Seeing detection method for large aperture and large field of view active optical telescope camera

Abstract

The present invention provides a method for detecting the seeing of a large-aperture, large-field active optical telescope camera, comprising the following steps: S1. Performing short-time exposure on a specific sky area to obtain a defocused star image in the specific sky area. S2. Constructing a low-order phase-difference defocused star image template based on the defocused star image in the specific sky area. S3. Correlating the low-order phase-difference defocused star image template with the defocused star image obtained in step S1, and regarding the position corresponding to the highest correlation as the center of the defocused star image to achieve positioning selection of the star image. S4. Ignoring the influence of low-order aberrations, utilizing the basic principle of curvature sensing to extract the aberration of the star image, and decomposing it onto a multi-order Zernike polynomial basis, synthesizing the obtained low-order information with the high-order information, and comparing it with the actual defocused star image to calculate the difference result. The present invention clarifies the mechanism of the influence of camera seeing on the final sky survey detection, as well as the boundary of its accuracy influence.

Description

Technical Field

[0001] The present invention relates to the field of optical technology, and in particular to a method for detecting the seeing of a large-aperture, large-field-of-view active optical telescope camera. Background Art

[0002] In order to better complete the exploration of dark matter and dark energy, scientists have put forward higher resolution and imaging quality requirements for the next generation of large-aperture and large-field telescopes.

[0003] The curvature sensor was proposed by Roddier in 1988. Its basic principle is to estimate the change in wavefront curvature through the light intensity distribution of the pre-focus and post-focus images and to calculate the wavefront information. Because it can meet the specific needs of large-aperture active optical photographic survey telescopes, and can use the same devices as scientific cameras, it is convenient for image acquisition and subsequent maintenance. It has many unique advantages, such as non-interference (no reference light required), simple structure, good environmental adaptability, stable solution (no iteration required), and minimal influence of aperture obstruction. It has been widely used in the active optical wavefront sensing systems of large-aperture photographic survey telescopes. Summary of the Invention

[0004] In view of the above problems, the purpose of the present invention is to propose a method for detecting the seeing of a large-aperture, large-field-of-view active optical telescope camera. By testing the camera seeing, the mechanism of the influence of the camera seeing on the final sky survey detection and the boundary of its precision influence are clarified, and the manufacturing and design of future large-field-of-view seeing extreme sky survey equipment, as well as the precision boundaries and test range requirements of the seeing detection equipment are guided.

[0005] To achieve the above objectives, the present invention adopts the following specific technical solutions:

[0006] The present invention provides a method for detecting seeing of a large-aperture, large-field-of-view active optical telescope camera, comprising the following steps:

[0007] S1. Take a short exposure for a specific area of ​​the sky to obtain a defocused star image in that area.

[0008] S2. Constructing a low-order phase difference defocused star image template according to the defocused star image in the specific sky area.

[0009] S3. Correlation operation is performed on the low-order phase difference defocused star image template and the defocused star image obtained in step S1, and the position corresponding to the highest correlation is regarded as the center of the defocused star image to achieve positioning selection of the star image.

[0010] S4. Ignore the influence of low-order aberrations, use the basic principle of curvature sensing to extract the aberrations of the star point image, and decompose it onto a multi-order Zernike polynomial basis. Then synthesize the obtained low-order information with the high-order information, and compare it with the actual defocused star point image to calculate the difference result.

[0011] Preferably, the method further comprises step S5, performing correction iteration according to the difference result: taking the difference result as a new input, repeating step S4 until the difference result is less than 1 / 20 wavelength.

[0012] Preferably, the wavefront light field distribution model at a single wavelength is as shown in formula (1):

[0013]

[0014] Where λ is the wavelength, A is the amplitude of a single phase spatial frequency component, r is the pupil coordinate vector, f is the spatial frequency domain coordinate, z i is the defocus amount, i is an integer, representing the i-th field of view;

[0015] Based on the incoherent synthesis theory, the non-narrowband light field model is obtained as shown in formula (2):

[0016]

[0017] Where Δλ is the bandwidth. According to the basic principle of curvature sensing, the curvature of the wavefront phase is proportional to the difference in light intensity along the optical axis, and we can obtain:

[0018]

[0019] Among them, I + and Ι - is the energy distribution before and after focus, Δz i Represents the defocus amount of the i-th field of view; for the formula (3), the Fourier series is used as the basis for regional curvature sensing, and the required wavefront information is obtained through two numerical integrations.

[0020] Compared with existing technologies, the present invention clarifies the impact mechanism of camera seeing on the final sky survey detection and the boundary of its accuracy impact through camera seeing testing, and guides the manufacture and design of future large-field seeing extreme sky survey equipment, as well as the accuracy boundaries and test range requirements of seeing detection equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 1 is a flow chart of a method for detecting seeing of a large-aperture, large-field-of-view active optical telescope camera according to an embodiment of the present invention.

