photon detector receives the scattered signals of 6 fields of view in turn, and the acquisition card records the time domain waveform of each field of view. The motor controls the rotation of the rotating wheel. According to the preset positioning, when the field of view angle switches to a certain field of view angle from small to large, the signal at the current field of view angle is collected within the preset time period, and it switches to the next field of view angle after the collection is completed. No signal is collected during the switching process to avoid data confusion.

[0032] In the embodiments of the present application, multi-field-of-view switching is achieved through a single rotating wheel, replacing multiple detectors or spectroscopic systems, which greatly simplifies the hardware complexity of the aerosol lidar.

[0033] In one embodiment of the application, the horizontal polarization signal detector 9 and the vertical polarization signal detector 10 are both PMT single-photon detectors; wherein, the detection laser can use a laser with a wavelength of 532nm; the Mie scattering cross section of the aerosol at a wavelength of 532nm is 30%-50% higher than that of 1.06μm; and the quantum efficiency of the PMT in the PMT single-photon detector at 532nm is >25%, the dark noise is <50Hz, and it supports single-photon counting under micro-pulses (100μJ), and the aerosol scattering signal signal-to-noise ratio (SNR) can be increased to more than 20dB.

[0034] In the embodiment of the present application, the detection laser with a wavelength of 532 nm works synergistically with the PMT single-photon detector to significantly enhance the signal-to-noise ratio of the aerosol scattering signal.

[0035] In one embodiment of the application, the optical transmission module further includes a power monitoring module, and the power monitoring module includes a laser beam sampling mirror 15 and a power monitor 16; wherein, The laser beam sampling mirror 15 samples 1-10% of the laser light from the incident light based on the polarization direction of the incident detection laser light through Fresnel reflection of the uncoated optical surface for power monitoring. The power monitor 16 receives the trace sampled laser beam emitted by the laser beam sampling mirror 15 for monitoring the fluctuation of the laser light power.

[0036] In one embodiment of the application, the laser radar includes a scanning platform 17, and the scanning platform 17 is used to carry a laser, an optical transmitting module, an optical receiving module, and an acquisition processing and control module.

[0037] Specifically, the scanning gimbal 17 is driven by a servo motor, and closed-loop control without cumulative error is achieved through a harmonic reducer and an encoder. In addition, the scanning data of the horizontal azimuth and pitch angles of the scanning gimbal are synchronously collected with the scattering signal, and motion artifacts are eliminated through a spatiotemporal registration algorithm. The three-dimensional extinction coefficient and particle size distribution of aerosols and clouds are obtained through a programmed scanning path, breaking through the limitations of traditional vertical fixed observations.

[0038] In an embodiment of the present application, a scanning device is added to the laser radar, and a single device can replace the traditional multi-site network observation, reducing the hardware deployment cost, which is particularly suitable for urban environmental monitoring networks and field stations.

[0039] The above description is only 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 protection scope of the present invention.

Claims

1. A scanning multi-field-of-view aerosol laser radar, the laser radar comprising a laser, an optical transmitting module, an optical receiving module, and an acquisition processing and control module; the laser, the optical transmitting module, the optical receiving module, and the acquisition processing and control module are sequentially connected by optical fibers, characterized in that: The optical transmitting module comprises a beam expander and a laser reflector; the beam expander and the laser reflector are sequentially connected via an optical fiber; The optical receiving module comprises a Kepler transmission structure, a rotating wheel device arranged on the image side focal plane of the Kepler transmission structure, a polarization beam splitter cube and a coupling lens; the Kepler transmission structure, the polarization beam splitter cube and the coupling lens are sequentially connected through optical fibers; Wherein, the rotating wheel device includes a rotating wheel and a rotating motor, and the rotating wheel is driven by the rotating motor to adjust the field of view angle of the Kepler transmission structure.

2. The scanning multi-field-of-view aerosol laser radar according to claim 1, characterized in that: A plurality of small aperture diaphragms with different apertures are evenly distributed on the circumference of the rotating wheel. The rotating wheel is driven by the rotating motor so that each of the small aperture diaphragms is aligned with the focal position of the Kepler transmission structure in sequence.

3. The scanning multi-field-of-view aerosol laser radar according to claim 1, characterized in that: The rotating motor is electrically connected to the acquisition processing and control module; the rotating wheel device also includes a feedback controller and a limit photoelectric sensor.

4. The scanning multi-field-of-view aerosol laser radar according to claim 1, characterized in that: The optical receiving module further includes a narrowband filter.

5. The scanning multi-field-of-view aerosol laser radar according to claim 1, characterized in that: The acquisition processing and control module comprises a horizontal polarization signal detector, a vertical polarization signal detector and an acquisition card; the acquisition card is electrically connected to the horizontal polarization signal detector and the vertical polarization signal detector respectively.

6. The scanning multi-field-of-view aerosol laser radar according to claim 5, characterized in that: The horizontal polarization signal detector and the vertical polarization signal detector are both PMT single-photon detectors.

7. The scanning multi-field-of-view aerosol laser radar according to claim 1, characterized in that: The optical emission module also includes a power monitoring module, which includes a laser beam sampling mirror and a power monitor; the power monitoring module is connected to the laser through an optical fiber.

8. The scanning multi-field-of-view aerosol laser radar according to claim 1, characterized in that: The laser radar includes a scanning platform, which is used to carry the laser, the optical transmitting module, the optical receiving module and the acquisition processing and control module.

Images