A fully static interferometric wind sensor for near-space exploration and a method for vector wind field inversion

Abstract

The present invention relates to a fully static interferometric anemometer for near-space detection and a method for inverting vector wind fields. The interferometric anemometer includes a Michelson interferometer that uses an annular partition-coated mirror as a phase modulation device; the annular partition-coated mirror is formed by coaxially arranging four circular reflective film systems with the same thickness on a glass substrate; at the incident end of the Michelson interferometer, a front conical mirror, a large-aperture doublet lens, and a conical prism are coaxially arranged in sequence along the light incident direction; at the exit end, an imaging camera is arranged along the light exit direction; the light from the near-space airglow layer forms annular parallel light after passing through the front conical mirror and the conical prism and is incident on the interferometer, forming two sets of coherent light beams. The two sets of coherent light beams are incident on the imaging camera to form a circular image for inverting the vector wind; the interferometric anemometer can obtain the vector wind within the observation field of view through one shot, greatly improving the time resolution of wind field detection.

Description

Technical Field

[0001] The present invention relates to the field of near-space wind field detection, and particularly to a fully static interferometric wind sensor and a method for vector wind field inversion. Background Art

[0002] In recent years, the research on the near space (the region of the Earth's atmosphere from 20 to 100 km) has become a research hotspot in the fields of atmosphere and space. The wind field is an important basic state parameter in this region and an important indicator for studying the dynamics, thermodynamics, and climate change of the near space. Implementing high spatio-temporal resolution accurate detection of it can play an important supporting role in evaluating the long-term climate change of the Earth, environmental protection for space operations, etc.

[0003] Among various detection technologies for the near-space wind field, the optical passive remote sensing technology based on a wide-angle Michelson interferometer and the "four-intensity method" has received increasing attention due to its flexible structure and simple observation mode. The core of this technology is to drive the interferometer mirror to move by a piezoelectric ceramic to generate a quarter-wavelength step optical path difference, obtain four interference images, and calculate the Doppler frequency shift of the airglow spectrum in the interference fringes through equivalent Fourier transform calculation, so as to invert the wind speed. With the continuous progress of technology, in recent years, technical means using a static LCOS liquid crystal and a four-quadrant partition-coated mirror to replace the traditional piezoelectric ceramic moving mirror have emerged. However, it is still necessary to take multiple shots and extend the exposure time to obtain a higher signal-to-noise ratio method to achieve wind field measurement. In addition, since the current whole-machine detection requires installing a traditional servo turntable pointing mirror at the top of the instrument to achieve detection of at least 4 different azimuths of the sky, and then calculate and synthesize the vector wind field, the stability and time resolution of the instrument are always greatly limited. Summary of the Invention

[0004] In order to solve the problems existing in the prior art, the present invention provides a fully static interferometric wind sensor that can obtain the vector wind in the observation field of view by taking one shot, greatly improving the time resolution of detection, and a corresponding method for vector wind field inversion.

[0005] To achieve the above object, the technical solution proposed by the present invention is as follows: A fully static interferometric anemometer for near-space detection, comprising a Michelson interferometer. The Michelson interferometer includes a solid beam-splitting prism with a semi-transparent and semi-reflective film inside. After an air gap is spaced from the relative outgoing end of the solid beam-splitting prism, there is an annular partition-coated reflecting mirror. The annular partition-coated reflecting mirror is formed by coaxially stacking four or more circular reflecting film systems with the same thickness on a glass substrate. The areas of the circular reflecting film systems of each layer decrease sequentially in the stacking direction, and the areas of the reflecting surfaces formed by the circular reflecting film systems of each layer are equal; a high-refractive-index glass arm is glued to the relative incident end of the solid beam-splitting prism, and a planar reflective coating is provided at one end of the high-refractive-index glass arm away from the solid beam-splitting prism; at the incident end of the Michelson interferometer, a front conical reflecting mirror, a high-refractive-index optical window, a field stop a, a large-aperture doublet lens, a conical prism, and a field stop b are coaxially arranged in sequence along the light incident direction; at the outgoing end of the Michelson interferometer, a narrow-band interference filter and an imaging camera are arranged in sequence along the light outgoing direction; the light of the near-space airglow layer forms annular parallel light after passing through the front conical reflecting mirror, the high-refractive-index optical window, the field stop a, the large-aperture doublet lens, the conical prism, and the field stop b and is incident on the Michelson interferometer. The Michelson interferometer divides the annular parallel light into two groups of coherent light beams, and the two groups of coherent light beams are incident on the imaging camera to form a circular image for inverting the vector wind.

[0006] A further design of the above technical solution is: The tip of the front conical reflecting mirror is in close contact with the high-refractive-index optical window. The field stop a is located at the intersection of the reflected light of the front conical reflecting mirror. The distance between the field stop a and the large-aperture doublet lens is one focal length of the large-aperture doublet lens. The conical prism is arranged in close contact with the large-aperture doublet lens, and the distance from the conical prism to the planar reflective coating does not exceed one focal length of the large-aperture doublet lens.

[0007] The thickness of the circular reflecting film system is λ λ / 4, λ where λ is the light wavelength. A micro-light trap is provided at the center of the annular partition-coated reflecting mirror near the solid beam-splitting prism, and the area of the micro-light trap is 1 / 10 of the area of the smallest circular reflecting film system.

