On-orbit satellite response calculation method based on point light source

Abstract

The invention relates to the technical field of absolute response calculation of in-orbit optical remote sensing satellites, in particular to an in-orbit satellite response calculation method based on a point light source, which comprises the following steps of: calculating entrance pupil radiance and a response value of a remote sensing camera; calculating a spectral response function and a spectral response bandwidth of the remote sensing camera; equivalent entrance pupil radiance is calculated through wavelength infinitesimal elements; performing least square fitting calculation through the equivalent entrance pupil radiation brightness and the response value to obtain an absolute radiation calibration coefficient; calculating the absolute radiation brightness under the equivalent extended light source; the atmospheric upper bound absolute radiation brightness is calculated through the atmospheric transmittance and the absolute radiation brightness under the equivalent extended light source, and the equivalent radiation brightness is calculated through the spectral response bandwidth; and the output response value of the remote sensing camera is calculated according to the equivalent spectral radiation brightness. According to the method, on-orbit satellite response calculation based on the point light source is realized by utilizing a point source target radiation transmission principle and combining a basic principle of optical remote sensing camera radiation calibration.

Description

Technical Field

[0001] This invention belongs to the field of on-orbit optical remote sensing satellite absolute response calculation technology, and particularly relates to an on-orbit satellite response calculation method based on a point light source. Background Technology

[0002] With the booming development of my country's commercial space industry, the number of satellites in orbit is increasing daily. Remote sensing satellites roam in space, safeguarding the land, maritime, and meteorological fields on which humanity depends for survival. People hope that these "space eyes" can see increasingly clearly. Satellites are devices launched into space by spacecraft such as rockets and space shuttles, orbiting the Earth or other planets like natural satellites. Satellites are classified in different ways according to their size. After launch, the ground needs to control the satellite to ensure that it can successfully enter its orbit around the celestial body, thereby improving the calibration accuracy of remote sensing satellites, which plays a decisive role in ensuring the accuracy of satellite product inversion.

[0003] The goal of radiometric calibration is to determine the quantitative conversion relationship between the radiance at the sensor's entrance pupil and its output value. Once the sensor is in orbit and operational, its optical characteristics may change due to the intense vibrations during launch, the strong radiation environment of space, and the decay of the optical sensors themselves. If laboratory calibration coefficients are continued to be used, the accuracy of the remote sensing data cannot be guaranteed. Therefore, on-orbit alternative calibration methods are needed for continuous on-orbit calibration to monitor and correct the sensor's radiometric response.

[0004] Existing on-orbit calibration methods suffer from problems such as large workload, long calibration cycle, poor calibration effect of site calibration and reflector calibration at low solar angles and at night, or even inability to perform calibration. Based on the above problems, this invention proposes an on-orbit satellite response calculation method based on point light source. Summary of the Invention

[0005] In view of this, the present invention aims to provide an on-orbit satellite response calculation method based on a point source, which utilizes the point source target radiative transfer principle and combines it with the radiometric calibration of an optical remote sensing camera to realize the on-orbit satellite response calculation.

[0006] To achieve the above objectives, the technical solution created by this invention is implemented as follows: A method for calculating the on-orbit satellite response based on a point light source includes the following steps: S1: Radiometric calibration of the remote sensing camera is performed in the laboratory to calculate the entrance pupil radiance and response value of the remote sensing camera. S2: Perform spectral calibration on the remote sensing camera in the laboratory, and calculate the spectral response function and spectral response bandwidth of the remote sensing camera; S3: Calculate the equivalent entrance pupil radiance of the remote sensing camera using entrance pupil radiance, spectral response function, spectral response bandwidth, and wavelength infinitesimal. S4: The absolute radiation calibration coefficients are obtained by least-squares fitting calculation using the equivalent entrance pupil radiance and response value; S5: Calculate the absolute radiance of the equivalent extended light source by using the light source radiance, the light source aperture area, and the ground resolution of the optical remote sensing satellite; S6: The absolute radiance of the upper atmospheric boundary is calculated using atmospheric transmittance and the absolute radiance under an equivalent extended light source. S7: The equivalent radiance is calculated by using the absolute radiance and spectral response bandwidth of the upper atmospheric boundary. S8: The on-orbit satellite response value is calculated based on the equivalent spectral radiance and the absolute radiative calibration coefficient. Furthermore, in step S3, the formula for calculating the equivalent entrance pupil radiance is: ; In the formula: L The equivalent entrance pupil radiance, L s ( l () represents the entrance pupil radiance. R ( l ) is the spectral response function, [ l 1 , l 2] represents the spectral response bandwidth. ,dλ It is a wavelength element.

