A Greenwood frequency measurement system and method of using the same

Abstract

The invention discloses a Greenwood frequency measurement system and a method for using the same. The measurement system comprises an optical receiving system, an optical imaging system, an image acquisition and analysis system, a turntable and control system and an auxiliary system, wherein the optical receiving system comprises an apodization mirror and an optical telescope; the optical imaging system comprises a lens group and a filter; the image acquisition and analysis system mainly comprises a high frame rate CCD camera, an image acquisition card and a monitor; the turntable and control system comprises a servo system and a control system; the auxiliary system mainly comprises a guide telescope, an attenuation plate and a power supply; when the system is used, it can select the optimal target star by assigning different weights through real-time all-sky star catalog screening, considering information such as the magnitude value, spectral type and coordinate position of the star catalog; at the same time, the equipment selected by the system has a complete control interface, can realize the automation of Greenwood measurement, and has the characteristics of simple and convenient use, high measurement accuracy and high automation.

Description

Technical Field

[0001] The present invention relates to the technical field of atmospheric turbulence measurement, and in particular to a Greenwood frequency measurement system and a use method thereof. Background Art

[0002] Greenwood frequency is a physical quantity that describes the spectrum of atmospheric turbulence. It is an atmospheric turbulence parameter that controls the bandwidth required for closed-loop correction of deformable mirrors in adaptive optical systems. The concept was first proposed by Roddier in 1981 and has since been widely used in the fields of adaptive optics, astronomical optics, atmospheric optics, etc. It always appears together with the atmospheric coherence time.

[0003] The early Greenwood frequency measurement methods mainly used SCIDAR, MASS or sounding balloons to measure atmospheric turbulence profiles, and then combined them with wind profiles to give Greenwood frequency values. Although these methods have clear physical ideas and simple measurement methods, their disadvantages are that the cost of measuring profiles is expensive, especially for wind profile measurements, the measurement height and accuracy are limited, and the balloon trajectory cannot be controlled, resulting in large measurement errors. After adaptive optical systems became more common, Fusco proposed a method in 2004 to calculate the Greenwood frequency by measuring the parameters of the adaptive optical system and the spot parameters. The main problem of this method is that it requires an adaptive optical system, which is inconvenient to use and carry.

[0004] Therefore, it is urgent to design a new Greenwood frequency measurement method and optical system to solve the problems existing in the above-mentioned prior art. Summary of the invention

[0005] In view of the above-mentioned problems, the present invention aims to provide a Greenwood frequency measurement system and a method of using the same. The system is designed to screen the measurement system. When in use, the system can select the optimal target star by assigning different weights through real-time all-sky star catalog screening, taking into account the magnitude, spectral type, coordinate position and other information of the star catalog. At the same time, the equipment selected for the above-mentioned Greenwood frequency measurement system has a complete control interface. As long as the computer program is fully utilized to integrate the entire equipment and multiple tests are carried out, the coordinated operation of each device can be fully controlled to achieve the automation of Greenwood measurement. The system is simple and convenient to use and has high measurement accuracy and automation.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0007] A Greenwood frequency measurement system includes an optical receiving system, an optical imaging system, an image acquisition and analysis system, a turntable and control system, and an auxiliary system, wherein

[0008] The optical receiving system includes an apodization mirror and an optical telescope, which are used to receive light waves emitted by a space target light source or an artificial beacon light source;

[0009] The optical imaging system includes a lens group and a filter for imaging the received light waves;

[0010] The main components of the image acquisition and analysis system are high frame rate CCD camera, image acquisition card and monitor, which are used for light wave image signal acquisition, monitoring and real-time processing;

[0011] The turntable and control system include a servo system and a control system, wherein the servo system is used to automatically track the beacon light source under the control of the control system;

[0012] The auxiliary system is used to provide feedback on the rotation of the servo system under the control of the control system, and mainly includes a guide telescope, an attenuation plate, and a power supply.

