Method for analyzing fixed star detection capability of star sensor based on polarization degree image

Abstract

The invention discloses a star sensor fixed star detection capability analysis method based on a polarization degree image, and belongs to the technical field of star sensor detection. In order to solve the problems of few detection means and low utilization rate of sky light radiation information during star observation of a near-earth space all-time star sensor, the method comprises the following steps: constructing a star sensor integrated with a focal plane micro-polarizer array, and acquiring four gray star maps through short exposure by using the star sensor integrated with the focal plane micro-polarizer array; a star sky Stokes vector diagram is calculated; calculating star sky polarization degree distribution to obtain a polarization degree star map; constructing a fixed star polarization signal-to-noise ratio calculation formula in the polarization degree star map by utilizing a physical process of converting radiation energy into polarization degree; the calculation formula calculates the polarization signal-to-noise ratio of the fixed star in the field of view; and comparing the polarization signal-to-noise ratio of the fixed star with a signal-to-noise ratio threshold value detected by the near-earth space all-time star sensor, and judging the detectable capability of the fixed star in the polarization degree star map. According to the method, the robustness of the near-earth space all-day star-sensitive technology to a complex environment is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of star sensor detection, and in particular relates to a method for analyzing star detection capability of a star sensor based on polarization degree images. Background Art

[0002] As the astronomical navigation device with the highest attitude determination accuracy currently available, star sensors are gradually expanding their application from space exploration equipment such as satellites and spacecraft in outer space to a variety of vehicles used both inside and outside the atmosphere, including tanks, armored vehicles, ships, aircraft, and missiles. To meet the needs of navigation within the atmosphere, the concept of near-Earth space all-day star sensors has been gradually proposed and refined in recent years in the astronomical navigation field. To address the challenges of a small number of navigation stars, strong background radiation, and large optical perturbations within the atmosphere, near-Earth space all-day star sensors are used in the near-infrared and short-wave infrared bands. The 2MASS point source catalog, with its larger number of stars, is selected as the navigation catalog. InGaAs detectors, with their higher full-well electron count, are less sensitive to smoke and less affected by optical turbulence, and are used as optical cameras to further suppress atmospheric background radiation and improve the signal-to-noise ratio of star images.

[0003] Unlike the cosmic environment, after sunlight enters the Earth's atmosphere, it is affected by factors such as Rayleigh scattering of atmospheric molecules, Mie scattering of aerosol particles, surface reflection, and the anisotropy of atmospheric molecules, forming a stable polarization state in the sky, which is called the sky polarization distribution pattern. As the angle between the observation direction and the sun increases, the sky polarization degree gradually increases. When the observation direction is perpendicular to the sun, the sky polarization degree reaches its maximum. Since stellar radiation has almost no polarization characteristics, the difference in polarization characteristics between stars and the sky background can be used to further improve the star detection capabilities of near-Earth space all-day star sensors. Based on this principle, researchers have developed polarization filtering technology.

[0004] Current near-Earth space all-day star sensors use polarization filtering technology to improve the signal-to-noise ratio of star images. They only utilize information from one dimension of the Stokes vector of sky light, and are essentially intensity detection of light radiation. They do not break through the limitations of traditional detection methods, nor do they fully utilize all the information in the polarization dimension of the light vector, resulting in low utilization of target and background light radiation information. Summary of the Invention

[0005] The problem to be solved by the present invention is that near-Earth space all-day star sensors have few detection means and low utilization rate of sky light radiation information when observing stars. A method for analyzing the star detection capability of star sensors based on polarization images is proposed.

[0006] To achieve the above object, the present invention is implemented through the following technical solutions:

[0007] A method for analyzing star detection capability of a star sensor based on polarization degree images comprises the following steps:

[0008] S1. Build a star sensor with an integrated split-focal-plane micro-polarizer array, and then use it to acquire four grayscale star images using short exposures.

