On-board radiation calibration method, system and satellite detection system

Abstract

The present application discloses an on-board radiation calibration method, system, and satellite detection system, relating to the technical field of satellite remote sensing, including: providing an on-board radiation calibration system consisting of a calibration observation port, a pinhole plate, a semi-transparent and semi-reflective mirror, a scanning mirror, and a satellite camera; setting the calibration light path to pass through the sun, the calibration observation port, the pinhole on the pinhole plate, the semi-transparent and semi-reflective mirror, the scanning mirror, and the satellite camera in sequence; and adjusting the attitude of the artificial satellite so that the incident solar light passes vertically through the target pinhole on the pinhole plate, thereby completing the hardware construction and preparation work for on-board radiation calibration. Then, based on the theoretical radiance of the standard detector and the actual response value of each pixel of the satellite camera, the calibration coefficient of each pixel of the satellite camera is determined. Thus, in order to address the defects of uncorrected diffraction effects and insufficient correction of array non-uniformity, the accuracy of on-board radiation calibration is improved by determining the calibration coefficient of each pixel of the satellite camera.

Description

Technical Field

[0001] The present application relates to the technical field of satellite remote sensing, and in particular to an on-board radiation calibration method, an on-board radiation calibration system, and a satellite detection system. Background Art

[0002] Current onboard radiometric calibration systems primarily utilize two technologies: 1) Solar diffuse reflectors: Made from highly reflective materials, they reflect sunlight into the camera's field of view and measure reflectivity in conjunction with a standard detector. 2) LED calibration sources: Integrated within the satellite, they simulate the solar spectrum using a stable array of light-emitting diodes and require a temperature control module. Their operating principle is that sunlight or an LED light source is uniformly applied to the camera's focal plane through an optical system. Calibration is achieved by measuring the linear relationship between the output digital value (DN) and the standard radiometric value.

[0003] Solar diffuse reflectors and LED calibration sources degrade over time, making stable calibration impossible over long lifespans. Consequently, new on-board radiometric calibration methods have emerged, using pinholes or slits and sunlight as on-board radiometric calibration sources.

[0004] However, new on-board radiometric calibration methods that use pinholes, slits, and sunlight as on-board radiometric calibration sources often fail to consider the following issues: 1. Uncorrected diffraction effects: Calibration based on pinholes or slits ignores inter-pixel variations in luminous flux distribution caused by the Airy pattern, leading to calibration errors. 2. Inadequate correction for array non-uniformity: Relying solely on statistical averaging, without modeling the response characteristics of each pixel, the method fails to eliminate spatial sensitivity variations.

[0005] The above content is only used to assist in understanding the technical solution of this application and does not constitute an admission that the above content is prior art. Summary of the Invention

[0006] The main purpose of this application is to provide an on-board radiation calibration method, an on-board radiation calibration system and a satellite detection system, aiming to solve the technical problem of inaccurate on-board radiation calibration.

[0007] To achieve the above objectives, the present application proposes an on-board radiation calibration method, which is applied to an on-board radiation calibration system. The system includes a calibration observation port, a pinhole plate, a semi-transparent and semi-reflective mirror, a scanning mirror, and a satellite camera. The calibration optical path of the on-board radiation calibration system passes through the sun, the calibration observation port, the pinhole on the pinhole plate, the semi-transparent and semi-reflective mirror, the scanning mirror, and the satellite camera in sequence. The method includes:

[0008] Adjusting the attitude of the artificial satellite, the adjustment target is that the incident sunlight passes vertically through the target pinhole on the pinhole plate;

[0009] Obtaining the theoretical radiance of the standard detector and the actual response value of each pixel of the satellite camera;

[0010] Based on the theoretical radiance and the actual response value of each pixel of the satellite camera, a calibration coefficient of each pixel of the satellite camera is determined.

[0011] In one embodiment, when there is a single pinhole on the pinhole plate, the step of determining the calibration coefficient of each pixel of the satellite camera based on the theoretical radiance and the actual response value of each pixel of the satellite camera includes:

[0012] determining a target pixel having an optimal response of the satellite camera;

[0013] Obtaining a current actual response value of the satellite camera at the target pixel;

[0014] Determining a standard calibration coefficient at the target pixel according to the theoretical radiance at the target pixel and the current actual response value;

[0015] A target calibration coefficient for each non-target pixel of the satellite camera is determined according to the standard calibration coefficient and a response difference between each non-target pixel and the target pixel.

[0016] In one embodiment, the step of determining the target calibration coefficients for each non-target pixel of the satellite camera based on the standard calibration coefficients and the response difference between each non-target pixel and the target pixel includes:

[0017] Obtaining a historical actual response value of each pixel of the satellite camera by rotating the scanning mirror;

[0018] The relative difference between each non-target pixel and the target pixel in the historical actual response value is determined, and the relative difference is used as the response difference of each non-target pixel compared with the target pixel.

[0019] In one embodiment, when pinholes of different sizes exist on the pinhole plate, the step of determining the calibration coefficient of each pixel of the satellite camera based on the theoretical radiance and the actual response value of each pixel of the satellite camera includes:

[0020] Obtaining data pairs of the theoretical radiance and the actual response value of each pixel of the satellite camera at different aperture scales;

[0021] The calibration coefficient of each pixel of the satellite camera is determined by fitting the data pair.