[0013] Preferably, in the system optical path of the optical receiving system:

[0014] (1) The telescope has its own ACF, and the system optical path apodization mirror is a parabolic design with an aperture of 356 mm, a center plus obstruction diameter of 150 mm, and a focal length of 3910 mm;

[0015] (2) The plano-convex lens and plano-concave lens used in the optical path have a focal length of 50 mm, a spacing of 0.7 mm, and are placed 93.5 mm in front of the system focus.

[0016] Preferably, the image acquisition and analysis system is a central processing unit, and a CCD control module, a Greenwood frequency calculation module, a telescope control module, a star catalog selection module, an atmosphere module and a monitoring module are built in the image acquisition and analysis system, wherein

[0017] The CCD control module is used to control the high frame rate CCD camera, the primary mirror CCD and the guide star CCD;

[0018] The Greenwood frequency calculation module is completed by PinPoint software, which is used to obtain the fluctuation variance of the ring radius modulated by the apodization mirror by using the image information captured by the primary mirror CCD camera through noise reduction processing, and thus calculate the Greenwood frequency value;

[0019] The telescope control module is completed by ACP software;

[0020] The star catalog selection module converts local geographic coordinates and altitude into celestial coordinates based on the skymap software database and combined with GPS data, so as to select a suitable observation target and notify the main control software ACP of the selection result;

[0021] The data of the atmosphere module comes from the atmospheric parameter detection unit. By using the atmospheric condition parameters and compiling corresponding programs, the water vapor concentration parameters are calculated and transmitted to the main control software ACP.

[0022] The data source of the monitoring module is mainly the guide CCD camera, and its main function is to calculate the offset of the target star image relative to the optical axis and transmit it to the main control software ACP.

[0023] Preferably, the specific control process of the CCD control module includes:

[0024] (1) The control module completes the control of the high frame rate CCD camera through MaxIMDL;

[0025] (2) When the control module controls the primary mirror CCD and the guide star CCD, it needs to be set and identified during initialization;

[0026] (3) The control module is equipped with ASCOM software, which can be used to set the parameters of the guide CCD camera by writing corresponding scripts.

[0027] Preferably, the working principle of the telescope control module includes:

[0028] (1) ACP software is used to read the weather module data and determine whether the telescope has started working;

[0029] (2) Read the GPS data when the telescope starts working and initialize the telescope;

[0030] (3) Reading data from the star catalog selection module and sending instructions to the telescope to enable the telescope to automatically search for stars;

[0031] (4) Finally, data is read from the guide star CCD module to correct the telescope’s pitch and azimuth in real time to achieve precise tracking.

[0032] A method for using a Greenwood frequency measurement system, comprising:

[0033] Step 1: First, use an optical receiving system to receive the light waves emitted by a space target light source or an artificial beacon light source, and after receiving the light waves, use an optical imaging system to focus and image the light waves;

[0034] Step 2: After the image acquisition card of the image acquisition and analysis system is used to acquire the image signal, the Greenwood frequency calculation module of the image acquisition and analysis system is used to calculate and obtain the fluctuation variance of the radius of the circular ring modulated by the apodization mirror, thereby calculating and saving the Greenwood frequency value.

[0035] Preferably, the process of calculating the Greenwood frequency using the Greenwood frequency calculation module in step 2 includes the steps of:

[0036] S1. Derivation of Greenwood frequency f g The calculation formula of

[0037] S2. The Greenwood frequency f is obtained by deriving it in step S1. g On this basis, the fluctuation variance of the ring radius change for a certain number of frames in the image is calculated to invert the Greenwood frequency.

[0038] Preferably, the Greenwood frequency f in step S1 is g The derivation process of the calculation formula includes

[0039] S101. The Greenwood frequency of atmospheric turbulence can be expressed as:

[0040]

[0041] In formula (1), k0 is the wave number, is the zenith angle, C n 2 (h) is the height profile of the refractive index structure constant, V(h) is the atmospheric wind profile;

[0042] The structure function D4(t) of the defocus caused by atmospheric turbulence can be expressed as:

[0043]

[0044] In formula (2), C is a constant related to wavelength λ, telescope aperture d, and central obscuration ε, and is expressed as follows:

[0045]

