A wavefront detection system for dim targets under strong skylight background

Abstract

The present invention relates to the field of adaptive optics technology, and specifically provides a wavefront detection system for dim targets under strong skylight background, including: a Shack-Hartmann wavefront sensor system and a wavefront detection and processing unit. The Shack-Hartmann wavefront sensor system performs wavefront detection in the short-wave infrared band of 1.3 μm - 1.7 μm. The wavefront detection and processing unit corrects the sub-aperture images obtained by detection through a weighted self-threshold local contrast algorithm, performs a self-threshold operation on the pixels within the central unit according to the gray-scale ratio weight between the central unit and the background unit of the sub-aperture image, and introduces an energy weight to eliminate PNHB noise and reconstruct the centroid of the sub-aperture image. By applying the Shack-Hartmann wavefront sensor system in the short-wave infrared band, the present invention effectively blocks the skylight background spectrum, while ensuring the target brightness, minimizing the background light radiation photons received by the detector to the greatest extent, and suppressing various noises and background interferences through an optimized threshold algorithm, significantly improving the wavefront detection accuracy.

Description

Technical Field

[0001] The present invention relates to the field of adaptive optics technology, and specifically provides a wavefront detection system for dim targets under strong skylight background. Background Art

[0002] One of the main applications of ground-based large-aperture optical imaging telescopes is to obtain high-resolution images of space targets. Adaptive optics technology is the core technology of ground-based large-aperture imaging telescopes, which is used to compensate for imaging aberrations caused by atmospheric turbulence in real time, and its ability directly determines the imaging quality of optical telescopes. Limited by the strong skylight background during the day, the adaptive optics system generally can only work at night or during twilight hours, and conventional ground-based optoelectronic detection systems cannot work during the entire daytime period, which seriously affects the detection timeliness of space targets.

[0003] The traditional ground-based optical telescope adaptive optics (AO) system only works under extremely weak background light conditions, that is, during twilight hours. Compared with twilight hours, the AO aberration correction technology during the day faces many challenges. On the one hand, due to the strong skylight background radiation, optoelectronic detection devices are extremely easy to saturate, which limits the effective exposure time of the optical system and results in a very low signal-to-noise ratio; on the other hand, the spatio-temporal distribution of the skylight background is uneven in different sub-apertures and even in the same sub-aperture, and the fixed threshold algorithm fails. Therefore, a core strategy for improving the centroid extraction accuracy of the Shack-Hartman wavefront sensor (SHWS) lies in improving the hardware design of the optical system and increasing the signal-to-noise ratio of the system wavefront detection. For example, using a method combining spectral filtering and polarization filtering or combining the advantages of SHWS and other wavefront sensors, but while reducing the skylight background, it also causes attenuation of the target energy. Another method is to optimize the threshold setting strategy to accurately eliminate background interference, such as threshold methods like TmCOG, WCOG, The brightest pixel selection algorithm, etc., but when applied to the daytime period, the centroid extraction accuracy decreases.

[0004] In order to eliminate the interference of the fluctuating strong skylight background, increase the signal-to-noise ratio of wavefront detection, achieve adaptive closed-loop correction of dim targets in daytime scenes, and obtain high-resolution imaging during the day, all existing solutions currently are to use target signal modulation methods such as polarization and spectral filtering to enhance the signal-to-noise ratio, but different degrees of target energy loss will occur while enhancing the signal-to-noise ratio. In addition, some people have proposed combining the Shack-Hartmann wavefront sensor with other wavefront sensors to compensate for large-scale wavefronts and perform high-sensitivity correction on small-scale wavefronts, but this method involves the combination of the Shack-Hartmann wavefront sensor and other wavefront sensors, which will lead to an overly complex optical structure, and it still cannot meet the application requirements of adaptive correction of dim space targets under strong skylight background during the day after combination. Summary of the Invention

[0005] To solve the above problems, the present invention provides a wavefront detection system for dim targets under strong skylight background, which conducts wavefront detection in the short-wave infrared band. By applying the Shack-Hartmann wavefront sensing technology with high-efficiency transmission of the spatial target spectrum and effective blocking of the skylight background spectrum, it can minimize the background light radiation photons received by the detector while maintaining the target brightness, significantly improving the signal-to-noise ratio of spatial target detection. In addition, by improving the optical design and developing a new threshold algorithm, it is optimized for the uneven skylight background and the PNHB phenomenon that appears in the short-wave infrared band. Utilizing the differences between the target and non-target features, the target is separated from the non-targets, significantly improving the imaging resolution of dim targets under strong skylight background during the day.