[0022] In one embodiment, the onboard radiation calibration system further includes a standard detector, and the aperture dynamic compensation optical path of the onboard radiation calibration system sequentially passes through the sun, a calibration observation port, a pinhole on a pinhole plate, a semi-transparent and semi-reflective mirror, and the standard detector; the step of obtaining the theoretical radiance of the standard detector includes:

[0023] obtaining an actual diffraction pattern of the standard detector;

[0024] determining an actual pinhole aperture of the pinhole on the pinhole plate according to the actual diffraction pattern;

[0025] Determining a directional transmission distribution function at each pixel of a standard detector based on the actual pinhole aperture;

[0026] Based on the directional transmission distribution function at each pixel of the standard detector, the theoretical radiance at each pixel of the standard detector is determined.

[0027] In one embodiment, the step of determining the actual pinhole aperture of the pinhole on the pinhole plate according to the actual diffraction pattern comprises:

[0028] Based on a pre-established mapping model between the diffraction pattern and the pinhole aperture of the standard detector, the actual pinhole aperture of the pinhole corresponding to the actual diffraction pattern is determined.

[0029] In one embodiment, the step of determining the actual pinhole aperture of the pinhole on the pinhole plate according to the actual diffraction pattern further comprises:

[0030] Based on a pre-trained neural network model of the diffraction pattern and pinhole aperture of the standard detector, an actual pinhole aperture of the pinhole corresponding to the actual diffraction pattern is determined.

[0031] In addition, to achieve the above-mentioned purpose, the present application also proposes an on-board radiation calibration system, which includes: a calibration observation port, a pinhole plate, a semi-transparent and semi-reflective mirror, a scanning mirror and a satellite camera. The calibration light path of the on-board radiation calibration system passes through the sun, the calibration observation port, the pinhole on the pinhole plate, the semi-transparent and semi-reflective mirror, the scanning mirror and the satellite camera in sequence; the system implements the steps of the on-board radiation calibration method as described above.

[0032] In one embodiment, the on-board radiation calibration system also includes a standard detector, and the aperture dynamic compensation optical path of the on-board radiation calibration system passes through the sun, the calibration observation port, the pinhole on the pinhole plate, the semi-transparent and semi-reflective mirror, and the standard detector in sequence; the system implements the steps of the on-board radiation calibration method as described above.

[0033] In addition, to achieve the above-mentioned purpose, the present application also proposes a satellite detection system, which includes a target satellite camera, a scanning mirror and a ground observation port calibrated by the on-board radiation calibration system as described above, and the ground detection optical path passes through the earth's surface, the ground observation port, the scanning mirror and the target satellite camera in sequence.

[0034] One or more technical solutions proposed in this application have at least the following technical effects:

[0035] An onboard radiometric calibration system is set up, consisting of a calibration observation port, a pinhole plate, a semi-transparent and semi-reflective mirror, a scanning mirror, and a satellite camera. The calibration optical path is set to pass through the sun, the calibration observation port, the pinhole on the pinhole plate, the semi-transparent and semi-reflective mirror, the scanning mirror, and the satellite camera. The satellite's attitude is determined using a sun sensor, and the satellite's attitude is adjusted so that the incident solar light passes perpendicularly through the target pinhole on the pinhole plate. This completes the hardware setup and preparation for onboard radiometric calibration. The calibration coefficients for each pixel in the satellite camera are then determined based on the theoretical radiance of the standard detector and the actual response values ​​of each pixel in the satellite camera. This improves the accuracy of onboard radiometric calibration by determining the calibration coefficients for each pixel in the satellite camera, addressing issues such as uncorrected diffraction effects and insufficient correction for array non-uniformity. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present application and, together with the description, serve to explain the principles of the present application.

[0037] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0038] Figure 1 Schematic diagram of the onboard radiation calibration system provided in an embodiment of the present application;

[0039] Figure 2 This is a flowchart of the on-board radiation calibration method provided in Example 1 of the present application;

[0040] Figure 3 This is a flow chart of the on-board radiation calibration method provided in Example 2 of the present application;

[0041] Figure 4 A schematic diagram of a neural network model provided in Example 2 of the present application;

[0042] Figure 5 Schematic diagram of a satellite detection system provided in Example 3 of this application;

[0043] Figure 6 Schematic diagram of the on-board radiation calibration system provided in Example 4 of the present application.

[0044] The purpose, features and advantages of this application will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0045] It should be understood that the specific embodiments described herein are merely used to explain the technical solutions of the present application and are not intended to limit the present application.

[0046] In order to better understand the technical solution of the present application, a detailed description will be given below in conjunction with the accompanying drawings and specific implementation methods.

[0047] Onboard radiometric calibration is a critical step in satellite remote sensing, ensuring that sensor-measured radiometric data accurately reflects actual radiation levels. This process involves calibrating sensors on a satellite platform to ensure that the measured data accurately reflects the true radiation intensity. Its objectives are: 1. Accuracy: ensuring that sensor measurements accurately reflect actual radiation levels; 2. Consistency: ensuring consistent data across time and from different sensors; and 3. Stability: compensating for the effects of environmental changes, such as temperature fluctuations, on the sensor.

