A star sensor star detection capability analysis method based on a polarization degree image

Abstract

A kind of star sensor star detection capability analysis method based on polarization degree image belongs to star sensor detection technical field.For solving the problem that less detection means and low utilization rate of sky light radiation information when near-earth space all-time star sensor observes star, the present application includes the star sensor of integrated focal plane micro-polaroid array is built, four gray star maps are collected by short exposure using the star sensor of integrated focal plane micro-polaroid array;Calculate the sky Stokes vector diagram;Calculate the polarization degree distribution of starry sky to obtain the polarization degree star map;Utilize the physical process of radiation energy to polarization degree conversion to construct the polarization signal-to-noise ratio calculation formula of star in polarization degree star map;The polarization signal-to-noise ratio of star in field of view is calculated;The polarization signal-to-noise ratio of star is compared with the signal-to-noise ratio threshold value of near-earth space all-time star sensor detection, and the detectable ability of star in polarization degree star map is judged.The present application improves the robustness of near-earth space all-time star sensor technology to complex environment.

Description

Technical Field

[0001] This invention belongs to the field of star sensor detection technology, specifically relating to a method for analyzing the star detection capability of star sensors based on polarization degree images. Background Technology

[0002] As the most accurate astronomical navigation device currently available, star sensors are increasingly being used on a wider range of vehicles, from spacecraft and satellites to tanks, armored vehicles, ships, aircraft, and missiles operating both within and outside the atmosphere. To meet the navigation requirements within the atmosphere, the concept of near-Earth space all-weather star sensors has been gradually proposed and refined in recent years. To address the challenges of fewer navigation stars, stronger background radiation, and greater optical disturbances within the atmosphere, near-Earth space all-weather star sensors are applied in the near-infrared and short-wave infrared bands. They utilize the 2MASS point source catalog, which contains a greater number of stars, as the navigation star catalog. Furthermore, they employ InGaAs detectors, which have a higher number of full-well electrons, are less sensitive to smoke, and are less affected by optical turbulence, as the optical camera to further suppress atmospheric background radiation and improve the signal-to-noise ratio of the star chart.

[0003] Unlike the cosmic environment, sunlight entering the Earth's atmosphere is affected by Rayleigh scattering by atmospheric molecules, Mie scattering by aerosol particles, surface reflection, and the anisotropy of atmospheric molecules, resulting in a stable polarization state in the sky, known as the sky polarization distribution pattern. As the angle between the observation direction and the sun increases, the degree of sky polarization gradually increases, reaching its maximum when the observation direction is perpendicular to the sun. 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 capability of near-Earth space all-sky star sensors. Based on this principle, researchers have developed polarization filtering technology.

[0004] Current near-Earth space all-weather star sensors use polarization filtering technology to improve the signal-to-noise ratio of star charts. They only utilize information from one dimension of the Stokes vector of sky light, which is essentially a detection of the intensity of light radiation. This does not break through the limitations of traditional detection methods and does not fully utilize all the information from 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 this invention aims to solve is the limited means of star observation and low utilization rate of sky light radiation information for near-Earth space all-time star sensors. It proposes a method for analyzing the star detection capability of star sensors based on polarization degree images.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

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

[0008] S1. Construct a star sensor with an integrated focal plane micro-polarizer array, and then use the star sensor with the integrated focal plane micro-polarizer array to acquire four grayscale star images through short exposure;

[0009] S2. Calculate the Stokes vector of the starry sky based on the data in the four grayscale star images obtained in step S1, and obtain the Stokes vector image of the starry sky;

[0010] S3. Calculate the polarization distribution of the starry sky based on the Stokes vector map of the starry sky obtained in step S2, and obtain the polarization star map;

[0011] S4. Construct a formula for calculating the polarization signal-to-noise ratio of stars in a polarization degree star map by utilizing the physical process of converting radiant energy into polarization degree;

[0012] S5. Calculate the polarization signal-to-noise ratio of stars within the field of view based on the formula for calculating the polarization signal-to-noise ratio of stars in the polarization degree 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 detected by the near-Earth space all-day star sensor, and determine the detectability of the star in the polarization degree star map.