[0006] To achieve the above object, the technical solution of the present invention is realized as follows:

[0007] The wavefront detection system for dim targets under strong skylight background provided by the present invention includes: a Shack-Hartmann wavefront sensor system and a wavefront detection processing unit;

[0008] The Shack-Hartmann wavefront sensor system is sequentially provided with a dichroic mirror, a beam reduction unit, a microlens array, and a Hartmann detector along the incident light path. Among them, the dichroic mirror is used to inject the short-wave infrared band into the Shack-Hartmann wavefront sensor system; the beam reduction unit includes a field stop, which constrains the sub-aperture field of view through the field stop, and obtains sub-aperture images on the Hartmann detector through the microlens array;

[0009] The wavefront detection processing unit is used to correct the sub-aperture images.

[0010] Preferably, the dichroic mirror reflects and injects the short-wave infrared band of 1.3μm - 1.7μm into the beam reduction unit.

[0011] Preferably, the beam reduction unit further includes a first beam reduction mirror and a second beam reduction mirror, and the rear focus of the first beam reduction mirror coincides with the front focus of the second beam reduction mirror.

[0012] Preferably, the center of the field stop coincides with the rear focus of the first beam reduction mirror and the front focus of the second beam reduction mirror.

[0013] Preferably, the detection band of the Hartmann detector is 1.3μm - 1.7μm.

[0014] Preferably, the wavefront detection processing unit corrects the sub-aperture images through a weighted self-threshold local contrast algorithm.

[0015] Preferably, the process of correcting the sub-aperture images through the weighted self-threshold local contrast algorithm is as follows:

[0016] S1: Divide each sub-aperture image into nine-unit image blocks in the form of 3×3. The image block at the center position is the central unit, and each image block surrounding the central unit is a background unit. Perform self-thresholding on the pixels within the central unit according to the gray-scale ratio weight between the central unit and the background units.

[0017] S2: Introduce energy weight to eliminate PNHB noise in the sub-aperture image.

[0018] S3: Calculate the centroid of the sub-aperture image by the centroid method.

[0019] Preferably, in S1, the gray-scale calculation method of the central unit is as follows:

[0020] Take the average gray-scale of all pixels within the cross region centered on the central pixel of the central unit as the gray-scale of the central unit.

[0021] Preferably, in S1, the gray-scale calculation method of each background unit is as follows:

[0022] Remove the pixel with the maximum gray-scale value in the background unit, and take the average gray-scale of the remaining pixels in the background unit as the gray-scale of the background unit.

[0023] Preferably, the energy weight is:

[0024] ;

[0025] where is the maximum gray-scale value within the cross region, is the predicted gray-scale value, which satisfies a linear distribution with the minimum gray-scale value and the second maximum gray-scale value within the cross region;

[0026] According to the energy weight weighted calculation of the pixels within the central unit is:

[0027] ;

[0028] where is the gray-scale of the pixels within the central unit obtained after introducing the energy weight, is the gray-scale of the pixels within the central unit obtained after the self-thresholding operation.

[0029] Compared with the prior art, the present invention can achieve the following beneficial effects:

[0030] The present invention performs specific screening on the incident light band through a dichroic mirror, and applies a Shack-Hartmann wavefront sensor system (SHWS) in the short-wave infrared band that can efficiently transmit the spectrum of space targets and effectively block the sky background spectrum. Compared with the SHWS traditionally applied in the visible light band, the sky background radiation power in the short-wave infrared band is much lower than that in the visible light band, and the sky background has less influence on the detected target. Therefore, the present invention can ensure that the target has a high brightness while minimizing the number of background light radiation photons received by the detector, thereby significantly improving the signal-to-noise ratio of space target detection.

[0031] The present invention adds a field stop in the beam reduction optical path and sets the position of the field stop to suppress crosstalk between sub-apertures and constrain the field of view of each sub-aperture, greatly suppressing the influence of strong sky background during the day on the Hartmann wavefront sensor and improving the optical performance of the system.

