Large-aperture space telescope sub-field flux calibration method and device

Abstract

The present application relates to a kind of large aperture space telescope sub-field flow calibration method and device, belong to flow calibration technical field.The integral sphere method and collimator method of prior art are used to carry out flow calibration to space telescope, and approximate Lambert light source is introduced, which introduces larger error.Collimator method is used to carry out flow calibration to space telescope, although higher accuracy, but cannot take into account the technical problems of large field and high image quality.The calibration device of the present application includes calibration light source, optical fiber, integrating sphere, precision pinhole, collimator, absolute radiance meter, space telescope and two-dimensional rotating platform.The present application uses the method of sub-field calibration to carry out flow calibration to space telescope, and takes into account the optical characteristics of large aperture and large field of space telescope, realizes the full aperture, full field calibration of large aperture and large field space telescope, greatly improves the precision of space telescope laboratory flow calibration, reduces the transfer error, effectively improves the observation accuracy of space telescope.

Description

Technical Field

[0001] This invention belongs to the field of flow calibration technology, specifically relating to a method and apparatus for flow calibration of a large-aperture space telescope in the field of view. Background Technology

[0002] Large-aperture, wide-field-of-view space telescopes avoid the limitations of ground-based telescopes affected by atmospheric and gravitational factors, possessing high resolution and high observation efficiency. They are an important avenue for astronomical optical observation equipment and a crucial link in the development of astronomical observation equipment in my country. Space telescopes observe faint objects in deep space. Due to the non-Lambert nature of the observed objects and the response characteristics of the telescope's sensors, the radiation information received by the space telescope contains radiation distortion. Therefore, radiometric calibration of the space telescope is necessary to obtain the intrinsic radiation characteristics of the observed objects. Laboratory radiometric calibration of astronomical observation equipment includes flat-field calibration and flux calibration. The purpose of flux calibration is to establish a quantitative relationship between the radiance at the telescope's entrance and the DN value (detector output luminance value) of the image detector, reducing transmission errors and promoting the upgrading of deep space exploration towards quantitative and refined technologies.

[0003] Current flow rate calibration methods for space telescopes include the integrating sphere method, the flat-screen method, and the collimator method. In the integrating sphere method, the calibration light source is placed inside the integrating sphere, simulating a Lambertian source at the sphere's exit port, achieving full-aperture, full-field-of-view irradiation of the telescope. The flat-screen method uses a broadband white light source to illuminate a flat-screen, generating a reference flat field after reflection or transmission, used for telescope calibration. The collimator method uses a collimator as the radiation source, with parallel light directly illuminating the telescope to calibrate the flow rate of optical telescopes. When performing deep-space observation missions, space telescopes receive parallel light reflected from the observed target. The integrating sphere and flat-screen methods are commonly used for flow rate calibration of ground-based telescopes, often simulating Lambertian sources. However, their operating environment differs from that of space telescopes, introducing significant errors when calibrating space telescopes using these methods, failing to meet the high-precision flow rate calibration requirements of space telescopes. The collimator method, with parallel light directly illuminating the space telescope, avoids the significant errors introduced by the Lambertian source, but it cannot simultaneously achieve a large field of view and high image quality. Summary of the Invention

[0004] This invention addresses the shortcomings of existing methods for flow calibration of space telescopes, such as the integrating sphere method and collimator method, which use approximate Lambertian light sources and introduce significant errors. While the collimator method offers high accuracy, it cannot simultaneously achieve a large field of view and high image quality. This invention provides a field-by-field flow calibration method and apparatus for large-aperture space telescopes. The calibration method and apparatus of this invention utilize a field-by-field calibration approach to calibrate the flow of space telescopes, taking into account the optical characteristics of large aperture and large field of view. It achieves full-aperture, full-field-of-view calibration for large-aperture, large-field-of-view space telescopes, significantly improving the accuracy of laboratory flow calibration for space telescopes, reducing transmission errors, and effectively enhancing the observation accuracy of space telescopes.

[0005] The technical solution adopted by the present invention to achieve the above objectives is as follows.

[0006] This invention provides a large-aperture space telescope field-of-view flow calibration device, including a calibration light source, optical fiber, integrating sphere, precision pinhole, collimator, absolute radiance meter, space telescope, and two-dimensional rotating platform;

[0007] The calibration light source is used to emit light, and the luminous intensity of the calibration light source is variable;

[0008] The optical fiber is used for light transmission, coupling the light emitted by the calibration light source into the integrating sphere;

[0009] The integrating sphere is used to simulate a Lambertian light source. After light enters the integrating sphere, it undergoes multiple diffuse reflections inside the integrating sphere, and the light exiting the integrating sphere simulates a Lambertian light source.

