Target extraction method under fixed star background and electronic equipment

Abstract

The invention discloses a target extraction method under a fixed star background and electronic equipment. The method comprises the following steps: carrying out gray correction on imaging points at all positions in an image plane of a space sensor; dividing the imaging points into a fixed star set and a target set according to fixed star projection of a complete star catalogue; performing gray scale-star magnitude calibration based on the spectrum property of the fixed star; and calculating an accurate position of a target imaging point in the image plane according to the imaging point, which is greatly deviated from the gray scale-star magnitude calibration, in the fixed star set, and classifying the accurate position into the target set. According to the method, the imaging points of the image plane are divided through fixed star projection and gray scale correction, and the fixed star and the target can be distinguished only through single-frame image information. And the position of the target is calculated according to the imaging point for the condition that the target is shielded by the fixed star through gray scale-star magnitude calibration, so that the accuracy is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of space target extraction, and particularly to a method for target extraction under a stellar background and an electronic device. Background Art

[0002] A space sensor refers to a sensor that is applied to a space environment and obtains spacecraft attitude or navigation information based on an optical detection principle. As the "eyes" of a spacecraft, space sensors can provide accurate pointing or position information for space missions such as remote sensing mapping, weapon tracking, scientific observation, and deep space exploration. Compared with optical payloads such as remote sensing cameras, space telescopes, and ground laser altimeters, the data of optical sensors can be directly connected to a control closed-loop, and the output requirements are real-time, accurate, and reliable, which is an important guarantee for the safe and stable operation of a spacecraft platform.

[0003] However, when a space sensor detects a target, it is easily interfered by a stellar background, especially for a space sensor with high sensitivity. In order to avoid the interference of the stellar background in the prior art, it is necessary to correlate multiple frames of star maps to obtain the motion characteristics of stars, so as to distinguish stars from the detection targets of space sensors. However, the motion of most high-orbit targets is very slow. When using the above method, it is necessary to accumulate a sufficient amount of data to distinguish from stars, which requires high memory and computational requirements and is not conducive to on-orbit implementation. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for target extraction under a stellar background and an electronic device, which are used to solve the problem that the prior art has high requirements for memory and computational amount and is not conducive to on-orbit implementation. By dividing the imaging points on the image plane through stellar projection, it is possible to distinguish stars and targets only with single-frame image information. And through gray-scale - magnitude calibration, in the case where the target is blocked by a star, the target position is further calculated through the imaging points, which is beneficial to improving the accuracy. It is conducive to on-orbit implementation and has low requirements for memory and computational amount.

[0005] In order to achieve the above purpose, the present invention is realized through the following technical solutions:

[0006] The first aspect of the present invention provides a method for target extraction under a stellar background, including:

[0007] Performing gray-scale correction on the imaging points at various positions in the image plane of the space sensor;

[0008] Dividing the imaging points into a star set and a target set according to the stellar projection of a complete star catalog;

[0009] Performing gray-scale - magnitude calibration based on the spectroscopic properties of stars;

[0010] Calculate the accurate position of the target imaging point in the image plane according to the imaging points in the set of stars that deviate greatly from the gray-scale magnitude calibration, and classify the accurate position into the target set.

[0011] Optionally, the gray-scale correction includes:

[0012] Fit the angle X between the imaging position and the center field of view and the percentage Y of the imaging energy in the imaging energy of the center field of view through the following formula:

[0013] Y = a*X 6 +b*X 4 +c*X 2 +d;

[0014] According to the fitting result, correct the gray-scale of the imaging point through the following formula:

[0015]

[0016] where X i is the angle between the imaging point and the center field of view; grey i is the gray-scale of the imaging point; grey_cali i is the corrected gray-scale.

[0017] Optionally, calculate the angle X between the imaging point and the center field of view through the following formula i :

[0018]

[0019] where imagex i is the x coordinate of the imaging point, imagey i is the y coordinate of the imaging point; x 0 is the x coordinate of the camera principal point, y 0 is the y coordinate of the camera principal point; f is the focal length of the camera.

