CN112229607B - Device and method for measuring far-field beam expansion and scintillation characteristics in turbulent atmosphere - Google Patents
Device and method for measuring far-field beam expansion and scintillation characteristics in turbulent atmosphere Download PDFInfo
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Abstract
The invention discloses a device and a method for measuring far-field beam expansion and scintillation characteristics in turbulent atmosphere. The optical emission unit comprises an emission end laser light source, and an electric control diaphragm a is arranged on the emission side of the emission end laser light source. The optical receiving unit comprises a CCD camera, the CCD camera is arranged on one side, away from the laser light source of the transmitting end, of the electric control diaphragm a, the electric control diaphragm b is arranged on one side, away from the electric control diaphragm a, of the CCD camera, the receiving antenna is arranged on one side, away from the CCD camera, of the electric control diaphragm b, the beam waist radii of the two electric control diaphragms can be measured under different conditions (near field and far field), and the beam divergence angle is used for directly calculating the beam divergence angle variable quantity caused by atmospheric turbulence. The fluctuation of the arrival angle can be synchronously calculated by measuring the diameter change of the light spot on the CCD to reflect different conditions; meanwhile, the data measured by the CCD is utilized to obtain the voltage of a measuring signal, and the light intensity flicker coefficient is further solved.
Description
Technical Field
The invention belongs to the technical field of photoelectric measurement, and particularly relates to a novel method for measuring beam divergence angle and arrival angle fluctuation caused by atmospheric turbulence.
Background
The laser is widely applied to modern life scenes, such as communication, material processing, medical treatment, remote sensing, distance measurement, aerospace industry and the like, and is also widely applied to the fields of laser communication, laser radar, laser distance measurement, laser guidance, photoelectric tracking and the like. The detection of laser performance parameters also has direct influence on the development of the laser, and is also an important index for evaluating the quality of a laser device. The importance of accurate metrology of beam quality to accurately assess laser performance in a system is self-evident.
The beam divergence angle can reflect the divergence characteristic of laser in long-distance transmission, and the quality of the related laser instrument and the transmission quality of the laser can be accurately evaluated. The increase in laser spot diameter with propagation distance is called beam divergence, and the degree of divergence is measured by the size of the beam divergence angle. The beam divergence angle measurement method is various, wherein the focal spot method and the slit scanning method are suitable for near-field measurement and have low precision; the threshold value method and the multi-element lens method are suitable for measuring a far field with a large divergence angle, but the precision error is too large; the trepanning method is suitable for near-field measurement, but is difficult to operate practically; the aperture method and the moving knife edge method have higher requirements on the characteristics of laser beams, and only part of laser beams can be measured; the parallel flat-crystal interference method is suitable for near-field measurement, but the cost of required devices and materials is relatively high, and the structure is relatively complex; the CCD method is suitable for far-field measurement, but the device is relatively complex, the price is relatively high, and the like. In the prior art, the beam divergence angle is mainly calculated by measuring a light spot image, and the beam divergence angle variable quantity caused by atmospheric turbulence under the conditions of a near field and a far field cannot be intuitively measured and calculated. Aiming at the problems of high complexity and few direct calculation (caused by atmospheric turbulence) of beam divergence angle variation of the traditional method, the invention adopts two electric control diaphragms to complete the measurement of beam waist radius of the light beam, and then calculates the beam divergence angle variation by a formula, thereby reducing the calculation complexity and solving the problem of beam divergence angle variation measurement in an atmospheric turbulence channel.