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

[0015] S1.1. Construct a star sensor with an integrated focal plane micro-polarizer array, including a detector, a focal plane array, a micro-polarizer array, an optical system, a filter, and a light shield. The detector, focal plane array, micro-polarizer array, optical system, filter, and light shield are connected sequentially. The micro-polarizer array is arranged in the following order from the transmission direction: , , and It consists of alternating subwavelength metal gratings, the position and size of each subwavelength metal grating strictly correspond to the position and size of the pixels in the focal plane array of the star sensor, and every four subwavelength metal gratings with different transmission polarization directions constitute a 2×2 pixel superpixel.

[0016] S1.2. Construct a light intensity response model for the micro-polarizer, the expression of which is:

[0017]

[0018] in, The intensity of light transmitted through the micropolarizer. The transmittance of the micropolarizer is... The intensity of the light incident on the micropolarizer, The extinction ratio of the micropolarizer. The polarization degree of the incident light. To observe the polarization angle of the incident light along the field of view, Let be the transmission angle of the k-th micro-polarizer in the micro-polarizer array;

[0019] S1.3. Based on the principle that the grayscale response of a set of pixels in the transmission direction is consistent before and after the integration of the micro-polarizer, determine the exposure time of the star sensor of the integrated focal plane micro-polarizer array. The expression is:

[0020]

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

[0022] S1.4. Four grayscale star images were acquired via short exposure using a star sensor with an integrated focal plane micro-polarizer array, including images with the polarization direction as shown. The grayscale star map and transmission direction after the micro-polarizer are as follows: The grayscale star map and transmission direction after the micro-polarizer are as follows: The grayscale star map and transmission direction after micropolarization are as follows: Grayscale star map behind a micropolarizer.

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

[0024]

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

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

[0027]

[0028] in, This represents the polarization degree of the star map.

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

[0030] S4.1. Based on the observation conditions, the Stokes vector calculation error is calculated from the radiation noise level received by the star sensor, expressed as follows:

[0031]

[0032]

[0033]

[0034] in, The calculation error of the first component of the Stokes vector. This represents the calculation error of the second component of the Stokes vector. This represents the calculation error of the third component of the Stokes vector. The calculated value is for the first component of the Stokes vector of a stellar pixel. The calculated value for the second component of the Stokes vector for stellar pixels. The calculated value for the third component of the Stokes vector for stellar pixels. Let be the number of photoelectrons generated by the light transmitted through the micropolarizer with polarization direction i. The noise on the micro-polarizer pixel with polarization direction i;

[0035] S4.2. Solving the Sky Polarization Degree Calculation Error by Combining Stokes Vector Calculation Error with the Calculation Error The calculation formula is:

[0036]

[0037] in, The degree of polarization of a stellar pixel;

[0038] S4.3. Based on the sky polarization degree calculation error obtained in step S4.2, and combined with the polarization degree difference between stars and the sky background in the polarization degree image, the polarization signal-to-noise ratio calculation formula is defined as follows:

[0039]

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

[0041] Furthermore, step S5 is specifically implemented by using an adaptive threshold segmentation method to segment the star and sky background regions, and determining the star coordinates to obtain the polarization degree of the star pixels. The polarization degree of the sky background is determined based on the average value of the polarization degree measurement results of the sky background region. The root mean square error of the polarization degree measurement results in the sky background region is used as the error in the polarization degree calculation. Then, the polarization signal-to-noise ratio is calculated using the polarization signal-to-noise ratio calculation formula in step S4.3.

