Spaceborne nadir hyperspectral imaging load calibration test system and method

Abstract

The invention provides a calibration test system and method for a satellite-borne nadir hyperspectral imaging load, and belongs to the technical field of hyperspectral imaging load test.The calibration test method mainly comprises the steps that (1) installation and debugging of the calibration test system are completed in an ultra-clean room, and the load is installed to a theoretical position; (2) selecting a calibration light source according to a load wave band and a view field range, and sequentially completing spectrum calibration and radiation calibration through the calibration test system; (3) installing a sample gas pool assembly in the calibration test system to complete the sample gas test of the load; and a debugging light path is established, and the spatial resolution test of the load is completed. Through the technical scheme provided by the invention, on the basis of meeting the calibration test requirement and precision, the calibration test process can be simplified, the calibration test efficiency is improved, and the method is suitable for the calibration test of the hyperspectral imaging load of the same type.

Description

Technical Field

[0001] This invention belongs to the field of hyperspectral imaging payload calibration and testing technology, specifically relating to a calibration and testing system and method for a spaceborne nadir hyperspectral imaging payload. Background Technology

[0002] The nadir hyperspectral imaging payload employs a 114° wide-field pushbroom operation to measure the spectral information of ultraviolet and visible light reflected and scattered from the Earth's surface, and to invert the vertical distribution of pollutants such as SO2 and NO2. During the development process, calibration and performance testing in the laboratory are necessary conditions for the nadir hyperspectral imaging payload to quantitatively invert observational data in the practical application stage.

[0003] Calibration includes spectral calibration and radiometric calibration. Currently, spectral calibration often uses the standard spectral line method, which uses a lamp capable of emitting a specific wavelength range as a standard light source to illuminate the load to be calibrated. Through data analysis, the spectral calibration equation is obtained, and the spectral range and spectral resolution are determined. Radiometric calibration uses the integrating sphere method, which uses an integrating sphere as a standard light source to provide a stable, uniform, large-aperture surface light source to illuminate the load to be calibrated. The quantitative relationship between the load's output signal and the radiance of the integrating sphere is obtained, and an equivalent equation is established to obtain the radiometric calibration coefficients.

[0004] Performance testing is divided into sample gas testing and spatial resolution testing. Sample gas testing involves obtaining spectral absorption curves of the nadir hyperspectral imaging payload under different sample gases and concentrations, based on the detection bands and main detection gases. This provides data verification for retrieving the distribution of pollutants such as SO2 and NO2 after the payload enters orbit. In spatial resolution testing, the nadir hyperspectral imaging payload operates in a pushbroom mode. Spatial resolution represents the geometric size of the corresponding ground pixels and is divided into vertical flight direction resolution and along the flight direction resolution, which can be obtained through laboratory testing and calculation.

[0005] In existing technologies, spectral calibration and radiometric calibration use different calibration devices. The calibration testing process requires multiple transfers and installations of the payload, making the operation complex and cumbersome. For different payloads, corresponding calibration devices need to be designed based on their technical characteristics and calibration requirements, lacking versatility and cost-effectiveness. Furthermore, there is currently a lack of testing devices and methods for performance testing of nadir hyperspectral imaging payloads. In summary, a suitable calibration testing device and specific method are still lacking in the development of nadir hyperspectral imaging payloads. Summary of the Invention

[0006] This invention provides a calibration and testing system and method for spaceborne nadir hyperspectral imaging payloads, which solves the problems of complex and cumbersome calibration process, the need for customized calibration devices, and the lack of suitable testing technology for nadir hyperspectral imaging payloads in the prior art.

[0007] To achieve the above objectives, this invention provides a calibration and testing system for a spaceborne nadir hyperspectral imaging payload. The system includes a test frame, a vertical lead screw module, a horizontal lead screw module, a load mounting base, an integrating sphere, a calibration turntable, a nadir hyperspectral imaging payload, a transfer fixture, and a cleanroom. The test frame is constructed within the cleanroom, and the integrating sphere is installed at the center of the test frame. The vertical and horizontal lead screw modules are mounted on the test frame, and the load mounting base is mounted on the horizontal lead screw module. The nadir hyperspectral imaging payload and the transfer fixture are mounted on the calibration turntable, wherein the rotation axis of the calibration turntable is coaxial with the center of the light entrance of the nadir hyperspectral imaging payload. The calibration turntable and the nadir hyperspectral imaging payload are located in front of the test frame, with the opening of the integrating sphere directly facing the light entrance of the nadir hyperspectral imaging payload, and the surface of the calibration turntable is horizontal.

[0008] Preferably, the calibration and testing system for a spaceborne nadir hyperspectral imaging payload provided by the present invention further includes a payload ground testing device, a control cabinet, a standard lamp assembly, and a spectroradiometer. This system is used for spectral calibration testing, wherein: the standard lamp assembly includes a standard lamp and a narrow-linewidth laser; the standard lamp assembly is mounted on the payload mounting base; the payload ground testing device is deployed in the cleanroom; the payload ground testing device is connected via cables to the control cabinet for controlling the integrating sphere, the nadir hyperspectral imaging payload, the calibration turntable, and the standard lamp assembly; the standard lamp assembly is located directly in front of the light entrance of the nadir hyperspectral imaging payload; and the spectroradiometer is used to measure the radiance of the integrating sphere.

[0009] Preferably, the calibration and testing system for the spaceborne nadir hyperspectral imaging payload provided by the present invention further includes a sample gas cell assembly, wherein: the sample gas cell assembly is mounted on the payload mounting base, the sample gas cell assembly includes a sample gas cell for containing sample gas; and the sample gas cell assembly is located directly in front of the light entrance of the nadir hyperspectral imaging payload.

