CN108362697B - Atmospheric seeing layering measurement method for increasing layering number - Google Patents
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Abstract
The invention discloses an atmospheric seeing layering measurement method for increasing layering number, which takes the sub-aperture slopes of a plurality of targets obtained by a large-view field shack-Hartmann wave-front sensor as input, local atmospheric seeing obtained by previous atmospheric seeing layering measurement is taken as constraint, and finally, the measurement result of atmospheric seeing distributed along with height is output by carrying out iterative calculation on atmospheric seeing in different height ranges. The method overcomes the limitation of the sub-aperture array of the wavefront sensor on the atmospheric seeing layering number, improves the defect that the strength of a strong turbulent layer is overestimated due to sparse seeing layering nodes, does not introduce new hardware, and is high in practicability and innovation.
Description
Technical Field
The invention belongs to the technical field of atmospheric optics, and particularly relates to an atmospheric seeing layering measurement method for increasing layering number.
Background
Atmospheric refractive index structural constant for distribution of atmospheric optical turbulence along with atmospheric vertical height
The characterization is also the core knowledge of Multi-layer Conjugate Adaptive Optics (MCAO) and is also a key parameter for evaluating the condition of the telescope station address,
the measurements can be used to optimize system parameters including servo closed loop bandwidth, wavefront reconstruction algorithm, and conjugate height of MCAO system mirrors. Atmospheric vision r0Is an important parameter for evaluating the atmospheric turbulence characteristic and is the structural constant of the refractive index of the atmosphere
The functional relationship between the two is as follows:
it is possible to measure the seeing parameter r of each atmosphere layer by dispersing the atmosphere layer into a limited number of uniform thin layers0(h) Thereby obtaining the structural constant of the atmospheric refractive index
At present, the most popular methods for measuring atmospheric seeing layering are as follows: (1) scintillation Detection rangefinders (science Detection and Ranging, SCDAR, starlight-based wavefront flashing, Shepherd H W, Osborn J, Wilson R W, et al. Stereo-SCDAR: optical tissue profiling with high sensitivity using a modified SCDAR instrument [ J ]. monomer notifications of the Royal imaging facility, 2013,437(4):3568-, (2) slope detection rangefinder (SLODAR, based on wavefront slope, Butterley T, Wilson R W, SarazinM. degree of the profile of the external optical structural hierarchy from SLODAR data [ J ]. Monthly notes of the Royal analytical Society,2006,369(2): 835. 845.), (3) a solar differential image motion monitor plus (S-DIMM +, Schamer G B, VanWerkhoven T I M.S-DIMM + height conversion of day-time cutting using analysis [ J ]. analysis & analysis, 2010,513: A25.). However, when the shack-hartmann wavefront sensor is used for layered measurement of atmospheric seeing, the number of layers is limited by the size of the sub-aperture array of the wavefront sensor. For a wavefront sensor with a small number of sub-apertures, sparse height nodes (i.e. height positions of atmosphere layers of each layer) are caused, which causes two obvious defects, namely that the result of layered measurement cannot accurately present the positions of strong turbulence layers; secondly, if the altitude nodes which can not be detected by the wave-front sensor have strong turbulence layers, the turbulence intensity of the altitude nodes is superposed to the atmospheric layer of the altitude nodes which can be detected by the wave-front sensor, which leads to the overestimation of the atmospheric turbulence at the positions, and thus the vision acuity with smaller numerical value is obtained.
According to the background, in order to overcome the limitation of the sub-aperture number of the wavefront sensor on the atmospheric layering number and obtain an atmospheric seeing layered measurement result with more layering nodes and more uniform distribution, the method provided by the invention provides an atmospheric seeing layered measurement method for increasing the layering number.
Disclosure of Invention
The invention aims to solve the defects of the prior art, provides an atmospheric seeing layering measurement method for increasing the layering number, solves the problem that the limitation of the number of sub-apertures of a wavefront sensor to the atmospheric layering number is solved, and obtains an atmospheric seeing layering measurement result with more layering nodes and more uniform distribution.