[0032] In addition, the present invention designs a new threshold algorithm. Aiming at the phenomenon of uneven sky background and high-brightness pixel-sized noises (PNHB) in the short-wave infrared band, through local contrast self-threshold operation and energy weight judgment, it suppresses background noise and detector response deviation. Utilizing the difference between the characteristics of the target and non-target, it separates the target from the non-target, eliminates various noises and background interferences, realizes effective adaptive closed-loop correction of dim space targets, and improves the centroid extraction accuracy of sub-aperture images during the wavefront detection process. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The schematic embodiments and descriptions of the present invention are used to explain the present invention and do not constitute an improper limitation to the present invention. In the drawings:

[0034] Figure 1 is a schematic optical path diagram of a wavefront detection system for a dim target under a strong sky background according to an embodiment of the present invention;

[0035] Figure 2 is a correction flowchart of a sub-aperture image according to an embodiment of the present invention;

[0036] Figure 3 is a schematic diagram of the graphical division of a sub-aperture image according to an embodiment of the present invention;

[0037] Figure 4 is a schematic diagram of sub-aperture reconstruction according to an embodiment of the present invention.

[0038] The reference numerals therein include:

[0039] Dichroic mirror 1, first beam expander 2, field stop 3, second beam expander 4, microlens array 5, Hartmann detector 6. Detailed implementation mode

[0040] In order to make the purpose, technical solution and advantages of the present invention clearer, the following further details the present invention in combination 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 to the present invention. Similar elements in different embodiments are labeled with related similar element numbers. In the following embodiments, many details are described to enable a better understanding of the present invention. However, those skilled in the art can easily recognize that some of the features can be omitted in different situations, or can be replaced by other elements, materials, and methods. In some cases, some operations related to the present invention are not shown or described in the specification, which is to avoid the core part of the present invention being overwhelmed by excessive description. For those skilled in the art, it is not necessary to describe these related operations in detail, and they can fully understand the related operations based on the description in the specification and the general technical knowledge in the art.

[0041] It should be noted that, without conflict, the embodiments and features in the embodiments of the present invention can be combined with each other to form various implementation manners. At the same time, the steps or actions in the method description can also be reordered or adjusted in a manner obvious to those skilled in the art. Therefore, the various sequences in the specification and drawings are only for clearly describing a certain embodiment and do not mean that they are the necessary sequences, unless it is stated that a certain sequence must be followed.

[0042] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", etc. indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, it cannot be understood as a limitation to the present invention. In addition, the terms "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first", "second", etc. can explicitly or implicitly include one or more of such features. In the description of the present invention, unless otherwise stated, the meaning of "a plurality" is two or more.

[0043] In the description of the present invention, it should be noted that, unless otherwise clearly defined and limited, the terms "installation", "connection", and "coupling" should be understood in a broad sense. For example, it may be a fixed connection, a detachable connection, or an integral connection; it may be a mechanical connection or an electrical connection; it may be a direct connection or an indirect connection through an intermediate medium, and it may be the communication inside two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

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

[0045] Please refer to Figure 1 , in an embodiment of the present invention, a wavefront detection system for a dim target under a strong skylight background is provided to overcome the problem that the adaptive optical system of a traditional ground-based optical telescope can only work under extremely weak background light conditions. By performing wavefront detection for a specific wavelength band, improving the system structure, and optimizing the correction algorithm of the Hartmann image, the adaptive closed-loop correction of a dim target in a daytime scene is realized, meeting the current detection requirements under a strong skylight background during the day. Specifically, the wavefront detection system includes: a Shack-Hartmann wavefront sensor system and a wavefront detection processing unit. Among them, the Shack-Hartmann wavefront sensor system includes, arranged along the incident light optical path: a dichroic mirror 1, a beam reduction unit, a microlens array 5, and a Hartmann detector 6. Taking the embodiment of the present invention as an example, to suppress the interference of background light, Shack-Hartmann wavefront detection is only performed for a specific short-wave infrared wavelength band. By adding a dichroic mirror 1, the short-wave infrared wavelength band of 1.3 μm - 1.7 μm is reflected into the beam reduction unit. Compared with the wavefront detection process of a traditional detection system, the skylight background radiation power for only the short-wave infrared wavelength band is much lower than that of the visible light wavelength band, which can greatly reduce the influence of the skylight background on target detection.