The fluctuation of the arrival angle is a main factor causing tracking errors of wireless optical communication. When laser beams propagate in atmospheric turbulence, because the atmospheric refractive indexes at different positions in beam sections fluctuate, different phase shifts exist at different positions of beam wavefronts, and the phase fluctuation causes the beam wavefronts to have distortion, so that the integral wavefront inclination angle at the front end of a receiving aperture changes, image points in a telescope are jittered, and the arrival angle fluctuates. And measuring the statistical variation of the fluctuation of the arrival angle, and reflecting the variation condition of the atmospheric refractive index structural constant. Flicker is also a common problem in turbulence effect, and light intensity flicker has important influence on laser atmospheric detection, measurement of atmospheric parameters, wave front detection of Hartmann sensors in adaptive optics, atmospheric laser communication and the like. In the prior art, the fluctuation measurement of the arrival angle is mainly calculated by using the position size change of a light spot on a CCD. The invention aims at the problem of measuring the fluctuation of the arrival angle through the position of the light spot in the prior art, changes the receiving structure, calculates the fluctuation of the arrival angle through the radius change of the light spot, solves the problem of measuring the fluctuation of the arrival angle in an atmospheric turbulence channel, and simultaneously obtains the measured signal voltage through a data processing module by using the data measured by a CCD (charge coupled device) while measuring the fluctuation of the arrival angle, thereby solving the light intensity flicker coefficient.
Disclosure of Invention
The invention aims to provide a device for measuring far-field beam expansion and scintillation characteristics in turbulent atmosphere, which is used for measuring far-field beam characteristics in an atmosphere turbulence channel. The far-field beam spread angle variation and scintillation characteristics caused by atmospheric turbulence are mainly measured.
Another object of the present invention is to provide a method for measuring far-field beam expansion and scintillation characteristics in turbulent atmosphere
The technical scheme adopted by the invention is that the device for measuring far-field beam expansion and scintillation characteristics in turbulent atmosphere comprises an optical transmitting unit, an optical receiving unit and a data processing unit.
The invention is also characterized in that:
the optical emission unit comprises an emission end laser light source, and an electric control diaphragm a is arranged on the emission side of the emission end laser light source.
The optical receiving unit comprises a CCD camera, the CCD camera is arranged on one side, away from the laser light source of the transmitting end, of the electric control diaphragm a, the electric control diaphragm b is arranged on one side, away from the electric control diaphragm a, of the CCD camera, and a receiving antenna is arranged on one side, away from the CCD camera, of the electric control diaphragm b.
The center points of the transmitting end laser light source and the CCD camera are on the same optical axis.
The electric control diaphragm a and the electric control diaphragm b are on the same optical axis with the laser light source at the transmitting end.
The CCD camera frame is 20Hz, the resolution is 160031200, and the pixel size is 4.434.5 μm.
The data processing unit comprises a data preprocessing module, an A/D conversion module, an image processing module and a display module.
A method for measuring far-field beam expansion and scintillation characteristics in turbulent atmosphere adopts a device for measuring far-field beam expansion and scintillation characteristics in turbulent atmosphere, and is implemented according to the following steps:
step 1: opening a laser light source at an emitting end to enable laser beams to pass through an electric control diaphragm a;
and 2, step: the light beam reaches a receiving end through an atmospheric channel, and the beam waist radius of the light beam is measured at an electric control diaphragm b of the receiving end;
and 3, step 3: after reaching the receiving and reflecting antenna device, reflecting the light beam into the CCD camera, processing the recorded light spot image on the CCD target surface, identifying the image by using a light spot center positioning algorithm, and recording the circle center and the radius;
and 4, step 4: calculating the variation of the beam divergence angle caused by the atmospheric turbulence;
and 5: and calculating the flicker index according to the principle that the signal voltage U is in direct proportion to the incident signal light intensity I.
The method for calculating the beam divergence angle variation specifically comprises the following steps:
and adjusting the aperture of the variable diaphragm, wherein when the energy value of a light beam passing through the diaphragm is 80% of the total energy value, the corresponding diaphragm diameter is the diameter of a laser beam spot, and the divergence angle value of the laser beam can be further calculated. D1(6)、D2(7) The beam waist diameters measured by the two electric control diaphragms are respectively, the distance between the two electric control diaphragms is L (9), and theta is a beam divergence angle; defining the far field divergence angle of the Gaussian beam according to the formula:
wherein, lambda light beam wavelength, n is medium refractive index, and D is beam waist radius.
By measuring the beam divergence angles of the two electric control diaphragms, the beam divergence angles of the sending end and the receiving end can be respectively calculated, and the beam divergence of the light beam can be increased along with the increase of the distance in the atmospheric propagation. Thus, the beam spread angle θ obtained at the end1Minus the originating beam divergence angle theta2The beam divergence angle change amount Δ θ caused by the atmospheric turbulence can be finally obtained.
