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

Abstract

The invention discloses an on-satellite radiometric calibration method and system and a satellite detection system, and relates to the technical field of satellite remote sensing, and the method comprises the steps: setting an on-satellite radiometric calibration system composed of a calibration observation port, a pinhole plate, a semi-transparent and semi-reflective mirror, a scanning mirror and a satellite camera, a calibration light path is set to sequentially pass through the sun, a calibration observation port, a pinhole in a pinhole plate, a semi-transparent and semi-reflecting mirror, a scanning mirror and a satellite camera, and the attitude of an artificial satellite is adjusted, so that the incident light of the sun vertically passes through a target pinhole in the pinhole plate, and the hardware construction and preparation work of on-satellite radiometric calibration are completed. And then determining the calibration coefficient of each pixel of the satellite camera based on the theoretical radiance of the standard detector and the actual response value of each pixel of the satellite camera. Therefore, aiming at the defects that the diffraction effect is not corrected and the non-uniformity correction of the area array is insufficient, the accuracy of on-satellite radiometric calibration is improved by determining the calibration coefficient of each pixel of the satellite camera.

Description

Technical Field

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

[0002] Currently, on-orbit radiation calibration systems mainly adopt two types of technologies: 1) Based on a solar diffuser: Made of a high-reflectivity material, it reflects sunlight into the camera's field of view and combines with a standard detector to measure the reflectivity. 2) Based on an LED calibration source: Integrated inside the satellite, it simulates the solar spectrum through a stable light-emitting diode array and requires a temperature control module. Its working principle is: sunlight or the LED light source is evenly irradiated onto the camera's focal plane through an optical system, and calibration is achieved by measuring the linear relationship between the output digital value (DN) and the standard radiation value.

[0003] Among them, the solar diffuser and the LED calibration source will decay as the number of uses increases, and stable calibration cannot be achieved within a long service life. Based on this, a new on-orbit radiation calibration method using a pinhole or slit and sunlight as the on-orbit radiation calibration source has emerged.

[0004] However, in the new on-orbit radiation calibration method using a pinhole or slit and sunlight as the on-orbit radiation calibration source, the following problems are usually not considered: 1. Diffraction effect not corrected: When calibrating based on a pinhole or slit, the difference in the light flux distribution between pixels caused by the Airy Pattern is ignored, resulting in calibration errors. 2. Insufficient correction of the non-uniformity of the area array: Only relying on statistical averaging and not modeling the response characteristics of each pixel, the spatial sensitivity difference cannot be eliminated.

[0005] The above content is only used to assist in understanding the technical solution of this application and does not represent 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-orbit radiation calibration method, an on-orbit radiation calibration system, and a satellite detection system, aiming to solve the technical problem of inaccurate on-orbit radiation calibration.

[0007] To achieve the above purpose, this application proposes an on-orbit radiation calibration method. The on-orbit radiation calibration method is applied to an on-orbit radiation calibration system, and 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-orbit 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 includes: Adjust the attitude of the artificial satellite, and the adjustment target is that the sun incident light vertically passes through the target pinhole on the pinhole plate; Obtain the theoretical radiance of the standard detector and the actual response values of each pixel of the satellite camera; Based on the theoretical radiance and the actual response values of each pixel of the satellite camera, determine the calibration coefficients of each pixel of the satellite camera.

[0008] In one embodiment, when there is a single pinhole on the pinhole plate, the step of determining the calibration coefficients of each pixel of the satellite camera based on the theoretical radiance and the actual response values of each pixel of the satellite camera includes: Determine the target pixel with the best response of the satellite camera; Obtain the current actual response value of the satellite camera at the target pixel; According to the theoretical radiance and the current actual response value at the target pixel, determine the standard calibration coefficient at the target pixel; According to the standard calibration coefficient and the response difference of each non-target pixel compared to the target pixel, determine the target calibration coefficients of each non-target pixel of the satellite camera.

[0009] In one embodiment, before the step of determining the target calibration coefficients 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 to the target pixel, include: By rotating the scanning mirror, obtain the historical actual response values of each pixel of the satellite camera; Determine the relative difference between each non-target pixel and the target pixel in the historical actual response values, and use the relative difference as the response difference of each non-target pixel compared to the target pixel.

[0010] In one embodiment, when there are pinholes of different scales on the pinhole plate, the step of determining the calibration coefficients of each pixel of the satellite camera based on the theoretical radiance and the actual response values of each pixel of the satellite camera includes: Obtain the data pairs of the theoretical radiance and the actual response values of each pixel of the satellite camera at different aperture scales; By fitting the data pairs, determine the calibration coefficients of each pixel of the satellite camera.