[0009] S2. Calculate the Stokes vector of the sky based on the data in the four grayscale star maps obtained in step S1 to obtain a Stokes vector map of the sky;

[0010] S3. Calculate the star polarization distribution based on the Stokes vector diagram obtained in step S2 to obtain a polarization star map;

[0011] S4. Utilize the physical process of converting radiant energy into polarization to construct a formula for calculating the polarization signal-to-noise ratio of stars in polarization star maps;

[0012] S5. Calculate the polarization signal-to-noise ratio of stars in the field of view based on the polarization signal-to-noise ratio calculation formula in the star polarization star map obtained in step S4;

[0013] S6. Compare the polarization signal-to-noise ratio of the star obtained in step S5 with the signal-to-noise ratio threshold of the near-Earth space all-day star sensor detection, and determine the detectability of the star in the polarization star map.

[0014] Furthermore, the specific implementation method of step S1 includes the following steps:

[0015] S1.1. Build a star sensor with an integrated focal plane micropolarizer array, including a detector, a focal plane array, a micropolarizer array, an optical system, a filter, and a light shield. The detector, focal plane array, micropolarizer array, optical system, filter, and light shield are connected in sequence. The micropolarizer array is arranged in the order of transmission and polarization. 、 、 and It is composed of alternating sub-wavelength metal gratings. The position and size of each sub-wavelength metal grating strictly correspond to the position and size of the pixel of the focal plane array of the star sensor. Every four sub-wavelength metal gratings with different transmission and deflection directions form a 2×2 pixel super pixel.

[0016] S1.2. Construct a model for the light intensity response of a micropolarizer, expressed as:

[0017]

[0018] in, is the light intensity transmitted by the micropolarizer, is the transmittance of the micropolarizer, is the intensity of light incident on the micropolarizer, is the extinction ratio of the micropolarizer, is the polarization degree of the incident light, is the polarization angle of the incident light in the direction of the observation field, is the transmission angle of the kth micropolarizer on the micropolarizer array;

[0019] S1.3. Determine the exposure time of a star sensor with an integrated micropolarizer array in a focal plane, based on the principle that the grayscale response of a group of pixels in the polarization direction is consistent before and after the integration of the micropolarizer. , the expression is:

[0020]

[0021] in, is the exposure time of the traditional near-Earth space all-day star sensor, is the difference between the transmission angle of the kth micro-polarizer pixel and the polarization angle of the incident light in the observation field direction;

[0022] S1.4. Use a star sensor with an integrated split-focal plane micropolarizer array to collect four grayscale star images using short exposures, including the polarization direction. Grayscale star map after micro-polarizer, transmission direction is Grayscale star map after micro-polarizer, transmission direction is The grayscale star map and transmission direction after the micro-polarizer are Grayscale star image after micro-polarizer.

[0023] Furthermore, in step S2, the expression for calculating the starry sky Stokes vector based on the data in the four grayscale star images obtained in step S1 is:

[0024]

[0025] in, Indicates that the corresponding transmission direction is The number of photoelectrons received by the pixel behind the micropolarizer, Indicates that the corresponding transmission direction is The number of photoelectrons received by the pixel behind the micropolarizer, Indicates that the corresponding transmission direction is The number of photoelectrons received by the pixel behind the micropolarizer, Indicates that the corresponding transmission direction is The number of photoelectrons received by the pixel behind the micropolarizer, is the first component of the Stokes vector calculation, is the second component of the Stokes vector calculation, is the third component of the Stokes vector calculation, is the fourth component of the Stokes vector calculation.

[0026] Furthermore, the relationship between the polarization degree of the star image and the calculated Stokes vector value in step S3 is:

[0027]

[0028] in, is the polarization degree of the star image.