[0020] Optionally, the dividing the imaging points into the set of stars and the target set according to the stellar projection of the complete star catalog includes:

[0021] Project the stars in the complete star catalog onto the image plane using the camera attitude solved by star map recognition to obtain the stellar projection, classify the imaging points corresponding to the stellar projection into the set of stars, and classify the remaining imaging points into the target set.

[0022] Optionally, the gray-scale magnitude calibration based on the spectroscopic properties of the stars includes:

[0023] The spectroscopic properties are obtained based on the surface temperature of the star, the G-band magnitude, and the G-band passband;

[0024] Based on the spectroscopic properties, calculate the number of photoelectrons excited by the star on the space sensor, and calculate the instrumental magnitude of the star on the space sensor according to the number of photoelectrons;

[0025] Perform least squares fitting on the gray level of the imaging point in the star set and the instrumental magnitude.

[0026] Optionally, the obtaining of the spectroscopic properties based on the surface temperature of the star, the G-band magnitude, and the G-band passband includes:

[0027] Calculate the number of photoelectrons A(λ, T) radiated per unit volume of the blackbody per unit time and per unit wavelength through the following formula:

[0028]

[0029] where λ is the radiation wavelength; T is the surface temperature of the star; h is Planck's constant; c is the speed of light; kB is Boltzmann's constant;

[0030] Calculate the constant R representing the spectroscopic properties through the following formula:

[0031]

[0032] where Mv is the G-band magnitude of the star; E0 is the number of photoelectrons excited by the star on the Gaia detection instrument when the G-band magnitude of the star is 0; Trans_Gaia is the G-band passband of the Gaia detection instrument;

[0033] The range of the G-band is 330 nm to 1050 nm.

[0034] Optionally, calculate the number of photoelectrons excited by the star on the space sensor through the following formula:

[0035]

[0036] where Trans_Search is the passband of the search camera of the space sensor;

[0037] Calculate the instrumental magnitude through the following formula:

[0038]

[0039] where, Mv i is the instrumental magnitude of star i; E base is the number of photoelectrons excited by Vega on the space sensor; Ei is the number of photoelectrons excited by star i on the space sensor.

[0040] Optionally, the least squares fitting is performed according to the following formula:

[0041] 2.512 -Mv = k1 * grey + k2;

[0042] where grey is the gray scale of the imaging point in the star set; Mv is the instrumental magnitude.

[0043] Optionally, record the coordinates of the imaging point in the image plane that deviates greatly from the result of the least squares fitting in the star set as (x, y), and the gray scale value is g;

[0044] Record the coordinates of the star projection of the star corresponding to the imaging point in the image plane as (x0, y0), and the gray scale value calculated through the result of the least squares fitting according to the instrumental magnitude is g0;

[0045] The coordinates of the accurate position are: ((g * x - g0 * x0) / (g - g0), (g * y - g0 * y0) / (g - g0)).

[0046] The second aspect of the present invention provides an electronic device, including a processor and a memory, and a computer program is stored on the memory. When the computer program is executed by the processor, the method for extracting a target under the star background described in any one of the above first aspects is implemented.

[0047] The present invention has at least one of the following technical effects:

[0048] By dividing the imaging points in the image plane of the space sensor that have been gray-scale corrected according to the star projections of the complete star catalog into a star set and a target set, it is possible to initially distinguish the star background from the detection target of the space sensor only with single-frame image information, which is beneficial for on-orbit implementation, and is applicable to the space environments of low orbits and high orbits, with low requirements for memory and computational workload.