[0007] Furthermore, in step S4, the least squares fitting calculation formula is as follows: ; In the formula, L The equivalent entrance pupil radiance, and This is the absolute radiation calibration coefficient. DN This represents the response value of the remote sensing camera.

[0008] Furthermore, in step S5, the formula for calculating the absolute radiance under the equivalent extended light source is: ; In the formula, L point The radiance of the light source. S Let be the area of ​​the light source opening. For optical remote sensing satellite ground resolution, L extention This refers to the absolute radiance under an equivalent extended light source.

[0009] Furthermore, in step S5, the radiance of the light source is measured using a spectroradiometer. The ground resolution of the optical remote sensing satellite is calculated using the orbital altitude of the satellite in orbit, the sensor pixel size, and the camera focal length. The calculation formula is as follows: GSD =( D × H ) / f; In the formula, For optical remote sensing satellite ground resolution, f For the focal length of the remote sensing camera, H The orbital altitude of the satellite in orbit. D This refers to the sensor pixel size.

[0010] Furthermore, in step S6, the formula for calculating the absolute radiance of the upper atmospheric boundary is: ; In the formula, L atm The absolute radiance at the upper boundary of the atmosphere. Atmospheric transmittance, L extention Absolute radiance under equivalent extended light source.

[0011] Furthermore, in step S7, the formula for calculating the equivalent radiance is: L 1= L atm ×1000 / ( l 2- l 1) In the formula, L 1 represents the equivalent radiance. L atm The absolute radiance of the upper atmospheric boundary, [ l 1 ,l [2] represents the spectral response bandwidth.

[0012] Furthermore, in step S8, the formula for calculating the on-orbit satellite response value is as follows: DN 1=( L 1- ) / ; In the formula, L 1 represents the equivalent radiance. and This is the absolute radiation calibration coefficient. DN 1 represents the response value of the satellite in orbit.

[0013] Furthermore, in step S1, the remote sensing camera is radiometrically calibrated using a spherical radiometric calibration system.

[0014] Furthermore, in step S2, the remote sensing camera is spectrally calibrated using a monochromator and a collimator spectral calibration system.

[0015] Compared with the prior art, the present invention can achieve the following beneficial effects: (1) This invention utilizes the principle of point source target radiation transmission and combines it with the basic principle of optical remote sensing camera radiometric calibration to realize on-orbit satellite response calculation based on point source.

[0016] (2) The overall calculation accuracy of the calculation method created by this invention is controllable.

[0017] (3) This invention can provide important technical support for the quantitative inversion of optical remote sensing satellite products, and can also examine the quality of optical remote sensing satellites, which is of great significance to the development of aerospace optical remote sensing satellites. Attached Figure Description

[0018] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments and descriptions of the invention are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings: Figure 1 A flowchart illustrating the on-orbit satellite response calculation method based on a point light source, as described in an embodiment of the present invention; Figure 2 This is a geometric diagram showing the relationship between the area of ​​a point light source and the area of ​​the image plane. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and do not constitute a limitation thereof.