[0010] Preferably, the calibration and testing system for the spaceborne nadir hyperspectral imaging payload provided by the present invention further includes a collimator assembly, an elevation slide, a positioning prism, and a xenon lamp, wherein: the collimator assembly is fixed on the elevation slide, and both the collimator assembly and the elevation slide are mounted on the load mounting base; when the calibration turntable is at 0 degrees, on the mechanical positioning surface at the light inlet of the nadir hyperspectral imaging payload, close to the positioning prism, the horizontal, vertical, and elevation positions of the collimator assembly are adjusted by the vertical lead screw module, the horizontal lead screw module, and the elevation slide, so that the parallel light emitted by the collimator assembly is incident directly onto the nadir hyperspectral imaging payload; the xenon lamp is fixed in front of the target of the collimator assembly; and the position of the collimator assembly is adjusted by the vertical lead screw module and the horizontal lead screw module so that the spectral image of the xenon lamp is located at the center of the field of view of the nadir hyperspectral imaging payload, corresponding to a 0° field of view.

[0011] Accordingly, the present invention provides a calibration test method for a spaceborne nadir hyperspectral imaging payload. This method is used in the calibration test system of the above-mentioned spaceborne nadir hyperspectral imaging payload. The method includes performing a spectral calibration test, including: activating the standard lamp assembly; using 0 degrees of the calibration turntable as the field of view center of the nadir hyperspectral imaging payload; controlling the calibration turntable to rotate the nadir hyperspectral imaging payload, and adjusting the angle with a test starting angle of -57 degrees and an angle increment of 3 degrees; and after each angle adjustment, imaging is performed through the payload ground detection equipment to obtain a spectral calibration spectral image until the nadir hyperspectral imaging payload rotates to +57 degrees.

[0012] Preferably, the spectral calibration test further includes: imaging in a dark background environment to obtain a dark background spectrum; and removing the dark background spectrum from the spectral calibration spectrum image to obtain a spectral calibration spectrum image with the dark background spectrum removed, for performing a full-field spectral calibration test.

[0013] Preferably, the calibration test method for the spaceborne nadir hyperspectral imaging payload provided by the present invention further includes performing a radiometric calibration test, including: lighting the lamp source of the integrating sphere through the control cabinet, and controlling the number of lamps turned on of the integrating sphere according to a pre-set first radiance; controlling the calibration turntable to drive the nadir hyperspectral imaging payload to rotate, with a test starting angle of -60 degrees and three angle adjustments at 40-degree step angle intervals; after each angle adjustment, imaging is performed through the payload ground testing equipment to obtain a radiometric calibration spectrum image, until three angle adjustments are completed to perform a full-field radiometric calibration test.

[0014] Preferably, the radiometric calibration test further includes: performing full-field radiometric calibration tests for various operating modes, multiple integration times, and various radiance values ​​of the integrating sphere for the nadir hyperspectral imaging payload.

[0015] Accordingly, the present invention also provides a calibration test method for a spaceborne nadir hyperspectral imaging payload. This method is used in the calibration test system of the above-mentioned spaceborne nadir hyperspectral imaging payload. The method includes performing a full-field-of-view sample gas test, including: lighting the lamp source of the integrating sphere through the control cabinet, controlling the number of lamps turned on by the integrating sphere according to a preset second radiance, and making the surface light source emitted by the integrating sphere pass through the sample gas cell assembly; when the sample gas in the sample gas cell of the sample gas cell assembly reaches a predetermined concentration, controlling the calibration turntable to drive the nadir payload to rotate, adjusting the angle with a test starting angle of -60 degrees and an angle adjustment in 10-degree increments; after each angle adjustment, imaging is performed through the payload ground detection equipment to obtain a sample gas test spectral image, until the nadir payload rotates to +60 degrees to perform a full-field-of-view sample gas test; wherein, the sample gas includes multiple concentrations of SO2 sample gas and multiple concentrations of NO2 sample gas.

[0016] Accordingly, the present invention also provides a calibration test method for a spaceborne nadir hyperspectral imaging payload. This method is used in the calibration test system for the aforementioned spaceborne nadir hyperspectral imaging payload. The method includes performing a spatial resolution test, comprising: controlling a calibration turntable to rotate the nadir payload, performing 11 angle adjustments at 0.1-degree step intervals; imaging after each angle adjustment and obtaining a resolution test spectral image; obtaining the maximum intensity I0 of the brightest row pixel from the spectral image, and determining that when the maximum intensity I0 decreases to 0.5I0, the two rotation angles of the calibration turntable are α1 and α2, respectively. The payload angular resolution α of the nadir payload is calculated using the formula α = |α1| + |α2|; the spatial resolution along the flight direction is calculated based on the flight speed and integration time of the nadir hyperspectral imaging payload, specifically: spatial resolution along the flight direction = flight speed × integration time; and the spatial resolution in the vertical flight direction is calculated based on the orbital altitude and the payload angular resolution α, specifically: .

[0017] The beneficial effects of this invention are as follows:

[0018] The technical solution provided by this invention not only meets the basic requirements and accuracy of calibration testing, but also simplifies the calibration testing process and improves calibration testing efficiency. It is applicable to calibration testing of similar hyperspectral imaging payloads, as detailed below:

[0019] (1) The technical solution provided by the present invention is universal and simple. The calibration test of the whole process can be completed with one installation. According to the shape and band of different loads, the adapter tool and standard lamp can be replaced and used for subsequent calibration test of spectral imaging instruments.

[0020] (2) The mechanical precision of the calibration turntable and lead screw module can ensure the accuracy of the relative position of the calibration light source and the nadir hyperspectral imaging load and the consistency of multiple rounds of testing. The system can be used in a dark room environment, which can minimize the influence of stray light and jointly ensure the calibration test accuracy.