[0008] The front conical reflecting mirror is ground from glass material, and the surface accuracy is not lower than λ λ / 4. The front conical reflecting mirror is coated with a reflective film system, and the cone angle is 7.5° - 22.5°.

[0009] The high-refractive-index glass arm is made of glass doped with rare earth elements, and the refractive index is 1.9 - 2.2. The transmission and reflection ratios of the semi-transparent and semi-reflective film are 1:1.

[0010] A plane reflector is arranged between the narrow-band interference filter and the imaging camera, and is arranged at an angle of 45° to the direction of the light.

[0011] The imaging camera comprises an imaging lens and a scientific-grade deep-cooling camera which are coaxially arranged in sequence. A CCD sensor chip is arranged inside the scientific-grade deep-cooling camera, and the CCD sensor chip is located on the focal plane of the imaging lens.

[0012] The fully static interferometric wind meter also includes a quartz glass lens barrel arranged around the bottom of the front conical reflector, a light-shielding lens barrel a connected to the quartz glass lens barrel, an interferometer fixed cavity for placing a Michelson interferometer, an electric filter wheel for placing a narrow-band interference filter, a light-shielding lens barrel b for placing a plane reflector, and a light-shielding lens barrel c arranged outside the imaging lens; the light-shielding lens barrel a is arranged at the incident end of the interferometer fixed cavity, and a high refractive index optical window, a field diaphragm a, a large-caliber doublet lens, a conical prism and a field diaphragm b are coaxially arranged on the light-shielding lens barrel a in sequence along the incident direction of light; two outlets of the electric filter wheel are respectively connected to the exit end of the interferometer fixed cavity and the light-shielding lens barrel b, and the light-shielding lens barrel c is connected to the light-shielding lens barrel b.

[0013] The fully static interferometric anemometer also includes an instrument housing, the front conical reflector and the quartz glass lens barrel pass through the top cover of the instrument housing and are located above the top cover of the instrument housing, and the remaining components are located inside the instrument housing; the inner wall of the instrument housing is affixed with a heat insulation layer, a TEC semiconductor air conditioner is provided above the side panel of the instrument housing, and an electronic compass is fixed to the inner wall of the top cover of the instrument housing.

[0014] A vector wind field inversion method comprises the following steps:

[0015] Step 1, performing multi-parameter calibration including effective signal threshold calibration, dark noise image calibration, flat field image calibration, real-time image atmospheric background radiation calibration, image center position calibration and distribution edge pixel value calibration;

[0016] Step 2, using the above-mentioned interferometer to conduct an observation to obtain a circular image;

[0017] Step 3, remove cosmic rays in the circular image by effective signal threshold calibration; remove dark current signals in the circular image by dark noise image calibration; remove vignetting effect at the edge of the circular image by normal image calibration; remove stray signal noise by atmospheric background radiation calibration of real-time image; partition the processed circular image into 8 or 16 compass sectors based on image center position calibration and distribution edge pixel value calibration;

[0018] Step 4, calculate the average intensity of four equal-area areas in each compass sector;

[0019] Step 5: Calculate the radial wind speed within each compass sector using the four-intensity method;

[0020] Step 6: Establish a coordinate system with due north and due east as the positive x-axis and y-axis directions. Let the radial wind speed measured in the i-th compass direction be V i , project this radial wind speed onto the x-axis and y-axis to obtain the components V ix and V iy , as shown in the following formula:

[0021] ;

[0022] where β i is the angle between the i-th compass direction and the x-axis. Then, take the arithmetic mean of i for all compass directions of V ix and V iy to obtain the following formula:

[0023] ;

[0024] Perform the following processing on and to obtain the final wind speed V and wind direction β , thereby obtaining the vector wind for this observation;

[0025] .

[0026] The beneficial effects of the present invention are as follows:

[0027] 1) The all-static interferometric anemometer proposed by the present invention couples a front conical reflector and an annular partition-coated reflector to the main optical structure, making the whole machine have no mechanical moving parts, and the vector wind within the observation field of view can be obtained through a single shot. Compared with the existing equipment that requires at least 4 or even 16 shots to obtain the vector wind, the present invention greatly improves the time resolution of wind field detection and provides a new technical means for the research of small-scale short-period dynamic processes in the near space.

[0028] 2) The present invention uses a front conical reflector as the light-receiving system, replaces the servo turntable pointing mirror and imaging lens in the existing equipment, and designs an optical structure for secondary imaging based on the photometric optical system. Through two optical path foldings of the interferometer and the plane mirror, the overall optical structure is more compact and the volume is reduced, thereby improving the stability and reliability of the instrument during long-term operation.

[0029] 3) The present invention uses an annular partition-coated reflecting mirror as a phase modulation device in a wide-angle Michelson interferometer, and generates an annular parallel light beam by designing a conical prism, thereby coupling the novel wide-angle Michelson interferometer to the entire optical system. Compared with the existing four-partition-coated interferometer, the present invention ensures the large light flux advantage of the Michelson interferometer, can achieve the ability to obtain high signal-to-noise ratio in one shot, and thus improves the detection time resolution.