[0048] Current onboard radiometric calibration methods include: 1. Internal reference sources: Sensors are regularly calibrated using a source of known radiation intensity (such as a blackbody or lamp). 2. External reference sources: Calibration utilizes known radiation properties of the Earth's surface or solar radiation. 3. Cross-calibration: Data from different sensors or satellites are cross-calibrated to ensure consistency. These methods are primarily used to accurately monitor atmospheric parameters such as temperature and humidity via meteorological satellites, or to precisely measure surface radiation via remote sensing satellites, for environmental monitoring and resource management.

[0049] However, solar diffuse reflectors and LED calibration sources degrade over time, making stable calibration impossible over long lifespans. Consequently, new on-board radiometric calibration methods have emerged, using pinholes or slits and sunlight as on-board radiometric calibration sources.

[0050] Furthermore, new on-board radiometric calibration methods that use pinholes, slits, and sunlight as on-board radiometric calibration sources often fail to consider the following issues: 1. Uncorrected diffraction effects: Calibration based on pinholes or slits ignores inter-pixel variations in luminous flux distribution caused by the Airy pattern, leading to calibration errors. 2. Inadequate correction for array non-uniformity: Relying solely on statistical averaging, without modeling the response characteristics of each pixel, the method fails to eliminate spatial sensitivity variations.

[0051] The main solutions of the embodiments of this application are:

[0052] An onboard radiometric calibration system is set up, consisting of a calibration observation port, a pinhole plate, a semi-transparent and semi-reflective mirror, a scanning mirror, and a satellite camera. The calibration optical path is set to pass through the sun, the calibration observation port, the pinhole on the pinhole plate, the semi-transparent and semi-reflective mirror, the scanning mirror, and the satellite camera. The satellite's attitude is adjusted so that the incident solar light passes perpendicularly through the target pinhole on the pinhole plate. This completes the hardware setup and preparation for onboard radiometric calibration. The calibration coefficients for each pixel in the satellite camera are then determined based on the theoretical radiance of the standard detector and the actual response values ​​of each pixel in the satellite camera. This improves the accuracy of onboard radiometric calibration by determining the calibration coefficients for each pixel in the satellite camera, addressing the drawbacks of uncorrected diffraction effects and insufficient correction for array non-uniformity.

[0053] Example 1

[0054] The present application embodiment provides a satellite radiation calibration system, referring to Figure 1 , Figure 1 Schematic diagram of the onboard radiometric calibration system provided in an embodiment of the present application. In this embodiment, the onboard radiometric calibration system includes a calibration observation port, a pinhole plate A, a semi-transparent and semi-reflective mirror B, a scanning mirror C, and a satellite camera D. The calibration optical path of the onboard radiometric calibration system passes through the sun, the calibration observation port, the pinhole on the pinhole plate A, the semi-transparent and semi-reflective mirror B, the scanning mirror C, and the satellite camera D in sequence.

[0055] Pinhole plate A has a single pinhole or multiple pinholes. In one embodiment, it comprises an array of pinholes with a diameter dp of 10 to 100 μm. Its surface is a matte-treated metal plate. It also includes a rotary mechanism that enables satellite cameras D to sequentially measure diffraction energy. Satellite cameras D can be area or linear array satellite cameras, employing multi-pixel focal plane detectors (e.g., CMOS or CCD), and are radiation-collecting cameras such as infrared cameras or visible light cameras.

[0056] Furthermore, the present invention provides a method for calibrating on-board radiation. Figure 2 , Figure 2 This is a flow chart of the on-board radiation calibration method provided in Example 1 of the present application. In this embodiment, the on-board radiation calibration method is applied to an on-board radiation calibration system, and the on-board radiation calibration method includes steps S10 to S30:

[0057] Step S10: Adjusting the attitude of the artificial satellite, adjusting the target so that the incident sunlight passes vertically through the target pinhole on the pinhole plate;

[0058] In one embodiment, referring to Figure 1 , the satellite attitude is determined according to the direction of the sun through the sun sensor E, and at the same time, the satellite attitude control module ( Figure 1(Not shown) Pinhole plate A is adjusted to face the direction of solar incidence. This allows the satellite's position relative to the sun to be determined using sun sensor E. The satellite's attitude is then adjusted to face pinhole plate A directly toward the sun, ensuring that incident light passes perpendicularly through the target aperture on pinhole plate A.

[0059] Step S20: Obtain the theoretical radiance of the standard detector and the actual response value of each pixel of the satellite camera;

[0060] Next, diffraction spot imaging is achieved, i.e., satellite camera D captures a pinhole diffraction image. The actual response value of satellite camera D at the pixel in row i and column j is DN(i, j). Furthermore, the integration time t and the energy distribution of the standard detector are synchronously recorded. Since sunlight is a relatively stable light source, the theoretical radiance of the standard detector can be calculated.

[0061] In one embodiment, the theoretical radiance of a standard detector is calculated as follows:

[0062]

[0063] In the above formula, It represents the theoretical radiance of the sun in band B that theoretically reaches the standard detector through pinhole plate A at time t; and are the upper and lower wavelength limits of the B band; represents the directional transmission distribution function of the pinhole plate A. The output value of this function is the transmittance in different directions after passing through the aperture; Represents the solar incident angle parameter. Since the detection angle is fixed, the only directional variable is the incident angle, that is, the azimuth and zenith angle of the incident light. It represents the solar spectral irradiance reaching the upper boundary of the atmosphere at the average distance between the sun and the earth, which can be obtained from the Wehrli85 solar spectrum published by the World Meteorological Organization; The Sun-Earth distance factor at calibration time t represents the astronomical distance between the Sun and the Earth in astronomical units (AU), which varies between two extreme values ​​(perihelion and aphelion); It represents the spectral response function of the standard detector, that is, the ratio of the received radiance to the incident radiance at each wavelength, which describes the response intensity of the sensor at different wavelengths.

