A micro-light target device and an absolute radiation calibration method for a spaceborne micro-light load

Abstract

The application discloses a micro-light target device and an absolute radiation calibration method for a spaceborne micro-light load, and adopts a light source which is industrialized and customized and meets corresponding conditions in terms of spectral energy stability, waveband response, light source emission energy stability, light source emission energy uniformity in each direction and light source power as a calibration light source of the target, so that the problem that the light source in the prior art has great uncertainty due to the influence of lamp temperature and the narrow spectral range cannot meet the full spectral range calibration requirement can be overcome. In addition, the application arranges multiple targets with different openings to form an absolute radiation calibration target array of the spaceborne micro-light load, so that multi-point and full waveband radiation calibration can be realized, and through the combination of the micro-light targets with different openings, the measured target radiance, the atmospheric profile and the aerosol content and other parameters, and the simulation of the entrance pupil radiance of the spaceborne micro-light load at the top of the atmosphere by means of a radiation transmission model, high-precision absolute radiation calibration of the spaceborne micro-light load with different spatial resolutions can be realized.

Description

Technical Field

[0001] This application belongs to the field of satellite remote sensing technology, and in particular relates to a low-light target device and an absolute radiometric calibration method for spaceborne low-light payloads. Background Technology

[0002] Existing methods for absolute radiometric calibration of spaceborne low-light payloads primarily select large, flat, uniform terrains such as deserts, ice sheets, and deep convective clouds as calibration sites. Relying on the lunar reflection mechanism, and based on the Earth-Sun distance, Earth-Moon distance, and lunar phase angle, they use a lunar irradiance model to simulate the payload's entrance pupil radiance, thereby achieving absolute radiometric calibration of the spaceborne low-light payload. In other words, this method uses a lunar irradiance model to simulate the payload's entrance pupil radiance using the Earth-Sun distance, Earth-Moon distance, and lunar phase angle. However, during the calibration process, changes in atmospheric profiles (water vapor, air pressure, and temperature) and atmospheric parameters (aerosol) content affect the actual atmospheric transmittance and uplink and downlink radiation, thus impacting the accuracy of the lunar irradiance model. Furthermore, the accuracy of the lunar irradiance model (5–15%) significantly affects the accuracy of the absolute radiometric calibration.

[0003] In addition, on-site absolute radiometric calibration methods for spaceborne low-light payloads based on active light sources have been gradually developed, such as using bridge lights, fishing boat lights, city lights, and specially designed xenon lamps and LED lights as active light sources. However, existing calibration methods based on active light sources cannot meet the full-band calibration requirements of high spatial resolution low-light payloads. Summary of the Invention

[0004] In view of this, this application provides a low-light target device and a method for absolute radiometric calibration of spaceborne low-light payloads. By developing an absolute radiometric calibration device for spaceborne high-resolution low-light payloads, high-precision absolute radiometric calibration of low-light payloads is achieved, while meeting the calibration requirements of high spatial resolution low-light payloads across the entire wavelength band.

[0005] The specific plan is as follows:

[0006] A low-light target device, comprising:

[0007] Target box body;

[0008] A light source bracket is located at the bottom inner side of the target box body;

[0009] A low-light target light source is mounted on and supported and fixed by the light source bracket, and is used to radiate light at a preset angle; wherein, the low-light target light source satisfies some or all of the following conditions: the stability of the spectral energy satisfies the first stability condition and all bands have response; the stability of the light source emission energy satisfies the second stability condition; the isotropic uniformity of the light source emission energy satisfies the quality condition; and the light source power satisfies the power condition.

[0010] The target box opening, located at the top of the target box body, is used to control the luminous area of ​​the low-light target light source so that the low-light target light source has the required radiation output;

[0011] A light-diffusing plate is disposed at the top of the target box opening to dilute the emitted light from the low-light target light source, so as to make the emitted light radiation uniform.

[0012] Optionally, the dimensions of the target box body are determined based on the dimensions of the low-light target light source;

[0013] The surface of the target box body is coated with a preset color of paint; the material of the target box body and the preset color of paint can be used to ensure that the light emitted by the low-light target light source does not suffer loss or the loss rate is lower than a preset value.

[0014] Optionally, the low-light target light source is a high-power metal halide lamp with a preset power; the light-diffusing plate is an acrylic plate.