[0010] The precision pinhole is placed at the focal plane of the collimator to simulate a point light source, and light enters the collimator through the precision pinhole.

[0011] The collimator outputs uniformly irradiated parallel light to irradiate the entire aperture of the space telescope.

[0012] The absolute radiance meter is placed between the collimator and the space telescope to measure the radiance at the entrance pupil of the space telescope and trace the measurement results back to the radiation standard.

[0013] The space telescope is fixed on a two-dimensional rotating platform, and the space telescope image plane detector outputs the DN value;

[0014] The two-dimensional rotating platform drives the space telescope to rotate in the meridional and sagittal directions.

[0015] Furthermore, the optical path of the large-aperture space telescope field-of-view flow calibration device is as follows: the light emitted by the calibration light source is transmitted to the integrating sphere via optical fiber, the light undergoes multiple diffuse reflections in the integrating sphere, and the output simulates the output of the Lambertian light source at the opening. The output light is coupled to the collimator through a precision pinhole, and the collimator outputs parallel light to simulate the target to be observed by the space telescope, thus irradiating the space telescope with its entire aperture.

[0016] Furthermore, the calibration light source is a halogen lamp.

[0017] This invention also provides a method for calibrating a large-aperture space telescope using a field-of-view flow calibration device, comprising the following steps:

[0018] Step 1: Plan the sub-field of view calibration path for the space telescope;

[0019] Step 2: Turn on the calibration light source and adjust its irradiance. The light emitted by the calibration light source is transmitted through optical fiber to the integrating sphere. The light undergoes multiple diffuse reflections in the integrating sphere and is output at the opening, simulating the output of a Lambertian light source. The output light is coupled to the collimator through a precision pinhole. The collimator outputs parallel light, simulating the target to be observed by the space telescope, and irradiates the entire aperture of the space telescope.

[0020] Step 3: Adjust the sub-field of view, output the measured DN value from the image plane detector of the space telescope, measure the radiance value L at the entrance pupil of the space telescope using the absolute radiance meter, trace the measurement results back to the radiation standard, establish the quantitative relationship between the DN value and the radiance value according to the formula, and obtain the flow calibration coefficient R of the space telescope.

[0021] DN-DN0=R·L (1)

[0022] In equation (1), R is the flow calibration coefficient, L is the radiance at the entrance pupil of the space telescope, and DN0 is the grayscale output value of the dark signal.

[0023] Step 4: Determine whether all sub-fields of view have been calibrated. If yes, correct the sub-field of view calibration coefficients, calculate the calibration accuracy, and proceed to Step 5. If no, return to Step 3 and adjust the calibrated sub-fields of view by rotating the space telescope through the two-dimensional rotating platform.

[0024] Step 5: Determine if all magnitudes have been calibrated. If yes, output the calibration coefficients and calibration accuracy. If no, return to Step 2, adjust the irradiance of the calibration light source to simulate the next magnitude, and establish a quantitative relationship between the calibration coefficients and the visual magnitude.

[0025] Furthermore, prior to step two, the space telescope is flat-field calibrated to ensure that different pixels on the space telescope's image detector respond consistently to the same irradiance.

[0026] Furthermore, in step one, the image plane of the space telescope is evenly divided into four rotationally symmetrical rectangular regions. A single region is selected for flow calibration to obtain full field-of-view calibration data. Using the sub-field-of-view image point size as the standard, the single region is divided into multiple grids, with each 3×3 grid as a sampling region. The sub-field-of-view at the middle position of the sampling region is used for flow calibration. By calibrating the sub-field-of-view at the middle position of all sampling regions, the flow calibration of a single region is completed, thereby completing the flow calibration of the space telescope.

[0027] Furthermore, the image plane of the space telescope is 1174mm×1467mm, each sampling area is a square of 14.66mm×14.66mm, the sub-field image point is a square with a side length of 4.89mm, and the number of calibrated sub-fields in a single area is 2000.

