Radiometric calibration method for multi-ccd mosaic wide-field camera in orbit

Abstract

The application provides a method for on-orbit radiation calibration of a multi-CCD (Charge-Coupled Device) spliced wide camera, which comprises the following steps: obtaining spliced remote sensing image data obtained when the wide camera with multiple CCDs passes through a calibration field; determining an absolute radiation calibration coefficient of any CCD as a reference CCD; recording a CCD with overlapping area of remote sensing image data of the reference CCD as a CCD to be calibrated; selecting multiple first areas in the remote sensing image data of the reference CCD in the overlapping area, and obtaining multiple second areas of remote sensing image data of the CCD to be calibrated based on the first areas; obtaining a third area in each first area and calculating radiance, and obtaining a fourth area in each second area and calculating an average pixel brightness value; obtaining an absolute radiation calibration coefficient of the CCD to be calibrated through linear fitting, and completing radiation calibration of other CCDs to be calibrated according to the absolute radiation calibration coefficient.

Description

Technical Field

[0001] The present invention relates to the technical field of aerospace remote sensing image data processing, and in particular to an on-orbit radiometric calibration method for a multi-charge coupled device (CCD) spliced ​​wide-format camera. Background Art

[0002] At present, for the acquisition of medium and high resolution satellite images, wide-format cameras composed of multiple charge-coupled devices are often used to achieve large-scale coverage imaging. For example, the wide-format camera carried by Gaofen-1 (GF-1) and the wide-format cameras of the Environmental Satellite-2A / B are typical systems of this type. In the data preprocessing stage, the observation data of each charge-coupled device is usually subjected to dark current subtraction, relative radiation correction, and geometric correction. At present, for the on-orbit radiation calibration of wide-format cameras composed of multiple charge-coupled devices, the strategy of processing and calibrating each charge-coupled device separately is generally adopted. Specifically, it includes: (1) Field calibration scheme: by arranging each charge-coupled device to pass through the ground calibration field separately, combined with synchronous ground observation data, the radiation calibration coefficient of each charge-coupled device is calculated separately. This scheme is complex to operate, expensive, and subject to many time and space conditions. Related methods can be found in references [1] and [2]. (2) Cross-calibration scheme: Using the cross-matching data of the images acquired by each CCD and a high-precision reference satellite imaged at the same time, based on the synchronous observation of the reference target, a one-to-one calibration between each CCD and the reference satellite is achieved. This method is essentially still matching multiple CCDs with the reference source separately. The calibration process is lengthy and does not fully consider the radiation consistency between multiple CCDs. For related work, please refer to references [3] and [4].

[0003] The above radiation calibration method has the following shortcomings:

[0004] (1) High calibration cost and complex implementation: Each charge-coupled device needs to perform field calibration tasks separately, which not only increases the frequency and complexity of satellite-ground synchronous measurements, but also significantly increases the cost of manpower and material resources. It is also easily affected by weather conditions and satellite orbit period, making it difficult to meet the needs of high-frequency on-orbit calibration.

[0005] (2) It is difficult to ensure the radiation consistency between multiple charge-coupled devices: Since each charge-coupled device is calibrated separately, it is affected by factors such as different imaging conditions and differences in ground samples, which may lead to systematic deviations in the final calculated radiance, affecting the overall radiation consistency and quality of the stitched image.

[0006] (3) The frequency of calibration data acquisition is limited: Traditional field calibration relies on satellite-ground synchronization and is greatly affected by weather and orbital cycles, making it difficult to achieve high-frequency calibration.

[0007] Related references [1], [2], [3], [4] are as follows:

[0008] [1] Wei Wei, Zhang Yanna, Zhang Meng, et al. Multi-site high-frequency radiation calibration of GF-1 wide-field imager [J]. Acta Photonica Sinica, 2018, 47(02): 154-161.

[0009] [2] Han Qijin, Fu Qiaoyan, Zhang Xuewen, et al. High-frequency radiometric calibration of wide-field imager on Gaofen-1 satellite [J]. Optics and Precision Engineering, 2014, 22(07): 1707-1714.