[0046] S102. When the exposure time is short enough, D4(t) can be expressed as:

[0047]

[0048] In equation (4), r0 is the atmospheric coherence length, and the variance of the defocus value σ is 2 4 is:

[0049]

[0050] S103. When t is much smaller than hour, Combining equation (1) with equation (5), we can get the Greenwood frequency with respect to constant C and defocus variance σ: 2 Function 4:

[0051]

[0052] By measuring the fluctuation variance of the circular spot radius, we can obtain:

[0053]

[0054] From formula (5) and formula (7), we know

[0055]

[0056] In formula (8), σ 2 ρ It is known that substituting equation (8) into equation (6) yields the Greenwood frequency f g .

[0057] Preferably, the inversion process of the Greenwood frequency described in step S2 includes:

[0058] S201. Assume that the exposure time t is much smaller than If this condition is not met, the measurement results will be biased; the telescope measurement aperture is Ф0.36m, the average wind speed is 36m / s, and the exposure time t is less than 10ms;

[0059] S202. The sampling frequency of the measurement system is f, the sample size is N, and the sampling time is set to T = N / f, that is, a Greenwood frequency value is calculated every T time; or the sample size is set to N, that is, a calculation is performed every time N data are collected to obtain and output a Greenwood frequency value; when the system collects without frame loss, fT = N, if it cannot be guaranteed that N frames of data are continuously collected without frame loss, it will lead to fT < N. Therefore, in order to ensure that the data volume is sufficient, the sample size N is selected to set the value of the Greenwood frequency;

[0060] Calculate the radius fluctuation variance σ ρ 2 ,definition:

[0061]

[0062] For the imaging ring, the center of the ring is (Xc, Yc), and we have:

[0063]

[0064] Ring radius ρ:

[0065]

[0066] in

[0067] r l,k 2 =(x l,k -xc ) 2 +(y l,k -y c ) 2 (12)

[0068] The Greenwood frequency is obtained by inverting the measurement result of equation (9).

[0069] The beneficial effects of the present invention are as follows: the present invention discloses a Greenwood frequency measurement system and a method for using the same. Compared with the prior art, the present invention has the following improvements:

[0070] The present invention designs a Greenwood frequency measurement system.

[0071] (1) The annular off-axis spectroscopic technique is used to measure the radius change rate and then analyze the high-order aberrations caused by turbulence, which reduces the measurement errors of the horizontal and vertical axes caused by simple statistics and effectively improves the measurement accuracy of the system;

[0072] (2) Within the foreseeable range of wind speed changes in the Earth's atmosphere, the theoretical derivation is approximated, which effectively reduces the difficulty of system implementation, improves the theoretical measurement rate, and enhances the practicality of the system;

[0073] (3) The optical path and component structure of the system were designed, the imaging quality was analyzed, the technical indicators for engineering implementation were given, and the closed-loop verification of the system was achieved. It has the advantages of being simple and convenient to use, with high measurement accuracy and a high degree of automation. BRIEF DESCRIPTION OF THE DRAWINGS

[0074] Figure 1 The figure is a flow chart of the use of the Greenwood frequency measurement system of the present invention.

[0075] Figure 2 This is a system structure diagram of the Greenwood frequency measurement system of the present invention.

[0076] Figure 3 This is the optical path diagram of the Greenwood frequency measurement system of the present invention.

[0077] Figure 4 This is a light path diagram of the incident wavefront of the Greenwood frequency measurement system of the present invention.

[0078] Figure 5 This is the light intensity distribution diagram of the light spot of the present invention.

[0079] Figure 6 The control link diagram is measured for the present invention. DETAILED DESCRIPTION

[0080] In order to enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0081] Embodiment 1: refer to the attached Figure 1-6 The Greenwood frequency measurement system shown in the figure mainly includes an optical receiving system, an optical imaging system, an image acquisition and analysis system, a turntable and control system, and an auxiliary system.