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

[0043] The beneficial effects of this invention are:

[0044] This invention presents a method for analyzing the star detection capability of star sensors based on polarization degree images. It fully utilizes the polarization dimension information in natural light and combines it with the measurement and solution method of the Stokes vector, effectively expanding the means of all-weather star detection by star sensors in near-Earth space. This invention can acquire polarization degree star maps that differ from energy distribution patterns. Based on error propagation laws, it derives the definition of polarization signal-to-noise ratio (PSNR). By fully considering the optical performance of micro-polarizers, it analyzes the PSNR and, by controlling the star sensor system parameters, effectively analyzes the improvement in star detection capability based on polarization degree star maps compared to star detection capabilities based on traditional star sensor star maps.

[0045] The present invention provides a method for analyzing the star detection capability of star sensors based on polarization degree images. This method fully considers the differences in polarization characteristics between the target and the background. It has guiding significance for the segmentation technology of complex cloud interference regions and the removal technology of interference sources such as artificial satellites and drones involved in near-Earth space star detection scenarios, and improves the robustness of near-Earth space all-weather star sensing technology to complex environments. Attached Figure Description

[0046] Figure 1 This is a flowchart of a star sensor star detection capability analysis method based on polarization degree image, as described in this invention.

[0047] Figure 2 This is a schematic diagram illustrating the definition of polarization signal-to-noise ratio in this invention;

[0048] Figure 3This is a schematic diagram of the star sensor with an integrated focal plane micro-polarizer array in this invention. Detailed Implementation

[0049] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be 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 for explaining the invention and are not intended to limit the invention; that is, the described specific embodiments are merely a part of the embodiments of the invention, and not all of them. The components of the specific embodiments of the invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations, and the invention may also have other embodiments.

[0050] Therefore, the following detailed description of specific embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected specific embodiments of the invention. All other specific embodiments obtained by those skilled in the art based on these specific embodiments without inventive effort are within the scope of protection of this invention.

[0051] To further understand the invention's content, features, and effects, the following specific embodiments are provided, along with accompanying drawings. Figure 1 -Appendix Figure 3 Detailed explanation is as follows:

[0052] Example 1:

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

[0054] S1. Construct a star sensor with an integrated focal plane micro-polarizer array, and then use the star sensor with the integrated focal plane micro-polarizer array to acquire four grayscale star images through short exposure;

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

[0056] S1.1. Construct a star sensor with an integrated focal plane micro-polarizer array, including a detector, a focal plane array, a micro-polarizer array, an optical system, a filter, and a light shield. The detector, focal plane array, micro-polarizer array, optical system, filter, and light shield are connected sequentially. The micro-polarizer array is arranged in the following order from the transmission direction: , , and It consists of alternating subwavelength metal gratings, the position and size of each subwavelength metal grating strictly correspond to the position and size of the pixels in the focal plane array of the star sensor, and every four subwavelength metal gratings with different transmission polarization directions constitute a 2×2 pixel superpixel.

[0057] S1.2. Construct a light intensity response model for the micro-polarizer, the expression of which is:

[0058]

[0059] in, The intensity of light transmitted through the micropolarizer. The transmittance of the micropolarizer is... The intensity of the light incident on the micropolarizer, The extinction ratio of the micropolarizer. The polarization degree of the incident light. To observe the polarization angle of the incident light along the field of view, Let be the transmission angle of the k-th micro-polarizer in the micro-polarizer array;

[0060] S1.3. Based on the principle that the grayscale response of a set of pixels in the transmission direction is consistent before and after the integration of the micro-polarizer, determine the exposure time of the star sensor of the integrated focal plane micro-polarizer array. The expression is:

[0061]

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

[0063] S1.4. Four grayscale star images were acquired via short exposure using a star sensor with an integrated focal plane micro-polarizer array, including images with the polarization direction as shown. The grayscale star map and transmission direction after the micro-polarizer are as follows: The grayscale star map and transmission direction after the micro-polarizer are as follows: The grayscale star map and transmission direction after micropolarization are as follows: Grayscale star map behind a micropolarizer.

[0064] S2. Calculate the Stokes vector of the starry sky based on the data in the four grayscale star images obtained in step S1, and obtain the Stokes vector image of the starry sky;

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

[0066]

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

[0068] S3. Calculate the polarization distribution of the starry sky based on the Stokes vector map of the starry sky obtained in step S2, and obtain the polarization star map;

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

[0070]

[0071] in, This represents the polarization degree of the star map.

