A method for automatic preparation of an infrared star catalogue

Abstract

The application discloses a preparation method of an infrared star table and belongs to the field of astronomical navigation. Visible light star magnitudes and color indexes of stars in an original star table are acquired to estimate surface temperatures; the radiation power ratio of each star to Vega in infrared and visible light wave bands is calculated with Vega as a zero-magnitude star benchmark; visible light star magnitudes are converted into target infrared wave band star magnitudes through a formula; and an infrared star table is generated through correlation storage. The application converts visible light star magnitudes into infrared star magnitudes to generate a special infrared star table, thereby improving the star map recognition success rate and the attitude solution reliability.

Description

Technical Field

[0001] This invention relates to the fields of photoelectric imaging and high-precision measurement technology, and specifically to a method for automatically generating star tables for star sensors. Background Technology

[0002] The star sensor is a fixed-focus lens camera, with the photoelectric sensor mounted on the focal plane of the lens. Starlight (parallel light) is focused onto the photoelectric sensor after passing through the lens, where photoelectric conversion is completed to form a digital star map. Stars appear as small bright spots with a bright center and dark edges in the image.

[0003] The star sensor extracts the position coordinates of the star image on the sensor and the position vector in the star sensor coordinate system by extracting the star target. Then, it identifies the star using a star image recognition algorithm. The current attitude of the star sensor can be calculated based on the position vector of the star point in the star sensor coordinate system and the position vector in the inertial frame.

[0004] Star brightness information is one of the most important pieces of information in captured images, and many star map recognition algorithms utilize this information. However, existing infrared star sensor products directly use the Hipparcos star catalog as their base catalog. The magnitudes in this catalog are visible light magnitudes, which cannot perfectly match the brightness in actual captured images. Therefore, in actual star measurement, discrepancies arise between the brightness of stars in the captured images and the theoretical brightness of stars in the star catalog. This leads to the failure of all-sky star map matching, thus preventing the correct attitude output. Summary of the Invention

[0005] Existing methods for preparing visible light star catalogs often lead to attitude calculation failures due to a mismatch between theoretical brightness and actual brightness measured by infrared star sensors. The main objective of this invention is to propose a star catalog preparation method adapted to infrared star sensors, converting visible light magnitudes to infrared magnitudes to generate a dedicated infrared star catalog, thereby improving the success rate of star chart recognition and the reliability of attitude calculation.

[0006] This invention provides a method for automatically preparing an infrared star catalog, comprising: Acquire visible light magnitude data and color index data of stars; Estimate the surface temperature of the star based on the color index data; Using the star as a blackbody, the radiant power of the star in the infrared band is calculated based on the surface temperature using Planck's blackbody radiation formula. The infrared magnitude of the star is calculated based on the ratio of the star's radiant power in the infrared band to that of a preset standard 0 magnitude star in the same infrared band, and the visible light magnitude data. The calculated infrared magnitudes are associated with and stored with the identification information of each star to generate an infrared star catalog.

[0007] In some instances, calculating the infrared magnitude of a star based on the ratio of its radiant power in the infrared band to that of a preset standard 0-magnitude star in the same infrared band includes: Obtain the radiant power of a preset standard 0 magnitude star in the infrared band. ,as well as The radiant power of a pre-defined standard 0 magnitude star in the visible light band ; Calculate the radiant power of stars in the same infrared band using Planck's blackbody radiation formula. And the radiant power of stars in the same visible light band. ; based on , , as well as Calculate the infrared magnitude. The surface temperature of a star. λ represents the surface temperature of a standard 0 magnitude star, and λ1 and λ2 represent the start and end wavelengths of the infrared band, respectively.

[0008] In some instances, by The infrared magnitude was obtained , The visible light magnitude corresponding to a star.

[0009] In some instances, estimating the surface temperature of the star based on the color index data includes: Obtain the BV color index of the star; The BV color index is converted into the surface temperature using a preset temperature-color index relationship model.