[0015] Optionally, the low-light target device further includes at least one of the following:

[0016] A power socket is provided in the light source bracket;

[0017] The casters are located at the bottom of the target box.

[0018] A method for absolute radiometric calibration of a spaceborne low-light payload, based on the low-light target device described in any of the above claims, the method comprising:

[0019] The emitted radiance of multiple deployed low-light target devices is measured in a satellite transit scenario; wherein, the target boxes of the multiple low-light target devices have different openings, and by deploying multiple low-light target devices with different openings, a spaceborne low-light payload absolute radiation calibration target array is formed, which can be used to achieve multi-point, full-band radiation calibration.

[0020] In the satellite transit scenario, atmospheric parameters are measured in a first preset area near the deployment area of ​​the low-light target equipment;

[0021] In the satellite transit scenario, atmospheric profiles are measured in a second preset area near the deployment area of ​​the low-light target equipment;

[0022] Radiometric calibration is performed based on the measured emitted radiance, atmospheric parameters, and atmospheric profile.

[0023] Optionally, the difference in emission radiance between the light sources of different low-light target devices is less than a preset threshold.

[0024] Optionally, measuring the emitted radiance of the multiple deployed low-light target devices in a satellite transit scenario includes:

[0025] Before the satellite passes overhead, after the low-light target equipment has been fully preheated and reached a stable state, the emitted radiance of each low-light target equipment is measured using a ground object spectrometer.

[0026] Optionally, in the satellite transit scenario, atmospheric parameters are measured in a first preset area near the deployment area of ​​the low-light target device, including:

[0027] During the period before and after the satellite passes overhead, atmospheric parameters are continuously measured in a first preset area near the deployment area of ​​the low-light target equipment, based on the deployed atmospheric parameter measuring instrument.

[0028] Optionally, in the satellite transit scenario, atmospheric profile measurement is performed in a second preset area near the deployment area of ​​the low-light target device, including:

[0029] During the period before and after the satellite passes overhead, a high-altitude balloon for atmospheric profile measurement is released in a second preset area near the area where the low-light target equipment is deployed, and the atmospheric profile is continuously measured.

[0030] Optionally, the radiometric calibration based on the measured emitted radiance, atmospheric parameters, and atmospheric profile includes:

[0031] Based on atmospheric parameters and atmospheric profiles at the time of satellite transit, atmospheric transmittance at the time of satellite transit is simulated using a radiative transfer model.

[0032] The entrance pupil radiance of the satellite payload at the moment of satellite transit is simulated based on the atmospheric transmittance at the simulated satellite transit time, as well as the ratio between the outgoing radiance and the target aperture to the satellite payload spatial resolution.

[0033] Extract target images from satellite payload imagery and obtain the overall DN value for each target region;

[0034] A quantitative relationship between the entrance pupil radiance and the overall DN value was established through load simulation to achieve radiometric calibration.

[0035] In summary, this application employs an industrially customized light source in its low-light target device that meets specific requirements in terms of spectral energy stability, band response, light source emission energy stability, isotropic uniformity of light source emission energy, and light source power as the calibration light source. This effectively overcomes the problems of existing active light source-based site absolute radiometric calibration methods for spaceborne low-light payloads, which use LED (Light-emitting Diode) lamps and other light sources, which suffer from significant uncertainties due to the influence of lamp temperature and have narrow spectral ranges, failing to meet full-spectrum calibration requirements. Furthermore, this application deploys multiple low-light target devices with different openings to form a spaceborne low-light payload absolute radiometric calibration target array, enabling multi-point, full-band radiometric calibration. By combining low-light targets with different openings and using measured target radiance, atmospheric profile, and aerosol content parameters, and employing a radiative transfer model to simulate the entrance pupil radiance of the spaceborne low-light payload at the top of the atmosphere, high-precision absolute radiometric calibration of spaceborne low-light payloads with different spatial resolutions can be achieved. Attached Figure Description

[0036] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of this application. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0037] Figure 1 This is a schematic diagram of the composition and structure of the low-light target device provided in this application;

[0038] Figure 2 This is a flowchart illustrating the absolute radiometric calibration method for spaceborne low-light payloads provided in this application. Detailed Implementation

[0039] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0040] The applicant's research found that existing absolute radiometric calibration methods based on active light sources suffer from significant uncertainties due to the influence of light source temperature on the LED lamps and other light sources. Furthermore, the narrow spectral range and single-point calibration limitations prevent these methods from meeting the full-band calibration requirements of high spatial resolution low-light payloads. Therefore, this application aims to develop an absolute radiometric calibration device for spaceborne high-resolution low-light payloads, providing a low-light target device that overcomes the aforementioned problems, and using this device as a basis to achieve high-precision absolute radiometric calibration of low-light payloads.