[0046] The beam reduction unit mainly includes a first beam reduction lens 2, a field stop 3, and a second beam reduction lens 4. Among them, the short-wave infrared band reflected by the dichroic mirror 1 first enters the first beam reduction lens 2, and after being processed by the first beam reduction lens 2, it is directed towards the second beam reduction lens 4. The rear focal point of the first beam reduction lens 2 coincides with the front focal point of the second beam reduction lens 4, and the center of the field stop 3 is set at the position where the focal points coincide. It can be understood that the focal points of the two sides of the first beam reduction lens 2 and the second beam reduction lens 4 that are close to each other coincide. This confocal configuration can ensure that the light remains highly collimated when transmitted between the two beam reduction lenses, and setting the field stop 3 at the confocal position can effectively control the field of view and aperture of the light beam, helping to limit the diameter of the light beam entering the system, reducing stray light and background noise, and at the same time improving the beam quality and imaging resolution of the system. In addition, in the Shack-Hartmann wavefront sensor system, the design of the field stop 3 helps to suppress the crosstalk between sub-apertures. By precisely controlling the field of view of each sub-aperture, it can be ensured that the short-wave infrared band light beam captured by each sub-aperture does not overlap with the light beams of other sub-apertures, thereby improving the signal-to-noise ratio and imaging quality of the system.

[0047] The short-wave infrared band light beam is transmitted through the beam reduction unit and then passes through the microlens array 5, and is imaged on the target surface of the Hartmann detector 6. The microlens array 5 is an array composed of multiple small-sized lenses. The microlens array 5 divides the incident light wavefront into multiple sub-wavefronts, and each sub-wavefront forms a light spot on the focal plane. Each light spot is an image of a sub-aperture. The detection band of the Hartmann detector 6 is 1.3 μm - 1.7 μm.

[0048] Since the sub-aperture images are affected by the strong skylight background during the day and the PNHB phenomenon caused by the response deviation of the infrared detector and electronic noise, it is necessary to further correct the sub-aperture images through the wavefront detection and processing unit, and reconstruct the centroid of the light spot of the sub-aperture images.

[0049] In the embodiment of the present invention, the wavefront detection and processing unit mainly corrects the short-wave infrared Hartmann image of the weak target with a strong skylight background detected on the target surface of the Hartmann detector 6 through a weighted self-threshold local contrast algorithm. Specifically, please refer to Figure 2 , and the image correction process includes the following steps:

[0050] S1: For each sub-aperture image in the short-wave infrared Hartmann image of the weak target with a strong skylight background, a nine-cell image block in the form of 3×3 as shown in Figure 3 is used to traverse each sub-aperture image pixel by pixel, that is, each sub-aperture image is divided into nine-cell image blocks in the form of 3×3. Among them, the image block T in the central position is called the central unit, and the 8 image blocks surrounding the central unit T are called background units, that is , , , , , , and . By calculating the gray - scale ratio weights of the central unit T and the background units , , , , , , and respectively, perform a self - threshold operation on the pixels within the central unit to obtain the local feature saliency map of the sub - aperture image. The specific calculation process is as follows:

[0051] First, to ensure the integrity of the features of the central unit, define a cross - shaped region centered on the central pixel of the central unit , that is, extend in the horizontal and vertical directions from the central pixel. The average gray - scale value of all pixels within this region represents the gray - scale of the central unit T and is used as the comparison object in the subsequent self - threshold process. For the sake of convenience of expression, use the gray - scale of the central pixel to represent the central pixel. The gray - scale of the central unit T reflects the target gray - scale. Among them, the cross - shaped region can be expressed as:

[0052] ;

[0053] where is the coordinate of the central pixel , is the coordinate of the neighboring pixel, that is, the other pixels within the cross - shaped region except the central pixel , and k is the pixel radius of the cross - shaped region . In the embodiments of the present invention, the size of each image block is defined according to the theoretical size of the target light spot, that is, the central unit T and the background units , , , , , , and all have the same size. However, for the central unit T, we only take the central pixel and its four - neighborhood range. Therefore, the value of k is 1.

[0054] The gray - scale of the central unit T can be expressed as:

[0055] ;

[0056] where is the cross - shaped region The number of pixels within, in the embodiments of the present invention takes a value of 5, represents the cross region and the grayscale of any pixel within.

[0057] To avoid interference from background units , , , , , , and on the central unit T, define the grayscale of each background unit as the average grayscale of the other pixel regions after removing the pixel with the maximum grayscale in its image block. The specific grayscale of the background unit The calculation formula is:

[0058] ;

[0059] Among them, takes values of 1, 2, 3, 4, 5, 6, 7, and 8, corresponding to the background units , , , , , , and , is the number of pixels after removing the pixel with the maximum grayscale for each background unit, takes a value of the total number of pixels in the image block minus 1, represents the label of the other pixels after removing the pixel with the maximum grayscale in the background unit.