The calculation method of the flicker index specifically comprises the following steps:
the diameter change of the light spot on the CCD can reflect fluctuation of the arrival angle, the image is identified by using a light spot center positioning algorithm to find out the circle center and the radius, and then the corresponding arrival angle alpha can be calculated by using the light spot radius change quantity delta x, the pixel size p and the receiving antenna focal length f. The calculation formula is as follows:
the ideal spot radius is r1The spot radius of the turbulent flow is r2So that Δ x ═ r2-r1The above formula can be written as:
index of scintillation
The ratio of the light intensity fluctuation variance to the light intensity mean square is as follows:
wherein < > represents a statistical average; the I represents the random light intensity of the light beam, the measured value in actual work is a voltage signal, the signal voltage U is in direct proportion to the incident signal light intensity I, and the flicker index is obtained through calculation by the formula.
The invention has the advantages that
Firstly, two electric control diaphragms can be used for measuring the beam waist radius under different conditions (near field and far field), and the beam divergence angle is used for directly calculating the beam divergence angle variation caused by the atmospheric turbulence.
Secondly, the fluctuation of the arrival angle can be synchronously calculated by measuring the diameter change of the light spot on the CCD to reflect different conditions (ideal conditions and turbulent flow conditions); meanwhile, the data measured by the CCD is utilized to obtain the voltage of a measuring signal, and the light intensity flicker coefficient is further solved.
Drawings
FIG. 1 is a schematic diagram of the main structure of the measuring device of the present invention;
FIG. 2 is a schematic view of a module connection of the measuring device of the present invention;
FIG. 3 is a schematic view of CCD light spot imaging of the measuring device of the present invention;
fig. 4 is a simplified measurement flow chart of the measurement method of the present invention.
In the figure, 1 is a laser light source at the transmitting end, 2 is an electric control diaphragm a, 3 is an electric control diaphragm b, 4 is a receiving antenna, 5 is a CCD camera, and 6 is a beam width measuring device of the electric control diaphragm at the transmitting end 17, measuring beam width D by electric control diaphragm at receiving end 28, beam divergence angle theta, 9, two electric control diaphragm spacing, 10, computer display end, 11, light emitting unit, 12, light receiving unit, 13, data processing display unit, 14, ideal light spot radius r1And 15. spot radius r for turbulent conditions2。
Detailed Description
The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.
The device for measuring far-field beam expansion and scintillation characteristics in turbulent atmosphere comprises an optical transmitting unit 11, an optical receiving unit 12 and a data processing unit 13.
The optical emission unit 11 includes an emission-end laser light source 1, and an emission side of the emission-end laser light source 1 is provided with an electrically controlled diaphragm a 2.
The optical receiving unit 12 comprises a CCD camera 5, the CCD camera 5 is arranged on one side of the electric control diaphragm a2 far away from the transmitting end laser light source 1, one side of the CCD camera 5 far away from the electric control diaphragm a2 is provided with an electric control diaphragm b3, and one side of the electric control diaphragm b3 far away from the CCD camera 5 is provided with a receiving antenna 4.
The central points of the transmitting end laser light source 1 and the CCD camera 5 are on the same optical axis.
The electric control diaphragm a2 and the electric control diaphragm b3 are on the same optical axis with the emission end laser light source 1.
The CCD camera frame is 20Hz, the resolution is 160031200, and the pixel size is 4.434.5 μm.
The data processing unit 13 includes a data preprocessing module, an a/D conversion module, an image processing module, and a display module.
A method for measuring far-field beam expansion and scintillation characteristics in turbulent atmosphere adopts a device for measuring the far-field beam expansion and scintillation characteristics in turbulent atmosphere, and if 4 is shown, the method is implemented according to the following steps:
step 1: opening the laser light source 1 at the transmitting end to enable the laser beam to pass through the electric control diaphragm a 2;
step 2: the light beam reaches a receiving end through an atmospheric channel, and the beam waist radius of the light beam is measured at an electric control diaphragm b (3) of the receiving end;
and step 3: after reaching the receiving and reflecting antenna device 4, the light beam is reflected to the CCD camera 5, the recorded light spot image on the CCD target surface is processed, the image is identified by using a light spot center positioning algorithm, and the circle center and the radius are recorded;
and 4, step 4: calculating the variation of the beam divergence angle caused by the atmospheric turbulence;
and 5: and calculating the flicker index according to the principle that the signal voltage U is in direct proportion to the incident signal light intensity I.