The technical scheme adopted by the invention is as follows: an atmospheric seeing layering measurement method for increasing the number of layers, comprising the steps of:
the method comprises the following steps of (1) recording continuous frames of large-visual-field shack-Hartmann wavefront sensor images, the sub-aperture arrangement of the wavefront sensor and hardware parameters of the wavefront sensor and a telescope. Selecting a plurality of targets in a single sub-aperture image, and calculating the slope of each target in each sub-aperture;
step (2), determining an initial height range of an atmospheric seeing layering node by taking the sub-aperture arrangement and the sub-aperture slopes of a plurality of targets as initial input, and acquiring an atmospheric seeing layering result;
step (3), updating the height range, acquiring the local seeing of the height range as a new input item, performing iterative calculation on the atmospheric seeing of the new height range, and obtaining the atmospheric seeing layering result in the height range again;
and (4) repeating the step (3) for K-2 times until the number of the vision acuity layered nodes and the height range meet the requirements, stopping iteration, and outputting a measurement result of the vision acuity distributed along with the height.
The calculation principle of obtaining the atmospheric seeing layering result in the steps (2) to (4) is as follows:
wherein,
cn＝0.358λ2r0,j(hn)-5/3(D+αhn)-1/3(4)
b0＝0.358λ2D-1/3(5) j is equal to 1 in the step (2), and the method is a traditional sun difference image motion monitor plus (S-DIMM +) method; j is 2 in the case of step (3) and j in the case of step (4)>2; wherein:<x1(s,0)x2(s,α)>representing the covariance of the slopes of two targets at an angular separation of α at two sub-apertures at a distance s, wherein the x-direction is defined as the direction of the line connecting the centers of the two sub-apertures and the direction perpendicular thereto is defined as the y-direction, and the same principle is applied<y1(s,0)y2(s,α)>Represents the covariance of the y-direction; fx(s,α,hn) Spatial structure function representing the x-direction, which is the distance s, angular separation α, seeing hierarchical node height hnA function of (a); in the same way, Fy(s,α,hn) A spatial structure function representing the y-direction; λ represents the wavelength of the detection light wave, D represents the sub-aperture diameter, r0,j-1(hn) Denotes a height h at the time of j-1 th measurementnOf the atmosphere, r0,j(hn) Denotes the height h at the j-th measurementnThe vision of each atmosphere is obtained by solving a non-negative linear least square interpolation problem, the total number of layers is N, and the height range is 0-hN-1。
Wherein the updated height range during the jth measurement is 0-hM-1Wherein h isM-1Less than the height range of 0 to h in the j-1 th measurementNM is the Mth atmosphere calculated from the pupil plane of the telescope for the j-1 th measurement; local vernity introduced by the j-th measurement
The atmospheric vision degree layered measurement result obtained according to the j-1 measurement is obtained, and the expression relationship is as follows:
wherein, one of the demand-meeting requirements of the number and the height range of the seeing level hierarchical nodes is defined as: and the height range of the layer node of the layered atmosphere seeing degree measured at the last time is the minimum value which can be detected by the wave-front sensor.
Wherein, the measurement result of the output vision acuity along with the height distribution in the step (4) is as follows: a combination of the layered measurement of vergence measured when j is K, the measurement of vergence measured when j is K-1 not including the range of heights when j is K, and …, the measurement of vergence measured when j is 1 not including the range of heights when j is 2.
Wherein, the hardware parameters of the wavefront sensor and the telescope comprise: the wavefront sensor sub-aperture diameter D, the wavefront sensor sub-aperture array number N and the telescope pupil surface diameter.
Compared with the prior art, the invention has the advantages that:
(1) according to the invention, the atmospheric seeing in different height ranges is measured in a layered mode, and a distribution result of the seeing along with the atmospheric height is finally obtained. The method can overcome the limitation of the sub-aperture array of the wavefront sensor on the number of height nodes (namely the number of layers), and obtains a height node with more number and more uniform distribution to quantify the distribution of the vision along with the height.