[0049] By performing gray-scale - magnitude calibration, for the situation where the detection target of the space sensor is often blocked by stars, it is considered that the imaging points in the star set that deviate greatly from the gray-scale - instrumental magnitude calibration result may be the overlapping imaging of stars and the detection target, and further calculate the possible position of the detection target through the imaging points, improving the accuracy of target extraction. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 is a schematic flowchart of the method for extracting a target under the star background provided by an embodiment of the present invention;

[0051] Figure 2 A schematic diagram for fitting the angle X of the imaging position from the center field of view and the percentage Y of the imaging energy in the imaging energy of the center field of view provided by an embodiment of the present invention;

[0052] Figure 3 A schematic diagram for least squares fitting of the gray level of the imaging point and the instrumental magnitude provided by an embodiment of the present invention. Detailed implementation manners

[0053] The following further describes in detail a method for target extraction and an electronic device under a stellar background proposed by the present invention in conjunction with the accompanying drawings and specific implementation manners. According to the following description, the advantages and features of the present invention will be clearer. It should be noted that the accompanying drawings are in a very simplified form and all use non-precise scales, only for the purpose of facilitating and clearly assisting in explaining the embodiments of the present invention. In order to make the objectives, features, and advantages of the present invention more obvious and understandable, please refer to the accompanying drawings. It should be noted that the structures, ratios, sizes, etc. shown in the drawings of this specification are only used to cooperate with the content disclosed in the specification for those skilled in the art to understand and read, and are not used to limit the limiting conditions for the implementation of the present invention. Therefore, they do not have a substantial technical meaning. Any modification of the structure, change of the proportional relationship, or adjustment of the size, without affecting the effects that the present invention can produce and the objectives that can be achieved, should still fall within the scope covered by the technical content disclosed by the present invention.

[0054] As Figure 1 shown, in the first aspect of this embodiment, a method for target extraction under a stellar background is provided, including: performing gray level correction on the imaging points at various positions in the image plane of the space sensor; dividing the imaging points into a stellar set and a target set according to the stellar projection of the complete star catalog; performing gray level - magnitude calibration based on the spectroscopic properties of the stars; calculating the accurate position of the target imaging point in the image plane according to the imaging points in the stellar set that deviate greatly from the gray level - magnitude calibration, and classifying the accurate position into the target set.

[0055] Specifically, the imaging point may be a pixel region in the image plane, and the gray level of the imaging point may be obtained, for example, by summing the gray levels of all pixel points in the pixel region. As Figure 2 shown, in order to perform the gray level correction on the imaging points, the angle X of each imaging position in the image plane of the space sensor from the center field of view and the percentage Y of the imaging energy in the imaging energy of the center field of view may be fitted by the following formula:

[0056] Y = a * X 6 + b * X 4 + c * X 2 + d;

[0057] Among them, a, b, c, and d in the formula are constants obtained by fitting X and Y using fitting software according to the above fitting formula.

[0058] Furthermore, according to the fitting result, the gray level of the imaging point can be corrected uniformly through the following formula:

[0059]

[0060] Among them, X i is the angle of the imaging point from the central field of view, grey i is the gray level of the imaging point, and grey_cali i is the corrected gray level of the imaging point.

[0061] The angle X of the imaging point from the central field of view can be calculated through the following formula i :

[0062]

[0063] Among them, imagex i is the x coordinate of the imaging point, imagey i is the y coordinate of the imaging point, x 0 is the x coordinate of the camera principal point, y 0 is the y coordinate of the camera principal point, and f is the focal length of the camera.

[0064] As Figure 1 shown, in order to divide the imaging points into the star set and the target set, it is necessary to project the stars in the complete star catalog onto the image plane using the camera attitude solved by star map recognition, so as to obtain the star projection. After gray level comparison, the imaging points corresponding to the star projection can be classified into the star set, and the remaining imaging points can be classified into the target set. Thus, the division of the imaging points is completed, and the distinction between the star background and the detection target of the space sensor is initially realized. The above star map recognition can be, for example, star map recognition of the on-orbit star map and the navigation star catalog.

[0065] Specifically, the following set I is the set of imaging points:

[0066] {(imagex 1 , imagey 1 ) (imagex 2 , imagey 2 )…(imagex n , imagey n )}

[0067] ; Let the following set P be the set of stellar points obtained by projecting the stars in the complete star catalog:

[0068] {(projectx 1 , projecty 1 ) (projectx 2 , projecty 2 )…(projectx n , projecty n )}

[0069] Compare set I and set P, and classify the imaging points whose distance from the projected stellar points is within the threshold as stellar imaging points and classify them into the stellar set.