[0021] (3) The technical solution provided by the present invention can reduce repetitive work. After setting the corresponding ground inspection software according to the test requirements, the stepping rotation, spectral imaging and data storage can be completed automatically, which significantly improves the calibration test efficiency. Attached Figure Description

[0022] The accompanying drawings are provided to further illustrate embodiments of the present invention and form part of the specification. They are used together with the following detailed description to explain the embodiments of the present invention, but do not constitute a limitation thereof. In the drawings:

[0023] Figure 1 This is a schematic diagram of the calibration and testing system for the spaceborne nadir hyperspectral imaging payload provided by the present invention;

[0024] Figure 2 This is a schematic diagram of spectral calibration provided by the present invention;

[0025] Figure 3 This is the spectral calibration imaging diagram provided by the present invention;

[0026] Figure 4 This is a schematic diagram of radiation calibration and sample gas testing provided by the present invention;

[0027] Figure 5 This is a radiometric calibration imaging diagram provided by the present invention;

[0028] Figure 6 This is a schematic diagram of spatial resolution testing provided by the present invention;

[0029] Figure 7 This is a spatial resolution imaging image provided by the present invention.

[0030] Figure label:

[0031] 1. Test frame; 2. Vertical lead screw module; 3. Horizontal lead screw module; 4. Load mounting base; 5. Integrating sphere; 6. Calibration turntable; 7. Nadir hyperspectral imaging load; 8. Adapter fixture; 9. Load testing equipment; 10. Control cabinet; 11. Clean room; 12. Standard lamp assembly; 13. Spectroradiometer; 14. Sample gas cell assembly; 15. Collimator assembly; 16. Pitch slide; 17. Positioning prism; 18. Xenon lamp. Detailed Implementation

[0032] 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 embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other. To achieve the above objectives, this invention adopts the following technical solution.

[0033] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0034] The calibration and testing system for a spaceborne nadir hyperspectral imaging payload provided by this invention includes: a test frame 1, a vertical lead screw module 2, a horizontal lead screw module 3, a load mounting base 4, an integrating sphere 5, a calibration turntable 6, a nadir hyperspectral imaging payload 7, a transfer fixture 8, a payload ground testing device 9, a control cabinet 10, a clean room 11, a standard lamp assembly 12, a spectroradiometer 13, a sample gas cell assembly 14, a collimator assembly 15, a pitch slide 16, a positioning ridge 17, and a xenon lamp 18.

[0035] Figure 1 This is a schematic diagram of the calibration and testing system for the spaceborne nadir hyperspectral imaging payload provided by the present invention, as shown below. Figure 1 As shown, the structural relationship between the test frame 1, vertical lead screw module 2, horizontal lead screw module 3, load mounting base 4, integrating sphere 5, calibration turntable 6, nadir hyperspectral imaging payload 7, adapter fixture 8, and cleanroom 11 in this system is as follows: The test frame 1 is built inside the cleanroom 11, and the integrating sphere 5 is installed at the center of the test frame 1; the vertical lead screw module 2 and the horizontal lead screw module 3 are installed on the test frame 1, and the load mounting base 4 is installed on the horizontal lead screw module 3; the nadir hyperspectral imaging payload 7 and the adapter fixture 8 are installed on the calibration turntable 6, wherein the rotation axis of the calibration turntable 6 is on the same axis as the center of the light inlet of the nadir hyperspectral imaging payload 7; the calibration turntable 6 and the nadir hyperspectral imaging payload 7 are located in front of the test frame 1, the opening of the integrating sphere 5 is directly opposite the light inlet of the nadir hyperspectral imaging payload 7, and the table surface of the calibration turntable 6 is horizontal.

[0036] The operation process consists of step one, which includes: designing and building the calibration test system. Based on the calibration test requirements, and considering the actual size, mass, and future versatility of the nadir hyperspectral imaging payload and integrating sphere, the entire system is designed. The calibration test system includes: a test frame, vertical lead screw module, horizontal lead screw module, load mounting base, integrating sphere, calibration turntable, nadir hyperspectral imaging payload, adapter fixture, load testing equipment, control cabinet, cleanroom, standard lamp assembly, spectroradiometer, sample gas cell assembly, collimator assembly, pitch slide, positioning prism, and xenon lamp. After all equipment is assembled, the entire system is installed and debugged. Each component is adjusted to its theoretical position using a level, dial indicator, and linear encoder before being fixed. Specific operating steps are as follows:

[0037] Step 1.1: Based on the calibration test requirements, and considering the actual size, mass, and subsequent versatility of the nadir hyperspectral imaging payload 7 and integrating sphere 5, complete the design of the entire system.

[0038] Step 1.2: After all components are assembled, construct the test frame 1 using aluminum profiles in the cleanroom 11, install the integrating sphere 5 at the center of the test frame 1, measure the center height and horizontal position of the integrating sphere 5, adjust it to be centered, and then fix the integrating sphere 5.

[0039] Step 1.3: Install the vertical lead screw module 2 and the horizontal lead screw module 3 onto the test frame 1. Use a level, dial indicator, and grating ruler to check and adjust. After fixing, test the positioning accuracy to be better than ±0.1mm. Then, install the load mounting seat 4 onto the horizontal lead screw module 3 according to the screw hole positions.

[0040] Step 1.4: Based on the mounting holes and positioning pin holes on the calibration turntable 6, install the nadir hyperspectral imaging payload 7 and the adapter 8 onto the calibration turntable 6, ensuring that the rotation axis of the positioning turntable 6 is on the same axis as the center of the light inlet of the nadir hyperspectral imaging payload 7.

[0041] Step 1.5: Move the calibration turntable 6 and the nadir hyperspectral imaging payload 7 together to the front of the test frame 1, so that the opening of the integrating sphere 5 is directly opposite the light inlet of the nadir hyperspectral imaging payload 7. Use a level to adjust the anchor bolts of the calibration turntable 6 until the table surface of the calibration turntable 6 is level, and then fix the calibration turntable 6.