The method for calculating the beam divergence angle variation specifically comprises the following steps:
and adjusting the aperture of the variable diaphragm, wherein when the energy value of the light beam passing through the diaphragm is 80% of the total energy value, the corresponding diaphragm diameter is the diameter of the laser beam spot, and the divergence angle value of the laser beam can be further calculated. D1(6)、D2(7) The beam waist diameters measured by the two electric control diaphragms are respectively, the distance between the two electric control diaphragms is L (9), and theta is a light beam divergence angle; defining the far field divergence angle of the Gaussian beam according to the formula:
wherein, lambda light beam wavelength, n is medium refractive index, and D is beam waist radius.
By measuring the beam divergence angles of the two electric control diaphragms, the beam divergence angles of the sending end and the receiving end can be respectively calculated, and the beam divergence of the light beam can be increased along with the increase of the distance in the atmospheric propagation. Thus, the beam spread angle θ obtained at the end1Minus the originating beam divergence angle theta2The beam divergence angle change amount Δ θ caused by the atmospheric turbulence can be finally obtained.
The calculation method of the flicker index specifically comprises the following steps:
the diameter change of the light spot on the CCD can reflect fluctuation of the arrival angle, the image is identified by using a light spot center positioning algorithm to find out the circle center and the radius, and then the corresponding arrival angle alpha can be calculated by using the light spot radius change quantity delta x, the pixel size p and the receiving antenna focal length f. The calculation formula is as follows:
the ideal spot radius is r1The spot radius of the turbulent flow is r2So that Δ x ═ r2-r1The above formula can be written as:
index of scintillation
The ratio of the light intensity fluctuation variance to the light intensity mean square is as follows:
wherein < > represents a statistical average; the I represents the random light intensity of the light beam, the measured value in actual work is a voltage signal, the signal voltage U is in direct proportion to the incident signal light intensity I, and the flicker index is obtained through calculation by the formula.
As shown in the figure, the invention provides a facula flicker measuring device which can synchronously measure the beam divergence angle and flicker characteristics caused by atmospheric turbulence. Including an optical transmitting unit 11, an optical receiving unit 12, and a data processing unit 13. Wherein:
as shown in fig. 1, the optical emission unit 11 includes a laser light source 1 and an electronic control diaphragm 2, the laser light source is composed of a laser and an emission antenna, for example, a 650nm laser light source emits a laser beam with a wavelength of 650nm and a power of 80mW, the aperture of the emission antenna is 105mm, the beam passes through the electronic control diaphragm after being emitted, the aperture range is 5-98 mm, the beam waist radius is measured, and the beam angle can be calculated by combining the laser beam wavelength according to the beam waist radius;
the optical receiving unit 12 comprises an electric control diaphragm 3, a receiving antenna 4 and a CCD camera 5, wherein the electric control diaphragm is used for measuring the beam waist radius of a light beam received by a receiving end and then calculating the beam divergence angle, the receiving antenna is a hemispherical reflecting antenna with the focal length of fmm, the light beam is reflected into the CCD camera after the light is received, the CCD camera records the shape and the size of a light spot, the frequency frame of the CCD camera is 20HZ, the resolution is 160031200, and the pixel size is 4.434.5 mu m;
the data processing unit 13 includes a data preprocessing module, an a/D conversion module, an image processing module, and a display module. After passing through the preprocessing module, the A/D conversion module and the image processing module, the result is finally displayed on the display module.