[0030] 4) The projection of the detection field of view of the present invention in the near-space airglow layer is an annular region, which can be divided into 8 or 16 compass directions. Compared with the traditional device with only 4 detection directions, the synthetic vector wind field of the present invention has higher reliability and more reasonable error evaluation.

[0031] 5) In addition to the main optical structure, the present invention is also equipped with a housing that can achieve constant temperature control, which minimizes the defect that the optical characteristics of the filter change with temperature. At the same time, an industrial control computer and a power supply module are equipped, making the whole machine easier to assemble and operate, not relying on the observation shelter, and having strong field observation adaptability.

[0032] 6) In the wind field inversion process of the present invention, multiple steps only need to be completed with the help of laboratory calibration, without relying on in-aircraft calibration during observation. The actual observation operation is simpler and has higher accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 is a schematic diagram of the main optical structure of the all-static interferometric wind sensor of the present invention;

[0034] Figure 2 is a schematic diagram of the opto-mechanical structure of the all-static interferometric wind sensor of the present invention;

[0035] Figure 3 is a schematic diagram of the three-dimensional overall structure of the all-static interferometric wind sensor of the present invention;

[0036] Figure 4 is a schematic diagram of the working principle of the interferometer based on the annular partition-coated reflecting mirror of the present invention;

[0037] Figure 5 is a front view of the annular partition-coated reflecting mirror;

[0038] Figure 6 is the variation of the optical path difference change amount with the incident angle of the wind sensor of the present invention at different wavelengths;

[0039] Figure 7 is the variation of the optical path difference change amount and the interference fringe visibility with the incident angle of the wind sensor of the present invention;

[0040] Figure 8 is a schematic diagram of the fast wind measurement principle based on the front-mounted conical mirror of the present invention;

[0041] Figure 9 It is a schematic diagram of wind field inversion based on the interference pattern obtained by CCD in the present invention;

[0042] Figure 10 It is a flow chart of the preprocessing of the original image data and wind field inversion in the present invention;

[0043] In the figure: 1 - front conical reflector; 2 - quartz glass barrel; 3 - high refractive index optical window; 4 - field stop a; 5 - light-shielding barrel a; 6 - large-aperture doublet lens; 7 - conical prism; 8 - field stop b; 9 - interferometer fixed cavity; 10 - solid beam splitter prism; 11 - micro optical trap; 12 - mirror support frame; 13 - annular partition coated mirror, 14 - air gap, 15 - semi-transparent and semi-reflective film; 16 - high refractive index glass arm; 17 - plane reflective coating; 18 - electric filter wheel, 19 - narrow-band interference filter; 20 - plane mirror; 21 - light-shielding barrel b; 22 - imaging lens; 23 - light-shielding barrel c; 24 - CCD sensor chip; 25 - scientific-grade deep-cooling camera; 26 - instrument housing; 27 - assembly fixed side plate; 28 - annular fixator; 29 - power module; 30 - industrial computer control module; 31 - waterproof aviation plug; 32 - TEC semiconductor air conditioner; 33 - electronic compass. Specific embodiments

[0044] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0045] Embodiment 1:

[0046] As Figure 1 shown, the all-static interferometric wind sensor for near-space detection in this example includes a Michelson interferometer. The Michelson interferometer includes a solid beam splitter prism 10 with a semi-transparent and semi-reflective film inside. An annular partition coated mirror 13 is provided at an interval with an air gap relative to the outgoing end of the solid beam splitter prism 10. The annular partition coated mirror 13 is formed by coaxially stacking four or more circular reflective film systems with the same thickness on a glass substrate. In this example, four layers are provided. The areas of the circular reflective film systems of each layer decrease in turn along the stacking direction, and the areas of the reflective surfaces formed by the circular reflective film systems of each layer are equal. The reflective surface of the central layer of the annular partition coated mirror 13 is circular, and the reflective surfaces of the remaining layers are annular. The coating area needs to make the areas of each layer of the reflective film system exposed to the light beam equal. A high refractive index glass arm 16 is glued to the incident end of the solid beam splitter prism 10, and a plane reflective coating is provided at one end of the high refractive index glass arm 16 away from the solid beam splitter prism 10.

[0047] At the incident end of the Michelson interferometer, a front - mounted conical reflector 1, a high - refractive - index optical window 3, a field stop a4, a large - aperture doublet lens 6, a conical prism 7, and a field stop b8 are coaxially arranged in sequence along the light incident direction.

[0048] At the exit end of the Michelson interferometer, a narrow - band interference filter 19 and an imaging camera are arranged in sequence along the light exit direction;

[0049] The light from the near - space airglow layer, after passing through the front - mounted conical reflector 1, the high - refractive - index optical window 3, the field stop a4, the large - aperture doublet lens 6, the conical prism 7, and the field stop b8, forms annular parallel light and is incident on the Michelson interferometer. The Michelson interferometer divides the annular parallel light into two groups of coherent light beams, and the two groups of coherent light beams are incident on the imaging camera to form a circular image for inverting the vector wind.