[0042] The calibration and testing system for a spaceborne nadir hyperspectral imaging payload provided by this invention also includes a payload ground inspection device 9, a control cabinet 10, a standard lamp assembly 12, and a spectroradiometer 13. This system is used for spectral calibration testing. The standard lamp assembly 12 includes a standard lamp and a narrow linewidth laser. The standard lamp assembly 12 is mounted on the payload mounting base 4. The payload ground inspection device 9 is deployed in a cleanroom 11. The payload ground inspection device 9 is connected via cables to the control cabinet 10, the nadir hyperspectral imaging payload 7, the calibration turntable 6, and the standard lamp assembly 12, which are used to control the integrating sphere 5. The standard lamp assembly 12 is located directly in front of the light entrance of the nadir hyperspectral imaging payload 7. The spectroradiometer 13 is used to measure the radiance of the integrating sphere 5.

[0043] The calibration test method for a spaceborne hyperspectral imaging payload provided by this invention includes performing a spectral calibration test, comprising: setting 0 degrees of the calibration turntable 6 as the field of view center of the nadir hyperspectral imaging payload 7; controlling the calibration turntable 6 to rotate the nadir hyperspectral imaging payload 7, and adjusting the angle at 3-degree increments with a starting angle of -57 degrees; after each angle adjustment, imaging is performed through the payload ground testing device 9 to obtain a spectral calibration spectrum image, until the nadir hyperspectral imaging payload 7 rotates to +57 degrees. The spectral calibration test further includes: performing imaging in a dark background environment to obtain a dark background spectrum; removing the dark background spectrum from the spectral calibration spectrum image to obtain a spectral calibration spectrum image with the dark background spectrum removed, for performing a full-field-of-view spectral calibration test.

[0044] The operation process is as follows: Step Two, Spectral Calibration. Based on the actual spectral band of the nadir hyperspectral imaging payload, a mercury lamp and a narrow-linewidth laser are selected as the standard light sources for spectral calibration. The entire calibration test system is connected, and the relative position of the standard lamp assembly and the nadir hyperspectral imaging payload is adjusted via the lead screw module. The display on the ground testing software interface is observed until the characteristic peak spectral image of the standard lamp appears, and the DN value of the strongest characteristic peak spectral line reaches 80%-90% of the CCD detector saturation value in the nadir hyperspectral imaging payload. Based on the 114° field of view of the nadir hyperspectral imaging payload and the single effective coverage range of the standard lamp assembly, the test steps (including: start / end angle, step angle, spectral imaging, and data storage) are set in the ground testing software of the payload ground testing equipment. After completing the above settings, the calibration turntable will drive the nadir hyperspectral imaging payload for automated spectral calibration. The specific operation steps are as follows:

[0045] Step 2.1: Based on the spectral band of the nadir hyperspectral imaging payload 7, select a standard lamp with corresponding characteristic peaks. The standard lamp assembly 12 includes a standard lamp (e.g., a mercury lamp) and a narrow-linewidth laser (with an installation interface for replacing different light sources). Install the standard lamp assembly 12 onto the payload mounting base 4.

[0046] Step 2.2: The spectral bands of the nadir hyperspectral imaging payload 7 are channel 1: 300-400nm and channel 2: 400-500nm. The characteristic peaks of mercury lamps mainly include: 313nm, 365nm, 404nm, 407nm, 435nm, 546nm, 576nm, and 579nm. Since there are no characteristic peaks of mercury lamps in the 435-500nm band, a narrow-linewidth laser with a center wavelength of 488nm is added to supplement the spectral calibration in this band. It should be understood that when the characteristic peaks of the standard lamp are insufficient to cover the calibration band, a laser of the corresponding wavelength can be connected for supplementation.

[0047] Step 2.3: Deploy the load testing equipment 9 inside the cleanroom 11. Connect the control cabinet 10 (for controlling the integrating sphere 5), the nadir hyperspectral imaging load 7, the calibration turntable 6, and the standard lamp assembly 12 via cables. Confirm that the calibration turntable 6 can rotate within ±90° without interference. Turn off all lights in the cleanroom 11 to ensure that no external light is generated inside the cleanroom 11 except for the standard lamp assembly 12.

[0048] Step 2.4: Start the nadir hyperspectral imaging payload 7 and the payload ground inspection equipment 9. After powering on, wait for the nadir hyperspectral imaging payload 7 to enter a stable working state; turn on the power of the standard lamp assembly 12, and wait for 5 minutes for the standard lamp assembly 12 to enter a stable state.

[0049] Step 2.5, as follows Figure 2 As shown, Figure 2 This is a schematic diagram of spectral calibration provided by the present invention. Adjust the vertical and horizontal positions of the vertical lead screw module 2 and the horizontal lead screw module 3 so that the standard lamp assembly 12 is directly in front of the light entrance of the nadir hyperspectral imaging payload 7. Observe the interface display of the ground inspection software in the payload ground inspection equipment 9 until the characteristic peak spectral image of the standard lamp appears, such as... Figure 3 As shown, Figure 3 This is the spectral calibration imaging image provided by the present invention. The integration time of the nadir hyperspectral imaging payload 7 is adjusted on the ground inspection software, and the spectral lines of the characteristic peaks are examined. The DN (Digital Number) value of the strongest characteristic peak of the standard lamp assembly 12 is made to be the original brightness value of each pixel in the remote sensing image, reaching 80%-90% of the saturation value of the CCD (Charge-coupled Device) detector in the nadir hyperspectral imaging payload 7. The CCD detector is a photoelectric conversion device.

[0050] Step 2.6: Take 0° of the calibration turntable 6 as the field of view center of the nadir hyperspectral imaging payload 7, and control the calibration turntable 6 to rotate the nadir hyperspectral imaging payload 7 to -57°. At this time, the characteristic peak spectral image of the standard lamp assembly 12 appears at the edge of the field of view of the nadir hyperspectral imaging payload 7.

[0051] Step 2.7: Set the angle of the calibration turntable 6, -57°, as the test starting angle, and set 3° as the step angle. After each rotation to the desired position, the ground inspection software of the load inspection device 9 automatically performs spectral imaging and data storage, and then steps to the next angle to continue spectral imaging and data storage until the turntable steps from -57° to 57°, completing the calibration test within the entire 114° field of view. In this invention, the load field of view is 114°.