[0072] S4. Construct a formula for calculating the polarization signal-to-noise ratio of stars in a polarization degree star map by utilizing the physical process of converting radiant energy into polarization degree;

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

[0074] S4.1. Based on the observation conditions, the Stokes vector calculation error is calculated from the radiation noise level received by the star sensor, expressed as follows:

[0075]

[0076]

[0077]

[0078] in, The calculation error of the first component of the Stokes vector. This represents the calculation error of the second component of the Stokes vector. This represents the calculation error of the third component of the Stokes vector. Calculate the value for the first component of the Stokes vector for stellar pixels. The calculated value for the second component of the Stokes vector for stellar pixels. The calculated value for the third component of the Stokes vector for stellar pixels. Let be the number of photoelectrons generated by the light transmitted through the micropolarizer with polarization direction i. The noise on the micro-polarizer pixel with polarization direction i;

[0079] S4.2. Solving the Sky Polarization Degree Calculation Error by Combining Stokes Vector Calculation Error with the Calculation Error The calculation formula is:

[0080]

[0081] in, The degree of polarization of a stellar pixel;

[0082] S4.3. Based on the sky polarization degree calculation error obtained in step S4.2, and combined with the polarization degree difference between stars and the sky background in the polarization degree image, the polarization signal-to-noise ratio calculation formula is defined as follows:

[0083]

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

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

[0086] Furthermore, step S5 is specifically implemented by using an adaptive threshold segmentation method to segment the star and sky background regions, and determining the star coordinates to obtain the polarization degree of the star pixels. The polarization degree of the sky background is determined based on the average value of the polarization degree measurement results of the sky background region. The root mean square error of the polarization degree measurement results in the sky background region is used as the error in the polarization degree calculation. Then, the polarization signal-to-noise ratio is calculated 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 detected by the near-Earth space all-day star sensor, and determine the detectability of the star in the polarization degree star map.

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

[0089] It should be noted that relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0090] Although this application has been described above with reference to specific embodiments, various modifications can be made and components can be replaced with equivalents without departing from the scope of this application. In particular, as long as there is no structural conflict, the features in the specific embodiments disclosed in this application can be combined with each other in any way. The lack of an exhaustive description of these combinations in this specification is merely for the sake of brevity and resource conservation. Therefore, this application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A method for analyzing the star detection capability of a star sensor based on polarization degree images, characterized in that, Includes the following steps: S1. Construct a star sensor with an integrated focal plane micro-polarizer array, and then use the star sensor with the integrated focal plane micro-polarizer array to acquire four grayscale star images through short exposure; The specific implementation method of step S1 includes the following steps: S1.

1. Construct a star sensor with an integrated focal plane micro-polarizer array, including a detector, a focal plane array, a micro-polarizer array, an optical system, a filter, and a light shield. The detector, focal plane array, micro-polarizer array, optical system, filter, and light shield are connected sequentially. The micro-polarizer array is arranged in the following order from the transmission direction: , , and It consists of alternating subwavelength metal gratings, the position and size of each subwavelength metal grating strictly correspond to the position and size of the pixels in the focal plane array of the star sensor, and every four subwavelength metal gratings with different transmission polarization directions constitute a 2×2 pixel superpixel. S1.

2. Construct a light intensity response model for the micro-polarizer, the expression of which is: ； in, The intensity of light transmitted through the micropolarizer. The transmittance of the micropolarizer is... The intensity of the light incident on the micropolarizer, The extinction ratio of the micropolarizer. The polarization degree of the incident light. To observe the polarization angle of the incident light along the field of view, Let be the transmission angle of the k-th micro-polarizer in the micro-polarizer array; S1.