(2) The measurement result of the method can clearly present the position of the strong turbulence layer, and the defect that the strength of the strong turbulence layer is overestimated caused by sparse seeing layering nodes is overcome.
(3) The invention does not need to add new hardware, does not change the existing light path structure, can fully utilize the existing telescope and wavefront sensor, and has strong innovation and practicability.
Drawings
FIG. 1 is a flow chart of an atmospheric vergence layer measurement method of increasing the number of layers according to the present invention;
FIG. 2 is a schematic diagram of arrangement of sub-apertures of a 37-unit large-field-of-view shack Hartmann wavefront sensor;
FIG. 3 is a comparison of the measurement results of the conventional method and the method of the present invention.
Detailed Description
The invention is further described with reference to the following figures and specific examples.
The specific embodiment is a 7 × 7 large-field shack-hartmann wavefront sensor (N ═ 7), and fig. 2 is a layout diagram of sub-apertures of the sensor, and the number of effective sub-apertures is 30. A continuously distributed atmosphere was created with Kolmogorov (Kolmogorov) phase screens with infinite external dimensions, generating a height of 0-13km, a separation of 1km between each layer, and a total atmospheric pennity of 10cm, where the parameters for each layer are as in table 1:
table 1 input continuously distributed atmospheric turbulence
| Height (Km) | Input r0(cm) | Weight (%) |
| 0 | 28.46 | 17.5 |
| 1 | 31.21 | 15 |
| 2 | 34.82 | 12.5 |
| 3 | 39.81 | 10 |
| 4 | 47.31 | 7.5 |
| 5 | 60.34 | 5 |
| 6 | 91.46 | 2.5 |
| 7 | 91.46 | 2.5 |
| 8 | 91.46 | 2.5 |
| 9 | 60.34 | 5 |
| 10 | 47.31 | 7.5 |
| 11 | 60.34 | 5 |
| 12 | 60.34 | 5 |
| 13 | 91.46 | 2.5 |
A simulation image with the frame frequency of 100Hz and the frame number of 500 is collected through a wavefront sensor.
According to the step (2), when j is 1, defining the range of the wavefront sensor detection height as 0-15km, because N is 7, the traditional method can only obtain the seeing layering result of 7 layers, and defining the height node as h is 0, 2,4,6,9,12,15km, according to the sun difference image motion monitor plus (S-DIMM +) method:
and obtaining an atmospheric vision acuity layered measurement result of 0-15 km.
According to the step (3) and the step (4), when the j is 2 to the j is K, the detection height range is sequentially reduced by 1km, so that the highest height is reduced from 14km to 6km, the iterative calculation is stopped, the total iterative times is 9,
TABLE 2 height node Range during measurement (j ≧ 2) from step (3) to step (4)
| j value | Location of altitude node (km) |
| 2 | 0,2,4,6,9,12,14 |
| 3 | 0,2,4,6,9,12,13 |
| 4 | 0,2,4,6,9,10,12 |
| 5 | 0,2,4,6,9,10,11 |
| 6 | 0,2,4,6,8,9,10 |
| 7 | 0,2,4,6,7,8,9 |
| 8 | 0,2,4,5,6,7,8 |
| 9 | 0,2,3,4,5,6,7 |
| 10 | 0,1,2,3,4,5,6 |
Fig. 3 is a result of a simulation experiment, in which the abscissa is the height of the atmosphere, the ordinate is the weight occupied by the atmosphere of each layer, a black histogram is an input value, a black solid line is the weight of the seeing of each layer restored by the method of the present invention, and a black dotted line is the result restored by the original method. The traditional method can only obtain the atmospheric turbulence information of a node with the height of 7 layers, while the method can obtain 16 layers, and the recovery result of each layer is closer to the input value. Therefore, the method of the invention not only can overcome the limitation of the sub-aperture array of the wavefront sensor on the number of height nodes (namely the layering number), obtain a height node with more number and more uniform distribution to quantify the distribution of the seeing along with the height, but also can more clearly present the position of the strong turbulence layer, and improve the defect that the strength of the strong turbulence layer is overestimated caused by sparse seeing layering nodes.