[0064] Step S30: determining the calibration coefficient of each pixel of the satellite camera based on the theoretical radiance and the actual response value of each pixel of the satellite camera.

[0065] In one embodiment, the theoretical radiance is L detector(i, j), the actual response value of each pixel is DN(i, j), and the calibration coefficient of each pixel of satellite camera D is defined as K(i, j), K(i, j)=DN(i, j) / L detector Furthermore, when using satellite camera D for actual ground detection, the true, real-time radiance corresponding to any pixel of satellite camera D can be calculated based on the real-time response value of the pixel and the calibration coefficient K of the pixel.

[0066] In summary, this embodiment addresses the technical issue of 1. uncorrected diffraction effects by fully accounting for inter-pixel luminous flux distribution differences caused by the Airy pattern, reducing calibration errors. Specifically, this corrects for luminous flux calculation errors caused by pinhole diffraction, thereby minimizing the impact of Airy disk energy distribution on calibration accuracy. Furthermore, this embodiment addresses the technical issue of 2. insufficient correction for array non-uniformity by eliminating spatial sensitivity differences through pixel-by-pixel response calibration, rather than relying on statistical averaging. This addresses the multi-pixel non-uniformity issue, thereby achieving accurate on-board radiometric calibration.

[0067] In a feasible implementation, when there is a single pinhole on the pinhole plate, step S30 may include steps S301 to S304:

[0068] Step S301: determining the target pixel with the best response of the satellite camera;

[0069] The pixel with the best response from the satellite camera is selected as the target pixel (i0, j0). In one embodiment, the center pixel of the satellite camera is temporarily selected as the target pixel. In this embodiment, the method for determining the target pixel and the method for selecting the best response are not limited.

[0070] Step S302: obtaining the current actual response value of the satellite camera at the target pixel;

[0071] Step S303: determining a standard calibration coefficient at the target pixel according to the theoretical radiance at the target pixel and the current actual response value;

[0072] The actual current response value of the satellite camera at the target pixel (i0, j0) is DN(i0, j0), and the theoretical radiance at the target pixel (i0, j0) is L detector (i0, j0), at this time, the standard calibration coefficient K(i0, j0)=DN(i0, j0) / L at the target pixel can be determined detector (i0, j0).

[0073] Step S304: determining a target calibration coefficient for each non-target pixel of the satellite camera according to the standard calibration coefficient and the response difference between each non-target pixel and the target pixel.

[0074] Since the actual responses of different pixels are not uniform or identical, each non-target pixel will have a different response than the target pixel. Furthermore, the target calibration coefficient K(i, j) for each non-target pixel in the satellite camera can be determined based on the standard calibration coefficient and the response difference C(i, j) between each non-target pixel and the target pixel: K(i, j) = K(i0, j0)·C(i, j).

[0075] In this embodiment, the method for determining the standard calibration coefficient and the response difference C(i, j) between each non-target pixel and the target pixel is not limited.

[0076] In a feasible implementation manner, before step S304, the following steps are included:

[0077] By rotating the scanning mirror, the historical actual response value of each pixel of the satellite camera is obtained;

[0078] The relative difference in historical actual response value between each non-target pixel and the target pixel is determined, and the relative difference is used as the response difference of each non-target pixel compared with the target pixel.

[0079] In this embodiment, a method for determining a standard calibration coefficient and a response difference C(i, j) between each non-target pixel and the target pixel is proposed.

[0080] By rotating the scanning mirror C, different pixels of the satellite camera D are facing the same target pinhole position to collect signals, so that the historical actual response value DN of each pixel of the satellite camera D can be obtained. history (i, j). Then, the historical actual response value DN of each non-target pixel (i, j) and the target pixel (i0, j0) can be determined. history The relative difference is taken as the response difference C(i, j)=DN between each non-target pixel and the target pixel. history (i, j) / DN history (i0, j0).

[0081] By default and ideally, the responsivities (response functions, response characteristics, and calibration coefficients) of different pixels in satellite camera D should be consistent, and their response values ​​should also be consistent. Therefore, differences in response values ​​can be used to determine differences in responsivities, which are the relative coefficients of the calibration coefficients.

[0082] In one embodiment, based on the historical actual response value DN of each non-target pixel history (i, j), establish the non-uniformity correction matrix C(i, j) of the satellite camera; the non-uniformity correction matrix C(i, j) is used as the response difference between each non-target pixel and the target pixel.

[0083] In the case of a single pinhole on the pinhole plate, since the relative difference in historical actual response values ​​between each non-target pixel and the target pixel is relatively small, the response difference between each non-target pixel and the target pixel can be determined periodically or irregularly. Each time the calibration coefficient for each pixel is determined, the latest response difference can be used to calculate the target calibration coefficient for each non-target pixel in real time.