[0020] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0021] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicating orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on this invention. Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, features defined with "first," "second," etc., may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0022] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art will understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0023] The invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0024] like Figure 1 As shown, the on-orbit satellite response calculation method based on a point light source includes the following steps: S1: In the laboratory, the remote sensing camera is radiometrically calibrated using a spherical radiometric calibration system according to the required imaging conditions, and the entrance pupil radiance and response value of the remote sensing camera are calculated. S2: In the laboratory, the remote sensing camera is spectrally calibrated according to the required imaging conditions using a monochromator and a collimator spectral calibration system, and the spectral response function and spectral response bandwidth of the remote sensing camera are calculated. S3: The equivalent entrance pupil radiance of the remote sensing camera is calculated using the entrance pupil radiance, spectral response function, spectral response bandwidth, and wavelength infinitesimal. The specific calculation formula is as follows: ; In the formula: L The equivalent entrance pupil radiance, L s ( l () represents the entrance pupil radiance. R ( l) is the spectral response function, [ l 1 , l 2] represents the spectral response bandwidth. ,dλ For wavelength infinitesimal elements; The wavelength element is an infinitesimal increment of the integral variable λ, used to continuously accumulate the spectral radiance over the wavelength range. Its physical meaning is to decompose the continuous spectrum into countless tiny wavelength intervals, calculate the radiant flux in each interval separately and then sum them up to obtain the total radiance. S4: The absolute radiation calibration coefficients are obtained by least-squares fitting of the equivalent entrance pupil radiance and response value. The calculation formula is as follows: ; In the formula, L The equivalent entrance pupil radiance, and This is the absolute radiation calibration coefficient; S5: Calculate the absolute radiance of the equivalent extended light source using the light source radiance, the calculated light source aperture area, and the ground resolution of the optical remote sensing satellite. The calculation formula is as follows: ; In the formula, L point The radiance of the light source. S Let be the area of ​​the light source opening. For optical remote sensing satellite ground resolution, L extention This refers to the absolute radiance under an equivalent extended light source; Among them, the aperture area of ​​the light source S The ground resolution of optical remote sensing satellites is calculated using the length and angle of the light source. GSD By the orbital altitude of the satellite in orbit H Sensor pixel size P Remote sensing camera focal length B The calculation is as follows: GSD =( D × H ) / f; In the formula, For optical remote sensing satellite ground resolution, f For the focal length of the remote sensing camera, H The orbital altitude of the satellite in orbit. D The sensor pixel size is given; the orbital altitude of the satellite in orbit, the sensor pixel size, and the focal length of the remote sensing camera are all known quantities. Measurement of light source radiance L pointThe main equipment is a spectroradiometer, which covers the entire 350-2500nm spectrum and uses a PDA and InGaAs detector to achieve low-noise detection. It supports a portable design and features a built-in shutter and drift-lock calibration function, enabling rapid spectral measurements of vegetation, water bodies, and other ground features. like Figure 2 As shown, Ad is the imaging size, As is the area of ​​the light source, c is the point light source, and e is the extended light source. Based on the spatial resolution of the remote sensing camera, the observed target may be a point target or an extended target. From a geometrical optics perspective, when the visual solid angle of the light source is much smaller than the visual solid angle of the remote sensing camera, the light source is considered a point light source; or, when the size of the target is much smaller than the ground projection of a pixel, it can be considered a point light source. For extended targets, the size of the light source is much larger than the spatial sampling interval, and the light source is considered an extended light source. For point target imaging systems, the response of the remote sensing camera depends on the ratio of the target's brightness to its area and the spatial sampling interval, equivalent to the homogenization of brightness over area. When the area of ​​the target is the same as the area of ​​the spatial sampling interval, the calculation formula is consistent with that for extended targets. When the area approaches infinity, i.e., a true point target, the product of brightness and area is used for calculation of luminous intensity. S6: The absolute radiance of the upper atmospheric boundary is calculated using atmospheric transmittance and the absolute radiance under an equivalent extended light source. The calculation formula is as follows: ; In the formula, L atm The absolute radiance at the upper boundary of the atmosphere. L extention Absolute radiance under equivalent extended light source Atmospheric transmittance; Atmospheric transmittance Atmospheric transmittance can be calculated by selecting appropriate atmospheric models and aerosol models using the radiative transfer software MODTRAN. MODTRAN's six standard atmospheric models (such as tropical, mid-latitude summer / winter, etc.) define the vertical distribution of temperature, water vapor, ozone, etc. under different geographical / seasonal conditions. When selecting a model, it is necessary to match the spatiotemporal conditions of the actual scenario. MODTRAN is a medium-resolution atmospheric radiative transfer model. The absorption band mode parameters are calculated using the latest HITRAN database. It uses the Curtis-Godson approximation to approximate multi-layered paths as equivalent uniform paths. It can also calculate thermal infrared radiance, irradiance, etc. S7: The equivalent radiance is calculated using the absolute radiance and spectral response bandwidth of the upper atmospheric boundary. The calculation formula is as follows: L 1= L atm ×1000 / ( l2- l 1) In the formula, L 1 represents the equivalent radiance. L atm The absolute radiance of the upper atmospheric boundary, [ l 1 ,l [2] represents the spectral response bandwidth; S8: The on-orbit satellite response value is calculated based on the equivalent spectral radiance and the absolute radiative calibration coefficient. The calculation formula is as follows: DN 1=( L 1- ) / ; In the formula, L1 For equivalent radiance, and This is the absolute radiation calibration coefficient. DN1 This represents the response value of the satellite in orbit.

[0025] This invention provides an on-orbit satellite response calculation method based on a point source. First, based on the principle of point source target radiative transfer and combined with the basic principle of radiometric calibration of optical remote sensing cameras, the on-orbit satellite response calculation based on a point source is achieved. This method can provide important technical support for the quantitative inversion of optical remote sensing satellite products, and can also assess the quality of optical remote sensing satellites, which is of great significance to the development of aerospace optical remote sensing satellites.

[0026] This application employs an active light source-based illumination device to provide active illumination for an optical remote sensing camera in orbit, thereby completing the absolute radiometric calibration of the optical remote sensing camera. This method features controllable radiance levels and distribution, ensuring that the radiance values ​​meet the sensor's on-orbit calibration requirements. Simultaneously, it enables high-precision, high-frequency, and operational on-orbit absolute radiometric calibration of high-resolution optical satellite sensors, offering advantages such as short cycle time, high frequency, low cost, and flexibility.