[0060] As a preferred embodiment, according to the degree of interference of background noise on the target, the number of pixels to be removed can be adaptively adjusted during the calculation of the grayscale of the background unit according to actual needs.

[0061] After calculating the grayscales of the central unit T and the background units , , , , , , and , calculate the similarity weight characterizing the features of different regions of the sub-aperture image, that is, calculate the similarity between the central unit T and the background units , , , , , , and Ratio of:

[0062] .

[0063] The similarity weight obtained according to the calculation , perform self-thresholding on the central pixel . Automatically determine the local threshold according to the local characteristics of the image. This local threshold is used to adjust the target gray level and the background gray level to the same level or a relatively consistent range. If the gray value of the central pixel is higher than the local threshold, it represents a part of the target, so it can be retained; if the gray value of the central pixel is lower than the local threshold, it may belong to the background, so it needs to be suppressed. In this way, the contrast between the target and the background can be improved, making the target features more prominent. The specific self-thresholding operation is:

[0064] ;

[0065] ;

[0066] Among them, represents the pixel gray level in the central unit T obtained after the self-thresholding operation, represents the decision function of the self-thresholding operation.

[0067] S2: Since the present invention performs wavefront detection for the short-wave infrared band, and during the infrared detection process, noise or signal instability phenomena will occur due to photon nonlinear response and hysteresis effect, that is, PNHB noise. In order to eliminate the PNHB noise interference in the sub-aperture image, the embodiments of the present invention introduce an energy weight W to adjust and optimize , to improve the accuracy and robustness of target detection. It is necessary to sort the pixels in the part of the central unit T by gray level, and determine its minimum value , sub-maximum value and maximum value . Their coordinates are (1, ), (2, ) and (3, ). Subsequently, a linear model can be constructed using (1, ) and (2, ) as follows:

[0068] ;

[0069] Among them: represents the slope, and B represents the intercept. , .

[0070] According to the constructed linear model, when x takes the value of 3, we get as follows:

[0071] ;

[0072] According to and determine the energy weight The expression is:

[0073] ;

[0074] According to the energy weight perform weighted calculation on the pixels in the central unit T, and obtain the corresponding for the central pixel in the central unit T after weighted calculation with the introduced energy weight as:

[0075] .

[0076] S3: For each sub-aperture image, the local contrast self-threshold operation and the energy weight are connected by multiplication. After the above operations are completed, as Figure 4 shown, select the pixel with the maximum gray level in the sub-aperture image as the center, and construct an N×N pixel region template to reconstruct a new sub-aperture image. Calculate the centroid of the light spot in the sub-aperture image through the centroid of gravity (COG) algorithm, that is, process and correct the original sub-aperture image, and the centroid of the newly constructed sub-aperture image obtained by calculation is:

[0077]

[0078] where represents the gray level of the newly constructed sub-aperture image, and represent the centroid coordinates of the newly constructed sub-aperture image. The calculation process of the centroid of the newly constructed sub-aperture image belongs to the prior art and will not be described in detail here.

[0079] Furthermore, the difference between the centroid coordinates of the newly constructed sub-aperture image and the centroid coordinates of the reference wavefront of the adaptive optical system of the ground-based optical telescope where the wavefront detection system is located can be calculated, and the average slope of each sub-wavefront of the telescope can be obtained according to simple geometric relationships. Then, the control voltage of each actuator of the deformable mirror in the telescope system can be obtained according to the direct slope method to achieve adaptive closed-loop correction.

[0080] In addition, in the embodiments of the present invention, it is shown for the short-wave infrared band of 1.3 μm - 1.7 μm. Beyond this range, the working bands of the dichroic mirror 1 and the Hartmann detector 6 can also be correspondingly adjusted and applied to other infrared bands. Moreover, the weighted self-threshold local contrast algorithm inside the wavefront detection processing unit can also be replaced by other local contrast algorithms. Correspondingly, the form of dividing the sub-aperture image into image blocks can also be replaced and optimized.

[0081] In summary, the above description is only for the preferred embodiments of this specification and is not intended to limit the protection scope of this specification. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of this specification shall be included within the protection scope of this specification.