[0011] In one embodiment, the on-orbit radiation calibration system further includes a standard detector. The aperture dynamic compensation optical path of the on-orbit 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: Obtain the actual diffraction pattern of the standard detector; According to the actual diffraction pattern, determine the actual pinhole aperture of the pinhole on the pinhole plate; Based on the actual pinhole aperture, determine the directional transmission distribution function at each pixel of the standard detector; Based on the directional transmission distribution function at each pixel of the standard detector, determine the theoretical radiance at each pixel of the standard detector.

[0012] In one embodiment, the step of determining the actual pinhole aperture of the pinhole on the pinhole plate according to the actual diffraction pattern includes: Based on the pre-established mapping model of the diffraction pattern and the pinhole aperture of the standard detector, determine the actual pinhole aperture of the pinhole corresponding to the actual diffraction pattern.

[0013] 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 includes: Based on the pre-trained neural network model of the diffraction pattern and the pinhole aperture of the standard detector, determine the actual pinhole aperture of the pinhole corresponding to the actual diffraction pattern.

[0014] In addition, to achieve the above object, the present application also proposes an on-orbit 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 optical path of the on-orbit 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 system implements the steps of the on-orbit radiation calibration method as described above.

[0015] In one embodiment, the on-orbit radiation calibration system further includes a standard detector. The aperture dynamic compensation optical path of the on-orbit 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 system implements the steps of the on-orbit radiation calibration method as described above.

[0016] In addition, to achieve the above object, the present application also proposes a satellite detection system, which includes a target satellite camera calibrated by the above on-orbit radiation calibration system, a scanning mirror, and a ground observation port. The ground detection optical path sequentially passes through the earth's surface, the ground observation port, the scanning mirror, and the target satellite camera.

[0017] One or more technical solutions proposed by the present application have at least the following technical effects: An on-orbit 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 is set up. 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 in sequence. The satellite attitude is determined through a sun sensor, and then the attitude of the artificial satellite is adjusted so that the incident sunlight perpendicularly passes through the target pinhole on the pinhole plate, thus completing the hardware setup and preparatory work for on-orbit radiation calibration. Then, based on the theoretical radiance of the standard detector and the actual response values of each pixel of the satellite camera, the calibration coefficients of each pixel of the satellite camera are determined. Therefore, aiming at the defects of uncorrected diffraction effects and insufficient correction of focal plane non-uniformity, the accuracy of on-orbit radiation calibration is improved by determining the calibration coefficients of each pixel of the satellite camera. Description of the Drawings

[0018] The drawings here are incorporated into the specification and form a part of this specification, showing embodiments consistent with this application and used together with the specification to explain the principles of this application.

[0019] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, for those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0020] Figure 1 Schematic diagram of the on-orbit radiation calibration system provided by the embodiment of this application; Figure 2 Schematic diagram of the on-orbit radiation calibration method flow provided by Embodiment 1 of this application; Figure 3 Schematic diagram of the on-orbit radiation calibration method flow provided by Embodiment 2 of this application; Figure 4 Schematic diagram of the neural network model provided by Embodiment 2 of this application; Figure 5 Schematic diagram of the satellite detection system provided by Embodiment 3 of this application; Figure 6 Schematic diagram of the on-orbit radiation calibration system provided by Embodiment 4 of this application.

[0021] The realization of the purpose of this application, its functional features, and advantages will be further described in combination with the embodiments with reference to the drawings. Detailed Embodiments

[0022] It should be understood that the specific embodiments described here are only used to explain the technical solutions of this application and are not used to limit this application.

[0023] To better understand the technical solution of this application, the following will be described in detail in conjunction with the accompanying drawings of the specification and specific embodiments.

[0024] On-orbit radiometric calibration is a crucial step in satellite remote sensing, which is used to ensure that the radiometric data measured by the sensor accurately reflects the actual radiation amount. That is, the calibration process performed on the sensor on the satellite platform aims to ensure that the measured data is accurate and error-free, reflecting the true radiation intensity. Its purposes are as follows: 1. Accuracy: Ensure that the sensor measurement value accurately reflects the actual radiation. 2. Consistency: Guarantee the consistency of data from different times and different sensors. 3. Stability: Compensate for the influence of environmental changes on the sensor, such as temperature fluctuations.

[0025] Current on-orbit radiometric calibration methods include: 1. Internal reference source: Regularly calibrate the sensor using a source with a known radiation intensity (such as a blackbody or a lamp). 2. External reference source: Calibrate using the known radiation characteristics of the Earth's surface or solar radiation. 3. Cross-calibration: Mutually calibrate the data of different sensors or satellites to ensure consistency. It is mainly applied to accurately monitor atmospheric parameters such as temperature and humidity through meteorological satellites, or precisely measure the surface radiation through remote sensing satellites for environmental monitoring and resource management.

[0026] However, the solar diffuser and LED calibration source will decay with the increase in the number of uses, and stable calibration cannot be achieved within a long service life. Based on this, a new on-orbit radiometric calibration method using a pinhole or slit and sunlight as the on-orbit radiometric calibration source has emerged.