Laser beams emitted by a laser light source pass through a transmitting-end electric control diaphragm 2 and then reach a receiving end through an atmospheric channel, pass through an electric control diaphragm 3 (beam waist radius is measured) at the receiving end, then reach a receiving reflection antenna device 4, reflect the beams into a CCD camera 5 (the beam spot diameter change on the CCD can reflect the fluctuation of the arrival angle), analyze the change of the beam spot radius through an image processing program after passing through a data processing unit and A/D conversion to obtain the fluctuation degree of the arrival angle, and display the result on a display module; meanwhile, signals are acquired in real time by an acquisition card in a computer after photoelectric conversion and analog/digital conversion, then the sampled data are calculated to obtain a flicker factor, and finally the result is displayed on a display module.
Specifically, the device of the invention calculates by the following way:
(1) beam divergence angle measurement principle: the beam waist refers to the place where the Gaussian light is transmitted absolutely in parallel, the place with the maximum amplitude as the origin point and the amplitude reduced to 1/e times of the original point, because the Gaussian light is symmetrical about the origin point, the 1/e place forms a circle, the radius of the circle is the radius of the light spot on the cross section, if the cross section of the beam waist is taken for inspection, the radius at the moment is the beamThe waist radius. And adjusting the aperture of the variable diaphragm, wherein when the energy value of the light beam passing through the diaphragm is 80% of the total energy value, the corresponding diaphragm diameter is the diameter of the laser beam spot, and the divergence angle value of the laser beam can be further calculated. As shown in FIG. 1, D 16、D 27 are beam waist diameters measured by the two electric control diaphragms respectively, the distance between the two electric control diaphragms is L9, and theta is a light beam divergence angle in the figure. Defining the far field divergence angle of the Gaussian beam according to the formula:
wherein, lambda light beam wavelength, n is medium refractive index, and D is beam waist radius.
The device can respectively calculate the beam divergence angles of the transmitting end and the receiving end by measuring the beam divergence angles of the two electric control diaphragms, and the beam divergence of the light beam is increased along with the increase of the distance in the atmospheric propagation. Thus, the beam spread angle θ obtained at the end1Minus the originating beam divergence angle theta2The beam divergence angle change amount Δ θ caused by the atmospheric turbulence can be finally obtained.
(2) The principle of facula scintillation measurement: the change of the diameter of the light spot on the CCD can reflect the fluctuation of the arrival angle. And processing the recorded light spot image on the CCD target surface by using an image processing program, identifying the image by using a light spot center positioning algorithm, finding out the circle center and the radius, and calculating the corresponding arrival angle alpha by using the light spot radius variation delta x, the pixel size p and the receiving antenna focal length f. The calculation formula is as follows:
as shown in fig. 3, the spot radius 13 is ideally r1The turbulent regime has a spot radius 14 of r2So that Δ x ═ r2-r1To aboveThe formula can be written as:
index of scintillation
The ratio of the light intensity fluctuation variance to the light intensity mean square is as follows:
< > represents the statistical average; the I represents the random light intensity of the light beam, the measured value in actual work is a voltage signal, the signal voltage U is in direct proportion to the incident signal light intensity I, and the flicker index is obtained through calculation by the formula.
Firstly, the beam divergence angle is mainly measured through a light spot image in the prior art, or the beam divergence angle of a certain point of a light beam is directly measured, and the beam divergence angle variable quantity caused by atmospheric turbulence under different conditions (near field and far field) can not be directly solved.
Secondly, in the prior art, the measurement of the fluctuation of the arrival angle is mainly calculated by using the position change of the light spot on the CCD, but the invention provides that the fluctuation of the arrival angle is calculated by using the radius change of the light spot on the CCD, thereby reducing the calculation complexity; meanwhile, when the fluctuation of the arrival angle is measured, the measured signal voltage is obtained by using the data measured by the CCD and the data processing module, and the light intensity flicker coefficient can be further solved.