[0070] To obtain the complete star catalog, it can be achieved by combining the Gaia star catalog and the Hipparcos star catalog. Among them, the Gaia star catalog is a star catalog created by the Gaia detection instrument of the European Space Agency. The Gaia detection instrument is used to observe one billion stars in the Milky Way, measure their positions, distances, and motions, and obtain clues about dark matter and dark energy. The Hipparcos star catalog is the main result obtained by observing with the Hipparcos astrometric satellite of the European Space Agency. The Hipparcos satellite is used to measure the parallax and proper motion of stars. The steps to obtain the complete star catalog can be carried out before performing the gray correction on the imaging points in the image plane to facilitate improving the efficiency of target extraction work.

[0071] Specifically, the above gray-scale - magnitude calibration based on the spectroscopic properties of stars includes the following steps: Obtain the spectroscopic properties according to the surface temperature of the star, the G-band magnitude, and the G-band passband; Calculate the number of photoelectrons excited by the star on the space sensor according to the spectroscopic properties, and calculate the instrumental magnitude of the star on the space sensor according to the number of photoelectrons; Perform a least-squares fit on the gray scale of the imaging points in the stellar set and the instrumental magnitude of the star.

[0072] First, to obtain the spectroscopic properties, it is necessary to calculate a constant R representing the spectroscopic properties. The constant R is related to the size and distance of the star. To calculate the constant R, the formula for the energy radiated by a blackbody per unit volume per unit time and per unit wavelength can be used:

[0073]

[0074] The following formula for calculating the number of photoelectrons A(λ, T) radiated by a blackbody per unit volume per unit time and per unit wavelength is obtained:

[0075]

[0076] Among them, λ is the radiation wavelength with the unit of m; T is the surface temperature of the star with the unit of K; h is Planck's constant, for example, taking 6.626e-34; c is the speed of light, for example, taking 2.997e8 m / s; kB is Boltzmann's constant, for example, taking 1.38e-23.

[0077] Furthermore, for a certain star with a surface temperature of T, the number of photoelectrons excited on the Gaia detection instrument in the G band with a range of 330 nm to 1050 nm can be calculated by the following formula:

[0078]

[0079] Therefore, the constant R representing the spectroscopic property can be calculated by the following formula:

[0080]

[0081] Among them, Mv is the G-band magnitude of the star, E0 is the number of photoelectrons excited on the Gaia detection instrument when the G-band magnitude of the star is 0, and Trans_Gaia is the G-band passband of the Gaia detection instrument.

[0082] After obtaining the constant R, the number of photoelectrons excited by the star on the space sensor can be calculated according to the constant R, and the instrumental magnitude of the star on the space sensor can be calculated according to the number of photoelectrons. Specifically, Vega can be used as the reference for the instrumental magnitude of the space sensor to calculate the instrumental magnitudes of other stars on the space sensor.

[0083] Specifically, the number of photoelectrons excited by the star on the space sensor can be calculated by the following formula:

[0084]

[0085] Among them, Trans_Search is the passband of the search camera of the space sensor, taking into account the quantum efficiency, lens transmittance, and protection window transmittance of the search camera of the space sensor.

[0086] And the instrumental magnitude can be calculated by the following formula:

[0087]

[0088] Among them, Mv i is the instrumental magnitude of star i; E base is the number of photoelectrons excited by Vega on the space sensor; E i is the number of photoelectrons excited by star i on the space sensor.

[0089] After calculating the instrumental magnitude of the instrument, as Figure 3 shown, the least squares fitting can be performed on the gray level of the imaging points in the star set and the instrumental magnitude of the corresponding stars according to the following formula:

[0090] 2.512 -Mv = k1 * grey + k2;

[0091] where grey is the gray level of the imaging points in the star set, and the gray level grey can be the corrected gray level; Mv is the instrumental magnitude.