[0027] Furthermore, in the new on-orbit radiometric calibration method using a pinhole or slit and sunlight as the on-orbit radiometric calibration source, the following problems are usually not considered: 1. Diffraction effect not corrected: When calibrating based on a pinhole or slit, the difference in the light flux distribution between pixels caused by the Airy Pattern is ignored, resulting in calibration errors. 2. Insufficient correction of focal plane array non-uniformity: Only relying on statistical averaging and not modeling the response characteristics of each pixel, the spatial sensitivity difference cannot be eliminated.

[0028] The main solution of the embodiment of this application is: An on-orbit 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 is set up. The calibration optical path is set to pass through the sun, the calibration observation port, the pinholes on the pinhole plate, the semi-transparent and semi-reflective mirror, the scanning mirror, and the satellite camera in sequence. Then, the attitude of the artificial satellite is adjusted so that the incident sunlight perpendicularly passes through the target pinhole on the pinhole plate, thereby completing the hardware construction and preparation work for on-orbit radiation calibration. Then, based on the theoretical radiance of the standard detector and the actual response values of each pixel of the satellite camera, the calibration coefficients of each pixel of the satellite camera are determined. Thus, aiming at the defects of uncorrected diffraction effects and insufficient correction of focal plane non-uniformity, the accuracy of on-orbit radiation calibration is improved by determining the calibration coefficients of each pixel of the satellite camera.

[0029] Embodiment 1 The embodiment of the present application provides an on-orbit radiation calibration system. Refer to Figure 1 , Figure 1 which is a schematic diagram of the on-orbit radiation calibration system provided by the embodiment of the present application. In this embodiment, the on-orbit radiation 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 on-orbit radiation calibration system passes through the sun, the calibration observation port, the pinholes on the pinhole plate A, the semi-transparent and semi-reflective mirror B, the scanning mirror C, and the satellite camera D in sequence.

[0030] Among them, the pinhole plate A has a single pinhole or multiple pinholes. In one embodiment, it includes a pinhole array with a diameter dp of 10 - 100 μm, and the surface is a metal plate with extinction treatment. Moreover, it has a rotating wheel mechanism, and through the rotating wheel, the satellite camera D measures the diffraction energy in sequence. The satellite camera D is a focal plane array or line array satellite camera, a multi-pixel focal plane detector (such as CMOS or CCD), and a radiation acquisition camera such as an infrared camera or a visible light camera.

[0031] Furthermore, the embodiment of the present application provides an on-orbit radiation calibration method. Refer to Figure 2 , Figure 2 which is a schematic flow chart of the on-orbit radiation calibration method provided by Embodiment 1 of the present application. In this embodiment, the on-orbit radiation calibration method is applied to the on-orbit radiation calibration system, and the on-orbit radiation calibration method includes steps S10 - S30: Step S10: Adjust the attitude of the artificial satellite, and the adjustment target is that the incident sunlight perpendicularly passes through the target pinhole on the pinhole plate; In one embodiment, refer to Figure 1 , the satellite attitude is determined according to the sun direction by a sun sensor E. At the same time, the pinhole plate A is adjusted to face the incident sunlight direction by using a satellite attitude control module ( Figure 1 not shown in the figure). In this way, the position and attitude of the satellite relative to the sun are determined by using the sun sensor E, and the satellite attitude is adjusted so that the pinhole plate A faces the sun, ensuring that the incident light perpendicularly passes through the target aperture on the pinhole plate A.

[0032] Step S20: Obtain the theoretical radiance of the standard detector and the actual response values of each pixel of the satellite camera; Next, implement diffraction spot imaging, that is, the satellite camera D collects the pinhole diffraction image, and the actual response value of the satellite camera D at the pixel, i.e., the pixel in the i-th row and j-th column, is DN(i, j). Further, synchronously record the integration time t and the energy distribution of the standard detector. Since sunlight is a relatively stable light source, the theoretical radiance of the standard detector can be calculated.

[0033] In one embodiment, the calculation method of the theoretical radiance of the standard detector is as follows:

[0034] In the above formula, represents the theoretical radiance of the B band that theoretically reaches the standard detector from the sun through the pinhole plate A at time t; and are the upper and lower limit wavelengths of the B band; represents the directional transmission distribution function of the pinhole plate A, and the output value of this function is the transmittance in different directions after passing through the aperture; represents the solar incidence angle parameter. Since the detection angle is fixed, the direction variable is only the incidence angle, that is, the azimuth angle and zenith angle of the incident light; represents the solar spectral irradiance reaching the top of the atmosphere at the mean sun-earth distance, which can be obtained from the Wehrli85 solar spectrum published by the World Meteorological Organization; represents the sun-earth distance factor at the calibration time t, which represents the astronomical distance between the sun and the earth, and the unit is astronomical unit (AU), and it varies between two extreme values (perihelion and aphelion); represents the spectral response function of the standard detector, that is, at each wavelength, the ratio of the received radiance to the incident radiance, which describes the response intensity of the sensor at different wavelengths.