[0050] Embodiment 2:

[0051] As Figure 1As shown in the figure, in the main optical structure of the all-static interferometric wind sensor of this embodiment, a front conical reflector 1 is provided at the top. The front conical reflector 1 is inverted with its tip facing downwards. A quartz glass lens barrel 2 with a thickness of 2 - 5 mm is arranged around its bottom. On the one hand, it is used to support the front conical reflector 1, and on the other hand, it has a high transmittance for light transmission. The tip of the front conical reflector 1 is closely attached to a high-refractive-index optical window 3 arranged coaxially behind it. The high-refractive-index optical window 3 is arranged at the top of the light-shielding lens barrel a5. At the same time, the light-shielding lens barrel a5 and the quartz glass lens barrel 2 are connected by gluing or threading to form an integral support. Subsequently, a field stop a4, a large-aperture doublet lens 6, a conical prism 7, and a field stop b8 are arranged coaxially in the light-shielding lens barrel a5 at a certain distance interval. Among them, the distance between the field stop a4 and the large-aperture doublet lens 6 is one focal length of the large-aperture doublet lens 6, and the conical prism 7 needs to be closely attached to the large-aperture doublet lens 6. An interferometer fixed cavity 9 is arranged below the field stop b8, and a Michelson interferometer body is arranged inside it. In the Michelson interferometer, the solid beam-splitting prism 10 and the semi-reflective and semi-transmissive film 15 inside the solid beam-splitting prism 10 are responsible for the beam-splitting function. At the right end, that is, at one end relative to the light exit end of the interferometer, an annular-zone coated mirror 13 is arranged after an air gap 14 with a certain thickness. The annular-zone coated mirror 13 is fixed to the inner wall of the interferometer fixed cavity 9 through a mirror support frame 12, and a micro-light trap 11 is arranged at the center of the front end of the annular-zone coated mirror 13. At the lower end of the solid beam-splitting prism 10, that is, at one end relative to the light entrance end of the interferometer, a high-refractive-index glass arm 16 is glued. The thickness of the high-refractive-index glass arm 16 needs to meet the conditions of optical path difference, thermodynamics, dispersion compensation, etc. A planar reflective coating 17 is arranged at the end of the high-refractive-index glass arm 16. At the left end of the solid beam-splitting prism 10, that is, at the light exit end, a narrow-band interference filter 19 is arranged, and the narrow-band interference filter 19 is fixed inside an electric filter wheel 18. At the same time, the two outlets of the electric filter wheel 18 are respectively connected to the interferometer fixed cavity 9 and the light-shielding lens barrel b21 through threading. A plane mirror 20 is arranged in the light-shielding lens barrel b21 at an angle of 45° with the optical axis. An imaging lens 22 and a scientific-grade deep-cooling camera 25 are arranged coaxially in sequence at the upper end of the light-shielding lens barrel b21. The two are connected through a lens bayonet, and a light-shielding lens barrel c23 is arranged outside the imaging lens 22 and connected to the light-shielding lens barrel b21. A CCD sensor chip 24 is arranged inside the scientific-grade deep-cooling camera 25 and is located on the focal plane of the imaging lens 22.

[0052] In the main optical structure of the all-static interferometric wind sensor of this embodiment, the front conical reflector 1 is ground from glass material, and the surface accuracy is not lower than λ / 4, λis the light wavelength, and is coated with a silver (or gold) reflective film system, whose cone angle is between 7.5° and 22.5°, replacing the traditional servo turntable pointing mirror to achieve full-static pointing. The function of the high-refractive-index optical window 3 is to perform focusing compensation on light within a wide wavelength band (557 nm to 890 nm), so its refractive index and thickness need to be accurately calculated and selected according to the differences between the long wavelength band and the short wavelength band. The position of the field stop a4 is at the intersection of the reflected light from the front conical mirror 1. The distance from the conical prism 7 to the planar reflective coating 17 does not exceed one focal length of the large-aperture doublet lens 6.

[0053] The overall optical path of the full-static interferometric wind sensor in this embodiment is based on the principle of photometric secondary imaging and adopts two-folded optical paths to reduce the volume of the entire optical structure. After the light emits from the adjacent airglow layer, it enters the high-refractive-index optical window 3 through the reflection of the front conical mirror 1 and converges at the position of the field stop a4, which is also the position of the first imaging; then it is incident on the large-aperture doublet lens 6 in the form of divergent light. Since the distance between the field stop a4 and the large-aperture doublet lens 6 is one focal length of the large-aperture doublet lens 6, after the action of the large-aperture doublet lens 6, the divergent light beam becomes a parallel light beam; through the action of the conical prism 7, the parallel light beam is turned at a certain angle in a conical shape to become an annular parallel light beam, and successively passes through the field stop b8 and the solid beam splitter prism 10 to reach the half-reflective and half-transmissive film 15; the transmission and reflection ratios of the half-reflective and half-transmissive film 15 are 1:1, and the annular parallel light beam is divided into two beams here; the reflected light travels to the right and is reflected again to reach the half-reflective and half-transmissive film 15 after passing through the air gap 14 and the annular partition coated mirror 13. At this time, a part of the light will be transmitted, and this part of the transmitted light will successively pass through the narrowband interference filter 19, the plane mirror 20, and the imaging lens, and thus converge on the CCD sensor chip 24; at the same time, the light transmitted downward through the half-reflective and half-transmissive film 15 successively passes through the high-refractive-index glass arm 16 and the planar reflective coating 17 and then reaches the half-reflective and half-transmissive film 15, and a part of it will be reflected. This part of the reflected light will also successively pass through the narrowband interference filter 19, the plane mirror 20, and the imaging lens, and thus converge on the CCD sensor chip 24; due to the different positions and structures of the annular partition coated mirror 13 and the planar reflective coating 17, the optical path differences of the two groups of light beams split by the half-reflective and half-transmissive film 15 are different. When these two groups of light beams finally converge on the CCD sensor chip 24, an interference effect of light will occur, thereby carrying a lot of physical information of the target light source and forming a circular image by secondary imaging on the CCD sensor chip 24.