[0082] The optical receiving system mainly includes an apodization mirror and an optical telescope, which are used to receive light waves emitted by space target light sources or artificial beacon light sources;

[0083] The optical imaging system mainly includes lens groups and filters, etc., which are used to image the received light waves;

[0084] The main components of the image acquisition and analysis system are high frame rate CCD cameras, image acquisition cards and monitors, etc., which are used for light wave image signal acquisition, monitoring and real-time processing;

[0085] The turntable and control system include a servo system and a control system, wherein the servo system is used to automatically track the beacon light source under the control of the control system;

[0086] The auxiliary system is used to provide feedback on the rotation of the servo system under the control of the control system, and mainly includes the guide telescope, attenuation plate, power supply, etc.

[0087] Preferably, the working principle of the Greenwood frequency measurement system includes: after the light source signal is disturbed by atmospheric turbulence, the light signal is received by the annular aperture receiving system (optical receiving system), and then imaged on a photoelectric detector (optical imaging system) after focusing. The image signal is collected by an image acquisition card (image acquisition and analysis system), and then sampled by a data acquisition and processing system to obtain a circular ring with a continuously changing radius. By calculating the fluctuation variance of the circular ring radius change for a certain number of frames in the image, the Greenwood frequency can be inverted to give.

[0088] Preferably, in the system optical path of the optical receiving system:

[0089] (1) The telescope has an ACF (Advanced coma-free optical system), the system optical path apodization mirror is a parabolic design, the aperture is Φ356 mm, the center plus obstruction diameter is 150 mm (i.e., obstruction ratio ε=0.42), and the focal length is 3910 mm;

[0090] (2) The plano-convex lens and plano-concave lens used in the optical path have a focal length of 50 mm, a spacing of 0.7 mm, and are placed 93.5 mm in front of the system focus;

[0091] (3) In this system design, for a standard plane wave with vertical incidence, image sampling is performed at the system focal plane;

[0092] The wavefront was analyzed using ZEMAX software, such as Figure 3 The incident wavefront optical path results of the Greenwood frequency measurement system shown in the Greenwood frequency measurement system optical path diagram are as follows Figure 4 As shown; Figure 5 The simulation gives the light intensity distribution of the bright ring. The ring radius is about 100um, which occupies about 13.6 pixels, taking a CCD camera with a pixel size of 7.4um as an example.

[0093] Preferably, the image acquisition and analysis system is a central processing unit, and a CCD control module, a Greenwood frequency calculation module, a telescope control module, a star catalog selection module, an atmosphere module and a monitoring module are built into the image acquisition and analysis system.

[0094] Preferably, Figure 6 As shown in the measurement control link, the CCD control module is mainly used to control the high frame rate CCD camera, the primary mirror CCD and the guide star CCD, wherein, Figure 2 As shown in the figure, the primary mirror CCD is responsible for precise star tracking; the guide star CCD is responsible for coarse star tracking. The data values ​​of these two CCDs need to be returned to the observatory control program to drive the servo turntable in real time through the serial port to complete the star tracking action. The specific control process of the above modules is as follows:

[0095] (1) The control module mainly controls the high frame rate CCD camera through MaxIMDL and uses the high frame rate CCD to collect image information;

[0096] (2) When the control module is in use, the skymap software calculates the required pitch angle and azimuth according to the local longitude and latitude, altitude and the specific position of the star in the earth coordinate system, and then drives the telescope to rotate. After roughly pointing to the star to be observed, the guide star CCD performs a large-field star search. After manually operating the star image point to the center, the primary mirror CCD is enabled to complete the lock tracking, and the telescope completes the control of the follow-up observation of the star target. When controlling the primary mirror CCD and the guide star CCD, it is necessary to set and identify them during initialization;

[0097] (3) The control module is equipped with ASCOM software. When using it, the corresponding script program can be written to set the parameters of the guide CCD camera, such as gain, exposure time, etc.

[0098] Preferably, the Greenwood frequency calculation module is mainly completed by PinPoint software, which is used to use the image information captured by a high frame rate CCD camera, and obtain the fluctuation variance of the circular ring radius modulated by the apodization mirror through noise reduction and other processing, thereby calculating and saving the Greenwood frequency value.