[0082] The systems, devices, modules or units illustrated in the above one or more embodiments can be specifically implemented by computer chips or entities, or by products with certain functions. A typical implementation device is a computer. Specifically, the computer can be, for example, a personal computer, a laptop computer, a cellular phone, a camera phone, a smart phone, a personal digital assistant, a media player, a navigation device, an email device, a game console, a tablet computer, a wearable device, or any combination of these devices.

[0083] It should also be noted that the term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, commodity or device including a series of elements not only includes those elements, but also includes other elements not explicitly listed, or further includes elements inherent to such process, method, commodity or device. Without further limitations, the element defined by the statement "including one..." does not exclude the existence of additional identical elements in the process, method, commodity or device including the said element.

[0084] Each embodiment in this specification is described in a progressive manner. The same or similar parts among the embodiments can be referred to each other, and each embodiment focuses on the differences from other embodiments. In particular, for the system embodiment, since it is basically similar to the method embodiment, the description is relatively simple, and the relevant parts can be referred to the partial description of the method embodiment.

[0085] The above description has been made of specific embodiments of this specification. Other embodiments are within the scope of the appended claims. In some cases, the acts or steps recited in the claims may be performed in a different order than in the embodiments and still achieve the desired result. Additionally, the processes depicted in the figures do not necessarily require the particular order shown or sequential order to achieve the desired result. In certain embodiments, multitasking and parallel processing are also possible or may be advantageous.

Claims

1. A wavefront detection system for dim targets under strong skylight background, characterized in that: include: Shack-Hartmann wavefront sensor system and wavefront detection processing unit; The Shack-Hartmann wavefront sensor system is provided with: a dichroic mirror, a beam reduction unit, a microlens array and a Hartmann detector in sequence along the incident light path, wherein the dichroic mirror is used to inject the short-wave infrared band into the Shack-Hartmann wavefront sensor system; the beam reduction unit includes a field diaphragm, through which the sub-aperture field of view is constrained, and a sub-aperture image is obtained on the Hartmann detector through the microlens array; The wavefront detection processing unit is used to correct the sub-aperture image; the wavefront detection processing unit corrects the sub-aperture image by a weighted self-threshold local contrast algorithm; The process of correcting the sub-aperture image by weighted self-threshold local contrast algorithm is: S1: Divide each sub-aperture image into nine-unit image blocks in the form of 3×3, wherein the image block at the center is a center unit, and each image block outside the center unit is a background unit, and perform a self-threshold operation on the pixels in the center unit according to the grayscale ratio weight of the center unit and the background unit; The grayscale calculation method of the central unit is: The grayscale average value of all pixels in a cross region centered on the central pixel of the central unit is taken as the grayscale of the central unit; S2: Introduce energy weights to remove PNHB noise in the sub-aperture image. for: ； in, is the maximum grayscale value in the cross area, is the predicted gray value of the pixel with the maximum gray value in the cross area of ​​the center unit T, which is equal to the minimum gray value in the cross area And the grayscale submaximum Satisfy linear distribution; S3: Calculate the centroid of the sub-aperture image by using a centroid method.

2. The wavefront detection system for dim targets under strong skylight background as claimed in claim 1, characterized in that: The dichroic mirror reflects the short-wave infrared band of 1.3 μm-1.7 μm into the beam reduction unit.

3. The wavefront detection system for dim targets under strong skylight background as claimed in claim 1, characterized in that: The beam reduction unit further includes a first beam reduction mirror and a second beam reduction mirror, wherein a rear focus of the first beam reduction mirror coincides with a front focus of the second beam reduction mirror.

4. The wavefront detection system for dim targets under strong skylight background as claimed in claim 3, characterized in that: The center of the field stop coincides with the rear focus of the first beam reducer and the front focus of the second beam reducer.

5. The wavefront detection system for dim targets under strong skylight background as claimed in claim 1, characterized in that: The detection band of the Hartmann detector is 1.3 μm-1.7 μm.

6. The wavefront detection system for dim targets under strong skylight background as claimed in claim 1, characterized in that: In S1, the grayscale calculation method of each background unit is: The pixel with the largest grayscale value in the background unit is removed, and the average grayscale value of the remaining pixels in the background unit is taken as the grayscale of the background unit.

7. The wavefront detection system for dim targets under strong skylight background as claimed in claim 1, characterized in that: According to the energy weight The weighted calculation of the pixels in the central unit is: ； in, is the pixel grayscale in the central unit obtained after introducing the energy weight, is the pixel grayscale within the central unit obtained after the threshold operation.

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