[0035] Step S30: Determine the calibration coefficients of each pixel of the satellite camera based on the theoretical radiance and the actual response values of each pixel of the satellite camera.

[0036] 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 the satellite camera D is defined as K(i, j), and K(i, j) = DN(i, j) / L detector (i, j). Furthermore, when using the satellite camera D for actual earth detection, the true and real-time radiance corresponding to any pixel of the satellite camera D can be calculated according to the real-time response value of the pixel and the calibration coefficient K of the pixel.

[0037] In summary, in this embodiment, for the technical problem that the diffraction effect is not corrected, by fully considering the difference in the light flux distribution between pixels caused by the Airy Pattern, the calibration error is reduced, that is, the light flux calculation error caused by pinhole diffraction is corrected, and the influence of the Airy Pattern energy distribution on the calibration accuracy is avoided; for the problem of insufficient correction of the area array non-uniformity, instead of relying on statistical averaging, the response characteristics are modeled pixel by pixel to eliminate the spatial sensitivity difference, that is, the response calibration of each pixel of the area array camera is realized, and the problem of multi-pixel non-uniformity is solved. Thus, accurate on-orbit radiometric calibration is achieved.

[0038] In a feasible implementation manner, when there is a single pinhole on the pinhole plate, step S30 may include steps S301 to S304: Step S301: Determine the target pixel at which the satellite camera has the best response; Select the pixel with the best response of the satellite camera as the target pixel (i0, j0). In one embodiment, temporarily take the pixel in the middle of the satellite camera as the target pixel. In this embodiment, the method for determining the target pixel is not limited, and the method for selecting the best response is not limited.

[0039] Step S302: Obtain the current actual response value of the satellite camera at the target pixel; Step S303: Determine the standard calibration coefficient at the target pixel according to the theoretical radiance and the current actual response value at the target pixel; The current actual 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 detector (i0, j0) can be determined.

[0040] Step S304: Determine the target calibration coefficients 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.

[0041] Since in fact the actual responses between different pixels are not uniform and are different, there is a response difference between each non-target pixel and the target pixel. Furthermore, according to the standard calibration coefficient and the response difference C(i, j) of each non-target pixel compared with the target pixel, the target calibration coefficient K(i, j) of each non-target pixel of the satellite camera can be determined, that is, K(i, j) = K(i0, j0)·C(i, j).

[0042] In this embodiment, the method for determining the standard calibration coefficient and the response difference C(i, j) of each non-target pixel relative to the target pixel is not limited.

[0043] In a feasible implementation manner, before step S304, it includes: By rotating the scanning mirror, the historical actual response values of each pixel of the satellite camera are obtained; Determine the relative difference in the historical actual response values between each non-target pixel and the target pixel, and use the relative difference as the response difference of each non-target pixel relative to the target pixel.

[0044] In this embodiment, a method for determining the standard calibration coefficient and the response difference C(i, j) of each non-target pixel relative to the target pixel is proposed.

[0045] By rotating the scanning mirror C, different pixels of the satellite camera D are made to face the same target pinhole position to collect signals, so that the historical actual response values DN history (i, j) of each pixel of the satellite camera D can be obtained. Furthermore, the relative difference between each non-target pixel (i, j) and the target pixel (i0, j0) in the historical actual response value DN history can be determined, and this relative difference is used as the response difference C(i, j) of each non-target pixel relative to the target pixel = DN history (i, j) / DN history (i0, j0).

[0046] Among them, by default and under ideal conditions, the responsivities (response functions, response characteristics, calibration coefficients) of different pixels of the satellite camera D should be consistent, and the response values should also be consistent. Then, according to the response value difference, the difference in responsivity can be obtained, that is, the relative coefficient of the calibration coefficient.

[0047] In an embodiment, based on the historical actual response value DN history (i, j) of each non-target pixel, a non-uniformity correction matrix C(i, j) of the satellite camera is established; the non-uniformity correction matrix C(i, j) is used as the response difference of each non-target pixel relative to the target pixel.

[0048] Above, when there is a single pinhole on the pinhole plate, since the relative difference change in the historical actual response values between each non-target pixel and the target pixel is small, therefore, the response difference of each non-target pixel relative to the target pixel can be determined regularly or irregularly. When determining the calibration coefficient of each pixel each time, the latest response difference can be called to calculate the target calibration coefficient of each non-target pixel in real time.

[0049] In a feasible implementation, when there are pinholes of different scales on the pinhole plate, step S30 may include steps S30A to S30B: Step S30A: Obtain data pairs of the theoretical radiance and the actual response values of each pixel of the satellite camera at different aperture scales; Step S30B: Determine the calibration coefficients of each pixel of the satellite camera by fitting the data pairs.