[0010] [3] Yang Lei, Fu Qiaoyan, Pan Zhiqiang, et al. Study on radiometric cross-calibration of Gaofen-1 satellite camera[J]. Infrared and Laser Engineering, 2015, 44(08): 2456-2460.

[0011] [4] Hu Xinkai. Research on cross-calibration of Gaofen-1 satellite time series based on stable target field[D]. Guilin University of Technology, 2020. Summary of the Invention

[0012] In view of this, the present invention proposes an on-orbit radiometric calibration method for a multi-charge coupled device (CCD) stitched wide-format camera. Without the need for individual field or cross-radiometric calibration of all CCDs, the "reference CCD + overlap area cross-transfer" strategy is applied to on-orbit radiometric calibration. This not only reduces calibration costs and improves calibration efficiency, but also significantly enhances the radiometric consistency of multi-charge coupled device stitched remote sensing images, thus having significant technical advantages and engineering practicality. The technical solution of the on-orbit radiometric calibration method for a multi-charge coupled device stitched wide-format camera provided by the present invention is as follows:

[0013] According to an embodiment of the present invention, a method for on-orbit radiation calibration of a multi-charge coupled device stitched wide-format camera is provided, comprising: operation S1: acquiring stitched remote sensing image data obtained when a wide-format camera having multiple charge coupled devices passes through a calibration field; operation S2: calibrating any one of the multiple charge coupled devices to determine its absolute radiation calibration coefficient; operation S3: recording the charge coupled device for which the absolute radiation calibration coefficient is determined as a reference charge coupled device, and recording the charge coupled device having an overlapping area with the remote sensing image data of the reference charge coupled device as a charge coupled device to be calibrated; operation S4: selecting, by means of a sliding window, multiple first areas whose spatial non-uniformity is not higher than a set value in the remote sensing image data of the reference charge coupled device in the overlapping area, and calibrating the calibration results based on the calibration results of each first area. The geographic coordinate information of the pixel is used to obtain multiple second areas of the remote sensing image data of the charge-coupled device to be calibrated corresponding to the position of the first area; operation S5: selecting a third area in each first area through a setting window, and calculating the radiance of each third area as a reference radiance, selecting a fourth area in each second area through a setting window, and obtaining the average pixel brightness value of each fourth area; operation S6: using the reference radiance of each third area and the average pixel brightness value of each fourth area to obtain the absolute radiation calibration coefficient of the charge-coupled device to be calibrated through linear fitting; and operation S7: using the charge-coupled device with the absolute radiation calibration coefficient as a new reference charge-coupled device, repeating operations S3-S6 to complete the radiation calibration of all charge-coupled devices to be calibrated.

[0014] According to an embodiment of the present invention, information that can be extracted from the stitched remote sensing image data includes observed pixel brightness value information of the calibration field, imaging time information, geographic coordinate information, and observed geometric parameter information.

[0015] According to an embodiment of the present invention, operation S2 further includes: determining whether an overlapping area of ​​the remote sensing image data of the reference CCD and the remote sensing image data of the CCD to be calibrated is valid.

[0016] According to an embodiment of the present invention, determining that the overlapping area of ​​the remote sensing image data of the reference charge coupled device and the remote sensing image data of the charge coupled device to be calibrated is valid includes: determining the coverage of the overlapping area; determining that the overlapping area is not affected by clouds; and determining that saturation does not occur in the overlapping area.

[0017] According to an embodiment of the present invention, in operation S4, regions having spatial non-uniformity not higher than 3% are selected to obtain a plurality of first regions.

[0018] According to an embodiment of the present invention, the first region and the second region correspond in position and have the same size.

[0019] According to an embodiment of the present invention, in operation S4, the sliding window is a square window of m×m pixels, where m>6.

[0020] According to an embodiment of the present invention, in operation S5 , the window is set to a square window of n×n pixels, where 2<n<m.