[0054] Embodiment Three:

[0055] As Figure 2As shown in the figure, in the opto-mechanical structure of the all-static interferometric anemometer of this embodiment, except for the front conical reflector 1 and the fused silica mirror tube 2, the entire optical main structure is installed inside the instrument housing 26. An opening for the front conical reflector 1 and the fused silica mirror tube 2 to extend out is provided on the top cover of the upper part of the instrument housing 26. The front conical reflector 1 and the fused silica mirror tube 2 all protrude above the top cover of the instrument housing 26, so as to effectively receive the airglow radiation from the sky without being blocked by the instrument housing 26; heat insulation cotton is pasted on the inner wall of the instrument housing 26; the scientific-grade deep-cooling camera 25 is fixed to one side of the assembly fixed side plate 27 through the annular holder 28, and the power module 29 is fixed to the other side of the assembly fixed side plate 27 and connected to the bottom plate of the instrument housing 26; the industrial computer control module 30 is fixed on the bottom plate of the instrument housing 26 and realizes the control function of the entire instrument; the waterproof aviation plug 31 is fixed below the side plate of the instrument housing 26 and is used for externally connecting the power cord and the network data cable; the TEC semiconductor air conditioner 32 is installed above the side plate of the instrument housing 26 and is used to implement temperature control (at 20°C ± 1°C) for the inside of the instrument through the air duct, realizing an approximately constant internal environment, which is beneficial to stabilizing the optical characteristics of the narrowband interference filter 19; the electronic compass 33 is fixed to the inner wall of the outer shell top cover and is used to record the observation azimuth angle for facilitating the later data inversion.

[0056] As Figure 3 shown, the instrument housing 26 is machined by CNC to improve the assembly accuracy, thereby ensuring the reliability and accuracy of the overall observation data.

[0057] As Figure 4 shown, in this embodiment, the Michelson interferometer mode is selected. This interferometer has two perpendicular arms, and each arm needs to experience one reflection and one transmission. After the light beam is converged at the output end, interference will occur. And due to the optical path difference between the two arms, the wavelength information can be obtained through mathematical calculations (such as Fourier transform). In the detection of the airglow layer wind field in the near space, the high-precision spectral detection mode of the interferometer is mainly used to obtain the Doppler frequency shift amount generated by the airglow spectrum due to the wind speed, so as to invert the wind field information. From a theoretical perspective, for a standard sine curve, as long as the intensity values of four points with uniform intervals are sampled within one period, the frequency value can be obtained through Fourier transform. Therefore, it is also called the "four-intensity method". Specifically, a parallel light beam with an original intensity of I 0 passes through the action of the Michelson interferometer, and the light intensity will become I, as shown in the following formula:

[0058]

[0059] where V is the modulation degree, expressed as contains temperature information, T is the atmospheric temperature, is the optical path difference between the two arms of the interferometer. , is the wave number at zero wind speed. M is the molecular weight of the light source component.

[0060] Assuming the interferometer is in a stationary state, its phase can be expressed as:

[0061]

[0062] where is the phase caused by the fixed optical path difference of the interferometer. is the phase caused by the wind speed. is the phase caused by the stepped optical path difference. v is the wind speed in the line-of-sight direction, and the optical path difference is , is the reference optical path difference. is the stepped optical path difference. It is assumed that the stepped optical path difference can start from and increase step by step by λ / 4 four times. That is, the corresponding phase can increase from 0 to 3π / 2 step by step by π / 2 four times, and the intensity of each step can be obtained respectively as:

[0063]

[0064] From equations (3) to (6), it can be obtained that

[0065]

[0066] The wind speed and temperature can be obtained from equations (8) and (9), which is the principle of the "four-intensity method".

[0067] From equations (2) and (9), it can be known that once the final phase is obtained, as long as the fixed optical path difference of the interferometer is known and four accurate stepped optical path differences can be provided precisely, the wind speed can be inverted. Therefore, this embodiment is designed based on the following two aspects: ① How to effectively provide four accurate stepped optical path differences; ② How to accurately design the optical path difference of the interferometer; The specific implementation methods are as follows:

[0068] As Figure 4 shown, a combination of an air gap 14 and an annular partition coated mirror 13 is set in the right arm of the interferometer. The function of the air gap 14 is to provide an optical path with a relatively small refractive index (refractive index ≈ 1.0). The annular partition coated mirror 13 is formed by sequentially coating 4 circular reflection film systems with the same thickness but different areas coaxially on a glass substrate. When measuring the wind with a wavelength λ = 557.7 nm, the thickness needs to be λ / 4 ≈ 139 nm is sufficient. At the same time, the coating area needs to ensure that the area of each layer of the reflective film exposed to the light beam is equal, that is, the area of the reflective surface is equal. For example, Figure 5 in S 1 = S 2 = S 3 = S 4, that is, the radius ratio needs to satisfy , so as to satisfy that when using the "four-intensity method", I 0 in equations (3) to (6) is equal. The reflective film system uses silver plating (visible light) or gold plating (infrared light) materials. In addition, a micro-optical trap 11 needs to be set at the center of the annular partition-coated mirror 13, aiming to absorb the directly incident light beam that cannot form effective interference. Its area size needs to be calculated according to the interference modulation degree. In this embodiment, it is 1 / 10 of the area of the fourth-layer film system, that is, S 4 / 10. The optical flux loss in this part needs to be numerically compensated by mathematical methods in the later inversion. Combining with Figure 1 , when the parallel light beam passes through the action of the conical prism 7, the parallel light beam is turned into a conical shape and deflected by a certain angle to become an annular parallel light. At this time, after the light beam passes through the field stop b8, it will enter the solid beam splitter prism 10 at different angles. After being reflected by the semi-transparent and semi-reflective film 15, it enters the right arm of the interferometer. At this time, the light beams at different angles will be incident on different reflective film systems on the annular partition-coated mirror 13, so as to carry different optical path differences and return to the semi-transparent and semi-reflective film 15 again, preparing for the subsequent interference. Similarly, in this embodiment, more than 4 layers of circular reflective film systems can also be set, and the setting method is the same as that of the above 4 layers, which will not be elaborated here.

[0069] As Figure 4 shown, in the lower arm of the interferometer, the solid beam splitter prism 10 is successively glued with a high-refractive-index glass arm 16 and a planar reflective coating 17. The high-refractive-index glass arm 16 uses glass doped with rare-earth elements, and the refractive index is between 1.9 and 2.2. The purpose is to form a large refractive index difference in the air gap 14 in the right arm, so that a large optical path difference can be achieved without a longer arm length. In addition, the high-refractive-index glass arm 16 is also for achieving the effect of field compensation, so that the trend of the optical path difference change with the incident angle is slowed down. After four different stepped optical path difference modulations at a large optical path difference, the number of fringe changes does not exceed 0.5 - 1.0. Assuming that the refractive index of the high-refractive-index glass arm 16 is n 1, the arm length is a , the refractive index of the air gap 14 is n 2, the arm length is b , then the fixed optical path difference of the interferometer is:

[0070]

[0071] To achieve field-of-view compensation, it is necessary to reduce the variation trend of the optical path difference with the incident angle, that is, the and in Equation (10) should be minimized as much as possible. Since the influence of can be ignored when the incident angle is small, it is only necessary to make

[0072]

[0073] Then the conditions for field-of-view compensation can be met. However, in the actual manufacturing process, no matter how it is selected, Equation (11) cannot be exactly zero, and it can only be made as small as possible.

[0074] As Figure 6 shown, in the case of the variation of the optical path difference with the incident angle at different wavelengths in this embodiment, when the high-refractive-index glass arm 16 is made of Schott BK7 material, a = 4.45 cm, b = 2.95 cm, the calculation results show that when the incident angle does not exceed 6°, the optical path difference variations of 5 common wavelengths do not exceed 0.7 fringes.

[0075] As Figure 7 shown, an interferometer prototype based on an annular-zone-coated mirror is developed using the scheme of this embodiment, and a test system is built using lasers with two wavelengths of 532 nm and 633 nm to measure the variation of the optical path difference phase with the incident angle. Figure 7 The curves shown in (a) are the experimental data and theoretical curves for the 532-nm wavelength, and the experimental data and theoretical curves for the 633-nm wavelength, respectively. The curves show that the optical path difference phase change increases with the increase of the incident angle, but when the incident angle is about 3.5°, the optical path difference phase changes of the two wavelengths do not exceed 0.6. Figure 7 The curves shown in (b) are the visibility values corresponding to the 532-nm and 633-nm wavelengths, respectively. The curves show that the visibility of the interference fringes does not decrease significantly with the increase of the angle, and is all above 0.14. The test results show that the optical path difference phase change and the visibility of the interference fringes are basically consistent with the design and calculation results, meeting the application requirements.

[0076] As Figure 8 shown, in this embodiment, the instrument is placed on the ground, and the airglow layer is generally located at an altitude of 85 - 100 km above the instrument. The weak light beam emitted in its natural state will enter the instrument. Due to the function of the front conical mirror 1, after passing through the optical system of the instrument, the circular image obtained on the CCD sensor chip 24 is projected onto the airglow layer as an annular region, and each different circular sub-region in the annular region (such as A W 、A S 、A N 、AE The light emitted by (such as) passes through the front - placed conical reflecting mirror 1 and the overall instrument, and will form a one - to - one correspondence with the fan - shaped regions at different angles of the CCD sensor chip 24. That is, the circular sub - regions at a unique position in the sky correspond to the fan - shaped regions at a unique angle of the CCD sensor chip 24. That is, all - space - azimuth spectral information can be obtained in one detection. However, traditional instruments of this type all use a servo turntable pointing mirror, with a very small field of view. Each time a photograph is taken, the turntable needs to be used to adjust the pointing mirror to point to four different directions respectively, and there are great limitations in light - intensity utilization rate and time resolution. Since the present invention adopts the front - placed conical reflecting mirror 1 and the principle of secondary imaging optical path, replacing the servo turntable pointing mirror, it realizes the simultaneous, synchronous and full - static detection of different regions of the airglow layer.