[0099] Preferably, the telescope control module is mainly implemented by ACP software, and its working principle includes:

[0100] (1) ACP software is used to read the weather module data and determine whether the telescope has started working;

[0101] (2) Read the GPS data when the telescope starts working and initialize the telescope;

[0102] (3) Reading data from the star catalog selection module and sending instructions to the telescope to enable the telescope to automatically search for stars;

[0103] (4) Finally, data is read from the guide star CCD module to correct the telescope’s pitch and azimuth in real time to achieve precise tracking.

[0104] Preferably, the star catalog selection module is mainly based on the skymap software database, combined with GPS data, to convert the local geographic coordinates and altitude into celestial coordinates, so as to select a suitable observation target (the star brightness is higher than 3 magnitude, the elevation angle is greater than 30 degrees, and the angle with the sun is greater than 30 degrees as the judgment conditions), and the selection result is notified to the main control software ACP;

[0105] Preferably, the data of the atmosphere module comes from the atmospheric parameter detection unit (this part belongs to the conventional infrastructure configuration, and the atmospheric parameter detection unit mainly includes a set of 5-element automated ground meteorological stations and temperature and humidity sensors), and uses atmospheric condition parameters (such as temperature, humidity, pressure, wind speed and direction, etc.) to calculate and give parameters such as water vapor concentration by compiling corresponding programs, and transmit them to the main control software ACP.

[0106] Preferably, the data source of the monitoring module is mainly the guide star CCD camera, and its main function is to calculate the offset of the target star image relative to the optical axis and transmit it to the main control software ACP.

[0107] Embodiment 2 is different from Embodiment 1 in that the process of using the Greenwood frequency measurement system to calculate the Greenwood frequency includes:

[0108] Step 1: First, use an optical receiving system to receive the light waves emitted by a space target light source or an artificial beacon light source, and after receiving the light waves, use an optical imaging system to focus and image the light waves;

[0109] Step 2: After the image acquisition card of the image acquisition and analysis system is used to acquire the image signal, the Greenwood frequency calculation module of the image acquisition and analysis system is used to calculate and obtain the fluctuation variance of the radius of the circular ring modulated by the apodization mirror, thereby calculating and saving the Greenwood frequency value.

[0110] Preferably, the process of calculating the Greenwood frequency using the Greenwood frequency calculation module in step 2 includes:

[0111] S1. Derivation of Greenwood frequency f g The calculation formula

[0112] S101. The Greenwood frequency of atmospheric turbulence can be expressed as:

[0113]

[0114] In formula (1), k0 is the wave number, is the zenith angle, C n 2 (h) is the height profile of the refractive index structure constant, V(h) is the atmospheric wind profile;

[0115] The structure function D4(t) of the defocus caused by atmospheric turbulence can be expressed as:

[0116]

[0117] In formula (2), C is a constant related to wavelength λ, telescope aperture d, and central obscuration ε, and is expressed as follows:

[0118]

[0119] S102. When the exposure time is short enough, D4(t) can be expressed as:

[0120]

[0121] In equation (4), r0 is the atmospheric coherence length, and the variance of the defocus value σ is 2 4 can be written as:

[0122]

[0123] S103. When t is much smaller than hour, Combining equation (1) to equation (5), we can get the Greenwood frequency with respect to constant C and defocus variance σ 2 Function 4:

[0124]

[0125] By measuring the fluctuation variance of the circular spot radius, we can obtain:

[0126]

[0127] From formula (5) and formula (7), we can know

[0128]

[0129] In formula (8), σ 2ρ It is known that substituting equation (8) into equation (6) can obtain the Greenwood frequency f g ;

[0130] S2. The Greenwood frequency f is obtained by deriving it in step S1. g Based on this, the fluctuation variance of the ring radius change for a certain number of frames in the image is calculated, and the Greenwood frequency is inverted to give

[0131] S201. In the theoretical derivation of the Greenwood frequency by measuring the variance of the defocus variation of the ring, it is assumed that the exposure time t is much less than If this condition is not met, the measurement results will be biased. For ease of calculation, the telescope measurement aperture can be set to Ф0.36m and the average wind speed to 36m / s, so the exposure time t needs to be less than 10ms. In engineering applications, the exposure time t is selected to be less than 3ms.