[0092] The above steps for implementing the gray level - magnitude calibration can be performed only at the initial stage of the operation of the space sensor, and can be executed on orbit or the data can be downloaded to the ground for execution. After obtaining the fitting relationship between the gray level of the imaging points corresponding to the stars and the instrumental magnitude of the stars, only other steps of this method need to be repeatedly executed to achieve the extraction of the target.

[0093] Finally, as Figure 1 shown, according to the imaging points in the star set that deviate greatly from the gray level - magnitude calibration, that is, the imaging points in the star set whose gray level values deviate greatly from the result of the least squares fitting, calculate the accurate position of the target imaging point in the image plane and classify the accurate position into the target set.

[0094] Specifically, record the coordinates of the imaging point in the image plane as (x, y), and the gray level value as g; the gray level value g can be the corrected gray level.

[0095] Record the coordinates of the star projection of the star corresponding to the imaging point in the image plane as (x0, y0), and the gray level value calculated through the result of the least squares fitting according to the instrumental magnitude as g0;

[0096] Then, the coordinates of the accurate position are: ((g * x - g0 * x0) / (g - g0), (g * y - g0 * y0) / (g - g0)).

[0097] By performing the gray level - magnitude calibration, the gray level that the corresponding star should have in the image plane can be calculated and compared with the actual gray level of the imaging point. Thus, it can be judged whether there are target imaging points in the image plane covered by the star spots of the stars, and further the imaging points of the space target can be extracted from the star spots, improving the accuracy of target extraction.

[0098] In other aspects, this embodiment also provides an electronic device, including a processor and a memory. A computer program is stored on the memory. When the computer program is executed by the processor, the methods described above are implemented.

[0099] In the present invention, by means of stellar projection and gray correction, the imaging points in the image plane are divided into a stellar set and a target set. Only single-frame image information is required to initially distinguish between the stellar background and the detection target of the space sensor. Through gray-magnitude calibration, in the case where the detection target is blocked by a star, the possible position of the detection target is further calculated through the imaging points deviated from the gray-magnitude calibration, improving the accuracy of target extraction. The target extraction method of the present invention is conducive to on-orbit implementation, applicable to the space environments of low orbits and high orbits, with low requirements for memory and computational amount, and has significant progress compared with the prior art.

[0100] It should be noted that in this article, the terms "including", "comprising" or any other variants thereof are intended to cover non-exclusive inclusion, such that a process, method, article or device including a series of elements not only includes those elements but also includes other elements not expressly listed, or further includes elements inherent to such process, method, article or device. Without further limitation, an element defined by the statement "including a..." does not exclude the existence of additional identical elements in the process, method, article or device including the said element.

[0101] It should be noted that the devices and methods disclosed in the embodiments of this article can also be implemented in other ways. The device embodiments described above are merely illustrative. For example, the flowcharts and block diagrams in the drawings show the possible architectures, functions and operations of devices, methods and computer program products according to multiple embodiments of this article. In this regard, each block in the flowchart or block diagram can represent a module, program or part of code, and the module, program segment or part of code contains one or more executable instructions for implementing the specified logical function. It should also be noted that in some alternative implementations, the functions marked in the blocks may occur in a different order from that marked in the drawings. For example, two consecutive blocks can actually be executed substantially in parallel, and they can sometimes be executed in the reverse order, depending on the functions involved. It should also be noted that each block in the block diagram and / or flowchart, and the combination of blocks in the block diagram and / or flowchart, can be implemented by a dedicated hardware-based system for performing the specified function or action, or can be implemented by a combination of dedicated hardware and computer instructions.

[0102] Although the content of the present invention has been described in detail through the above preferred embodiments, it should be recognized that the above description should not be considered as a limitation of the present invention. After those skilled in the art have read the above content, various modifications and alternatives to the present invention will be obvious. Therefore, the protection scope of the present invention should be defined by the appended claims.

Claims

1. A method for extracting a target under a star background, characterized in that: include: Performing grayscale correction on imaging points at various positions in the image plane of the spatial sensor; According to the star projection of the complete star catalog, the imaging points are divided into a star set and a target set; Grayscale-magnitude calibration based on the spectral properties of stars; According to the imaging point in the star set that deviates greatly from the grayscale-magnitude calibration, the accurate position of the target imaging point in the image plane is calculated, and the accurate position is classified into the target set.