[0052] Step 2.8: Turn off the standard lamp assembly 12 and record the observation data of the nadir hyperspectral imaging payload 7 in a dark background environment. This data will be used for dark background spectral subtraction during data processing. This completes the full-field spectral calibration test of the nadir hyperspectral imaging payload 7.

[0053] The calibration test method for a spaceborne nadir hyperspectral imaging payload provided by this invention also includes performing a radiometric calibration test, comprising: illuminating the lamp source of the integrating sphere 5 via the control cabinet 10, and controlling the number of lamps turned on in the integrating sphere 5 according to a pre-set first radiance; controlling the calibration turntable 6 to rotate the nadir hyperspectral imaging payload 7, adjusting the angle three times with a test starting angle of -60 degrees and a step angle interval of 40 degrees; after each angle adjustment, imaging is performed through the payload ground testing equipment 9 to obtain a radiometric calibration spectrum image, until the three angle adjustments are completed, to perform a full-field radiometric calibration test. The radiometric calibration test also includes performing full-field radiometric calibration tests for various operating modes, multiple integration times, and various radiance values ​​of the integrating sphere 5 for the nadir hyperspectral imaging payload 7.

[0054] The operation process is as follows: Step 3, radiometric calibration: Using the integrating sphere as the radiometric calibration light source, based on the 114° field of view of the nadir hyperspectral imaging payload and the effective coverage of the surface light source emitted by the integrating sphere in a single operation, the test steps are set on the ground inspection software of the payload ground inspection equipment. The calibration turntable will drive the nadir hyperspectral imaging payload to perform a single round of automated radiometric calibration. The working mode, integration time, and number of integrating sphere lamps are adjusted sequentially (each time the radiance of the integrating sphere needs to be measured using a spectroradiometer). After multiple rounds of radiometric calibration, the integrating sphere is turned off to perform dark background spectral measurements for dark background spectral subtraction during subsequent data processing. The specific operation steps are as follows:

[0055] Step 3.1, Figure 4 This is a schematic diagram of radiation calibration and sample gas testing provided by the present invention. The lamp source of integrating sphere 5 is lit by control cabinet 10 and preheated for 5 minutes. The spectral image displayed on the ground inspection software interface shows a single spectral image, such as... Figure 5 The radiometric calibration imaging pattern provided by the present invention shown covers all bands of the nadir hyperspectral imaging payload 7. The integrating sphere 5 provides a uniform surface light source, which can cover a field of view of 40° for the nadir hyperspectral imaging payload 7 in a single scan.

[0056] Step 3.2: Adjust the number of lamps turned on in the integrating sphere 5 according to the preset first radiance, and use the spectroradiometer 13 to measure the radiance of the integrating sphere 5. This radiance can be used for subsequent data processing.

[0057] Step 3.3: On the ground inspection software, set the calibration turntable 6 to rotate to -60° and set it as the starting test angle. Set 40° as the step angle. After each rotation to the correct position, automatically perform spectral imaging and data storage of the nadir hyperspectral imaging payload 7. The calibration turntable 6 needs to drive the nadir hyperspectral imaging payload 7 to rotate 3 times to cover the 114° full field of view radiometric calibration test.

[0058] Step 3.4: The nadir hyperspectral imaging payload 7 can also perform radiometric calibration under various operating modes (including full-frame, 4-bin, etc.), different integration times (including 60ms, 120ms, 250ms, 500ms, etc.) set by the ground inspection software, and different numbers of integrating spheres. Steps 3.2 and 3.3 are repeated each time until the radiometric calibration of the nadir hyperspectral imaging payload 7 under the corresponding operating conditions is completed. Among them, 4-bin is the pixel binning mode of the nadir hyperspectral imaging payload 7, which achieves the effect of reducing resolution but improving signal-to-noise ratio by merging 4 adjacent pixels into 1 pixel.

[0059] The calibration and testing system for the spaceborne nadir hyperspectral imaging payload provided by the present invention further includes a sample gas cell assembly 14, wherein: the sample gas cell assembly 14 is mounted on the load mounting base 4, and the sample gas cell assembly 14 includes a sample gas cell for containing sample gas; the sample gas cell assembly 14 is located directly in front of the light inlet of the nadir hyperspectral imaging payload 7.

[0060] The calibration test method for a spaceborne nadir hyperspectral imaging payload provided by this invention includes conducting a full-field-of-view sample gas test, comprising: lighting the lamp source of the integrating sphere 5 through the control cabinet 10, controlling the number of lamps turned on in the integrating sphere 5 according to a pre-set second radiance, and allowing the surface light source emitted from the integrating sphere 5 to pass through the sample gas cell assembly 14; when the sample gas in the sample gas cell of the sample gas cell assembly 14 reaches a predetermined concentration, controlling the calibration turntable 6 to drive the nadir hyperspectral imaging payload 7 to rotate, with a test starting angle of -60 degrees and an angle adjustment at 10-degree step angle intervals; after each angle adjustment, imaging is performed through the payload ground inspection device 9 to obtain a sample gas test spectral image, until the nadir hyperspectral imaging payload 7 rotates to +60 degrees to conduct a full-field-of-view sample gas test.