[0041] The low-light target device provided in this application includes a target box body, a light source bracket, a low-light target light source, a target box opening, and a light-diffusing plate.

[0042] See Figure 1 The following example provides the components of a low-light target device and their relative positions.

[0043] The dimensions of the target box body are determined based on the dimensions of the low-light target light source.

[0044] Taking a target light source with a diameter of 57cm as an example, the main body of the target box can be 80cm×80cm×60cm. The main reason for this size design is to ensure the stability of the light source in the box as much as possible.

[0045] The surface of the target box body is sprayed with a preset color of paint; the material of the target box body and the preset color of paint are used to ensure that the light emitted by the low-light target light source is not lost or the loss rate is lower than a preset value.

[0046] Preferably, the target box body can be made of lightweight sheet metal and sprayed with black paint.

[0047] A light source bracket, located at the bottom inner side of the target box body, is used to support and fix the low-light target light source. The light source bracket may be, but is not limited to, an H-shaped iron component capable of fixing the light source.

[0048] The low-light target light source is set on a light source bracket and supported and fixed by the light source bracket, and is used to radiate light at a preset angle.

[0049] Among them, the low-light target light source satisfies some or all of the following conditions: the stability of the spectral energy satisfies the first stability condition and each band has a response; the stability of the emitted energy of the light source satisfies the second stability condition; the isotropic uniformity of the emitted energy of the light source satisfies the quality condition; and the power of the light source satisfies the power condition.

[0050] Preferably, the light source for the low-light target is an industrially customized high-power metal halide lamp, such as a 1000W high-power metal halide lamp with a lamp source diameter of 57cm and a light emission angle of 130°.

[0051] The following provides further examples of the conditions that metal halide lamps must meet. For instance, the metal halide lamps used must meet the following conditions:

[0052] 1) The spectral energy is stable, with most of the energy located in the range of 400-900nm, and it has a response in all wavelength bands;

[0053] 2) The light source emits stable energy, meaning that the target light source has high stability and repeatability of power-on and power-off over a long period of time, to ensure that the radiation energy is highly stable for a period of time before and after the satellite passes over, such as half an hour.

[0054] 3) The target light source emits energy with good anisotropic uniformity, so that the target energy received by the satellite under different observation geometry is maintained at the same level;

[0055] 4) The target light source has moderate power to ensure that the target pixel is significantly different from the surrounding dark pixels during satellite observation, thus facilitating accurate positioning of the target light source in low-light payload image data.

[0056] The target box opening, located at the top of the target box body, is used to control the luminous area of ​​the low-light target light source so that the low-light target light source has the required radiation output.

[0057] A light-diffusing plate is placed at the top of the target box opening to dilute the emitted light from the low-light target light source, so as to make the emitted light radiation uniform.

[0058] Acrylic plates with good light-uniforming properties can be used as light-uniforming plates, but they are not limited to this. Frosted glass or other materials can also be used as alternatives. The selection of light-uniforming plates should mainly focus on the ability to homogenize the light emitted from the light source at the top opening of the box, while also considering the portability during field experiments.

[0059] Optionally, the low-light target device may also include a power socket located in the light source bracket to meet the working requirements of the light source.

[0060] Alternatively, the low-light target device may also include casters located at the bottom of the target box body to facilitate the transportation of the low-light target device.

[0061] In this embodiment of the application, an industrially customized light source that meets the corresponding conditions in terms of spectral energy stability, band response, light source emission energy stability, light source emission energy anisotropy uniformity, and light source power is used as the calibration light source in the low-light target device. This can effectively overcome the problem that the existing field absolute radiation calibration method for spaceborne low-light payloads based on active light sources has large uncertainties due to the influence of light source temperature, and the spectral range is narrow, which cannot meet the calibration requirements of the whole spectrum.

[0062] This application also provides an absolute radiometric calibration method for a spaceborne low-light payload. This method is based on the aforementioned low-light target device for absolute radiometric calibration. See [link to relevant documentation]. Figure 2 The flowchart shown is for the absolute radiometric calibration method of a spaceborne low-light payload. The processing steps of this method include:

[0063] Step 201: Measure the emitted radiance of the multiple low-light target devices deployed in the satellite transit scene.