[0029] Furthermore, the specific implementation method of step S4 includes the following steps:

[0030] S4.1. Combined with the observation conditions, the Stokes vector calculation error is calculated from the noise level of the radiation energy received by the star sensor. The expression is:

[0031]

[0032]

[0033]

[0034] in, is the calculation error of the first component of the Stokes vector, is the calculation error of the second component of the Stokes vector, is the calculation error of the third component of the Stokes vector, is the calculated value of the first component of the Stokes vector of the star pixel, Calculate the value of the second component of the Stokes vector for the star pixel, is the calculated value of the third component of the Stokes vector of the star pixel, is the number of photoelectrons generated by the light transmitted through the micro-polarizer with the transmission direction i, is the noise on the micro-polarizer pixel with the transmission direction i;

[0035] S4.2. Solving the sky polarization calculation error by combining the Stokes vector calculation error , the calculation formula is:

[0036]

[0037] in, is the polarization degree of the star pixel;

[0038] S4.3. Based on the sky polarization calculation error obtained in step S4.2, and the polarization signal-to-noise ratio (PSNR) calculation formula, we can define the polarization signal-to-noise ratio (PSNR) by combining the polarization difference between the stars and the sky background in the polarization image:

[0039]

[0040] in, is the polarization signal-to-noise ratio, is the polarization degree of the sky background.

[0041] Furthermore, the specific implementation method of step S5 is to use the adaptive threshold segmentation method to segment the star and sky background area, and determine the star point coordinates, so as to obtain the polarization degree of the star pixel. , the polarization degree of the sky background is determined based on the average polarization degree measurement results of the sky background area , the mean square error of the polarization degree measurement results of the sky background area is used as the error of the polarization degree calculation , and then calculate the polarization signal-to-noise ratio using the polarization signal-to-noise ratio calculation formula in step S4.3.

[0042] Furthermore, the criterion for determining whether a star is detectable in step S6 is that a star having a polarization signal-to-noise ratio greater than 5 is detectable.

[0043] Beneficial effects of the present invention:

[0044] The method for analyzing the star detection capability of star sensors based on polarization images, described in this paper, fully utilizes the polarization dimension information in natural light and, combined with the measurement and solution of the Stokes vector, effectively expands the capabilities of all-day star sensor star detection in near-Earth space. This method can obtain polarization star maps that differ from energy distribution patterns and, incorporating error propagation laws, derive the definition of the polarization signal-to-noise ratio (PSNR). This analysis takes the optical properties of micropolarizers into account, and by controlling star sensor system parameters, effectively analyzes the improvement in star detection capability using polarization star maps compared to that using traditional star sensor maps.

[0045] The method for analyzing the star detection capability of a star sensor based on polarization images described in the present invention fully considers the differences in polarization characteristics between the target and the background. It has guiding significance for the segmentation of complex cloud interference regions involved in near-Earth space star detection scenarios and the removal of small target interference sources such as artificial satellites and drones. It also improves the robustness of near-Earth space all-day star sensing technology in complex environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 This is a flow chart of a method for analyzing star detection capability of a star sensor based on polarization image according to the present invention;

[0047] Figure 2 A schematic diagram of the definition of polarization signal-to-noise ratio in the present invention;

[0048] Figure 3Schematic diagram of a star sensor integrated with a split-focal plane micro-polarizer array in the present invention. DETAILED DESCRIPTION

[0049] In order to make the objectives, technical solutions, and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only intended to explain the present invention and are not intended to limit the present invention. That is, the specific embodiments described herein are only some embodiments of the present invention, not all embodiments. Generally, the components of the specific embodiments of the present invention described and illustrated in the drawings herein can be arranged and designed in various different configurations, and the present invention can also have other embodiments.

[0050] Therefore, the following detailed description of the specific embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention as claimed, but is merely representative of selected specific embodiments of the present invention. All other specific embodiments obtained by those skilled in the art based on the specific embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0051] In order to further understand the content, features and effects of the present invention, the following specific embodiments are given as examples, and the attached Figure 1 -Attached Figure 3 The detailed instructions are as follows:

[0052] Example 1:

[0053] A method for analyzing star detection capability of a star sensor based on polarization degree images comprises the following steps:

[0054] S1. Build a star sensor with an integrated split-focal-plane micro-polarizer array, and then use it to acquire four grayscale star images using short exposures.