[0021] According to embodiments of the present invention, a single pass through a calibration field for a wide-format camera with multiple charge-coupled devices (CCDs) allows radiometric calibration of all other CCDs to be calibrated that overlap with the remote sensing image data of the CCD for which the absolute radiometric calibration coefficient has been determined. This method is suitable for radiometric calibration of CCDs in wide-format cameras onboard in-orbit spacecraft, including satellites and deep-space probes. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The above and other objects, features and advantages of the present invention will become more apparent through the following description of the embodiments of the present invention with reference to the accompanying drawings, in which:

[0023] Figure 1 The present invention provides a flowchart of an on-orbit radiometric calibration method for a multi-charge coupled device (CCD) stitched wide-format camera.

[0024] Figure 2 This is a schematic diagram of stitched remote sensing image data obtained when a multi-charge coupled device stitching wide-format camera passes through a calibration field according to an embodiment of the present invention.

[0025] Figure 3 Schematic diagram of a first region and a third region of overlapping areas of remote sensing image data of a reference charge coupled device and a charge coupled device to be calibrated according to an embodiment of the present invention.

[0026] Figure 4 Schematic diagram of the second region and the fourth region of the overlapping area of ​​remote sensing image data of the reference charge coupled device and the charge coupled device to be calibrated according to an embodiment of the present invention. DETAILED DESCRIPTION

[0027] The present invention provides an on-orbit radiometric calibration method for a wide-format camera spliced ​​with multiple charge-coupled devices. This method utilizes the overlapping regions between remote sensing image data from different charge-coupled devices (CCDs) of a satellite-borne wide-format camera to achieve radiometric consistency calibration of multiple CCDs. This method can significantly reduce the number of field calibrations and is particularly suitable for wide-format cameras spliced ​​with multiple CCDs (such as the 800 km wide-format cameras aboard the Gaofen-1 and Huanhuan-2 satellites). It offers the advantages of high calibration efficiency, low cost, and good radiometric consistency. The present invention's on-orbit radiometric calibration method for a wide-format camera spliced ​​with multiple CCDs utilizes field calibration to radiometrically calibrate one CCD in the wide-format camera, which serves as a reference CCD. Based on this reference CCD, transfer calibration is then performed on the remaining uncalibrated CCDs, achieving high-precision radiometric calibration of all CCDs in the wide-format camera.

[0028] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with specific embodiments and with reference to the accompanying drawings.

[0029] In an embodiment of the present invention, a method for on-orbit radiation calibration of a multi-charge coupled device spliced ​​wide-format camera is provided. Figure 1 and Figure 2-Figure 4 As shown, the method includes:

[0030] Operation S1: acquiring stitched remote sensing image data obtained when a wide-format camera with multiple charge-coupled devices passes through a calibration field;

[0031] Operation S2: calibrating any one of the plurality of charge coupled devices to determine its absolute radiation calibration coefficient;

[0032] Operation S3: The CCD for which the absolute radiation calibration coefficient is determined is recorded as a reference CCD, and the CCD having an overlapping area with the remote sensing image data of the reference CCD is recorded as a CCD to be calibrated;

[0033] Operation S4: selecting, using a sliding window method, a plurality of first regions in the reference charge-coupled device remote sensing image data of the overlapping region whose spatial non-uniformity is not greater than a set value, and obtaining, based on the geographic coordinate information of the pixels within each first region, a plurality of second regions of the charge-coupled device remote sensing image data to be calibrated corresponding to the positions of the first regions;

[0034] Operation S5: selecting a third area in each first area by setting a window, calculating the radiance of each third area as a reference radiance, selecting a fourth area in each second area by setting a window, and obtaining an average pixel luminance value of each fourth area;

[0035] Operation S6: using the reference radiance of each third region and the average pixel brightness value of each fourth region to obtain an absolute radiation calibration coefficient of the charge-coupled device to be calibrated through linear fitting; and

[0036] Operation S7: The CCD with the absolute radiation calibration coefficient obtained is used as a new reference CCD, and operations S3 to S6 are repeated to complete the radiation calibration of all CCDs to be calibrated.