[0061] The operation process is as follows: Step 4, Sample Gas Testing: After the radiometric calibration test is completed, adjust the number of integrated sphere lamps turned on and observe the continuous spectral image displayed on the ground inspection software interface of the payload until the DN value of the continuous spectral line reaches 80%-90% of the CCD detector saturation value in the nadir hyperspectral imaging payload. Install the sample gas cell assembly on the payload mounting base 4. Based on the field of view of the nadir hyperspectral imaging payload covered by the surface light source emitted from the integrating sphere after passing through the sample gas cell assembly, complete the test steps settings of the ground inspection software of the payload. The calibration turntable automatically rotates, performs spectral imaging, and stores data according to the settings of the ground inspection software of the payload, obtaining the full-field spectral absorption line of the nadir hyperspectral imaging payload for the sample gas. Different concentrations of SO2 and NO2 gases are sequentially introduced into the sample gas cell for multiple rounds of testing. The specific operation steps are as follows:

[0062] Step 4.1: After the radiometric calibration test is completed, adjust the number of integrated sphere lamps turned on (the number of lamps turned on in the integrated sphere 5 is controlled according to the pre-set second radiance control). Observe the continuous spectrum image that appears on the interface of the ground inspection software until the DN value of the continuous spectrum line reaches 80%-90% of the saturation value of the CCD detector in the nadir hyperspectral imaging payload 7. Use the spectroradiometer 13 to measure the radiance of the integrated sphere 5. The measurement of the radiance of the integrated sphere 5 here is for later data processing, specifically measuring the actual value of the emitted radiance of the integrated sphere.

[0063] Step 4.2, as follows Figure 4 As shown, Figure 4 This is a schematic diagram of the radiometric calibration and sample gas testing provided by the present invention. The sample gas cell assembly 14 is installed on the load mounting base 4, and the vertical and horizontal positions of the vertical lead screw module 2 and the horizontal lead screw module 3 are adjusted to position the sample gas cell assembly 14 directly in front of the entrance port of the nadir hyperspectral imaging payload 7. An N2 bottle is connected to the inlet pipe for purging; after 1 minute, the air in the gas pipe and sample gas cell is expelled. A sample gas bottle containing a certain concentration of SO2 is connected to the inlet pipe; after 2 minutes, the SO2 concentration in the sample gas cell reaches the preset SO2 concentration, and the test can then be performed. Here, SO2 is the sample gas to be tested.

[0064] Step 4.3: After the surface light source emitted from the integrating sphere 5 passes through the sample gas cell assembly 14, it can cover a field of view of 10° for the nadir hyperspectral imaging payload 7. In the ground testing software, the calibration turntable 6 is rotated to -60° and set as the starting test angle, with 10° as the step angle. After each rotation to the desired position, the spectral imaging and data storage of the nadir hyperspectral imaging payload 7 are automatically performed. To cover the entire 114° field of view, the calibration turntable 6 needs to rotate 12 times to complete the full-field-of-view sample gas test of the nadir hyperspectral imaging payload 7.

[0065] Step 4.4: Switch the concentration of the sample gas bottle and wait for 2 minutes. Then repeat step 4.3 until the test of the preset sample gas concentration is completed. The preset sample gas concentration is the total sample gas concentration.

[0066] Step 4.5: Connect the inlet pipe to the N2 bottle and purge for 3 minutes until the SO2 sample gas in the sample gas cell is emptied. Then connect the inlet pipe to a NO2 sample gas bottle with a certain concentration. After waiting for 2 minutes, the NO2 concentration in the sample gas cell will reach the concentration indicated on the sample gas bottle, and the test can be performed. Repeat steps 4.3 and 4.4 to complete the sample gas test of the pre-set NO2 concentration.

[0067] The calibration and testing system for the spaceborne nadir hyperspectral imaging payload provided by this invention also includes a collimator assembly 15, an elevation slide 16, a positioning prism 17, and a xenon lamp 18. The collimator assembly 15 is fixed on the elevation slide 16, and both the collimator assembly 15 and the elevation slide 16 are mounted on the load mounting base 4. With the calibration turntable 6 at 0 degrees, on the mechanical positioning surface at the light inlet of the nadir hyperspectral imaging payload 7, close to the positioning prism 17, and via the vertical lead screw module 2... The horizontal lead screw module 3 and the pitch slide 16 are used to adjust the horizontal, vertical, and pitch positions of the collimator assembly 15 so that the parallel light emitted by the collimator assembly 15 is incident directly into the nadir hyperspectral imaging payload 7. The xenon lamp 18 is fixed in front of the target of the collimator assembly 15. The position of the collimator assembly 15 is adjusted by the vertical lead screw module 2 and the horizontal lead screw module 3 so that the spectral image of the xenon lamp 18 is located at the center of the field of view of the nadir hyperspectral imaging payload 7, corresponding to a 0° field of view.

[0068] The calibration test method for a spaceborne nadir hyperspectral imaging payload provided by this invention includes spatial resolution testing, comprising: controlling the calibration turntable 6 to rotate the nadir payload 7, performing 11 angle adjustments at 0.1-degree step angle intervals; imaging after each angle adjustment and obtaining a resolution test spectral image; obtaining the maximum intensity I0 of the brightest row pixel from the spectral image, and determining the two rotation angles of the calibration turntable 6 corresponding to the decrease of the maximum intensity I0 to 0.5I0 as α1 and α2, respectively, and calculating the payload angular resolution α of the nadir payload 7 using the formula α=|α1|+|α2|; calculating the spatial resolution along the flight direction based on the flight speed and integration time of the nadir hyperspectral imaging payload 7, specifically: spatial resolution along the flight direction = flight speed × integration time; and calculating the spatial resolution in the vertical flight direction based on the orbital altitude and payload angular resolution α, specifically: .