[0055] Furthermore, the specific implementation method of step S1 includes the following steps:

[0056] S1.1. Build a star sensor with an integrated focal plane micropolarizer array, including a detector, a focal plane array, a micropolarizer array, an optical system, a filter, and a light shield. The detector, focal plane array, micropolarizer array, optical system, filter, and light shield are connected in sequence. The micropolarizer array is arranged in the order of transmission and polarization. 、 、 and It is composed of alternating sub-wavelength metal gratings. The position and size of each sub-wavelength metal grating strictly correspond to the position and size of the pixel of the focal plane array of the star sensor. Every four sub-wavelength metal gratings with different transmission and deflection directions form a 2×2 pixel super pixel.

[0057] S1.2. Construct a model for the light intensity response of a micropolarizer, expressed as:

[0058]

[0059] in, is the light intensity transmitted by the micropolarizer, is the transmittance of the micropolarizer, is the intensity of light incident on the micropolarizer, is the extinction ratio of the micropolarizer, is the polarization degree of the incident light, is the polarization angle of the incident light in the direction of the observation field, is the transmission angle of the kth micropolarizer on the micropolarizer array;

[0060] S1.3. Determine the exposure time of a star sensor with an integrated micropolarizer array in a focal plane, based on the principle that the grayscale response of a group of pixels in the polarization direction is consistent before and after the integration of the micropolarizer. , the expression is:

[0061]

[0062] in, is the exposure time of the traditional near-Earth space all-day star sensor, is the difference between the transmission angle of the kth micro-polarizer pixel and the polarization angle of the incident light in the observation field direction;

[0063] S1.4. Use a star sensor with an integrated split-focal plane micropolarizer array to collect four grayscale star images using short exposures, including the polarization direction. Grayscale star map after micro-polarizer, transmission direction is Grayscale star map after micro-polarizer, transmission direction is The grayscale star map and transmission direction after the micro-polarizer are Grayscale star image after micro-polarizer.

[0064] S2. Calculate the Stokes vector of the sky based on the data in the four grayscale star maps obtained in step S1 to obtain a Stokes vector map of the sky;

[0065] In the further step S2, the expression for calculating the starry sky Stokes vector based on the data in the four grayscale star images obtained in step S1 is:

[0066]

[0067] in, Indicates that the corresponding transmission direction is The number of photoelectrons received by the pixel behind the micropolarizer, Indicates that the corresponding transmission direction is The number of photoelectrons received by the pixel behind the micropolarizer, Indicates that the corresponding transmission direction is The number of photoelectrons received by the pixel behind the micropolarizer, Indicates that the corresponding transmission direction is The number of photoelectrons received by the pixel behind the micropolarizer, is the first component of the Stokes vector calculation, is the second component of the Stokes vector calculation, is the third component of the Stokes vector calculation, is the fourth component of the Stokes vector calculation.

[0068] S3. Calculate the star polarization distribution based on the Stokes vector diagram obtained in step S2 to obtain a polarization star map;

[0069] Furthermore, the relationship between the polarization degree of the star image and the calculated Stokes vector value in step S3 is:

[0070]

[0071] in, is the polarization degree of the star image.

[0072] S4. Utilize the physical process of converting radiant energy into polarization to construct a formula for calculating the polarization signal-to-noise ratio of stars in polarization star maps;

[0073] Furthermore, the specific implementation method of step S4 includes the following steps:

[0074] S4.1. Combined with the observation conditions, the Stokes vector calculation error is calculated from the noise level of the radiation energy received by the star sensor. The expression is:

[0075]

[0076]

[0077]

[0078] in, is the calculation error of the first component of the Stokes vector, is the calculation error of the second component of the Stokes vector, is the calculation error of the third component of the Stokes vector, is the calculated value of the first component of the Stokes vector of the star pixel, Calculate the value of the second component of the Stokes vector for the star pixel, is the calculated value of the third component of the Stokes vector of the star pixel, is the number of photoelectrons generated by the light transmitted through the micro-polarizer with the transmission direction i, is the noise on the micro-polarizer pixel with the transmission direction i;

[0079] S4.2. Solving the sky polarization calculation error by combining the Stokes vector calculation error , the calculation formula is:

[0080]

[0081] in, is the polarization degree of the star pixel;

[0082] S4.3. Based on the sky polarization calculation error obtained in step S4.2, and the polarization signal-to-noise ratio (PSNR) calculation formula, we can define the polarization signal-to-noise ratio (PSNR) by combining the polarization difference between the stars and the sky background in the polarization image:

[0083]

[0084] in, is the polarization signal-to-noise ratio, is the polarization degree of the sky background.