[0084] In a feasible embodiment, when there are pinholes of different sizes on the pinhole plate, step S30 may include steps S30A-S30B:

[0085] Step S30A: obtaining data pairs of theoretical radiance and actual response values ​​of each pixel of the satellite camera at different aperture scales;

[0086] Step S30B: Determine the calibration coefficient of each pixel of the satellite camera by fitting the data pairs.

[0087] In this embodiment, when pinholes of varying sizes are present on the pinhole plate, multiple apertures and gradients are used to obtain multiple pairs of response values ​​and radiance data. Specifically, pairs of theoretical radiance at varying aperture sizes and actual response values ​​for each pixel in the satellite camera are obtained. By fitting these data pairs, calibration coefficients for each pixel in the satellite camera are determined, thereby eliminating errors introduced by calculations using a single energy scale, i.e., a single pinhole size. For example, the accuracy of calibration coefficient calculations can be improved by fitting a linear function using the least squares method.

[0088] It should be noted that in the definition of the calibration coefficient K(i, j) of each pixel of the satellite camera, K(i, j)=DN(i, j) / L detector (i, j), where DN(i, j) and L detector (i, j) represents the camera response value DN and the theoretical radiance value L obtained at the same aperture. Ideally, the response value and radiance are directly proportional, so the calibration coefficient can be directly derived. However, in reality, aperture error can lead to errors in the theoretical radiance calculation. Similarly, camera response values ​​can also be affected by stray light and other factors, resulting in errors. Furthermore, camera responses are not perfectly proportional. Therefore, in this embodiment, multiple apertures and gradients are used to obtain multiple response value and radiance data pairs. Least squares linear fitting can improve the accuracy of calibration coefficient calculation.

[0089] Example 2

[0090] Based on the first embodiment of the present application, the second embodiment of the present application is proposed. In the second embodiment of the present application, the same or similar contents as those of the above-mentioned first embodiment can be referred to the above introduction and will not be repeated hereafter.

[0091] The present application embodiment provides a satellite radiation calibration system, referring to Figure 1 , Figure 1 Schematic diagram of the onboard radiometric calibration system provided in an embodiment of the present application. In this embodiment, the onboard radiometric calibration system also includes a standard detector F. The aperture dynamic compensation optical path of the onboard radiometric calibration system passes through the sun, the calibration observation port, the pinhole on the pinhole plate A, the semi-transparent and semi-reflective mirror B, and the standard detector F in sequence.

[0092] The standard detector F is the same source detector as the satellite camera D and is coaxial with the energy received by the satellite camera D.

[0093] In the new on-board radiation calibration method using pinhole and sunlight as the on-board radiation calibration source, in addition to the problems mentioned above, the following problems are usually not considered: 3. Poor adaptability to dynamic environments: On-orbit thermal deformation causes the pinhole diameter (dp) to drift, and the existing technology lacks a real-time geometric parameter correction mechanism.

[0094] Based on this, further, the embodiment of the present application provides a method for on-board radiation calibration, referring to Figure 3 , Figure 3 This is a flow chart of the on-board radiation calibration method provided in Example 2 of the present application. In this embodiment, step S20 may include steps S201 to S204:

[0095] Step S201: obtaining an actual diffraction pattern of a standard detector;

[0096] Step S202: determining the actual pinhole aperture of the pinhole on the pinhole plate according to the actual diffraction pattern;

[0097] Step S203: determining the directional transmission distribution function at each pixel of the standard detector based on the actual pinhole aperture;

[0098] Step S204: determining the theoretical radiance at each pixel of the standard detector based on the directional transmission distribution function at each pixel of the standard detector.

[0099] By analyzing the impact of the technical problem of poor adaptability to dynamic environments 3, that is, the change of the pinhole diameter in space, the directional transmission distribution function of the pinhole plate A is Inaccurate, which leads to the theoretical radiance being L detector Therefore, in this embodiment, dynamic compensation and parameter correction are performed for the change of the pinhole aperture parameter.

[0100] In this embodiment, a mapping model between the diffraction pattern (including the Airy disk at different optical path lengths of a coaxial optical path) and the pinhole aperture is pre-established based on the Fraunhofer diffraction model and actual experimental data. Specifically, using a laboratory diffraction generator, by varying the pinhole aperture and the wavelength of the incident light, different diffraction patterns can be obtained at the diffraction pattern receiving screen. This mapping model is constructed with the pinhole aperture and the wavelength of the incident light as variables, and the diffraction pattern as the dependent variable. This allows the aperture change to be inferred from the energy distribution of a standard detector. Using the actual diffraction pattern (the Airy disk portion) of the standard detector, the mapping model can be used to determine the actual pinhole aperture on the pinhole plate, which can then be corrected (the aperture changes in space, requiring real-time correction). Furthermore, a correction coefficient is obtained, allowing a more accurate diffraction energy distribution function (model) to be derived based on the Fraunhofer diffraction model and the correction coefficient.

[0101] It should be noted that the pinhole in the present application can be replaced by a rectangular slit, and correspondingly, the diffraction model uses the single-slit Fraunhofer formula instead.