[0028] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0029] The present invention provides a field-by-field flow calibration method and apparatus for large-aperture space telescopes. Considering that collimators cannot simultaneously achieve both a large field of view and high image quality, this invention employs field-by-field calibration based on the collimator method to perform high-precision flow calibration of the space telescope, thus balancing the optical characteristics of the space telescope's large aperture and large field of view. A large-aperture collimator performs full-aperture calibration of the space telescope, while a two-dimensional rotating platform adjusts the sub-field of view to achieve full-field calibration. The combination of these two methods reduces method errors, optimizing the laboratory flow calibration accuracy of the space telescope to 3.81%, thus achieving high-precision calibration of the space telescope. Attached Figure Description

[0030] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0031] Figure 1 This is a schematic diagram of the large-aperture space telescope field-of-view flow calibration device of the present invention;

[0032] In the diagram, 1 is a calibration light source, 2 is an optical fiber, 3 is an integrating sphere, 4 is a precision pinhole, 5 is a collimator, 6 is an absolute radiance meter, 7 is a space telescope, and 8 is a two-dimensional rotating platform.

[0033] Figure 2 This is a flowchart of the large-aperture space telescope field-of-view flow calibration method of the present invention;

[0034] Figure 3The figure shows the sub-field calibration path planning for the large-aperture space telescope sub-field calibration method of the present invention. In the figure, (a) is the image plane divided into four regions, (b) is the image plane of region 2 in (a) divided into multiple grids, and each 3×3 grid is a sampling region. (c) is the center field of view of the sampling region selected by the calibrated sub-field during the flow calibration process. Detailed Implementation

[0035] To further understand the present invention, preferred embodiments of the present invention are described below. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, and not for limiting the scope of the claims of the present invention.

[0036] like Figure 1 As shown, the large-aperture space telescope field-of-view flow calibration device of the present invention includes a calibration light source 1, an optical fiber 2, an integrating sphere 3, a precision pinhole 4, a collimator 5, an absolute radiance meter 6, a space telescope 7, and a two-dimensional rotating platform 8. The calibration light source 1 emits light, and the irradiance at the entrance pupil of the space telescope 7 can be changed by adjusting the intensity of the calibration light source 1 to simulate deep-sky objects of different magnitudes. The calibration light source 1 is typically a halogen lamp, but it should be noted that other commonly used light sources in the art can also be used. The optical fiber 2 is used for light transmission, coupling the light emitted by the calibration light source 1 into the integrating sphere 2. The integrating sphere 3 is used to simulate a Lambertian light source; after entering the integrating sphere 3, the light undergoes multiple diffuse reflections through a coating inside the integrating sphere 3, simulating a Lambertian light source at the exit port of the integrating sphere 3. The precision pinhole 4 is placed at the focal plane of the collimator 5 to simulate a point light source. Light enters the collimator 5 through the precision pinhole 4. The collimator 5 outputs uniformly irradiated parallel light, providing full-aperture irradiation to the space telescope 7. An absolute radiance meter 6 is placed between the collimator 5 and the space telescope 7 to measure the radiance at the entrance pupil of the space telescope 7 and trace the measurement results back to the radiation standard. The space telescope 7 is fixed on a two-dimensional rotating platform 8, and during the flow calibration process, the image detector of the space telescope 7 outputs the DN value (i.e., the observation results of the space telescope 7 are characterized using the DN value output by the image detector). The two-dimensional rotating platform 8 drives the space telescope 7 to rotate in the meridional and sagittal directions (e.g.,...). Figure 1 (As shown by the black arrow in the middle), the sub-field of view for flow calibration is then adjusted, and multiple sub-fields of view are selected for calibration to obtain full-field-of-view irradiance data. The large-aperture space telescope sub-field-of-view flow calibration device of this invention obtains the flow calibration coefficients of space telescope 7 by establishing a quantitative relationship between radiance values ​​and DN values. These flow calibration coefficients will be used to subsequently correct the observation results of space telescope 7, improve the observation accuracy of space telescope 7, and promote the refined upgrading of deep space exploration.

[0037] The optical path of the large-aperture space telescope field-of-view flow calibration device of the present invention is as follows: the light emitted by the calibration light source 1 is transmitted to the integrating sphere 3 through the optical fiber 2. The light undergoes multiple diffuse reflections in the integrating sphere 3 and is output at the opening simulating the output of the Lambertian light source. The output light is coupled to the collimator 5 through the precision pinhole 4. The collimator 5 outputs parallel light, simulating the target to be observed by the space telescope 7, and irradiating the space telescope 7 with full aperture.

[0038] like Figure 2 As shown, the large-aperture space telescope field-of-view flow calibration method of the present invention includes the following steps:

[0039] Step 1: Using the image point position as a reference, plan the sub-field calibration path for Space Telescope 7;

[0040] If a full-field calibration of the space telescope 7 is to be performed, two problems will be encountered: First, there are a total of 72,000 sub-fields of view. The single imaging time of the space telescope 7 is 15 seconds, and the full-field calibration would require 75 hours, which is too long and places excessive demands on the space telescope 7 and the measuring equipment, making it difficult to meet the requirements. Second, when adjusting the sub-fields of view using the two-dimensional rotating platform 8, the field of view of the collimator 5 is only 0.01°×0.01°, while the field of view of the space telescope is 2.4°×3.0°. The rotation angle of the space telescope 7 is too small when changing the sub-field of view being calibrated, which places excessively high demands on the accuracy of the two-dimensional rotating platform 8.