[0010] In some instances, the preset temperature-color index relationship model is as follows: When the original star catalog data provides the VB color index, the BV color index is the opposite of it.

[0011] In some instances, the standard 0 magnitude star is Vega, which has a BV color index and a magnitude of 0 in all wavelength bands, and its surface temperature is... It is 9986K.

[0012] In some instances, the method further includes: When the original star catalog data contains the spectral type of each star, the color index of each star is obtained by querying the spectral type and color index relationship table, which includes at least the correspondence between the spectral type, BV color index and VI color index of the star; For stars with a BV color index less than or equal to 1.33 corresponding to their spectral type, their VI color index is estimated using the linear fitting formula VI = 1.0466 × (BV) - 0.0509. For stars with a BV color index greater than 1.33 corresponding to a spectral type, their VI color index is estimated by piecewise linear interpolation. The surface temperature of the star is obtained from the estimated VI color index.

[0013] In some instances, the visible magnitudes in the original star catalog data are derived from visible star catalogs, and the color indices are derived from stellar spectral type classification data or photometric observation data.

[0014] In some instances, the method further includes: After calculating the initial infrared magnitude of each star, the initial infrared magnitude is corrected according to the detector quantum efficiency curve and atmospheric transmittance curve of the infrared star sensor to obtain the final infrared magnitude after instrument effect correction. The final infrared magnitude is then stored in the infrared star table instead of the initial infrared magnitude.

[0015] In summary, compared with the prior art, the above-described technical solutions conceived by this invention can achieve the following beneficial effects: This invention estimates the surface temperature of each star by acquiring its visible magnitude and color index from multiple stars in an original star catalog. Using Vega as a standard zero-magnitude star, it calculates the ratio of the radiant power of each star to Vega in the target infrared and visible light bands, and then calculates the infrared magnitude of each star in the target infrared band. Finally, it associates and stores the infrared magnitudes of each star with identification information to generate a dedicated infrared star catalog. This method uses Vega as a unified zero-point reference, is fully compatible with existing magnitude systems, and only requires easily obtainable visible magnitudes and color indices from the star catalog to complete the calculations. It can be flexibly adjusted for different infrared detection bands, fundamentally eliminating the systematic errors caused by differences in stellar temperature leading to different infrared and visible light radiation characteristics. This significantly improves the magnitude matching accuracy of infrared star sensors. Furthermore, by generating dedicated star catalog data products offline in batches, it avoids the burden of real-time on-orbit calculations for star sensors, providing high-precision, low-cost stellar identification data support for spacecraft attitude determination. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a schematic diagram of the method for automatically preparing an infrared star catalog provided in an embodiment of the present invention. Detailed Implementation

[0018] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] In the following description, specific embodiments of the invention will be illustrated with reference to steps and symbols performed by one or more computers, unless otherwise stated. Therefore, these steps and operations will be referred to several times as being performed by a computer, and computer execution as referred to herein includes operations by a computer processing unit representing electronic signals of data in a structured format. This operation transforms the data or maintains it at a location in the computer's memory system, which can be reconfigured or otherwise alter the operation of the computer in a manner well known to those skilled in the art. The data structure maintained by the data is the physical location of the memory, which has specific characteristics defined by the data format. However, the principles of the invention described above are not intended to be limiting, and those skilled in the art will understand that many of the following steps and operations can also be implemented in hardware.

[0020] The terms "module" or "unit" as used herein can be considered as software objects executing on the computing system. Different components, modules, engines, and services described herein can be considered as implementations on the computing system. The apparatus and methods described herein are preferably implemented in software, but can also be implemented in hardware, both of which are within the scope of this invention.

[0021] Those skilled in the art will understand that, unless specifically stated otherwise, the singular forms “a,” “an,” and “the” used herein may also include the plural forms. It should be further understood that the term “comprising” as used in this specification means the presence of features, integers, steps, operations, elements, and / or components, but does not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof. It should be understood that when we say an element is “connected” or “coupled” to another element, it can be directly connected or coupled to the other element, or there may be intermediate elements. Furthermore, “connected” or “coupled” as used herein can include wireless connections or wireless coupling. The term “and / or” as used herein includes all or any units and all combinations of one or more associated listed items.