[0050] In this embodiment, when there are pinholes of different scales on the pinhole plate, multiple response values and radiance data pairs are obtained with multiple apertures and multiple gradients, that is, data pairs of the theoretical radiance and the actual response values of each pixel of the satellite camera at different aperture scales are obtained. Then, by fitting the data pairs, the calibration coefficients of each pixel of the satellite camera are determined, thereby eliminating the errors introduced when calculating with a single energy scale, that is, a single pinhole size. For example, by fitting a linear function using the least squares method, the calculation accuracy of the calibration coefficients can be improved.

[0051] 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) are the camera response value DN and the calculated value L of the theoretical radiance obtained under the same aperture. Ideally, the response value and the radiance are in a direct proportional relationship, so the calibration coefficient can be directly obtained. However, in fact, the aperture error will cause an error in the calculation of the theoretical radiance, and the camera response value will also be affected by stray light and other factors and have errors. At the same time, the camera response is not a perfect direct proportional relationship. Therefore, in this embodiment, multiple response values and radiance data pairs are obtained with multiple apertures and multiple gradients, and the calculation accuracy of the calibration coefficients can be improved by fitting a linear function using the least squares method.

[0052] Embodiment 2 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 content as that in the above-mentioned Embodiment 1 can be referred to the above introduction and will not be repeated hereinafter.

[0053] The embodiment of the present application provides an on-orbit radiation calibration system. Refer to Figure 1 , Figure 1 which is a schematic diagram of the on-orbit radiation calibration system provided by the embodiment of the present application. In this embodiment, the on-orbit radiation calibration system further includes a standard detector F. The aperture dynamic compensation optical path of the on-orbit radiation calibration system sequentially passes through the sun, the calibration observation port, the pinhole on the pinhole plate A, the half-transmissive and half-reflective mirror B, and the standard detector F.

[0054] Among them, the standard detector F is a homologous detector of the satellite camera D and is coaxial with the energy received by the satellite camera D.

[0055] In a new on-orbit radiation calibration method that uses a pinhole and sunlight as on-orbit radiation calibration sources, in addition to the problems not considered above, the following problems are also usually not considered: 3. Poor adaptability to the dynamic environment: On-orbit thermal deformation causes the drift of the pinhole diameter (dp), and the existing technology lacks a real-time geometric parameter correction mechanism.

[0056] Based on this, furthermore, the embodiment of the present application provides an on-orbit radiation calibration method, referring to Figure 3 , Figure 3 which is a schematic flowchart of the on-orbit radiation calibration method provided in the second embodiment of the present application. In this embodiment, step S20 may include steps S201 to S204: Step S201: Obtain the actual diffraction pattern of the standard detector; Step S202: Determine the actual pinhole aperture of the pinholes on the pinhole plate according to the actual diffraction pattern; Step S203: Determine the directional transmission distribution function at each pixel of the standard detector based on the actual pinhole aperture; Step S204: Determine the theoretical radiance at each pixel of the standard detector based on the directional transmission distribution function at each pixel of the standard detector.

[0057] By analyzing the impact brought by the technical problem of 3. Poor adaptability to the dynamic environment, that is, the change of the pinhole diameter in space, the directional transmission distribution function of the pinhole plate A is inaccurate, which in turn leads to the inaccuracy of the theoretical radiance L detector (i, j). Therefore, in this embodiment, dynamic compensation and parameter correction are performed for the change of the parameter of the pinhole aperture.

[0058] In this embodiment, a mapping model between the diffraction pattern (including the Airy disk with different optical paths in the coaxial optical path) and the pinhole aperture is established in advance based on the Fraunhofer diffraction model and actual experimental data. Specifically, based on the laboratory diffraction generating device, by changing the small hole aperture and the incident light wavelength, different diffraction patterns can be obtained at the diffraction pattern receiving screen, so as to construct a mapping model with the small hole aperture and the incident light wavelength as variables and the diffraction pattern as the dependent variable. In this way, the change of the aperture can be deduced by using the energy distribution of the standard detector: through the actual diffraction pattern (the Airy disk part) of the standard detector, the actual pinhole aperture of the pinholes on the pinhole plate can be determined according to the mapping model, and then the actual pinhole aperture can be corrected (the aperture changes in the space environment, so real-time correction is required). Furthermore, a correction coefficient is obtained, so that a more accurate diffraction energy distribution function (model) can be obtained based on the Fraunhofer diffraction model and the correction coefficient.

[0059] It should be noted that the pinhole in this application can be replaced by a rectangular slit. Correspondingly, the diffraction model is changed to the single-slit Fraunhofer formula.