[0022] Figure 2 3 is a schematic diagram of a star point image provided according to an embodiment of the present invention.

[0023] Figure 3 3 is a schematic diagram of performing correlation calculation on a low-order phase difference defocused star point image template and a defocused star point image according to an embodiment of the present invention. DETAILED DESCRIPTION

[0024] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In the following description, identical modules are denoted by identical reference numerals. In the case of identical reference numerals, their names and functions are also identical. Therefore, their detailed description will not be repeated.

[0025] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and do not constitute a limitation of the present invention.

[0026] Figure 1 The flowchart of the method for detecting seeing of a large-aperture, large-field-of-view active optical telescope camera provided by an embodiment of the present invention is shown.

[0027] like Figure 1 As shown, the seeing detection method for a large-aperture, large-field-of-view active optical telescope camera provided by an embodiment of the present invention includes the following steps:

[0028] S1. Take a short exposure for a specific area of ​​the sky to obtain a defocused star image in that specific area. Figure 2 Schematic diagram of defocused star images under different atmospheric turbulences provided according to an embodiment of the present invention is shown.

[0029] S2. Construct a low-order phase difference defocused star image template based on the defocused star image in a specific sky area.

[0030] Figure 3 The figure shows the position determination process of performing correlation operation between the low-order phase difference defocused star point image template and the defocused star point image according to the embodiment of the present invention. Figure 3 As shown:

[0031] S3, performing correlation operation on the low-order phase difference defocused star image template and the defocused star image obtained in step S1, and considering the position corresponding to the highest correlation as the center of the defocused star image to achieve positioning selection of the star image.

[0032] S4. Ignoring the influence of low-order aberrations, we extract the aberrations using the basic principles of curvature sensing and decompose them onto a multi-order Zernike polynomial basis. We synthesize the obtained low-order information with the high-order information (the 15th-order fringe Zernike is used as the boundary between the low-order and high-order information) and compare it with the actual defocused star image to calculate the difference.

[0033] Low-order wavefront information for:

[0034] Among them, D i It is an out-of-focus star image.

[0035] High-order wavefront information D i 'for:

[0036] S5. Perform correction iterations based on the above difference results: use the difference results as new input and repeat step S4 until the difference results are less than 1 / 20 wavelength.

[0037] The wavefront light field distribution model under a single wavelength is shown in formula (1):

[0038]

[0039] Where λ is the wavelength, A is the amplitude of a single phase spatial frequency component, r is the pupil coordinate vector, f is the spatial frequency domain coordinate, z i is the defocus amount, i is an integer, representing the i-th field of view.

[0040] Based on the incoherent synthesis theory, the non-narrowband light field model can be obtained as shown in formula (2):

[0041]

[0042] Where Δλ is the bandwidth. According to the basic principle of curvature sensing, the curvature of the wavefront phase is proportional to the difference in light intensity along the optical axis, as shown in formula (3):

[0043]

[0044] Among them, I + and Ι - is the energy distribution before and after focus, Δz i represents the defocus value of the i-th field of view. Based on Equation (3), we use the Fourier series as the basis for regional curvature sensing (see the research foundation for details, which can reduce the impact of edge ringing effects and achieve effective utilization of overlapping guide stars). The required wavefront information can be obtained through two numerical integrations.

[0045] Although the embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are illustrative and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention.

[0046] The above specific embodiments of the present invention do not constitute a limitation on the scope of protection of the present invention. Any other corresponding changes and modifications made based on the technical concept of the present invention should be included in the scope of protection of the claims of the present invention.

Claims

1. A method for detecting seeing of a large-aperture, large-field-of-view active optical telescope camera, characterized in that: The following steps are involved: S1. Take a short exposure for a specific sky area to obtain a defocused star image in the specific sky area; S2. constructing a low-order aberration defocused star image template according to the defocused star image in the specific sky area; S3, performing a correlation operation on the low-order aberration defocused star image template and the defocused star image obtained in step S1, and considering the position corresponding to the highest correlation as the center of the defocused star image, so as to achieve positioning selection of the star image; S4. Ignore the influence of low-order aberrations, use the basic principle of curvature sensing to extract the aberrations of the star point image, and decompose it onto a multi-order Zernike polynomial basis. Then synthesize the obtained low-order information with the high-order information, and compare it with the actual defocused star point image to calculate the difference result.

2. The method for detecting seeing of a large-aperture, large-field-of-view active optical telescope camera according to claim 1, characterized in that: The method further includes step S5, performing correction iteration according to the difference result: taking the difference result as a new input, and repeating step S4 until the difference result is less than 1 / 20 wavelength.

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