[0037] Multi-charge coupled device stitching wide-format cameras are often used in medium- and high-resolution satellite image acquisition tasks. For example, the wide-format camera carried by the Gaofen-1 (GF-1) satellite includes four charge coupled devices and can acquire 16-meter multispectral color images (four bands: blue, green, red, and near-infrared). The imaging width can reach hundreds or thousands of kilometers. In an embodiment of the present invention, the multi-charge coupled device stitching wide-format camera includes four charge coupled devices, which are respectively denoted as charge coupled device CCD1, charge coupled device CCD2, charge coupled device CCD3, and charge coupled device CCD4. Figure 2 As shown in the figure, the four quadrilateral boxes represent the remote sensing image data acquired by the four charge coupled devices, the overlapping area A between the remote sensing image data of the charge coupled device CCD1 and the charge coupled device CCD2, the overlapping area B between the remote sensing image data of the charge coupled device CCD2 and the charge coupled device CCD3, and the overlapping area C between the remote sensing image data of the charge coupled device CCD3 and the charge coupled device CCD4; the imaging width of the remote sensing image data of a single charge coupled device is 200 km, and the width of the imaging of four charge coupled devices at the same time can reach about 800 km. If traditional radiometric calibration methods are used, each of the four CCDs in the wide-format camera must be individually calibrated in the field, requiring a total of four calibration passes. However, using the on-orbit radiometric calibration method for a multi-CCD stitched wide-format camera of the present invention, only one calibration pass is required to obtain stitched remote sensing image data from the four CCDs. Because the remote sensing image data from each of the four CCDs overlaps to a certain width, conventional field radiometric calibration is performed on one of the CCDs. The overlapping region between the remote sensing image data from each CCD can then be used to calibrate the radiometric data of all other CCDs to be calibrated. It should be noted that a multi-CCD stitched wide-format camera can also include other numbers of CCDs, such as three, five, or six CCDs. Using the on-orbit radiometric calibration method for a multi-CCD stitched wide-format camera of the present invention, radiometric calibration of all CCDs to be calibrated can be achieved.

[0038] According to an embodiment of the present invention, in operation S1, a spacecraft equipped with a wide-format camera having multiple charge-coupled devices passes through a selected calibration field once to obtain stitched remote sensing image data obtained when passing through the calibration field. Information that can be extracted from the stitched remote sensing image data includes the brightness value of the observed pixels of the calibration field, imaging time information, geographic coordinate information, and observation geometric parameter information, where the observation geometric parameter information includes, for example, the observation zenith angle, the observation azimuth angle, the solar zenith angle, and the solar azimuth angle.

[0039] According to an embodiment of the present invention, in operation S2, any one CCD is selected for calibration, and the CCD is used as a reference CCD. Figure 2 As shown, the charge-coupled device CCD2 is selected for conventional external field radiation calibration and used as the reference charge-coupled device. During calibration, the surface reflectivity data and atmospheric parameters observed synchronously in the calibration field are first obtained. The spectral radiance at the entrance pupil of the payload is calculated using the atmospheric radiation transmission simulation process. The equivalent channel radiance of the reference charge-coupled device is obtained by convolution with the spectral response function corresponding to the reference charge-coupled device. , combined with the mean brightness value of the observed pixels in the calibration field area in the reference charge coupled device remote sensing image data , calculate the absolute radiation calibration coefficient of the reference charge-coupled device by the following formula (1): and .

[0040] (1);

[0041] According to an embodiment of the present invention, operation S3 further includes determining whether the overlapping region between the remote sensing image data of the reference CCD and the remote sensing image data of the CCD to be calibrated is valid. Determining whether the overlapping region between the remote sensing image data of the reference CCD and the remote sensing image data of the CCD to be calibrated is valid includes: determining the coverage of the overlapping region; determining that the overlapping region is free of cloud cover; and determining that the overlapping region is free of saturation. For example, using CCD3 as the CCD to be calibrated, radiometric calibration of CCD3 is performed. The absolute radiometric calibration coefficient for CCD3 is calculated using the overlapping region B between the remote sensing image data of CCD2 (reference CCD) and CCD3. First, based on geographic coordinate matching, the overlapping region B of the remote sensing image data of CCD2 and CCD3 is determined, and geometric registration is performed on the image data in the overlapping region. Then, the validity of the remote sensing image data of the overlapping area B is checked. If it is determined that the remote sensing image data of the overlapping area B has full coverage, no cloud influence, no saturation phenomenon, etc., then the overlapping area B is considered valid.