[0060] By further analyzing the energy path, it can be known that there is a one-to-one correspondence among the Airy disk energy distribution, the pinhole aperture, and the transmittance distribution function, that is, the directional transmittance distribution function. Therefore, a corresponding look-up table for these three can be constructed in advance. In this look-up table, multiple sets of experimental data of the Airy disk energy distribution - pinhole aperture - directional transmittance distribution function are pre-stored, and interpolation fitting can be used to correct for aperture changes within a certain range. Thus, when using this look-up table, based on any one of the three known values, the values of the other two corresponding to this value can be obtained by looking up the table.

[0061] In this embodiment, based on the actual pinhole aperture, the directional transmittance distribution function at each pixel of the standard detector can be determined through the above look-up table. The obtained directional transmittance distribution function is the latest directional transmittance distribution function corresponding to the actual pinhole diameter after on-orbit thermal deformation. Furthermore, through, for example, the calculation method of the theoretical radiance of the standard detector in Embodiment 1 above, based on the latest directional transmittance distribution function at each pixel of the standard detector, a more accurate theoretical radiance at each pixel of the standard detector can be determined. Thereby, dynamically compensating for on-orbit geometric parameter drift (such as the change in the pinhole diameter dp), ensuring the long-term stability of calibration.

[0062] In a feasible implementation manner, step S202 includes: Based on the mapping model between the diffraction pattern of the pre-established standard detector and the pinhole aperture, determine the actual pinhole aperture of the pinhole corresponding to the actual diffraction pattern.

[0063] In this embodiment, a method for determining the actual pinhole aperture of the pinhole on the pinhole plate according to the actual diffraction pattern is proposed. Based on the mapping model between the diffraction pattern of the pre-established standard detector and the pinhole aperture, determine the actual pinhole aperture of the pinhole corresponding to the actual diffraction pattern. For the establishment of the mapping model, please refer to the above text and will not be elaborated here.

[0064] In a feasible implementation manner, step S202 further includes: Based on the neural network model of the diffraction pattern of the pre-trained standard detector and the pinhole aperture, determine the actual pinhole aperture of the pinhole corresponding to the actual diffraction pattern.

[0065] 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.

[0066] In the mapping model of the diffraction pattern and the pinhole aperture, that is, the mapping model of the Airy disk energy distribution - pinhole aperture in the look-up table (Airy disk energy distribution - pinhole aperture - directional transmission distribution function), due to the unavailability of the data range, that is, the diffraction pattern is incomplete, the types of pinhole apertures are few, etc., the look-up table obtained by interpolation fitting can only be applicable to the correction of the aperture change within a certain range.

[0067] Therefore, referring to Figure 4 , Figure 4 is the schematic diagram of the neural network model provided in the second embodiment of the present application. In addition to the above mapping model and look-up table methods, a neural network regression algorithm can also be used. Using the test data sets at different apertures with the same wavelength, a neural network model with the diffraction pattern as the input and the aperture as the output is constructed. Through this algorithm model, the actual aperture of the pinhole can be obtained based on the diffraction pattern of the standard detector as the input, and then the diffraction transmittance distribution of the actual aperture, that is, the directional transmission distribution function, can be obtained.

[0068] It should be noted that the above examples are only for understanding the present application and do not constitute a limitation to the on-orbit radiation calibration method of the present application. Based on this technical concept, more forms of simple transformations are within the protection scope of the present application.

[0069] Embodiment III 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 content as that in the above-mentioned second embodiment can be referred to the above introduction and will not be repeated hereinafter.

[0070] The embodiment of the present application provides a satellite detection system. Referring to Figure 5 , Figure 5 is the schematic diagram of the satellite detection system provided in the third embodiment of the present application. In this embodiment, the satellite detection system includes a target satellite camera D calibrated by the on-orbit radiation calibration system as described in the second embodiment, a scanning mirror C, and a ground viewing port. The ground detection optical path sequentially passes through the Earth's surface, the ground viewing port, the scanning mirror C, and the target satellite camera D.

[0071] Embodiment IV Furthermore, the on-orbit radiation calibration system provided by the present application further includes: at least one processor; and a memory communicatively connected to the at least one processor; wherein the memory stores instructions executable 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-orbit radiation calibration method in the first embodiment above.

[0072] Next, referring to Figure 6 , which shows the schematic structural diagram of the on-orbit radiation calibration system suitable for implementing the embodiments of the present application. Figure 6The on-board radiation calibration system shown is merely an example and should not impose any limitations on the functions and scope of use of the embodiments of this application.

[0073] As Figure 6 shown, the on-board radiation calibration system may include a processing device 1001 (such as a central processing unit, a graphics processing unit, etc.), which can perform various appropriate actions and processes according to a program stored in the read-only memory 1002 or a program loaded from the storage device 1003 into the random access memory 1004. In the random access memory 1004, various programs and data required for the operation of the on-board radiation calibration system are also stored. The processing device 1001, the read-only memory 1002, and the random access memory 1004 are connected to each other through a bus 1005. The input / output interface 1006 is also connected to the bus. Generally, the following systems may be connected to the input / output interface 1006: including an input device 1007 and an output device 1008; including a storage device 1003 such as a magnetic tape, a hard disk, etc.; and a communication device 1009. The communication device 1009 can allow the on-board radiation calibration system to communicate with other devices wirelessly or wiredly to exchange data. Although the on-board radiation calibration system with various systems is shown in the figure, it should be understood that it is not required to implement or have all the shown systems. Instead, more or fewer systems may be implemented or had.