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

4. Four grayscale star images were acquired via short exposure using a star sensor with an integrated focal plane micro-polarizer array, including images with the polarization direction as shown. The grayscale star map and transmission direction after the micro-polarizer are as follows: The grayscale star map and transmission direction after the micro-polarizer are as follows: The grayscale star map and transmission direction after micropolarization are as follows: Grayscale star map behind a micro-polarizer; S2. Calculate the Stokes vector of the starry sky based on the data in the four grayscale star images obtained in step S1, and obtain the Stokes vector image of the starry sky; In step S2, the expression for calculating the Stokes vector of the starry sky based on the data from the four grayscale star images obtained in step S1 is as follows: ； in, Indicates the corresponding polarization direction is The number of photoelectrons received by the pixel behind the micropolarizer Indicates the corresponding polarization direction is The number of photoelectrons received by the pixel behind the micropolarizer Indicates the corresponding polarization direction is The number of photoelectrons received by the pixel behind the micropolarizer Indicates the corresponding polarization direction is The number of photoelectrons received by the pixel behind the micropolarizer It is the first component of the Stokes vector calculation value. It is the second component of the Stokes vector calculation value. It is the third component of the Stokes vector calculation value. It is the fourth component of the Stokes vector calculation value; S3. Calculate the polarization distribution of the starry sky based on the Stokes vector map of the starry sky obtained in step S2, and obtain the polarization star map; S4. Construct a formula for calculating the polarization signal-to-noise ratio of stars in a polarization degree star map by utilizing the physical process of converting radiant energy into polarization degree; The specific implementation method of step S4 includes the following steps: S4.

1. Based on the observation conditions, the Stokes vector calculation error is calculated from the radiation noise level received by the star sensor, expressed as follows: ； ； ； in, The calculation error of the first component of the Stokes vector. This represents the calculation error of the second component of the Stokes vector. This represents the calculation error of the third component of the Stokes vector. Calculate the value for the first component of the Stokes vector for stellar pixels. The calculated value for the second component of the Stokes vector for stellar pixels. The calculated value for the third component of the Stokes vector for stellar pixels. Let be the number of photoelectrons generated by the light transmitted through the micropolarizer with polarization direction i. The noise on the micro-polarizer pixel with polarization direction i; S4.

2. Solving the Sky Polarization Degree Calculation Error by Combining Stokes Vector Calculation Error with the Calculation Error The calculation formula is: ； in, The degree of polarization of a stellar pixel; S4.

3. Based on the sky polarization degree calculation error obtained in step S4.2, and combined with the polarization degree difference between stars and the sky background in the polarization degree image, the polarization signal-to-noise ratio calculation formula is defined as follows: ； in, For polarization signal-to-noise ratio, The degree of polarization of the sky background; S5. Calculate the polarization signal-to-noise ratio of stars within the field of view based on the formula for calculating the polarization signal-to-noise ratio of stars in the polarization degree 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 detected by the near-Earth space all-day star sensor, and determine the detectability of the star in the polarization degree star map.

2. The method for analyzing the star detection capability of a star sensor based on polarization degree images according to claim 1, characterized in that, The relationship between the star map polarization degree and the calculated Stokes vector value in step S3 is as follows: ； in, This represents the polarization degree of the star map.

3. The method for analyzing the star detection capability of a star sensor based on polarization degree images according to claim 2, characterized in that, The specific implementation method of step S5 is to use an adaptive threshold segmentation method to segment the star and sky background regions, and determine the star point coordinates to obtain the polarization degree of the star pixels. The polarization degree of the sky background is determined based on the average value of the polarization degree measurement results of the sky background region. The root mean square error of the polarization degree measurement results in the sky background region is used as the error in the polarization degree calculation. Then, the polarization signal-to-noise ratio is calculated using the polarization signal-to-noise ratio calculation formula in step S4.

3.

4. The method for analyzing the star detection capability of a star sensor based on polarization degree images according to claim 3, characterized in that, In step S6, the criterion for determining whether a star is detectable is that stars with a polarization signal-to-noise ratio greater than 5 are detectable.

Images