[0027] It should be understood that the various forms of processes shown above can be used to reorder, add, or delete steps. For example, the steps described in this invention disclosure can be executed in parallel, sequentially, or in different orders, as long as the desired result of the technical solution disclosed in this invention can be achieved, and this is not limited herein.

[0028] The specific embodiments described above do not constitute a limitation on the scope of protection of this invention. Those skilled in the art should understand that various modifications, combinations, sub-combinations, and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A method for calculating the on-orbit satellite response based on a point light source, characterized in that, Includes the following steps: S1: Radiometric calibration of the remote sensing camera is performed in the laboratory to calculate the entrance pupil radiance and response value of the remote sensing camera. S2: Perform spectral calibration on the remote sensing camera in the laboratory, and calculate the spectral response function and spectral response bandwidth of the remote sensing camera; S3: Calculate the equivalent entrance pupil radiance of the remote sensing camera using the entrance pupil radiance, the spectral response function, the spectral response bandwidth, and the wavelength element; S4: The absolute radiation calibration coefficient is obtained by least squares fitting calculation using the equivalent entrance pupil radiance and the response value; S5: Calculate the absolute radiance of the equivalent extended light source by using the light source radiance, the light source aperture area, and the ground resolution of the optical remote sensing satellite; S6: The absolute radiance of the upper atmospheric boundary is calculated by atmospheric transmittance and the absolute radiance under the equivalent extended light source. S7: The equivalent radiance is calculated using the absolute radiance of the upper atmospheric boundary and the spectral response bandwidth; S8: The on-orbit satellite response value is calculated based on the equivalent spectral radiance and the absolute radiative calibration coefficient.

2. The on-orbit satellite response calculation method based on a point light source according to claim 1, characterized in that: In step S3, the formula for calculating the equivalent entrance pupil radiance is: ； In the formula: L The equivalent entrance pupil radiance, L s ( λ () represents the entrance pupil radiance. R ( λ ) is the spectral response function, [ λ 1 ,λ 2] represents the spectral response bandwidth. ,dλ It is a wavelength element.

3. The on-orbit satellite response calculation method based on a point light source according to claim 1, characterized in that: In step S4, the least squares fitting calculation formula is as follows: ； In the formula, L The equivalent entrance pupil radiance, and This is the absolute radiation calibration coefficient. DN This represents the response value of the remote sensing camera.

4. The on-orbit satellite response calculation method based on a point light source according to claim 1, characterized in that: In step S5, the formula for calculating the absolute radiance under the equivalent extended light source is: ； In the formula, L extention To provide the absolute radiance under an equivalent extended light source, L point The radiance of the light source. S Let be the area of ​​the light source opening. This refers to the ground resolution of optical remote sensing satellites.

5. The on-orbit satellite response calculation method based on a point light source according to claim 4, characterized in that: In step S5, the radiance of the light source is measured using a spectroradiometer. The ground resolution of the optical remote sensing satellite is calculated using the orbital altitude of the satellite in orbit, the sensor pixel size, and the camera focal length. The calculation formula is as follows: GSD =( D × H ) / f; In the formula, For optical remote sensing satellite ground resolution, f For the focal length of the remote sensing camera, H The orbital altitude of the satellite in orbit. D This refers to the sensor pixel size.

6. The on-orbit satellite response calculation method based on a point light source according to claim 1, characterized in that: In step S6, the formula for calculating the absolute radiance of the upper atmospheric boundary is: ； In the formula, L atm The absolute radiance at the upper boundary of the atmosphere. Atmospheric transmittance, L extention Absolute radiance under equivalent extended light source.

7. The on-orbit satellite response calculation method based on a point light source according to claim 1, characterized in that: In step S7, the formula for calculating the equivalent radiance is: L 1= L atm ×1000 / ( λ 2- λ 1) In the formula, L 1 represents the equivalent radiance. L atm The absolute radiance of the upper atmospheric boundary, [ λ 1 ,λ [2] represents the spectral response bandwidth.

8. The on-orbit satellite response calculation method based on a point light source according to claim 1, characterized in that: In step S8, the formula for calculating the response value of the remote sensing camera on the on-orbit satellite is as follows: DN 1=( L 1- ) / ； In the formula, DN 1 represents the response value of the remote sensing camera on the satellite in orbit. L 1 represents the equivalent radiance. and This is the absolute radiation calibration coefficient.

9. The on-orbit satellite response calculation method based on a point light source according to claim 1, characterized in that: In step S1, the remote sensing camera is radiometrically calibrated using a spherical radiometric calibration system.

10. The on-orbit satellite response calculation method based on a point light source according to claim 1, characterized in that: In step S2, the remote sensing camera is spectrally calibrated using a monochromator and a collimator spectral calibration system.

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