[0074] Specifically, according to the embodiments disclosed in this application, the process described above with reference to the flowchart can be implemented as a computer software program. For example, the embodiments disclosed in this application include a computer program product, which includes a computer program carried on a computer-readable medium, and the computer program contains program codes for executing the method shown in the flowchart. In such an embodiment, the computer program can be downloaded and installed from the network through the communication device, or installed from the storage device 1003, or installed from the read-only memory 1002. When the computer program is executed by the processing device 1001, the above functions defined in the method of the embodiments disclosed in this application are executed.

[0075] The on-board radiation calibration system provided by this application adopts the on-board radiation calibration method in the above embodiments and can solve the technical problem of inaccurate on-board radiation calibration. Compared with the prior art, the beneficial effects of the on-board radiation calibration system provided by this application are the same as those of the on-board radiation calibration method provided by the above embodiments, and other technical features in the on-board radiation calibration system are the same as the features disclosed in the method of the previous embodiment, which will not be elaborated here.

[0076] It should be understood that each part disclosed in this application can be implemented by hardware, software, firmware, or a combination of them. In the description of the above embodiments, specific features, structures, materials, or characteristics can be combined in a suitable manner in any one or more embodiments or examples.

[0077] As described above, it is only the specific implementation manner of the present application. However, the protection scope of the present application is not limited thereto. Any person skilled in the art can easily think of changes or substitutions within the technical scope disclosed in the present application, and all of them should be covered within the protection scope of the present application. Therefore, the protection scope of the present application shall be subject to the protection scope of the claimed rights.

[0078] Furthermore, the on-orbit radiation calibration system further includes a computer-readable storage medium having computer-readable program instructions (i.e., computer programs) stored thereon, and the computer-readable program instructions are used to execute the on-orbit radiation calibration method in the above embodiments.

[0079] The computer-readable storage medium provided by the present application can 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 of the above. More specific examples of the computer-readable storage medium may include, but are not limited to: an electrical connection having one or more wires, a portable computer disk, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM) or a flash memory, an optical fiber, a portable compact disk read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the above. In this embodiment, the computer-readable storage medium can be any tangible medium that contains or stores a program, and the program can be used by or in combination with an instruction execution system or device. The program code contained on the computer-readable storage medium can be transmitted by any appropriate medium, including but not limited to: wires, optical cables, RF (Radio Frequency), etc., or any suitable combination of the above.

[0080] The above computer-readable storage medium can be included in the on-orbit radiation calibration system; or it can exist separately without being assembled into the on-orbit radiation calibration system.

[0081] The above computer-readable storage medium carries one or more programs. When the one or more programs are executed by the on-orbit radiation calibration system, the on-orbit radiation calibration system is caused to: adjust the attitude of the artificial satellite, and the adjustment target is that the solar incident light vertically passes through the target pinhole on the pinhole plate; obtain the theoretical irradiance of the standard detector and the actual response values of each pixel of the satellite camera; and determine the calibration coefficients of each pixel of the satellite camera based on the theoretical irradiance and the actual response values of each pixel of the satellite camera.

[0082] Computer program code for performing the operations of this application can be written in one or more programming languages or combinations thereof. The above-mentioned programming languages include object-oriented programming languages such as Java, Smalltalk, C++, and also include conventional procedural programming languages such as the "C" language or similar programming languages. The program code can be executed entirely on the user's computer, partially on the user's computer, executed as an independent 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 can be connected to the user's computer through any kind of network, including a local area network (LAN: Local Area Network) or a wide area network (WAN: Wide Area Network), or it can be connected to an external computer (for example, by using an Internet service provider to connect through the Internet).

[0083] The flowcharts and block diagrams in the accompanying drawings illustrate the possible architectures, functions, and operations of systems, methods, and computer program products according to various embodiments of this application. In this regard, each block in the flowchart or block diagram may represent a module, a program segment, or a part of code that contains one or more executable instructions for implementing a specified logical function. It should also be noted that in some alternative implementations, the functions marked in the blocks may occur in a different order than marked in the accompanying drawings. For example, two consecutive blocks shown may actually be executed substantially in parallel, and they may sometimes be executed in the reverse order, depending on the functions involved. It should also be noted that each block in the block diagram and / or flowchart, as well as combinations of blocks in the block diagram and / or flowchart, can be implemented by a dedicated hardware-based system for performing the specified functions or operations, or can be implemented by a combination of dedicated hardware and computer instructions.