[0102] Further analysis of the energy path reveals a one-to-one correspondence between the Airy disk energy distribution, pinhole aperture, and transmittance distribution function, or directional transmission distribution function. Therefore, a lookup table can be constructed to pre-store experimental data for these three parameters. This table stores multiple experimental data sets for Airy disk energy distribution, pinhole aperture, and directional transmission distribution function. Interpolation and fitting can be used to correct for aperture variations within a certain range. Thus, when using this lookup table, given any known value for any of the three parameters, the corresponding values ​​for the other two parameters can be retrieved.

[0103] In this embodiment, based on the actual pinhole aperture, the directional transmission distribution function at each pixel of the standard detector can be determined using the aforementioned lookup table. This directional transmission distribution function is the latest directional transmission distribution function corresponding to the actual pinhole diameter after on-orbit thermal deformation. Furthermore, using the same method for calculating the theoretical radiance of the standard detector as described in the first embodiment above, a more accurate theoretical radiance at each pixel of the standard detector can be determined based on the latest directional transmission distribution function at each pixel of the standard detector. This dynamically compensates for on-orbit geometric parameter drift (such as changes in pinhole diameter dp) and ensures long-term calibration stability.

[0104] In a feasible implementation, step S202 includes:

[0105] Based on a pre-established mapping model of the diffraction pattern of a standard detector and the pinhole aperture, the actual pinhole aperture of the pinhole corresponding to the actual diffraction pattern is determined.

[0106] This embodiment proposes a method for determining the actual pinhole aperture of a pinhole in a pinhole plate based on an actual diffraction pattern. Using a pre-established mapping model between the diffraction pattern of a standard detector and the pinhole aperture, the actual pinhole aperture corresponding to the actual diffraction pattern is determined. The establishment of the mapping model is described above and will not be further elaborated here.

[0107] In a feasible implementation manner, step S202 further includes:

[0108] Based on the pre-trained neural network model of the diffraction pattern and pinhole aperture of the standard detector, the actual pinhole aperture of the pinhole corresponding to the actual diffraction pattern is determined.

[0109] In this embodiment, another method for determining the actual pinhole aperture of the pinhole on the pinhole plate according to the actual diffraction pattern is proposed.

[0110] In the mapping model of diffraction pattern and pinhole aperture, that is, the mapping model of Airy disk energy distribution-pinhole aperture in the lookup table (Airy disk energy distribution-pinhole aperture-directional transmission distribution function), due to the unavailable data interval, that is, the diffraction pattern is incomplete and the pinhole aperture types are relatively small, the lookup table obtained by interpolation fitting can only be used to correct aperture changes within a certain range.

[0111] Therefore, refer to Figure 4 , Figure 4 This is a schematic diagram of the neural network model provided in Example 2 of this application. In addition to the mapping model and lookup table described above, a neural network regression algorithm can also be used to test data sets at different apertures using the same wavelength to construct a neural network model with a diffraction pattern as input and aperture as output. Through this algorithm model, the actual aperture of the pinhole can be obtained based on the diffraction pattern of the standard detector as input, and the diffraction transmittance distribution of the actual aperture, i.e., the directional transmission distribution function, can be obtained.

[0112] It should be noted that the above examples are only used to understand the present application and do not constitute a limitation on the on-board radiation calibration method of the present application. More simple transformations based on this technical concept are all within the scope of protection of the present application.

[0113] Example 3

[0114] Based on the second embodiment of the present application, the third embodiment of the present application is proposed. In the third embodiment of the present application, the same or similar contents as those of the above-mentioned second embodiment can be referred to the above introduction and will not be repeated hereafter.

[0115] The present application embodiment provides a satellite detection system, referring to Figure 5 , Figure 5Schematic diagram of a satellite detection system provided in Example 3 of the present application. In this embodiment, the satellite detection system includes a target satellite camera D, a scanning mirror C, and a ground observation port, which have been calibrated using the onboard radiation calibration system described in Example 2. The ground detection optical path passes through the Earth's surface, the ground observation port, the scanning mirror C, and the target satellite camera D in sequence.

[0116] Example 4

[0117] Furthermore, the present application provides an on-board radiation calibration system that also includes: at least one processor; and a memory communicatively connected to the at least one processor; wherein the memory stores instructions that can be executed by the at least one processor, and the instructions are executed by the at least one processor so that the at least one processor can execute the on-board radiation calibration method in the above-mentioned embodiment one.

[0118] Reference below Figure 6 , which shows a structural schematic diagram of an on-board radiation calibration system suitable for implementing an embodiment of the present application. Figure 6 The on-board radiation calibration system shown is merely an example and should not limit the functions and scope of use of the embodiments of the present application.

[0119] like Figure 6 As shown, the onboard radiation calibration system may include a processing device 1001 (e.g., a central processing unit, graphics processing unit, etc.), which can perform various appropriate actions and processes based on programs stored in read-only memory 1002 or programs loaded from storage device 1003 into random access memory 1004. Random access memory 1004 also stores various programs and data required for the operation of the onboard radiation calibration system. Processing device 1001, read-only memory 1002, and random access memory 1004 are interconnected via bus 1005. An input / output interface 1006 is also connected to the bus. Typically, the following systems may be connected to input / output interface 1006: input device 1007 and output device 1008; storage device 1003, such as a magnetic tape or hard disk; and communication device 1009. Communication device 1009 allows the onboard radiation calibration system to communicate with other devices wirelessly or wired to exchange data. Although the figure shows an onboard radiation calibration system with various systems, it should be understood that implementation or availability of all of the illustrated systems is not required. Greater or fewer systems may alternatively be implemented or provided.