[0064] The target boxes of the various low-light target devices deployed have different openings. By deploying multiple low-light target devices with different openings, an absolute radiation calibration target array for spaceborne low-light payloads can be formed, which can be used to achieve multi-point, full-band radiation calibration.

[0065] For example, a specific time can be preset before the satellite passes over, such as 1 hour before the satellite passes over, to deploy low-light target devices in a large, uniform area with no stray light pollution and a dry and clean atmosphere. Each low-light target device is equipped with a separate generator, such as a 220V generator, and the generator is turned on to power the low-light target device for a period of time before the satellite passes over, such as half an hour, so that the low-light target device can be preheated to a stable state.

[0066] Among them, the difference in emission radiance between the light sources of different low-light target devices is less than a preset threshold to ensure consistent imaging of different target light sources during satellite observation.

[0067] Based on this, before the satellite passes overhead, after the low-light target equipment has been fully preheated and reached a stable state, the emitted radiance of each low-light target equipment is measured using a ground object spectrometer.

[0068] Optionally, the ground feature spectrometer used can be an ASD ground feature spectrometer, i.e., a portable ground feature spectrometer.

[0069] Step 202: In the satellite transit scenario, atmospheric parameters are measured in the first preset area near the deployment area of ​​the low-light target equipment.

[0070] Simultaneously, atmospheric parameter measuring instruments such as CE318 or lidar are pre-deployed in a first predetermined area near the deployment area of ​​the low-light target equipment. During the period before and after the satellite's transit, atmospheric parameters (e.g., aerosol content) are continuously measured in this first predetermined area based on the deployed atmospheric parameter measuring instruments.

[0071] Step 203: In the satellite transit scenario, measure the atmospheric profile in the second preset area near the deployment area of ​​the low-light target device.

[0072] In addition, a high-altitude balloon capable of measuring atmospheric profiles is released in a second pre-defined area near the deployment area of ​​the low-light target equipment. During the process before and after the satellite passes over, atmospheric profiles (such as water vapor, air pressure, and temperature) are continuously measured based on the high-altitude balloon released in this area.

[0073] The second preset region may completely overlap with or not completely overlap with the first preset region, without restriction.

[0074] Step 204: Perform radiometric calibration based on the measured emitted radiance, atmospheric parameters, and atmospheric profile.

[0075] Specifically, based on the atmospheric parameters and atmospheric profile at the time of satellite transit, the atmospheric transmittance at the time of satellite transit can be simulated using a radiative transfer model. Based on the simulated atmospheric transmittance at the time of satellite transit, as well as the ratio between the outgoing radiance and the target aperture and the spatial resolution of the satellite payload, the entrance pupil radiance at the time of satellite payload transit can be simulated. Then, the target image of the satellite payload image is extracted, the overall DN value of each target region is obtained, and a quantitative relationship between the simulated entrance pupil radiance of the payload and the overall DN value is constructed to achieve radiometric calibration.

[0076] DN is an abbreviation for Digital Number, which refers to the pixel brightness value of a remote sensing image, that is, the gray value of the recorded ground features.

[0077] This embodiment forms an absolute radiometric calibration target array for spaceborne micro-light payloads by deploying multiple micro-light target devices with different openings. This enables multi-point, full-band radiometric calibration. Furthermore, by combining micro-light targets with different openings and using measured parameters such as target radiance, atmospheric profile, and aerosol content, the entrance pupil radiance of the spaceborne micro-light payload at the top of the atmosphere can be simulated using a radiative transfer model. This allows for high-precision absolute radiometric calibration of spaceborne micro-light payloads with different spatial resolutions.

[0078] It should be noted that the various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0079] For ease of description, the above systems or devices are described separately as various modules or units based on their functions. Of course, in implementing this application, the functions of each unit can be implemented in one or more software and / or hardware components.

[0080] As can be seen from the above description of the embodiments, those skilled in the art can clearly understand that this application can be implemented by means of software plus necessary general-purpose hardware platforms. Based on this understanding, the technical solution of this application, in essence, or the part that contributes to the prior art, can be embodied in the form of a software product. This computer software product can be stored in a storage medium, such as ROM / RAM, magnetic disk, optical disk, etc., and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute the methods described in various embodiments or some parts of the embodiments of this application.