[0069] The operation process is as follows: Step 5, spatial resolution test: Install the collimator assembly and pitch slide onto the load mounting base. Use the positioning prism to complete the optical axis transfer at the light inlet of the nadir hyperspectral imaging payload. Adjust the position of the collimator assembly so that the parallel light emitted by the collimator is incident directly into the center of the field of view of the nadir hyperspectral imaging payload, corresponding to a 0° field of view. With a step angle of 0.1°, the single scan rotation test range is ±0.5°. Measure 11 sets of data, analyze the brightest row pixel of the CCD detector in each set of data, and observe the light intensity response at different angles. It can be found that the light intensity changes with the angle, with a maximum value of I0. When the light intensity drops to 0.5I0, the corresponding angles are α1 and α2, respectively. At this time, the angular resolution of the nadir hyperspectral imaging payload is α = |α1| + |α2|. Calculate the spatial resolution of the nadir hyperspectral imaging payload along the flight direction = flight speed × integration time; the spatial resolution in the vertical flight direction is... The specific operating steps are as follows:

[0070] Step 5.1, as follows Figure 6 As shown, Figure 6 This is a schematic diagram of spatial resolution testing provided by the present invention. The collimator assembly 15 is fixed to the pitch slide 16 and the whole assembly is installed on the load mounting base 4. A crosshair is installed at the target of the collimator assembly 15. The calibration turntable 6 is rotated to 0° and placed close to the positioning prism 17 on the mechanical positioning surface at the light inlet of the nadir hyperspectral imaging payload 7. The horizontal, vertical, and pitch positions of the collimator assembly 15 are adjusted by the vertical lead screw module 2, the horizontal lead screw module 3, and the pitch slide 16, so that the crosshair observed in the eyepiece of the collimator assembly 15 coincides with the returned image of the positioning prism 17. At this time, the parallel light emitted by the collimator assembly 15 will be incident directly into the nadir hyperspectral imaging payload 7.

[0071] Step 5.2: Replace the target crosshairs of the collimator assembly 15 with 200μm star-shaped apertures. Fix the xenon lamp 18 as the test light source in front of the target of the collimator assembly 15. Start the ground inspection software in the payload ground inspection device 9 and set the working mode of the nadir hyperspectral imaging payload 7 to full swath. Adjust the position of the collimator assembly 15 using the vertical lead screw module 2 and the horizontal lead screw module 3, while observing the display of the ground inspection software, until the spectral image of the xenon lamp 18 is located at the center of the field of view of the nadir hyperspectral imaging payload 7. Figure 7 As shown, Figure 7 This is the spatial resolution imaging image provided by the present invention, and the DN value of the spectral lines in the resolution test spectral image reaches its maximum. The integration time and gain of the nadir hyperspectral imaging payload 7 are adjusted so that the spectral intensity reaches more than 10% of the saturation value of the CCD detector in the nadir hyperspectral imaging payload 7.

[0072] Step 5.3: Set the test start angle of the calibration turntable 6 to -0.5° and the end angle to 0.5°. With a step angle of 0.1°, after each rotation to the desired position, automatically perform spectral imaging and data storage, and measure 11 sets of data.

[0073] Step 5.4 analyzes the intensity of the brightest row pixel (the row pixel with the largest DN value in the data) of the CCD detector in the nadir hyperspectral imaging payload 7 at different angles in the stored data of step 5.3. It can be found that the intensity of this row pixel changes with the angle. Let its maximum value be I0. When the intensity drops to 0.5I0, it corresponds to two rotation angles of the calibration turntable 6, α1 and α2. At this time, the payload angular resolution is α = |α1| + |α2|. The trend of row pixel brightness change is to increase to the maximum and then decrease. Therefore, when the intensity drops to 0.5I0, it corresponds to two rotation angles.

[0074] Step 5.5, spatial resolution along the flight direction = flight speed × integration time; where the flight speed is the flight speed of the nadir hyperspectral imaging payload 7, determined by the satellite platform, and the integration time is set by the nadir hyperspectral imaging payload 7. The spatial resolution in the vertical flight direction is... Where α is the payload angular resolution of the nadir hyperspectral imaging payload 7 calculated in step 5.4, the flight orbit altitude of the nadir hyperspectral imaging payload 7 is 705 km, and thus the spatial resolution in the vertical flight direction is... .

[0075] The optional embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the embodiments of the present invention are not limited to the specific details in the above embodiments. Within the scope of the technical concept of the embodiments of the present invention, various simple modifications can be made to the technical solutions of the embodiments of the present invention, and these simple modifications all fall within the protection scope of the embodiments of the present invention.

[0076] It should also be noted that the various specific technical features described in the above embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, the embodiments of the present invention will not describe the various possible combinations separately.

[0077] Furthermore, various different implementations of the present invention can be combined arbitrarily, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed in the present invention.

Claims

1. A calibration and testing system for a spaceborne nadir hyperspectral imaging payload, characterized in that, The system includes a test frame (1), a vertical lead screw module (2), a horizontal lead screw module (3), a load mounting base (4), an integrating sphere (5), a calibration turntable (6), a nadir hyperspectral imaging payload (7), and a transition fixture (8), wherein: The integrating sphere (5) is installed at the center of the test frame (1); The vertical lead screw module (2) and the horizontal lead screw module (3) are installed on the test frame (1), and the load mounting base (4) is installed on the horizontal lead screw module (3). The nadir hyperspectral imaging payload (7) and the adapter (8) are mounted on the calibration turntable (6), wherein the rotation axis of the positioning turntable (6) is on the same axis as the center of the light inlet of the nadir hyperspectral imaging payload (7); and, The calibration turntable (6) and the nadir hyperspectral imaging payload (7) are located in front of the test frame (1), the opening of the integrating sphere (5) is directly opposite the light inlet of the nadir hyperspectral imaging payload (7), and the table surface of the calibration turntable (6) is horizontal.

2. The calibration and testing system for a spaceborne nadir hyperspectral imaging payload according to claim 1, characterized in that, The system also includes a load testing device (9), a control cabinet (10), a cleanroom (11), a standard lamp assembly (12), and a spectroradiometer (13), which are used for spectral calibration testing, wherein: The standard lamp assembly (12) includes a standard lamp and a narrow linewidth laser. The standard lamp assembly (12) is installed on the load mounting base (4). The load testing equipment (9) is deployed in the clean room (11). The load testing equipment (9) is connected to the control cabinet (10) for controlling the integrating sphere (5), the nadir hyperspectral imaging load (7), the calibration turntable (6), and the standard lamp assembly (12) via cables. The test frame (1) is built in the clean room (11). The standard lamp assembly (12) is located directly in front of the light entrance of the nadir hyperspectral imaging payload (7); and, The spectroradiometer (13) is used to measure the radiance of the integrating sphere (5).