[0120] In particular, according to the embodiments disclosed in the present application, the processes described above with reference to the flowcharts can be implemented as computer software programs. For example, the embodiments disclosed in the present application include a computer program product comprising a computer program carried on a computer-readable medium, the computer program comprising program code for executing the method shown in the flowchart. In such an embodiment, the computer program can be downloaded and installed from a network via a communication device, or installed from a storage device 1003, or installed from a read-only memory 1002. When the computer program is executed by the processing device 1001, the above-mentioned functions defined in the method of the embodiment disclosed in the present application are performed.

[0121] The on-board radiometric calibration system provided in this application utilizes the on-board radiometric calibration method described in the aforementioned embodiment to address the technical issue of inaccurate on-board radiometric calibration. Compared to the prior art, the on-board radiometric calibration system provided in this application achieves the same beneficial effects as the on-board radiometric calibration method described in the aforementioned embodiment. Other technical features of the on-board radiometric calibration system are the same as those disclosed in the aforementioned embodiment and are not further detailed here.

[0122] It should be understood that the various parts disclosed in this application can be implemented using hardware, software, firmware, or a combination thereof. In the description of the above embodiments, specific features, structures, materials, or characteristics can be combined in any one or more embodiments or examples in a suitable manner.

[0123] The above description is merely a specific embodiment of the present application, but the scope of protection of the present application is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in this application should be included in the scope of protection of this application. Therefore, the scope of protection of this application should be based on the scope of protection of the claims.

[0124] Furthermore, the on-board radiation calibration system further includes a computer-readable storage medium having computer-readable program instructions (ie, computer program) stored thereon, and the computer-readable program instructions are used to execute the on-board radiation calibration method in the above embodiment.

[0125] The computer-readable storage medium provided in this application may be, for example, a USB flash drive, but is not limited to electrical, magnetic, optical, electromagnetic, infrared, or semiconductor systems or devices, or any combination thereof. More specific examples of computer-readable storage media may include, but are not limited to: an electrical connection with one or more wires, a portable computer disk, a hard disk, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM or flash memory), optical fiber, a portable compact disk read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination thereof. In this embodiment, the computer-readable storage medium may be any tangible medium that contains or stores a program that can be used by or in conjunction with an instruction execution system or device. The program code contained on the computer-readable storage medium may be transmitted using any suitable medium, including but not limited to: wires, optical cables, RF (Radio Frequency), etc., or any suitable combination thereof.

[0126] The computer-readable storage medium may be included in the onboard radiation calibration system; or may exist independently without being assembled into the onboard radiation calibration system.

[0127] The computer-readable storage medium carries one or more programs. When the one or more programs are executed by the onboard radiation calibration system, the onboard radiation calibration system is caused to: adjust the attitude of the artificial satellite, adjust the target so that the incident solar light passes vertically through the target pinhole on the pinhole plate; obtain the theoretical radiance of the standard detector and the actual response value of each pixel of the satellite camera; and determine the calibration coefficient of each pixel of the satellite camera based on the theoretical radiance and the actual response value of each pixel of the satellite camera.

[0128] Computer program code for performing the operations of the present application may be written in one or more programming languages, or a combination thereof, including object-oriented programming languages ​​such as Java, Smalltalk, C++, and conventional procedural programming languages ​​such as "C" or similar programming languages. The program code may be executed entirely on the user's computer, partially on the user's computer, as a stand-alone software package, partially on the user's computer and partially on a remote computer, or entirely on a remote computer or server. In the case of a remote computer, the remote computer may be connected to the user's computer via any type of network, including a local area network (LAN) or a wide area network (WAN), or may be connected to an external computer (e.g., via the Internet using an Internet service provider).

[0129] The flow charts and block diagrams in the accompanying drawings illustrate the possible architecture, functions and operations of the systems, methods and computer program products according to various embodiments of the present application. In this regard, each box in the flow chart or block diagram can represent a module, program segment or a part of code, and the module, program segment or a part of code contains one or more executable instructions for realizing the specified logical function. It should also be noted that in some alternative implementations, the functions marked in the box can also occur in a different order than that marked in the accompanying drawings. For example, two boxes represented in succession can actually be executed substantially in parallel, and they can sometimes be executed in the opposite order, depending on the functions involved. It should also be noted that each box in the block diagram and / or flow chart, and the combination of the boxes in the block diagram and / or flow chart can be implemented by a dedicated hardware-based system that performs the specified function or operation, or can be implemented by a combination of dedicated hardware and computer instructions.

[0130] The modules described in the embodiments of the present application may be implemented in software or hardware, wherein the name of a module does not necessarily limit the unit itself.

[0131] The computer-readable storage medium provided in this application stores computer-readable program instructions (i.e., a computer program) for executing the aforementioned onboard radiometric calibration method. This computer-readable storage medium can address the technical issue of inaccurate onboard radiometric calibration. Compared to the prior art, the computer-readable storage medium provided in this application offers the same beneficial effects as the onboard radiometric calibration method provided in the aforementioned embodiments, and therefore is not further elaborated here.