[0042] According to an embodiment of the present invention, in operation S4, a sliding window is used to select areas with spatial non-uniformity of no more than 3% in the remote sensing image data of the reference charge coupled device in the overlapping area to obtain multiple first areas, and the geographic coordinate information of each first area is recorded. It should be noted that, according to the actual application situation, multiple areas with spatial non-uniformity of no more than 2% or no more than 1% can also be selected as first areas, and areas with spatial non-uniformity of no more than 3% can be regarded as uniform areas. The sliding window is a square window of m×m pixels, m>6, for example, m is 8, 9, 10, and the present invention is explained by taking a sliding window of 9×9 pixels as an example. Specifically, in the overlapping area of ​​the remote sensing image data of the charge coupled device CCD2 as the reference charge coupled device and the charge coupled device CCD3 to be calibrated, a 9×9 sliding window is used to traverse the remote sensing image data of the overlapping area, and the spatial non-uniformity CV in the sliding window is calculated by the following formula (2): window :

[0043] (2);

[0044] μ window represents the average brightness value of the observed pixels in the 9×9 sliding window, σ window Indicates the standard deviation of the brightness value of the observed pixel in the sliding window, according to the spatial non-uniformity CV window ≤3% of the set value requirement, a plurality of regions can be screened out from the remote sensing image data of the charge coupled device CCD2 in the overlapping area by sliding the window, and recorded as the first region, such as Figure 3 As shown, there are four first regions, namely, first region 1, first region 2, first region 3, and first region 4. Furthermore, based on the geographic coordinate information of the pixels in each first region, multiple second regions of the remote sensing image data of the charge coupled device CCD3 to be calibrated corresponding to the position of each first region are obtained, such as Figure 4 As shown, there are four second areas, namely, second area 1', second area 2', second area 3', and second area 4'. The first area and the second area correspond to each other in position and have the same size.

[0045] According to an embodiment of the present invention, in operation S5, the window is set to a square window of n×n pixels, 2<n<m, for example, n is 3, 4, or 5, and n is 3 as an example. By setting the window to 3×3, a third area is selected at the middle position of each first area, such as Figure 3As shown, the third area 10 is obtained by selecting from the first area 1, the third area 20 is obtained by selecting from the first area 2, the third area 30 is obtained by selecting from the first area 3, and the third area 40 is obtained by selecting from the first area 4. Further, the reference radiance of each third area is calculated, and the local non-uniform areas caused by edge distortion, cloud cover, etc. are eliminated. The radiance of each third area is calculated as the reference radiance by the following formula (3): :

[0046] (3);

[0047] in, represents the radiance of each third region, serving as a reference radiance, n represents the number of samples in the third region, i represents the sample ordinal number, both n and i are positive integers. In the embodiment of the present invention, n=4; and is the absolute radiation calibration coefficient of the reference charge-coupled device, Indicates the average pixel brightness value of each third area.

[0048] Similarly, multiple fourth regions are obtained by selecting the center position of each second region through a 3×3 setting window, such as Figure 4 As shown, the fourth area 10' is selected from the second area 1', the fourth area 20' is selected from the second area 2', the fourth area 30' is selected from the second area 3', and the fourth area 40' is selected from the second area 4', and the average pixel brightness value of each fourth area is obtained. .

[0049] According to an embodiment of the present invention, in operation S6, the reference radiance of each third region is used. and the average pixel brightness value of each fourth area , through linear fitting, the absolute radiation calibration coefficient of the charge-coupled device to be calibrated is obtained as follows (4):

[0050] (4);

[0051] Where n represents the number of samples in the uniform area involved in the calculation, represents the brightness value of the observed pixels in each fourth region, Represents the reference radiance calculated for each third region. According to the above formula, the absolute radiation calibration coefficient of the charge-coupled device to be calibrated can be calculated. and After the above operations, the radiation calibration of the CCD3 to be calibrated is completed. Similarly, the radiation calibration of the CCD1 to be calibrated can be completed based on the overlapping area A between the remote sensing image data of the CCD3 and the CCD1.