[0041] Based on this, multiple sub-fields of view are selected for flow calibration, and the sub-field of view calibration paths are planned with image point positions as references. For example... Figure 3 As shown, the image plane of Space Telescope 7 is 1174mm × 1467mm. Due to its rotationally symmetric structure, the image plane is evenly divided into four rectangular regions of 587mm × 733.5mm, labeled 1 to 4 (e.g., ...). Figure 3 As shown in (a), by selecting a single region (e.g., region 2) for flow calibration, full field-of-view calibration data can be obtained. Using the sub-field-of-view image point size as the standard, a single region (e.g., region 2) is divided into multiple grids. The number of sub-fields of view in region 2 is 120×150. This region is divided into 2000 sampling regions, with each sampling region consisting of 3×3 grids. Each sampling region is a 14.66mm×14.66mm square, and the sub-field-of-view image point is a square with a side length of 4.89mm (e.g., region 2). Figure 3 As shown in (b)). Since the image irradiance variation between adjacent sub-fields of view is small, the sub-field of view at the middle position of the sampling area is used for calibration during the calibration process (e.g., Figure 3 (As shown in (c)). The number of calibration sub-fields of view was 2000, and the calibration time was 8.33 hours.

[0042] Step 2: Perform flat-field calibration on Space Telescope 7, that is, ensure that different pixels on the image detector of Space Telescope 7 respond consistently to the same irradiance.

[0043] Step 3: Turn on the calibration light source 1 and adjust the irradiance of the calibration light source 1. The light emitted by the calibration light source 1 is transmitted to the integrating sphere 3 through the optical fiber 2. The light undergoes multiple diffuse reflections in the integrating sphere 3 and is output at the opening to simulate the output of the Lambertian light source. The output light is coupled to the collimator 5 through the precision pinhole 4. The collimator 6 outputs parallel light to simulate the target to be observed by the space telescope 7 and irradiate the space telescope 7 with its full aperture.

[0044] Step 4: Adjust the sub-field of view. The image detector of space telescope 7 outputs the measured DN value. The absolute radiance meter 5 measures the radiance value L at the entrance pupil of space telescope 7 and traces the measurement results back to the radiation standard. According to formula (1), establish the quantitative relationship between DN value and radiance value, and then obtain the flow calibration coefficient R of space telescope 7.

[0045] DN-DN0=R·L (1)

[0046] In equation (1), R is the flow calibration coefficient, L is the radiance at the entrance pupil of space telescope 7, and DN0 is the grayscale output value of the dark signal.

[0047] Step 5: Determine whether all sub-fields of view have been calibrated. If yes, correct the sub-field of view calibration coefficients, calculate the calibration accuracy, and proceed to Step 6. If no, return to Step 4, that is, adjust the calibrated sub-fields of view by rotating the space telescope 7 through the two-dimensional rotating platform 8. Once multiple sub-fields of view are calibrated, full-field of view irradiance data can be obtained.

[0048] Step Six: Determine if all magnitudes have been calibrated. If yes, output the calibration coefficients and calibration accuracy. If not, return to Step Three and adjust the irradiance of calibration light source 1 to simulate the next magnitude, establishing a quantitative relationship between the calibration coefficients and the visual magnitude. The obtained flux calibration coefficients will be used to subsequently correct the observation results of Space Telescope 7, improve the observation accuracy of Space Telescope 7, and promote the refinement of deep space exploration.

[0049] Simulation analysis and experimental verification have shown that when the large-aperture space telescope field-of-view flow calibration method and device of this invention are used to perform laboratory flow calibration of space telescope 7, the calibration accuracy is 3.81%, which meets the calibration requirements of space telescope 7.