[0132] The above description is only part of the embodiments of the present application and does not limit the patent scope of the present application. All equivalent structural transformations made by using the contents of the present application specification and drawings under the technical concept of the present application, or direct / indirect application in other related technical fields are included in the patent protection scope of the present application.

Claims

1. A method for on-board radiation calibration, characterized in that: The on-board radiation calibration method is applied to an on-board radiation calibration system, the system comprising a calibration observation port, a pinhole plate, a semi-transparent and semi-reflective mirror, a scanning mirror, and a satellite camera. The calibration optical path of the on-board radiation calibration system sequentially passes through the sun, the calibration observation port, the pinhole on the pinhole plate, the semi-transparent and semi-reflective mirror, the scanning mirror, and the satellite camera. The method comprises: Adjusting the attitude of the artificial satellite, the adjustment target is that the incident sunlight passes vertically through the target pinhole on the pinhole plate; Obtaining the theoretical radiance of the standard detector and the actual response value of each pixel of the satellite camera; Based on the theoretical radiance and the actual response value of each pixel of the satellite camera, a calibration coefficient of each pixel of the satellite camera is determined.

2. The on-board radiation calibration method according to claim 1, wherein: When there is a single pinhole on the pinhole plate, the step of determining the calibration coefficient of each pixel of the satellite camera based on the theoretical radiance and the actual response value of each pixel of the satellite camera includes: determining a target pixel having an optimal response of the satellite camera; Obtaining a current actual response value of the satellite camera at the target pixel; Determining a standard calibration coefficient at the target pixel according to the theoretical radiance at the target pixel and the current actual response value; A target calibration coefficient for each non-target pixel of the satellite camera is determined according to the standard calibration coefficient and a response difference between each non-target pixel and the target pixel.

3. The on-board radiation calibration method according to claim 2, wherein: The step of determining the target calibration coefficient of each non-target pixel of the satellite camera according to the standard calibration coefficient and the response difference of each non-target pixel compared with the target pixel includes: Obtaining a historical actual response value of each pixel of the satellite camera by rotating the scanning mirror; The relative difference between each non-target pixel and the target pixel in the historical actual response value is determined, and the relative difference is used as the response difference of each non-target pixel compared with the target pixel.

4. The on-board radiation calibration method according to claim 1, wherein: When pinholes of different sizes exist on the pinhole plate, the step of determining the calibration coefficient of each pixel of the satellite camera based on the theoretical radiance and the actual response value of each pixel of the satellite camera includes: Obtaining data pairs of the theoretical radiance and the actual response value of each pixel of the satellite camera at different aperture scales; The calibration coefficient of each pixel of the satellite camera is determined by fitting the data pair.

5. The on-board radiation calibration method according to claim 1, wherein: The on-board radiation calibration system further includes a standard detector, and the aperture dynamic compensation optical path of the on-board radiation calibration system sequentially passes through the sun, the calibration observation port, the pinhole on the pinhole plate, the semi-transparent and semi-reflective mirror, and the standard detector; The step of obtaining the theoretical radiance of the standard detector includes: obtaining an actual diffraction pattern of the standard detector; determining an actual pinhole aperture of the pinhole on the pinhole plate according to the actual diffraction pattern; Determining a directional transmission distribution function at each pixel of a standard detector based on the actual pinhole aperture; Based on the directional transmission distribution function at each pixel of the standard detector, the theoretical radiance at each pixel of the standard detector is determined.

6. The on-board radiation calibration method according to claim 5, wherein: The step of determining the actual pinhole aperture of the pinhole on the pinhole plate according to the actual diffraction pattern comprises: Based on a pre-established mapping model between the diffraction pattern and the pinhole aperture of the standard detector, the actual pinhole aperture of the pinhole corresponding to the actual diffraction pattern is determined.

7. The on-board radiation calibration method according to claim 5, wherein: The step of determining the actual pinhole aperture of the pinhole on the pinhole plate according to the actual diffraction pattern further comprises: Based on a pre-trained neural network model of the diffraction pattern and pinhole aperture of the standard detector, an actual pinhole aperture of the pinhole corresponding to the actual diffraction pattern is determined.

8. An onboard radiation calibration system, characterized in that: The on-board radiation calibration system includes: a calibration observation port, a pinhole plate, a semi-transparent and semi-reflective mirror, a scanning mirror and a satellite camera. The calibration optical path of the on-board radiation calibration system passes through the sun, the calibration observation port, the pinhole on the pinhole plate, the semi-transparent and semi-reflective mirror, the scanning mirror and the satellite camera in sequence; the system implements the steps of the on-board radiation calibration method according to any one of claims 1 to 4.

9. The on-board radiation calibration system according to claim 8, wherein: The on-board radiation calibration system also includes a standard detector, and the aperture dynamic compensation optical path of the on-board radiation calibration system passes through the sun, the calibration observation port, the pinhole on the pinhole plate, the semi-transparent and semi-reflective mirror, and the standard detector in sequence; the system implements the steps of the on-board radiation calibration method as described in any one of claims 5 to 7.

10. A satellite detection system, characterized in that: The satellite detection system includes a target satellite camera, a scanning mirror and a ground observation port calibrated by the on-board radiation calibration system as described in claim 8 or 9, and the ground detection light path passes through the earth's surface, the ground observation port, the scanning mirror and the target satellite camera in sequence.

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