[0081] Finally, it should be noted that in this document, relational terms such as first, second, third, and fourth are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0082] The above description is only a preferred embodiment of this application. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of this application, and these improvements and modifications should also be considered within the scope of protection of this application.

Claims

1. A method for absolute radiometric calibration of a spaceborne low-light payload, characterized in that, Absolute radiometric calibration is performed using a low-light target device, which includes: Target box body; A light source bracket is located at the bottom inner side of the target box body; A low-light target light source is mounted on and supported and fixed by the light source bracket, and is used to radiate light at a preset angle; wherein, the low-light target light source satisfies some or all of the following conditions: the stability of the spectral energy satisfies the first stability condition and all bands have response; the stability of the light source emission energy satisfies the second stability condition; the isotropic uniformity of the light source emission energy satisfies the quality condition; and the light source power satisfies the power condition. The target box opening, located at the top of the target box body, is used to control the luminous area of ​​the low-light target light source so that the low-light target light source has the required radiation output; A light-diffusing plate is disposed at the top of the target box opening to dilute the emitted light from the low-light target light source so as to make the emitted light radiation uniform. The method includes: The emitted radiance of multiple deployed low-light target devices is measured in a satellite transit scenario; wherein, the target boxes of the multiple low-light target devices have different openings, and by deploying multiple low-light target devices with different openings, a spaceborne low-light payload absolute radiation calibration target array is formed, which can be used to achieve multi-point, full-band radiation calibration. In the satellite transit scenario, atmospheric parameters are measured in a first preset area near the deployment area of ​​the low-light target equipment; In the satellite transit scenario, atmospheric profiles are measured in a second preset area near the deployment area of ​​the low-light target equipment; Radiometric calibration is performed based on the measured emitted radiance, atmospheric parameters, and atmospheric profile.

2. The method according to claim 1, characterized in that, The dimensions of the target box body are determined based on the dimensions of the low-light target light source; The surface of the target box body is coated with a preset color of paint; the material of the target box body and the preset color of paint can be used to ensure that the light emitted by the low-light target light source does not suffer loss or the loss rate is lower than a preset value.

3. The method according to claim 1, characterized in that, The low-light target light source is a high-power metal halide lamp with a preset power; the light-diffusing plate is an acrylic plate.

4. The method according to claim 1, characterized in that, The low-light target device also includes at least one of the following: A power socket is provided in the light source bracket; The casters are located at the bottom of the target box.

5. The method according to claim 1, characterized in that, The difference in emission radiance between the light sources of different low-light target devices is less than a preset threshold.

6. The method according to claim 1, characterized in that, The measurement of the emitted radiance of multiple deployed low-light target devices in a satellite transit scenario includes: Before the satellite passes overhead, after the low-light target equipment has been fully preheated and reached a stable state, the emitted radiance of each low-light target equipment is measured using a ground object spectrometer.

7. The method according to claim 1, characterized in that, In the satellite transit scenario, atmospheric parameters are measured in a first preset area near the deployment area of ​​the low-light target device, including: During the period before and after the satellite passes overhead, atmospheric parameters are continuously measured in a first preset area near the deployment area of ​​the low-light target equipment, based on the deployed atmospheric parameter measuring instrument.

8. The method according to claim 1, characterized in that, In the satellite transit scenario, atmospheric profile measurement is performed in a second preset area near the deployment area of ​​the low-light target equipment, including: During the period before and after the satellite passes overhead, a high-altitude balloon for atmospheric profile measurement is released in a second preset area near the area where the low-light target equipment is deployed, and the atmospheric profile is continuously measured.

9. The method according to claim 1, characterized in that, The radiometric calibration based on the measured emitted radiance, atmospheric parameters, and atmospheric profile includes: Based on atmospheric parameters and atmospheric profiles at the time of satellite transit, atmospheric transmittance at the time of satellite transit is simulated using a radiative transfer model. The entrance pupil radiance of the satellite payload at the moment of satellite transit is simulated based on the atmospheric transmittance at the simulated satellite transit time, as well as the ratio between the outgoing radiance and the target aperture to the satellite payload spatial resolution. Extract target images from satellite payload imagery and obtain the overall DN value for each target region; A quantitative relationship between the entrance pupil radiance and the overall DN value was established through load simulation to achieve radiometric calibration.

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