[0132] S202. The sampling frequency of the measurement system is f, the sample size is N, and the sampling time is set to T = N / f, that is, a Greenwood frequency value is calculated every T time; or the sample size is set to N, that is, a calculation is performed every time N data are collected to obtain and output a Greenwood frequency value; when the system collects data without frame loss, fT = N. If it cannot be guaranteed that N frames of data are continuously collected without frame loss, fT < N. Therefore, in order to ensure that the data volume is sufficient, the sample size N is preferably used to set the value of the Greenwood frequency;

[0133] Calculate the radius fluctuation variance σ ρ 2 ,definition:

[0134]

[0135] For the imaging ring, the center of the ring is (Xc, Yc), and we have:

[0136]

[0137] Ring radius ρ:

[0138]

[0139] in

[0140] r l,k 2 =(x l,k -x c ) 2 +(y l,k -y c ) 2 (12)

[0141] The Greenwood frequency can be obtained by inverting the measurement result of equation (9).

[0142] The above shows and describes the basic principles, main features and advantages of the present invention. It should be understood by those skilled in the art that the present invention is not limited to the above embodiments, and the above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, which fall within the scope of the present invention to be protected. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. A Greenwood frequency measurement system, characterized in that: It includes optical receiving system, optical imaging system, image acquisition and analysis system, turntable and control system and auxiliary system. The optical receiving system includes an apodization mirror and an optical telescope, which are used to receive light waves emitted by a space target light source or an artificial beacon light source; The optical imaging system includes a lens group and a filter for imaging the received light waves; The main components of the image acquisition and analysis system are high frame rate CCD camera, image acquisition card and monitor, which are used for light wave image signal acquisition, monitoring and real-time processing; The image acquisition and analysis system is a central processing unit, and a CCD control module, a Greenwood frequency calculation module, a telescope control module, a star catalog selection module, an atmosphere module and a monitoring module are built into the image acquisition and analysis system; The CCD control module is used to control the high frame rate CCD camera, the primary mirror CCD and the guide star CCD; The telescope control module is completed by ACP software; The data of the atmosphere module comes from the atmospheric parameter detection unit. By using the atmospheric condition parameters and compiling corresponding programs, the water vapor concentration parameters are calculated and transmitted to the main control software ACP. The data source of the monitoring module is mainly the guide star CCD camera, and its main function is to calculate the offset of the target star image relative to the optical axis and transmit it to the main control software ACP; The turntable and control system include a servo system and a control system, wherein the servo system is used to automatically track the beacon light source under the control of the control system; The auxiliary system is used to provide feedback on the rotation of the servo system under the control of the control system, and mainly includes a guide telescope, an attenuation plate, and a power supply.

2. A Greenwood frequency measurement system according to claim 1, characterized in that: In the system optical path of the optical receiving system: (1) The telescope has its own ACF, and the system optical path apodization mirror is a parabolic design with an aperture of 356 mm, a center plus obstruction diameter of 150 mm, and a focal length of 3910 mm; (2) The plano-convex lens and plano-concave lens used in the optical path have a focal length of 50 mm, a spacing of 0.7 mm, and are placed 93.5 mm in front of the system focus.

3. A Greenwood frequency measurement system according to claim 1, characterized in that: The Greenwood frequency calculation module is completed by PinPoint software, which is used to obtain the fluctuation variance of the ring radius modulated by the apodization mirror by using the image information captured by the primary mirror CCD camera through noise reduction processing, and thus calculate the Greenwood frequency value; The star catalog selection module converts local geographic coordinates and altitude into celestial coordinates based on the skymap software database and combined with GPS data, so as to select a suitable observation target and notify the main control software ACP of the selection result.