3. The calibration and testing system for a spaceborne nadir hyperspectral imaging payload according to claim 2, characterized in that, The system also includes a sample gas cell assembly (14), wherein: The sample gas reservoir assembly (14) is mounted on the load mounting base (4), and the sample gas reservoir assembly (14) includes a sample gas reservoir for containing sample gas; and, The sample gas cell assembly (14) is located directly in front of the light inlet of the nadir hyperspectral imaging payload (7).

4. The calibration and testing system for a spaceborne nadir hyperspectral imaging payload according to claim 3, characterized in that, The system also includes a collimator assembly (15), a pitch slide (16), a positioning prism (17), and a xenon lamp (18), wherein: The collimator assembly (15) is fixed on the pitch slide (16), and both the collimator assembly (15) and the pitch slide (16) are mounted on the load mounting base (4). With the calibration turntable (6) at 0 degrees, on the mechanical positioning surface at the light inlet of the nadir hyperspectral imaging payload (7), close to the positioning prism (17), the horizontal, vertical, and pitch positions of the collimator assembly (15) are adjusted by the vertical lead screw module (2), the horizontal lead screw module (3), and the pitch slide (16) so that the parallel light emitted by the collimator assembly (15) is incident directly into the nadir hyperspectral imaging payload (7). The xenon lamp (18) is fixed in front of the target of the collimator assembly (15); and, The position of the collimator assembly (15) is adjusted by the vertical lead screw module (2) and the horizontal lead screw module (3) so that the spectral image of the xenon lamp (18) is located at the center of the field of view of the nadir hyperspectral imaging payload (7), corresponding to a 0° field of view.

5. A calibration and testing method for a spaceborne nadir hyperspectral imaging payload, the method being used in the calibration and testing system of the spaceborne nadir hyperspectral imaging payload as described in claim 2, characterized in that, This method includes performing spectral calibration tests, including: Start the standard lamp assembly (12); The 0-degree position of the calibration turntable (6) is the center of the field of view of the nadir hyperspectral imaging payload (7); The calibration turntable (6) is controlled to rotate the nadir hyperspectral imaging payload (7), and the angle is adjusted with a test starting angle of -57 degrees and a step angle interval of 3 degrees; and, After each angle adjustment, imaging is performed through the load-based ground inspection device (9) to obtain a spectral calibration image until the nadir hyperspectral imaging load (7) rotates to positive 57 degrees.

6. The calibration and testing method for a spaceborne nadir hyperspectral imaging payload according to claim 5, characterized in that, The spectral calibration test also includes: Imaging is performed in a dark background environment to obtain a dark background spectrum; and, The dark background spectrum is removed from the spectral calibration image to obtain a spectral calibration image with the dark background spectrum removed, for full-field spectral calibration testing.

7. The calibration and testing method for a spaceborne nadir hyperspectral imaging payload according to claim 6, characterized in that, The method also includes performing radiation calibration tests, including: The light source of the integrating sphere (5) is lit by the control cabinet (10), and the number of lights turned on by the integrating sphere (5) is controlled according to the preset first radiance. Control the calibration turntable (6) to drive the nadir hyperspectral imaging payload (7) to rotate, with a test starting angle of -60 degrees and an angle adjustment of 3 times with a step angle interval of 40 degrees; After each angle adjustment, the load testing equipment (9) is used to image and obtain a radiometric calibration spectrum image until three angle adjustments are completed, so as to carry out a full-field radiometric calibration test.

8. The calibration and testing method for a spaceborne nadir hyperspectral imaging payload according to claim 7, characterized in that, The radiometric calibration test also includes: performing full-field radiometric calibration tests on various working modes, multiple integration times, and the radiance of various integrating spheres (5) of the nadir hyperspectral imaging payload (7).

9. A calibration and testing method for a spaceborne nadir hyperspectral imaging payload, the method being used in the calibration and testing system of the spaceborne nadir hyperspectral imaging payload as described in claim 3, characterized in that, This method includes conducting full-field-of-view sample gas tests, including: The light source of the integrating sphere (5) is lit by the control cabinet (10), and the number of lights turned on by the integrating sphere (5) is controlled according to the preset second radiance, and the surface light source emitted by the integrating sphere (5) is made to pass through the sample gas cell assembly (14). When the sample gas in the sample gas pool of the sample gas pool assembly (14) reaches the predetermined concentration, the calibration turntable (6) is controlled to drive the nadir load (7) to rotate, with a test starting angle of -60 degrees and an angle adjustment in step angle intervals of 10 degrees. After each angle adjustment, the load ground inspection device (9) is used to image and obtain the sample gas test spectrum image until the nadir load (7) is rotated to positive 60 degrees to conduct full field of view sample gas test; The sample gas includes SO2 sample gas of different concentrations and NO2 sample gas of different concentrations.

10. A calibration and testing method for a spaceborne nadir hyperspectral imaging payload, the method being used in the calibration and testing system of the spaceborne nadir hyperspectral imaging payload as described in claim 4, characterized in that, This method includes performing spatial resolution testing, including: The calibration turntable (6) is controlled to drive the nacelle load (7) to rotate, and the angle is adjusted 11 times with a step angle interval of 0.1 degrees; Imaging was performed after each angle adjustment to obtain a resolution test spectral image; The maximum intensity value I0 of the brightest row pixel is obtained from the spectral image. When the maximum intensity value I0 drops to 0.5I0, the two rotation angles of the calibration turntable (6) are α1 and α2, respectively. The load angular resolution α of the nadir load (7) is calculated by the formula α=|α1|+|α2|. The spatial resolution along the flight direction is calculated based on the flight speed and integration time of the aforementioned nadir hyperspectral imaging payload (7), specifically: spatial resolution along the flight direction = flight speed × integration time; and, The spatial resolution in the vertical flight direction is calculated based on the orbital altitude and the load angular resolution α, specifically as follows: .

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