[0050] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the embodiments. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all embodiments here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method of calibrating a large aperture space telescope, characterized by, The method comprises the following steps: Step one, planning a sub-field calibration path of the space telescope (7); In step one, the image plane of the space telescope (7) is evenly divided into four rotationally symmetrical rectangular regions, a single region is selected for flux calibration, and then full-field calibration data are obtained, and the single region is divided into a plurality of grids according to the size of the sub-field image point, every 3*3 grids are a sampling region, the sub-field in the middle position of the sampling region is taken for flux calibration, the flux calibration of the single region is completed by calibrating the sub-field in the middle position of all sampling regions, and then the flux calibration of the space telescope (7) is completed; Step two, the calibration light source (1) is turned on, the irradiance of the calibration light source (1) is adjusted, the light emitted by the calibration light source (1) is transmitted to the integrating sphere (3) through the optical fiber (2), the light is reflected multiple times in the integrating sphere (3), and a Lambertian light source is simulated at the opening, the output light is coupled to the collimator (5) through the precision pinhole (4), the collimator (5) outputs parallel light, simulates the target to be observed of the space telescope (7), and the full-aperture irradiation of the space telescope (7) is performed; Step three, the sub-field is adjusted, the space telescope (7) image plane detector outputs a measured DN value, the absolute radiance meter (6) measures the radiance value L of the space telescope (7) at the entrance pupil, and the measurement result is traced to a radiation standard, a quantitative relationship between the DN value and the radiance value is established according to formula (1), and the flux calibration coefficient R of the space telescope (7) is obtained; DN-DN0=R·L (1) In formula (1), R is a flux calibration coefficient, L is the radiance at the entrance pupil of the space telescope (7), and DN0 is a gray output value of a dark signal; Step four, whether all sub-fields have been calibrated is judged, if yes, the sub-field calibration coefficient is corrected, the calibration accuracy is calculated, step five is performed, and if not, step three is returned, the calibrated sub-field is adjusted by rotating the space telescope (7) through the two-dimensional rotating platform (8); Step five, whether all magnitudes have been calibrated is judged, if yes, the calibration coefficient and the calibration accuracy are output, and if not, step two is returned, the irradiance of the calibration light source (1) is adjusted to simulate the next magnitude, and a quantitative relationship between the calibration coefficient and the visual magnitude is established.

2. The method of calibrating a large-aperture space telescope of claim 1, wherein, The large-aperture space telescope sub-field flux calibration device comprises a calibration light source (1), an optical fiber (2), an integrating sphere (3), a precision pinhole (4), a collimator (5), an absolute radiance meter (6), a space telescope (7) and a two-dimensional rotating platform (8); The calibration light source (1) is used for emitting light, and the light emitting intensity of the calibration light source (1) is variable; The optical fiber (2) is used for transmitting light, and the light emitted by the calibration light source (1) is coupled into the integrating sphere (3); The integrating sphere (3) is used for simulating a Lambertian light source, and the light entering the integrating sphere (3) is reflected multiple times inside the integrating sphere (3) and simulates a Lambertian light source at the light outlet of the integrating sphere (3); The precision pinhole (4) is placed at the focal plane of the collimator (5) and is used for simulating a point light source, and the light enters the collimator (5) through the precision pinhole (4); The parallel light pipe (5) outputs uniform irradiation parallel light, and the space telescope (7) is irradiated in full aperture; The absolute radiance meter (6) is placed between the parallel light pipe (5) and the space telescope (7), and is used for measuring the radiance at the entrance pupil of the space telescope (7) and tracing the measurement result to the radiation standard; The space telescope (7) is fixed on the two-dimensional rotating platform (8), and the DN value of the image plane detector of the space telescope (7) is outputted. The two-dimensional rotating platform (8) drives the space telescope (7) to rotate in the meridian direction and the sagittal direction.

3. The method of calibrating a large-aperture space telescope of claim 2, wherein, The light path of the large-aperture space telescope sub-field flux calibration device is as follows: the light emitted by the calibration light source (1) is transmitted to the integrating sphere (3) through the optical fiber (2), the light is reflected multiple times in the integrating sphere (3), and the output light is simulated as a Lambert light source at the opening, and the output light is coupled to the parallel light pipe (5) through the precise pinhole (4), the parallel light pipe (5) outputs parallel light, simulates the observed target of the space telescope (7), and irradiates the space telescope (7) in full aperture.

4. The method of calibrating a large-aperture space telescope of claim 2, wherein, The calibration light source (1) is a halogen lamp.

5. The method of calibrating a large-aperture space telescope of claim 1, wherein, Before step two, the space telescope (7) is subjected to flat field calibration, so that different image elements on the image plane detector of the space telescope (7) are uniformly responsive to the same irradiance.

6. The method of calibrating a large-aperture space telescope of claim 1, wherein, The image plane size of the space telescope (7) is 1174mm×1467mm, each sampling area is a square with a side length of 14.66mm×14.66mm, the sub-field image point is a square with a side length of 4.89mm, and the number of sub-fields calibrated in a single area is 2000.

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