The invention firstly measures the beam divergence angle of the laser beam transmitting end and the beam divergence angle of the laser beam receiving end through two electric control diaphragms, and then obtains the beam divergence angle variable quantity caused by the atmospheric turbulence by formula calculation, and further reflects the influence of the atmospheric turbulence on the beam divergence angle. Secondly, the invention tests the fluctuation of the arrival angle by measuring the diameter change of the light spot on the CCD. The light beam is influenced by the atmosphere to generate wavefront distortion, so that the integral wavefront inclination angle at the front end of the receiving aperture is changed to cause fluctuation of the arrival angle, and the arrival angle can be obtained by recording the diameter variation of a light spot on the CCD target surface and combining the focal length of the reflecting surface of the receiving antenna; finally, the invention uses the data measured by CCD to get the voltage of the measured signal through the data processing module, and carries on AD sampling to the signal, and then uses the defined formula of the flash coefficient to calculate the sampled data to get the flash factor, and further calculates the light intensity flash coefficient.
The working principle of the invention is that
The optical emission unit comprises a laser light source and an electric control diaphragm, wherein the laser light source is composed of a laser and an emission antenna, as shown in fig. 2, the angles of the laser light source and the electric control diaphragm in the device are firstly adjusted, the light source and the electric control diaphragm are kept on the same optical axis, and the light beam emitted by the laser passes through the center of the diaphragm. Taking a 650nm laser light source as an example, the laser light source emits a laser beam with a wavelength of 650nm, the laser beam is emitted through an emitting antenna, and the beam passes through an electric control diaphragm after being emitted.
A signal light beam emitted by an emitting unit forms a distorted wavefront after being transmitted by turbulent atmosphere, and then reaches an optical receiving unit (the optical receiving unit comprises an electric control diaphragm, a receiving antenna and a CCD camera), the electric control diaphragm and a reflecting surface of the receiving antenna are kept on the same optical axis, and under the condition that the light beam can be completely received by the receiving antenna, an incident light beam firstly reaches the electric control diaphragm and completely passes through the electric control diaphragm and then reaches a light reflecting surface of the receiving antenna, at the moment, the light beam is reflected and focused to the CCD camera by the reflecting surface to form annular imaging, and the light spot imaging continuously flickers and changes due to the influence of atmospheric turbulence.
The data processing unit comprises a data preprocessing module, an A/D conversion module, a data acquisition card, an image processing module and a display module, the image recorded by the CCD is subjected to preprocessing, A/D conversion and image processing modules, the circle center and the radius of a light spot are positioned through an image processing program, the radius variation is solved, the fluctuation degree of the arrival angle is calculated through a formula, and the result is displayed on the display module finally; meanwhile, signals are acquired in real time by an acquisition card in a computer after photoelectric conversion and analog/digital conversion, then the sampled data are calculated to obtain a flicker factor, and finally the result is displayed on a display module.
Claims (1)
1. The method for measuring the far-field beam expansion and scintillation characteristics in turbulent atmosphere is characterized in that the device for measuring the far-field beam expansion and scintillation characteristics in turbulent atmosphere comprises an optical transmitting unit (11), an optical receiving unit (12) and a data processing unit (13); the optical emission unit (11) comprises an emission end laser light source (1), and an electric control diaphragm a (2) is arranged on the emission side of the emission end laser light source (1); the optical receiving unit (12) comprises a CCD camera (5), the CCD camera (5) is arranged on one side, away from the transmitting end laser light source (1), of the electric control diaphragm a (2), an electric control diaphragm b (3) is arranged on one side, away from the electric control diaphragm a (2), of the CCD camera (5), and a receiving antenna (4) is arranged on one side, away from the CCD camera (5), of the electric control diaphragm b (3); the central points of the transmitting end laser light source (1) and the CCD camera (5) are on the same optical axis; the electric control diaphragm a (2) and the electric control diaphragm b (3) are on the same optical axis with the transmitting end laser light source (1); the CCD camera frequency frame is 20 HZ; the data processing unit (13) comprises a data preprocessing module, an A/D conversion module, an image processing module and a display module; the method is characterized by comprising the following steps:
step 1: opening a laser light source (1) at an emitting end to enable laser beams to pass through an electric control diaphragm a (2);
and 2, step: the light beam reaches a receiving end through an atmospheric channel, and the beam waist radius of the light beam is measured at an electric control diaphragm b (3) of the receiving end;
and step 3: after reaching the receiving antenna (4), reflecting the light beam into a CCD camera (5), processing the recorded light spot image on the CCD target surface, identifying the image by using a light spot center positioning algorithm, and recording the circle center and the radius;
and 4, step 4: calculating the variation of the beam divergence angle caused by the atmospheric turbulence;
and 5: calculating a flicker index according to the principle that the signal voltage U is in direct proportion to the incident signal light intensity I;
the method for calculating the beam divergence angle variation specifically comprises the following steps:
adjusting the aperture of the iris diaphragm, and when the energy value of the light beam passing through the iris diaphragm is 80% of the total energy value, the corresponding iris diaphragm diameter is the diameter of the laser beam spot, so that the divergence angle value of the laser beam can be calculated; d1(6)、D2(7) The beam waist radii measured by the two electric control diaphragms are respectively, the distance between the two electric control diaphragms is L (9), and theta is a light beam divergence angle; defining the far field divergence angle of the Gaussian beam according to the formula:
wherein, lambda light beam wavelength, n is medium refractive index, and D is beam waist radius;
by measuring the beam divergence angles of the two electric control diaphragms, the beam divergence angles of the sending end and the receiving end can be respectively calculated, and the beam divergence of the light beam is increased along with the increase of the distance when the light beam is transmitted in the atmosphere; thus, the beam spread angle θ obtained at the end1Minus the originating beam divergence angle theta2The beam divergence angle variation deltatheta due to the atmospheric turbulence can be finally obtained,
the calculation method of the flicker index specifically comprises the following steps:
the diameter change of the light spot on the CCD can reflect fluctuation of the arrival angle, the image is identified by using a light spot center positioning algorithm to find out the circle center and the radius, and then the corresponding arrival angle alpha can be calculated by using the light spot radius change quantity delta x, the pixel size p and the receiving antenna focal length f; the calculation formula is as follows:
the ideal spot radius is r1The spot radius of the turbulent flow is r2So that Δ x ═ r2-r1The above formula can be written as:
index of scintillation
The ratio of the light intensity fluctuation variance to the light intensity mean square is as follows:
wherein < > represents a statistical average; the I represents the random light intensity of the light beam, the measured value in actual work is a voltage signal, the signal voltage U is in direct proportion to the incident signal light intensity I, and the flicker index is obtained through calculation by the formula.
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| CN1407324A (en) * | 2001-08-20 | 2003-04-02 | 中国科学院光电技术研究所 | Laser beam divergence angle testing method |
| CN1786662A (en) * | 2005-12-21 | 2006-06-14 | 哈尔滨工业大学 | Double hole type measural apparatus for scattering angle of laser beam |
| CN102494639A (en) * | 2011-10-18 | 2012-06-13 | 北京理工大学 | Laser divergence angle measuring device and measuring method based on full-automatic hole alignment method |
| CN102519607A (en) * | 2011-11-29 | 2012-06-27 | 西安空间无线电技术研究所 | Satellite-borne atmospheric coherent length testing method and satellite-to-ground coherent optical communication method |
| CN102607798A (en) * | 2012-03-28 | 2012-07-25 | 中国人民解放军63655部队 | Device and method for measuring inner scale of atmospheric turbulence |
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| US20070077071A1 (en) * | 2005-09-30 | 2007-04-05 | Mikhail Belenkiy | System for measuring atmospheric turbulence |
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| CN1407324A (en) * | 2001-08-20 | 2003-04-02 | 中国科学院光电技术研究所 | Laser beam divergence angle testing method |
| CN1786662A (en) * | 2005-12-21 | 2006-06-14 | 哈尔滨工业大学 | Double hole type measural apparatus for scattering angle of laser beam |
| CN102494639A (en) * | 2011-10-18 | 2012-06-13 | 北京理工大学 | Laser divergence angle measuring device and measuring method based on full-automatic hole alignment method |
| CN102519607A (en) * | 2011-11-29 | 2012-06-27 | 西安空间无线电技术研究所 | Satellite-borne atmospheric coherent length testing method and satellite-to-ground coherent optical communication method |
| CN102607798A (en) * | 2012-03-28 | 2012-07-25 | 中国人民解放军63655部队 | Device and method for measuring inner scale of atmospheric turbulence |
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