[0022] In this embodiment of the invention, since the brightness of a star is mainly contributed by its own emission, and the brightness from reflected light is negligible, the star can be considered a blackbody, and its radiant power in a specific wavelength band can be calculated using Planck's blackbody radiation formula. By comparing the power with that of a 0-magnitude star in the corresponding wavelength band, the magnitude of the star can be obtained. Specifically, this embodiment of the invention provides a method for automatically preparing an infrared star catalog, such as... Figure 1 As shown, it includes the following steps: S101: Acquire visible light magnitude data and color index data of stars; S102: Estimating the surface temperature of stars based on color index data; S103: Using stars as blackbodies, calculate the radiant power of stars in the infrared band based on their surface temperature using Planck's blackbody radiation formula. S104: Calculate the infrared magnitude of a star based on the ratio of its radiant power in the infrared band to that of a pre-defined standard 0 magnitude star in the same infrared band, and visible light magnitude data. S105: Associate and store the calculated infrared magnitudes with the identification information of each star to generate an infrared star catalog.

[0023] In some instances, the calculation of a star's infrared magnitude based on the ratio of its radiant power in the infrared band to that of a pre-defined standard 0-magnitude star in the same infrared band can be achieved in the following ways: It can be obtained through theoretical calculations of blackbody radiation and comparison with visible light magnitudes. The relationship between magnitude and brightness is known to be... Therefore, assuming that the radiated power of each band conforms to this formula, we can calculate its relative radiated power:

[0024] in For the blackbody radiation formula:

[0025] The temperature of a star can be estimated using its color index (BV):

[0026] If the star chart provides the VB index, then BV is its opposite.

[0027] Specifically, as a standard magnitude 0 star, Vega has a magnitude and BV index of 0 in all wavelengths. According to the above formula, its temperature is... =9986K. Therefore, for a specific star, its visible magnitude can be found in the star catalog. By using the BV index, its surface temperature can be obtained, and then its infrared magnitude can be calculated. .

[0028] First, calculate its relative emissivity. :

[0029] In the infrared band, the formula takes a similar form:

[0030] here You can choose according to your needs; for example, for shortwave infrared, you can choose 700 or 900.

[0031] After sorting, you will get:

[0032] The visible light magnitude corresponding to a star.

[0033] The advantage of this method is its relatively accurate estimation, but the disadvantage is that it requires a large amount of computation. This can be addressed by pre-calculating various... The function values ​​are stored as a temperature-power lookup table, and then interpolated by looking up the table to reduce the amount of calculation, or infrared magnitude can be obtained using the following method when only a rough estimate is needed.

[0034] As a preferred implementation, a more accurate color index in the I band is obtained by looking up a table, one such table format being shown below:

[0035] Before the M-type star (BV ≤ 1.33), the relationship between BV and VI is linear. The linear fitting function is VI = 1.0466 × BV - 0.0509, R0. 2 =0.9955. When BV>1.33, piecewise linear interpolation is preferable, such as connecting every two data points with a straight line. Alternatively, piecewise linear interpolation can be used without linear fitting. Then, the infrared magnitude is obtained from visible magnitude - (VI) = infrared magnitude.

[0036] The advantage of this method is that it requires less computation, but the disadvantage is that it only follows the observation results of the Cousins ​​I band (644~952nm) and is not suitable for comprehensive quantitative calculations that include CMOS quantum efficiency curves and atmospheric transmittance.