[0077] Such as Figure 9 shown, in the schematic diagram of wind - field inversion for the interference pattern obtained in this embodiment, in order to improve the image signal - to - noise ratio and ensure the diversity of directions at the same time, the circular - ring region of the instrument's field - of - view projected on the airglow layer is divided into 8 (16 when necessary) compass directions, each region occupying 45°. Correspondingly, the circular image detected by the CCD sensor chip 24 is also divided into 8 fan - shaped regions. Figure 9 The left figure in is the projection of the instrument's observation field - of - view in the sky, and the right figure is the captured image obtained by the CCD sensor chip 24. Taking the S direction in the figure as an example, the airglow light radiation emitted within the 45° circular - ring segment of the S region projected on the airglow layer, after being modulated by the interferometer in the instrument, within the 45° fan - shaped region of the S area in the obtained image, 4 different light intensities carrying 4 different optical - path - difference information are respectively imaged into S 1 ’ 、 S 2 ’ 、 S 3 ’ 、 S 4 ’ inside. Since the areas of the 4 regions are equal, therefore, the average signal intensity of each region I s-1 、 I s-2 、 I s-3 、 I s-4 can directly replace I s-1 、 I s-2 、 I s-3 、 I s-4 in formula (9), so as to calculate the phase change caused by the Doppler frequency shift and obtain the radial wind speed in the S direction V r-s .

[0078] In the schematic diagram of wind field inversion in this embodiment, it is also necessary to assume that the temperature and wind field (wind speed and wind direction) are consistent within the circular ring area of the airglow layer projection. The all-static interferometric wind sensor of the present invention measures the line-of-sight wind speed in the direction of twice the cone angle of the front conical mirror 1, that is, the radial wind speed. In the later inversion, it is necessary to project the radial wind speed onto the horizontal plane to obtain the horizontal component.

[0079] Embodiment 4:

[0080] The flowchart of the method for wind field inversion based on the interference pattern obtained in the above embodiment is as follows Figure 10 As shown, before the start of the observation, it is necessary to perform multi-parameter calibration in the laboratory, including effective signal threshold calibration, dark noise image calibration, flat field image calibration, real-time image atmospheric background radiation calibration, image center position calibration, and distribution edge pixel value calibration. In actual observation, each detection will obtain an original image. Then, the cosmic rays in the image are removed by means of effective signal threshold calibration. A single threshold can be used for removal during the process, or the image can be divided into sliding blocks, and the threshold is calibrated separately for each sub-region and then removed; Next, the dark current signal in the image is removed by means of dark noise image calibration; Next, the flat field coefficient of each pixel is calculated by means of flat field image calibration, and then the coefficient is multiplied by the original image to remove the vignetting effect at the edge of the image; Next, the real-time image atmospheric background radiation calibration is used, which belongs to a unified stray signal noise of the entire image and needs to be removed from the original image; Then, based on the image center position calibration and the distribution edge pixel value calibration, the processed image is processed into 8 (or 16) compass partitions, and then the average intensity of 4 equal-area regions within each compass sector partition is calculated; The radial wind speed within each compass sector partition is calculated by using the "four-intensity method" of formulas (2), (7), and (9); Further, let the radial wind speed measured in the i-th compass direction be V i , it is necessary to project it onto the x-axis (due north N direction) and y-axis (due east E direction) to obtain the components V ix and V iy , as shown in the following formula:

[0081]

[0082] where β i is the angle between the i th compass direction and the x-axis (due north N direction), and then for all compass directions of V ix and V iy take the arithmetic mean to obtain the following formula:

[0083]

[0084] Then, perform the following processing on and to obtain the final wind speed V and wind direction β ,

[0085]

[0086] After calculating the vector wind of this observation and combining it with the signal-to-noise ratio, standard deviation, etc., calculate the wind speed measurement error, thereby completing the wind field inversion process of one observation.

[0087] The technical solution of the present invention is not limited to the above embodiments, and all technical solutions obtained by equivalent replacement fall within the scope of protection required by the present invention.

Claims

1. A fully static interferometric anemometer for near-space detection, characterized in that: It comprises a Michelson interferometer, which comprises a solid beam splitter prism with a semi-reflective and semi-transparent film inside, and an annular partitioned coated reflector is arranged behind the solid beam splitter prism with an air gap relative to the output end, and the annular partitioned coated reflector is formed by coaxially stacking four or more circular reflective film systems with the same thickness on a glass substrate, and the area of ​​each circular reflective film system decreases in sequence along the stacking direction, and the area of ​​the reflective surface formed by each circular reflective film system is equal; a high refractive index glass arm is glued to the incident end of the solid beam splitter prism, and a plane reflective coating is arranged at one end of the high refractive index glass arm away from the solid beam splitter prism; The incident end of the Michelson interferometer is coaxially provided with a front conical reflector, a high refractive index optical window, a field stop a, a large-aperture double cemented lens, a conical prism and a field stop b in sequence along the incident direction of the light; The output end of the Michelson interferometer is provided with a narrow-band interference filter and an imaging camera in sequence along the light output direction; The light from the near-space airglow layer passes through the front conical reflector, high-refractive-index optical window, field aperture a, large-aperture double-cemented lens, conical prism and field aperture b to form annular parallel light that is incident on the Michelson interferometer. The Michelson interferometer divides the annular parallel light into two groups of coherent light beams. The two groups of coherent light beams are incident on the imaging camera to form a circular image for inverting vector wind.