The above description is only an embodiment of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art can understand that the substitutions or additions and deletions within the technical scope of the present invention are included in the scope of the present invention, therefore, the scope of the present invention should be subject to the protection scope of the claims.
Claims (4)
1. An atmospheric seeing layering measurement method for increasing the number of layers, the method comprising the steps of:
recording continuous frames of large-view-field shack-Hartmann wavefront sensor images, wavefront sensor sub-aperture arrangement and hardware parameters of a wavefront sensor and a telescope, selecting a plurality of targets in a single sub-aperture image, and calculating the slope of each target in each sub-aperture;
step (2), determining an initial height range of an atmospheric seeing layering node by taking the sub-aperture arrangement and the sub-aperture slopes of a plurality of targets as initial input, and acquiring an atmospheric seeing layering result;
step (3), updating the height range, acquiring the local seeing of the height range as a new input item, performing iterative calculation on the atmospheric seeing of the new height range, and obtaining the atmospheric seeing layering result in the height range again;
step (4), repeating the step (3) for K-2 times until the number of the vision acuity layered nodes and the height range meet the requirements, stopping iteration, and outputting a measurement result of the vision acuity distributed along with the height;
the calculation principle of the atmospheric seeing layering result obtained in the steps (2) to (4) is as follows:
wherein,
cn＝0.358λ2r0,j(hn)-5/3(D+αhn)-1/3(4)
b0＝0.358λ2D-1/3(5)
j is equal to 1 in the step (2), and the method is a traditional sun difference image motion monitor plus (S-DIMM +) method; j is 2 in the case of step (3) and j in the case of step (4)>2; wherein:<x1(s,0)x2(s,α)>representing the covariance of the slopes of two targets at an angular separation of α at two sub-apertures at a distance s, wherein the x-direction is defined as the direction of the line connecting the centers of the two sub-apertures and the direction perpendicular thereto is defined as the y-direction, and the same principle is applied<y1(s,0)y2(s,α)>Represents the covariance of the y-direction; fx(s,α,hn) Spatial structure function representing the x-direction, which is the distance s, angular separation α, seeing hierarchical node height hnA function of (a); in the same way, Fy(s,α,hn) A spatial structure function representing the y-direction; λ represents the wavelength of the detection light wave, D represents the sub-aperture diameter, r0,j-1(hn) Denotes a height h at the time of j-1 th measurementnOf the atmosphere, r0,j(hn) Denotes the height h at the j-th measurementnThe vision of each atmosphere is obtained by solving a non-negative linear least square interpolation problem, the total number of layers is N, and the height range is 0-hN-1；
The updated height range in the jth measurement is 0-hM-1Wherein h isM-1Less than the height range of 0 to h in the j-1 th measurementNM is the pupil plane of the slave telescope measured at the j-1 th timeThe Mth atmosphere layer which starts to be calculated; local vernity introduced by the j-th measurement
The atmospheric vision degree layered measurement result obtained according to the j-1 measurement is obtained, and the expression relationship is as follows:
2. an atmospheric etching level hierarchy measurement method for increasing the number of layers according to claim 1, wherein one of the demand-met number of etching level hierarchy nodes and the demand-met height range is defined as: and the height range of the layer node of the layered atmosphere seeing degree measured at the last time is the minimum value which can be detected by the wave-front sensor.
3. An atmospheric acuity stratification measurement method according to claim 1, where the output acuity measurement with height in step (4) is: a combination of the layered measurement of vergence measured when j is K, the measurement of vergence measured when j is K-1 not including the range of heights when j is K, and …, the measurement of vergence measured when j is 1 not including the range of heights when j is 2.
4. An atmospheric penetrometry method with increased number of levels of stratification as recited in claim 1, wherein the wavefront sensor and telescope hardware parameters comprise: the wavefront sensor sub-aperture diameter D, the wavefront sensor sub-aperture array number N and the telescope pupil surface diameter.
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