[0085] S5. Calculate the polarization signal-to-noise ratio of stars in the field of view based on the polarization signal-to-noise ratio calculation formula in the star polarization star map obtained in step S4;

[0086] Furthermore, the specific implementation method of step S5 is to use the adaptive threshold segmentation method to segment the star and sky background area, and determine the star point coordinates, so as to obtain the polarization degree of the star pixel. , the polarization degree of the sky background is determined based on the average polarization degree measurement results of the sky background area , the mean square error of the polarization degree measurement results of the sky background area is used as the error of the polarization degree calculation , and then calculate the polarization signal-to-noise ratio using the polarization signal-to-noise ratio calculation formula in step S4.3.

[0087] S6. Compare the polarization signal-to-noise ratio of the star obtained in step S5 with the signal-to-noise ratio threshold of the near-Earth space all-day star sensor detection, and determine the detectability of the star in the polarization star map.

[0088] Furthermore, the criterion for determining whether a star is detectable in step S6 is that a star having a polarization signal-to-noise ratio greater than 5 is detectable.

[0089] It should be noted that relational terms such as "first" and "second" are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or elements inherent to such process, method, article, or apparatus. In the absence of further limitations, an element defined by the phrase "comprising a ..." does not exclude the presence of additional identical elements in the process, method, article, or apparatus comprising the element.

[0090] Although the present application has been described above with reference to specific embodiments, various modifications may be made thereto and components may be substituted with equivalents without departing from the scope of the present application. In particular, as long as there are no structural conflicts, the various features of the embodiments disclosed herein may be combined with each other in any manner, and the omission of an exhaustive description of these combinations in this specification is solely for the sake of space and resource conservation. Therefore, the present application is not limited to the specific embodiments disclosed herein, but includes all technical solutions within the scope of the claims.

Claims

1. A method for analyzing star detection capability of a star sensor based on polarization degree images, characterized in that: The steps include: S1. Build a star sensor with an integrated split-focal-plane micro-polarizer array, and then use it to acquire four grayscale star images using short exposures. S2. Calculate the Stokes vector of the sky based on the data in the four grayscale star maps obtained in step S1 to obtain a Stokes vector map of the sky; S3. Calculate the star polarization distribution based on the Stokes vector diagram obtained in step S2 to obtain a polarization star map; S4. Utilize the physical process of converting radiant energy into polarization to construct a formula for calculating the polarization signal-to-noise ratio of stars in polarization star maps; S5. Calculate the polarization signal-to-noise ratio of stars in the field of view based on the polarization signal-to-noise ratio calculation formula in the star polarization star map obtained in step S4; S6. Compare the polarization signal-to-noise ratio of the star obtained in step S5 with the signal-to-noise ratio threshold of the near-Earth space all-day star sensor detection, and determine the detectability of the star in the polarization star map.

2. The method for analyzing star detection capability of a star sensor based on polarization degree images according to claim 1, wherein: The specific implementation method of step S1 includes the following steps: S1.

1. Build a star sensor with an integrated focal plane micropolarizer array, including a detector, a focal plane array, a micropolarizer array, an optical system, a filter, and a light shield. The detector, focal plane array, micropolarizer array, optical system, filter, and light shield are connected in sequence. The micropolarizer array is arranged in the order of transmission and polarization. 、 、 and It is composed of alternating sub-wavelength metal gratings. The position and size of each sub-wavelength metal grating strictly correspond to the position and size of the pixel of the focal plane array of the star sensor. Every four sub-wavelength metal gratings with different transmission and deflection directions form a 2×2 pixel super pixel. S1.

2. Construct a model for the light intensity response of a micropolarizer, expressed as: in, is the light intensity transmitted by the micropolarizer, is the transmittance of the micropolarizer, is the intensity of light incident on the micropolarizer, is the extinction ratio of the micropolarizer, is the polarization degree of the incident light, is the polarization angle of the incident light in the direction of the observation field, is the transmission angle of the kth micropolarizer on the micropolarizer array; S1.