4. A Greenwood frequency measurement system according to claim 3, characterized in that: The specific control process of the CCD control module includes: (1) The control module controls the high frame rate CCD camera through MaxIM DL; (2) When the control module controls the primary mirror CCD and the guide star CCD, it needs to be set and identified during initialization; (3) The control module is equipped with ASCOM software, which can be used to set the parameters of the guide CCD camera by writing corresponding scripts.

5. A Greenwood frequency measurement system according to claim 3, characterized in that: The working principle of the telescope control module includes: (1) ACP software is used to read the weather module data and determine whether the telescope has started working; (2) Read the GPS data when the telescope starts working and initialize the telescope; (3) Reading data from the star catalog selection module and sending instructions to the telescope to enable the telescope to automatically search for stars; (4) Finally, data is read from the guide star CCD module to correct the telescope’s pitch and azimuth in real time to achieve precise tracking.

6. A method for using the Greenwood frequency measurement system as claimed in claim 1, characterized in that: include Step 1: First, use an optical receiving system to receive the light waves emitted by a space target light source or an artificial beacon light source, and after receiving the light waves, use an optical imaging system to focus and image the light waves; Step 2: After the image acquisition card of the image acquisition and analysis system is used to acquire the image signal, the Greenwood frequency calculation module of the image acquisition and analysis system is used to calculate and obtain the fluctuation variance of the radius of the circular ring modulated by the apodization mirror, thereby calculating and saving the Greenwood frequency value.

7. The method for using the Greenwood frequency measurement system according to claim 6, characterized in that: The process of calculating the Greenwood frequency using the Greenwood frequency calculation module in step 2 includes the steps of: S1. Derivation of Greenwood frequency f g The calculation formula of S2. The Greenwood frequency f is obtained by deriving it in step S1. g On this basis, the fluctuation variance of the ring radius change for a certain number of frames in the image is calculated to invert the Greenwood frequency.

8. The method for using the Greenwood frequency measurement system according to claim 7, characterized in that: The Greenwood frequency f in step S1 g The derivation process of the calculation formula includes S101. The Greenwood frequency of atmospheric turbulence can be expressed as: In formula (1), k0 is the wave number, is the zenith angle, C n 2 (h) is the height profile of the refractive index structure constant, V(h) is the atmospheric wind profile; The structure function D4(t) of the defocus caused by atmospheric turbulence can be expressed as: In formula (2), C is a constant related to wavelength λ, telescope aperture d, and central obscuration ε, and is expressed as follows: S102. When the exposure time is short enough, D4(t) can be expressed as: In equation (4), r0 is the atmospheric coherence length, and the variance of the defocus value σ is 2 4 is: S103. When t is much smaller than hour, Combining equation (1) with equation (5), we can get the Greenwood frequency with respect to constant C and defocus variance σ: 2 Function 4: By measuring the fluctuation variance of the circular spot radius, we can obtain: From formula (5) and formula (7), we know In formula (8), σ 2 ρ It is known that substituting equation (8) into equation (6) yields the Greenwood frequency f g .

9. The method for using the Greenwood frequency measurement system according to claim 7, characterized in that: The inversion process of the Greenwood frequency described in step S2 includes: S201. Assume that the exposure time t is much smaller than If this condition is not met, the measurement results will be biased; the telescope measurement aperture is Ф0.36m, the average wind speed is 36m / s, and the exposure time t is less than 10ms; S202. The sampling frequency of the measurement system is f, the sample size is N, and the sampling time is set to T = N / f, that is, a Greenwood frequency value is calculated every T time; or the sample size is set to N, that is, a calculation is performed every time N data are collected to obtain and output a Greenwood frequency value; when the system collects data without frame loss, fT = N. If it cannot be guaranteed that N frames of data are continuously collected without frame loss, fT < N. Therefore, in order to ensure that the data volume is sufficient, the sample size N is selected to set the value of the Greenwood frequency; Calculate the radius fluctuation variance σ ρ 2 ,definition: For the imaging ring, the center of the ring is (Xc, Yc), and we have: Ring radius ρ: in r l,k 2 =(x l,k -x c ) 2 +(y l,k -y c ) 2 (12) The Greenwood frequency is obtained by inverting the measurement result of equation (9).

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