[0052] According to an embodiment of the present invention, the charge-coupled device CCD3, which has completed the radiometric calibration by obtaining the absolute radiometric calibration coefficient, is used as a new reference charge-coupled device. The processes S3-S6 are repeated, and the radiometric calibration of the charge-coupled device CCD4 to be calibrated is completed by utilizing the overlapping area C between the remote sensing image data of the charge-coupled device CCD3 and the charge-coupled device CCD4. This achieves the goal of completing the radiometric calibration of all remaining charge-coupled devices by only having to carry a wide-format camera containing four charge-coupled devices through a single pass through the calibration field to acquire stitched remote sensing image data, and then completing the radiometric calibration of all remaining charge-coupled devices through a cross-transfer calibration method.

[0053] The on-orbit radiometric calibration method for a multi-charged coupled device (CCD) spliced ​​wide-format camera of the present invention can significantly reduce calibration costs and improve on-orbit calibration efficiency. Currently, field calibration methods require each CCD in a wide-format camera to independently acquire remote sensing image data from the calibration field, and only calibration can be completed in conjunction with satellite-ground synchronous measurements. This method has limited calibration frequency, is complex to operate, and is costly. The on-orbit radiometric calibration method for a multi-charged coupled device (CCD) spliced ​​wide-format camera of the present invention utilizes field calibration on only one CCD, which serves as a reference CCD. This method, combined with the naturally existing overlap between the remote sensing image data of each CCD, enables step-by-step radiometric calibration between the CCDs. This effectively avoids the need for separate field measurements for each CCD, reduces the number of field calibration tasks required from N (N equals the number of CCDs in the wide-format camera) to 1, and significantly conserves calibration resources.

[0054] The on-orbit radiation calibration method for a multi-charge coupled device (CCD) stitched wide-format camera of the present invention fully utilizes the information of the overlapping areas between the remote sensing image data of each CCD to improve radiation consistency. In traditional calibration methods, even if multiple CCDs have completed calibration, it is difficult to avoid radiation deviations caused by different time sequences and conditions, resulting in problems such as stripes and inconsistent brightness between the stitched image data of multiple CCDs. The on-orbit radiation calibration method for a multi-charge coupled device (CCD) stitched wide-format camera of the present invention combines a sliding window with a uniform area screening strategy, and utilizes the areas with high spatial uniformity in the overlapping areas between the remote sensing image data of each CCD to perform radiance comparison and coefficient transfer, which can effectively reduce the radiation deviation between different CCDs and improve the radiation continuity and consistency of the wide-coverage remote sensing image stitched by multiple CCDs.

[0055] The on-orbit radiation calibration method for a multi-charge coupled device (CCD) spliced ​​wide-format camera of the present invention can improve calibration adaptability and scalability, supporting higher-frequency on-orbit radiation monitoring. Traditional radiation calibration methods, which calibrate CCDs one by one, are difficult to adapt to the calibration requirements of high frequency, large scale, and multiple cameras. Due to the limitations of orbital repetition period and weather conditions, they are prone to problems such as long calibration data acquisition intervals and update lags. The "reference CCD + overlapping area transfer" mode proposed in the present invention can theoretically quickly achieve synchronous radiation calibration and update of other CCDs of the full-width camera as long as the calibration data of the reference CCD is determined. It has good time adaptability and mission flexibility, and is also more suitable for the calibration requirements of high-revisit remote sensing satellites equipped with multi-charge coupled device wide-format cameras or imagers. It can be seen that the on-orbit radiation calibration method for a multi-charge coupled device spliced ​​wide-format camera of the present invention is suitable for the radiation calibration of CCDs in wide-format cameras carried by on-orbit spacecraft, such as satellites or deep space probes.

[0056] Furthermore, unless specifically described or required to occur sequentially, the order of the steps is not limited to the order listed above and may be varied or rearranged based on desired design requirements. Furthermore, the above embodiments may be mixed and matched with each other or with other embodiments based on design and reliability considerations. That is, the technical features of different embodiments may be freely combined to form more embodiments.