3. Determine the exposure time of a star sensor with an integrated micropolarizer array in a focal plane, based on the principle that the grayscale response of a group of pixels in the polarization direction is consistent before and after the integration of the micropolarizer. , the expression is: in, is the exposure time of the traditional near-Earth space all-day star sensor, is the difference between the transmission angle of the kth micro-polarizer pixel and the polarization angle of the incident light in the observation field direction; S1.

4. Use a star sensor with an integrated split-focal plane micropolarizer array to collect four grayscale star images using short exposures, including the polarization direction. Grayscale star map after micro-polarizer, transmission direction is Grayscale star map after micro-polarizer, transmission direction is The grayscale star map and transmission direction after the micro-polarizer are Grayscale star image after micro-polarizer.

3. The method for analyzing star detection capability of a star sensor based on polarization degree images according to claim 2, wherein: In step S2, the expression for calculating the starry sky Stokes vector based on the data in the four grayscale star images obtained in step S1 is: in, Indicates that the corresponding transmission direction is The number of photoelectrons received by the pixel behind the micropolarizer, Indicates that the corresponding transmission direction is The number of photoelectrons received by the pixel behind the micropolarizer, Indicates that the corresponding transmission direction is The number of photoelectrons received by the pixel behind the micropolarizer, Indicates that the corresponding transmission direction is The number of photoelectrons received by the pixel behind the micropolarizer, is the first component of the Stokes vector calculation, is the second component of the Stokes vector calculation, is the third component of the Stokes vector calculation, is the fourth component of the Stokes vector calculation.

4. The method for analyzing star detection capability of a star sensor based on polarization degree images according to claim 3, wherein: The relationship between the polarization degree of the star image and the calculated value of the Stokes vector in step S3 is: in, is the polarization degree of the star image.

5. The method for analyzing star detection capability of a star sensor based on polarization degree images according to claim 4, wherein: The specific implementation method of step S4 includes the following steps: S4.

1. Combined with the observation conditions, the Stokes vector calculation error is calculated from the noise level of the radiation energy received by the star sensor. The expression is: in, is the calculation error of the first component of the Stokes vector, is the calculation error of the second component of the Stokes vector, is the calculation error of the third component of the Stokes vector, is the calculated value of the first component of the Stokes vector of the star pixel, Calculate the value of the second component of the Stokes vector for the star pixel, is the calculated value of the third component of the Stokes vector of the star pixel, is the number of photoelectrons generated by the light transmitted through the micro-polarizer with the transmission direction i, is the noise on the micro-polarizer pixel with the transmission direction i; S4.

2. Solving the sky polarization calculation error by combining the Stokes vector calculation error , the calculation formula is: in, is the polarization degree of the star pixel; S4.

3. Based on the sky polarization calculation error obtained in step S4.2, and the polarization signal-to-noise ratio (PSNR) calculation formula, we can define the polarization signal-to-noise ratio (PSNR) by combining the polarization difference between the stars and the sky background in the polarization image: in, is the polarization signal-to-noise ratio, is the polarization degree of the sky background.

6. The method for analyzing star detection capability of a star sensor based on polarization degree images according to claim 5, characterized in that: The specific implementation method of step S5 is to use the adaptive threshold segmentation method to segment the star and sky background area, and determine the star point coordinates, so as to obtain the polarization degree of the star pixel. , the polarization degree of the sky background is determined based on the average polarization degree measurement results of the sky background area , the mean square error of the polarization degree measurement results of the sky background area is used as the error of the polarization degree calculation , and then calculate the polarization signal-to-noise ratio using the polarization signal-to-noise ratio calculation formula in step S4.

3.

7. The method for analyzing star detection capability of a star sensor based on polarization degree images according to claim 6, characterized in that: The criterion for determining whether a star is detectable in step S6 is that a star with a polarization signal-to-noise ratio greater than 5 is detectable.

Images