[0037] The method provided in this invention improves the accuracy of infrared star sensor brightness matching compared to the original visible light star catalog, as shown in the table below:

[0038] As can be seen, the infrared magnitudes estimated using the method provided in this invention achieve a much higher fitting accuracy to the actual star map than those estimated using visible light magnitudes. In particular, for stars 4 and 8 in the table, directly matching with visible light magnitudes results in magnitude values ​​(0.50 and -1.09) that are completely disproportionate to the measured brightness (15435 and 9170), indicating that visible light magnitudes are fundamentally unsuitable for brightness estimation in the infrared band. However, the infrared magnitudes (-2.24 and -1.05) estimated using the method of this invention show a highly consistent trend with the measured brightness, fully demonstrating the significant effect of this invention in improving the brightness matching accuracy of infrared star sensors.

[0039] The above provides a detailed description of an automatic method for preparing an infrared star catalog according to embodiments of the present invention. Specific examples have been used to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the present invention. At the same time, those skilled in the art will recognize that there will be changes in the specific implementation methods and application scope based on the ideas of the present invention. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A method for automatically preparing an infrared star catalog, characterized in that, include: Acquire visible light magnitude data and color index data of stars; Estimate the surface temperature of the star based on the color index data; Using the star as a blackbody, the radiant power of the star in the infrared band is calculated based on the surface temperature using Planck's blackbody radiation formula. The infrared magnitude of the star is calculated based on the ratio of the star's radiant power in the infrared band to that of a preset standard 0 magnitude star in the same infrared band, and the visible light magnitude data. The calculated infrared magnitudes are associated with and stored with the identification information of each star to generate an infrared star catalog.

2. The method according to claim 1, characterized in that, The step of calculating the infrared magnitude of the star based on the ratio of its radiant power in the infrared band to that of a preset standard 0-magnitude star in the same infrared band includes: Obtain the radiant power of a preset standard 0 magnitude star in the infrared band. ,as well as The radiant power of a pre-defined standard 0 magnitude star in the visible light band ; Calculate the radiant power of stars in the same infrared band using Planck's blackbody radiation formula. And the radiant power of stars in the same visible light band. ; based on , , as well as Calculate the infrared magnitude. The surface temperature of a star. λ represents the surface temperature of a standard 0 magnitude star, and λ1 and λ2 represent the start and end wavelengths of the infrared band, respectively.

3. The method according to claim 2, characterized in that, Depend on The infrared magnitude was obtained , The visible light magnitude corresponding to a star.

4. The method according to claim 3, characterized in that, The step of estimating the surface temperature of the star based on the color index data includes: Obtain the BV color index of the star; The BV color index is converted into the surface temperature using a preset temperature-color index relationship model.

5. The method according to claim 4, characterized in that, The preset temperature-color index relationship model is as follows: When the original star catalog data provides the VB color index, the BV color index is the opposite of it.

6. The method according to claim 5, characterized in that, The standard 0 magnitude star is Vega, which has a BV color index and a magnitude of 0 in all wavelength bands, and its surface temperature is... It is 9986K.

7. The method according to claim 5, characterized in that, The method further includes: When the original star catalog data contains the spectral type of each star, the color index of each star is obtained by querying the spectral type and color index relationship table, which includes at least the correspondence between the spectral type, BV color index and VI color index of the star; For stars with a BV color index less than or equal to 1.33 corresponding to a spectral type, their VI color index is estimated using the linear fitting formula VI = 1.0466 × (BV) - 0.0509. For stars with a BV color index greater than 1.33 corresponding to a spectral type, their VI color index is estimated by piecewise linear interpolation. The surface temperature of the star is obtained from the estimated VI color index.

8. The method according to claim 7, characterized in that, The visible magnitudes in the original star catalog data are derived from the visible star catalog, and the color index is derived from stellar spectral type classification data or photometric observation data.

9. The method according to claim 1, characterized in that, The method further includes: After calculating the initial infrared magnitude of each star, the initial infrared magnitude is corrected according to the detector quantum efficiency curve and atmospheric transmittance curve of the infrared star sensor to obtain the final infrared magnitude after instrument effect correction. The final infrared magnitude is then stored in the infrared star table instead of the initial infrared magnitude.

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