2. The fully static interferometric anemometer for near-space detection according to claim 1, characterized in that: The tip of the front conical reflector is in close contact with the high refractive index optical window, the field stop a is located at the intersection of the light reflected by the front conical reflector, the distance between the field stop a and the large-aperture double-cemented lens is one times the focal length of the large-aperture double-cemented lens, the conical prism is in close contact with the large-aperture double-cemented lens, and the distance from the conical prism to the plane reflective coating does not exceed one times the focal length of the large-aperture double-cemented lens.

3. The fully static interferometric anemometer for near-space detection according to claim 2, characterized in that: The thickness of the circular reflective film system is λ / 4, λ is the wavelength of light, and a micro light trap is provided at the center of one end of the annular partitioned coated reflector close to the solid beam splitter prism, and the area of ​​the micro light trap is 1 / 10 of the area of ​​the minimum circular reflective film system.

4. The fully static interferometric anemometer for near-space detection according to claim 3, characterized in that: The front conical reflector is made of ground glass, and the surface accuracy is not less than λ / 4, the front conical reflector is coated with a reflective film system, and the cone angle is 7.5°~22.5°.

5. The fully static interferometric anemometer for near-space detection according to claim 4, characterized in that: The high refractive index glass arm is made of glass doped with rare earth elements, and has a refractive index of 1.9-2.

2. The transmission and reflection ratio of the semi-reflective and semi-transparent membrane is 1:

1.

6. The fully static interferometric anemometer for near space detection according to any one of claims 1 to 5, characterized in that: A plane reflector is arranged between the narrow-band interference filter and the imaging camera, and is arranged at an angle of 45° to the direction of the light.

7. The fully static interferometric anemometer for near-space detection according to claim 6, characterized in that: The imaging camera comprises an imaging lens and a scientific-grade deep-cooling camera which are coaxially arranged in sequence. A CCD sensor chip is arranged inside the scientific-grade deep-cooling camera, and the CCD sensor chip is located on the focal plane of the imaging lens.

8. The fully static interferometric anemometer for near-space detection according to claim 7, characterized in that: It also includes a quartz glass lens barrel arranged around the bottom of the front conical reflector, a light-shielding lens barrel a connected to the quartz glass lens barrel, an interferometer fixing cavity for placing a Michelson interferometer, an electric filter wheel for placing a narrow-band interference filter, a light-shielding lens barrel b for placing a plane reflector, and a light-shielding lens barrel c arranged outside the imaging lens; The shading lens barrel a is arranged at the incident end of the interferometer fixed cavity, and the high refractive index optical window, the field aperture a, the large-aperture double glued lens, the conical prism and the field aperture b are coaxially arranged on the shading lens barrel a in sequence along the incident direction of the light; the two outlets of the electric filter wheel are respectively connected to the exit end of the interferometer fixed cavity and the shading lens barrel b, and the shading lens barrel c is connected to the shading lens barrel b.

9. The fully static interferometric anemometer for near-space detection according to claim 8, characterized in that: The instrument also includes an instrument housing, wherein the front conical reflector and the quartz glass lens barrel pass through the top cover of the instrument housing and are located above the top cover of the instrument housing, and the remaining components are located inside the instrument housing; The inner wall of the instrument shell is affixed with a heat insulation layer, a TEC semiconductor air conditioner is arranged above the side plate of the instrument shell, and an electronic compass is fixed on the inner wall of the top cover of the instrument shell.

10. A vector wind field inversion method, characterized in that: The steps include: Step 1, performing multi-parameter calibration including effective signal threshold calibration, dark noise image calibration, flat field image calibration, real-time image atmospheric background radiation calibration, image center position calibration and distribution edge pixel value calibration; Step 2, using the interferometer wind meter described in claim 9 to perform an observation to obtain a circular image; Step 3, remove cosmic rays in the circular image by effective signal threshold calibration; remove dark current signals in the circular image by dark noise image calibration; remove vignetting effect at the edge of the circular image by normal image calibration; remove stray signal noise by atmospheric background radiation calibration of real-time image; partition the processed circular image into 8 or 16 compass sectors based on image center position calibration and distribution edge pixel value calibration; Step 4, calculate the average intensity of four equal-area areas in each compass sector; Step 5: Calculate the radial wind speed in each compass sector using the four-intensity method; Step 6: Establish a coordinate system with due north and due east as the x-axis and the positive y-axis, and let the radial wind speed measured in the i-th compass direction be V i , project the radial wind speed onto the x-axis and y-axis to obtain the components V ix and V iy , as shown below: ； in, β i For the i The angle between the compass direction and the x-axis, and then for all compass directions V ix and V iy Taking the arithmetic mean, we get the following formula: ； right and Perform the following processing to get the final wind speed V and wind direction β , thus obtaining the vector wind of this observation; 。

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