[0084] The modules described in the embodiments of this application can be implemented in software or in hardware. Among them, the name of the module does not constitute a limitation on the unit itself in some cases.

[0085] The readable storage medium provided by this application is a computer-readable storage medium that stores computer-readable program instructions (i.e., computer programs) for performing the above-mentioned on-orbit radiometric calibration method, and can solve the technical problem of inaccurate on-orbit radiometric calibration. Compared with the prior art, the beneficial effects of the computer-readable storage medium provided by this application are the same as those of the on-orbit radiometric calibration method provided by the above embodiments, and will not be elaborated here.

[0086] The above are only some embodiments of the present application, and thus do not limit the patent scope of the present application. Any equivalent structural transformation made under the technical concept of the present application by using the content of the specification and drawings of the present application, or any direct / indirect application in other related technical fields is included in the patent protection scope of the present application.

Claims

1. A method for on-orbit radiometric calibration, characterized in that, The on - satellite radiation calibration method is applied to an on - satellite 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 - satellite 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 includes: Adjust the attitude of the artificial satellite, with the adjustment target being that the incident sunlight perpendicularly passes through the target pinhole on the pinhole plate; Obtain the theoretical radiance of the standard detector and the actual response values of each pixel of the satellite camera; Based on the theoretical radiance and the actual response values of each pixel of the satellite camera, determine the calibration coefficients of each pixel of the satellite camera.

2. The on-orbit radiation calibration method according to claim 1, wherein When there is a single pinhole on the pinhole plate, the step of determining the calibration coefficients of each pixel of the satellite camera based on the theoretical radiance and the actual response values of each pixel of the satellite camera includes: Determine the target pixel of the satellite camera with the best response; Obtain the current actual response value of the satellite camera at the target pixel; According to the theoretical radiance and the current actual response value at the target pixel, determine the standard calibration coefficient at the target pixel; According to the standard calibration coefficient and the response difference of each non - target pixel compared to the target pixel, determine the target calibration coefficients of each non - target pixel of the satellite camera.

3. The on-orbit radiation calibration method according to claim 2, wherein Before the step of determining the target calibration coefficients 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 to the target pixel, it includes: By rotating the scanning mirror, obtain the historical actual response values of each pixel of the satellite camera; Determine the relative difference in the historical actual response values between each non - target pixel and the target pixel, and use the relative difference as the response difference of each non - target pixel compared to the target pixel.

4. The on-orbit radiometric calibration method according to claim 1, characterized in that When there are pinholes of different scales on the pinhole plate, the step of determining the calibration coefficients of each pixel of the satellite camera based on the theoretical radiance and the actual response values of each pixel of the satellite camera includes: Obtain the data pairs of the theoretical radiance and the actual response values of each pixel of the satellite camera at different aperture scales; By fitting the data pairs, determine the calibration coefficients of each pixel of the satellite camera.

5. The on-orbit radiation calibration method according to claim 1, wherein The on - satellite radiation calibration system further includes a standard detector. The aperture dynamic compensation optical path of the on - satellite 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: Obtain the actual diffraction pattern of the standard detector; According to the actual diffraction pattern, determine the actual pinhole aperture of the pinhole on the pinhole plate; Based on the actual pinhole aperture, determine the direction - transmission distribution function at each pixel of the standard detector; Based on the direction - transmission distribution function at each pixel of the standard detector, determine the theoretical radiance at each pixel of the standard detector.

6. The on-orbit radiation calibration method according to claim 5, characterized in that, The step of determining the actual pinhole aperture of the pinhole on the pinhole plate according to the actual diffraction pattern includes: Based on the pre-established mapping model of the diffraction pattern of the standard detector and the pinhole aperture, determine the actual pinhole aperture of the pinhole corresponding to the actual diffraction pattern.

7. The on-orbit radiometric calibration method according to claim 5, characterized in that, The step of determining the actual pinhole aperture of the pinhole on the pinhole plate according to the actual diffraction pattern further includes: Based on the pre-trained neural network model of the diffraction pattern of the standard detector and the pinhole aperture, determine the actual pinhole aperture of the pinhole corresponding to the actual diffraction pattern.

8. An on-orbit radiation calibration system, characterized in that, The on-orbit 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-orbit 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 system implements the steps of the on-orbit radiation calibration method according to any one of claims 1 to 4.

9. The on-orbit radiation calibration system according to claim 8, characterized in that The on-orbit radiation calibration system further includes a standard detector. The aperture dynamic compensation optical path of the on-orbit 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 system implements the steps of the on-orbit radiation calibration method according to any one of claims 5 to 7.

10. A satellite detection system, characterized in that, The satellite detection system includes a target satellite camera calibrated by the on-orbit radiation calibration system according to claim 8 or 9, a scanning mirror, and a ground observation port. The ground detection optical path sequentially passes through the Earth's surface, the ground observation port, the scanning mirror, and the target satellite camera.

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