2. The target extraction method under the star background according to claim 1, characterized in that: The grayscale correction comprises: The angle X between the imaging position and the center field of view and the percentage Y of the imaging energy in the center field of view are fitted by the following formula: Y=a*X 6 +b*X 4 +c*X 2 +d; According to the fitting result, the grayscale of the imaging point is corrected by the following formula: Among them, X i is the angle between the imaging point and the central field of view; grey i is the grayscale of the imaging point; grey_cali i is the corrected grayscale.

3. The target extraction method under the star background according to claim 2 is characterized in that: The angle X between the imaging point and the center field of view is calculated by the following formula i : Among them, imagex i is the x coordinate of the imaging point, imagey i is the y coordinate of the imaging point; x0 is the x coordinate of the camera principal point, y0 is the y coordinate of the camera principal point; f is the focal length of the camera.

4. The target extraction method under the star background according to claim 1 is characterized in that: The dividing the imaging points into the star set and the target set according to the star projection of the complete star catalog comprises: The stars in the complete star catalog are projected onto the image plane using the camera attitude solved by star map recognition to obtain the star projection, the imaging points corresponding to the star projection are classified into the star set, and the remaining imaging points are classified into the target set.

5. The target extraction method under the star background according to claim 4, characterized in that: The grayscale-magnitude calibration based on the spectral properties of stars includes: The spectral properties are obtained according to the stellar surface temperature, G-band magnitude and G-band passband; Calculate the number of photoelectrons excited by the star on the space sensor according to the spectral properties, and calculate the instrumental magnitude of the star on the space sensor according to the number of photoelectrons; A least squares fit is performed on the grayscale of the imaging point in the star set and the instrument magnitude.

6. The method for extracting a target under a star background according to claim 5, characterized in that: The spectral properties obtained according to the stellar surface temperature, G-band magnitude, and G-band passband include: The number of photoelectrons A(λ,T) radiated by a black body per unit volume per unit time and per unit wavelength is calculated by the following formula: Among them, λ is the wavelength of radiation; T is the surface temperature of the star; h is Planck's constant; c is the speed of light; kB is the Boltzmann constant; The constant R representing the spectroscopic properties is calculated by the following formula: Wherein, Mv is the G-band magnitude of the star; E0 is the number of photoelectrons excited on the Gaia detection instrument when the G-band magnitude of the star is 0; Trans_Gaia is the G-band passband of the Gaia detection instrument; The G band ranges from 330nm to 1050nm.

7. The method for extracting a target under a star background according to claim 6, characterized in that: The number of photoelectrons E excited by the star on the space sensor is calculated by the following formula: Wherein Trans_Search is the passband of the search camera of the spatial sensor; The instrument magnitude is calculated by the following formula: Among them, Mv i is the instrumental magnitude of star i; E base is the number of photoelectrons excited by Vega on the space sensor; E i is the number of photoelectrons excited by star i on the space sensor.

8. The method for extracting a target under a star background according to claim 5, characterized in that: The least squares fitting is performed according to the following formula: 2.512 -Mv =k1*grey+k2; Wherein, grey is the grayscale of the imaging point in the star set; Mv is the instrumental magnitude.

9. The method for extracting a target under a star background according to claim 5, characterized in that: Record the coordinates of the imaging point in the star set that deviates greatly from the result of the least squares fitting in the image plane as (x, y) and the gray value as g; Record the coordinates of the star projection of the star corresponding to the imaging point in the image plane as (x0, y0), and calculate the gray value g0 according to the instrument magnitude through the result of the least squares fitting; The coordinates of the exact position are: ((g*x-g0*x0) / (g-g0), (g*y-g0*y0) / (g-g0)).

10. An electronic device, characterized in that: The method comprises a processor and a memory, wherein a computer program is stored in the memory, and when the computer program is executed by the processor, the method for extracting a target under a star background according to any one of claims 1 to 9 is implemented.

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