[0057] The above specific embodiments further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above are only specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for on-orbit radiometric calibration of a multi-charge coupled device (CCD) spliced ​​wide-format camera, characterized in that: include: Operation S1: acquiring stitched remote sensing image data obtained when a wide-format camera with multiple charge-coupled devices passes through a calibration field; Operation S2: calibrating any one of the plurality of charge coupled devices to determine its absolute radiation calibration coefficient; Operation S3: Recording the CCD for which the absolute radiation calibration coefficient is determined as a reference CCD, and recording the CCD having an overlapping area with the remote sensing image data of the reference CCD as a CCD to be calibrated; Operation S4: selecting, in a sliding window manner, a plurality of first regions whose spatial non-uniformity is not greater than a set value in the reference charge-coupled device remote sensing image data of the overlapping region, and obtaining, based on geographic coordinate information of pixels within each of the first regions, a plurality of second regions of the charge-coupled device remote sensing image data to be calibrated corresponding to the positions of the first regions; Operation S5: selecting a third area in each of the first areas using a set window, calculating the radiance of each third area as a reference radiance, selecting a fourth area in each of the second areas using a set window, and obtaining an average pixel luminance value of each fourth area; Operation S6: using the reference radiance of each third area and the average pixel brightness value of each fourth area to obtain the absolute radiation calibration coefficient of the charge-coupled device to be calibrated through linear fitting; as well as Operation S7: The CCD with the absolute radiation calibration coefficient obtained is used as a new reference CCD, and operations S3 to S6 are repeated to complete the radiation calibration of all CCDs to be calibrated.

2. The on-orbit radiometric calibration method for a multi-charge coupled device (MCD) spliced ​​wide-format camera according to claim 1, characterized in that: The information that can be extracted from the stitched remote sensing image data includes the observed pixel brightness value information of the calibration field, imaging time information, geographic coordinate information, and observed geometric parameter information.

3. The on-orbit radiometric calibration method for a multi-charge coupled device (MCD) spliced ​​wide-format camera according to claim 1, characterized in that: Operation S3 further includes: determining whether an overlapping area of ​​the remote sensing image data of the reference CCD and the remote sensing image data of the CCD to be calibrated is valid.

4. The on-orbit radiometric calibration method for a multi-charge coupled device (CCD) spliced ​​wide-format camera according to claim 3, characterized in that: Determining that an overlapping area of ​​the remote sensing image data of the reference charge coupled device and the remote sensing image data of the charge coupled device to be calibrated is valid includes: determining the coverage of the overlapping area; Determining that the overlap region is free of cloud cover; and It is determined that no saturation occurs in the overlapping region.

5. The on-orbit radiometric calibration method for a multi-charge coupled device (CCD) spliced ​​wide-format camera according to claim 1, characterized in that: In operation S4, regions with spatial non-uniformity not higher than 3% are selected to obtain a plurality of first regions.

6. The on-orbit radiometric calibration method for a multi-charge coupled device (CCD) spliced ​​wide-format camera according to claim 1, characterized in that: The first area and the second area correspond in position and have the same size.

7. The on-orbit radiometric calibration method for a multi-charge coupled device (CCD) spliced ​​wide-format camera according to claim 1, characterized in that: In operation S4, the sliding window is a square window of m×m pixels, where m>6.

8. The on-orbit radiometric calibration method for a multi-charge coupled device (CCD) spliced ​​wide-format camera according to claim 7, characterized in that: In operation S5 , the setting window is a square window of n×n pixels, where 2<n<m.

9. The on-orbit radiometric calibration method for a multi-charge coupled device (CCD) spliced ​​wide-format camera according to claim 1, characterized in that: A wide-format camera with multiple charge-coupled devices can perform radiometric calibration on all other charge-coupled devices to be calibrated that have overlapping areas with the remote sensing image data of the charge-coupled device for which the absolute radiometric calibration coefficient has been determined, by passing through the calibration field once.

10. The on-orbit radiometric calibration method for a multi-charge coupled device (CCD) spliced ​​wide-format camera according to claim 1, characterized in that: The invention is applicable to the radiation calibration of charge-coupled devices in wide-format cameras carried by on-orbit spacecraft, which include satellites and deep space probes.

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