CN110120077B - Area array camera in-orbit relative radiation calibration method based on satellite attitude adjustment - Google Patents
Area array camera in-orbit relative radiation calibration method based on satellite attitude adjustment Download PDFInfo
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Abstract
An area array camera on-orbit relative radiation calibration method based on satellite attitude adjustment is disclosed, wherein CCD imaging parameters of a focal plane of a satellite are required to be set consistently before the satellite performs attitude adjustment and ground imaging; selecting a ground uniform dark target, wherein the uniform dark target can be covered by a plurality of lines of satellite imaging; under the condition that the uniform dark target can be covered by multiple satellite imaging lines, adjusting the satellite to a normal posture to obtain an image of the uniform dark target, counting DN values of the image, and taking the average DN value as a system dark signal; the satellite performs attitude adjustment to enable the long side direction of the satellite CCD area array to be consistent with the flight direction of the satellite, then the ground is imaged to obtain a ground image, and the satellite returns to the normal attitude of the satellite; and carrying out image processing on the ground image, carrying out in-orbit relative calibration on the processed image, dynamically acquiring a relative radiometric calibration coefficient according to the satellite operation and the response consistency of the area array optical camera, and ensuring the in-orbit relative calibration precision.
Description
Technical Field
The invention relates to an in-orbit relative radiometric calibration method for an area-array camera based on satellite attitude adjustment, and belongs to the technical field of radiometric calibration.
Background
The imaging optical cameras are calibrated on the ground before satellite transmission, but they must be re-calibrated after orbit so as to eliminate the imaging performance reduction caused by the drift of calibration coefficients, particle pollution and the like. Since these scaling changes are more or less independent between the probe elements, on-track relative scaling is necessary. Relative scaling, as the name implies, does not require transfer or calibration of absolute radiation values, but rather focuses on radiation response performance differences between detectors of channels of the optoelectronic imaging/detection system and between detector pixels of the array and how such differences are eliminated. The focal plane components of the imaging optical camera generally need to be spliced, so that the difference exists between imaging detector sheets, and the difference of pixels of the imaging detector and the spliced slit can influence the final imaging, which is particularly represented by that when the area array optical camera images a large-area uniform target, the image output is not uniform but obvious bright or dark stripes exist.
The area-array camera can determine the relation between the output characteristics of the area-array camera, such as uniformity among image elements, response nonlinearity and the like by carrying out relative calibration, and then image noise is eliminated by image inversion, so that the imaging effect is improved.
In the laboratory, it is relatively simple to produce a uniform surface light field (integrating sphere light source or large diffuse reflector), but it is difficult to photograph a uniform ground object with an on-orbit planar array optical camera because it is difficult to have many uniform targets with uniform radiation characteristics in a typical imaging area (tens to hundreds of kilometers) on the ground. The deep space is a good homogeneous field but is only suitable for measuring the bias level, and a certain radiance is needed for calculating the relative gain. In the solar illumination area, the ocean is an ideal uniform field but has insufficient brightness, and the whole dynamic range of the equipment cannot be well calibrated. There are many relatively uniform desert targets in north, but the area is not large enough for most optical cameras to be relatively scaled in-orbit.
Disclosure of Invention
The technical problem solved by the invention is as follows: the method combines the advantages of relative scaling algorithms of satellite attitude adjustment, ground uniform scene imaging and optimization, dynamically acquires a relative radiation scaling coefficient according to the satellite operation and the response consistency of an area array imaging optical camera, and ensures the in-orbit relative scaling precision;
the technical scheme of the invention is as follows: an in-orbit relative radiation calibration method for an area-array camera based on satellite attitude adjustment comprises the following steps:
1) before the attitude adjustment of the satellite is carried out on the ground imaging, the imaging parameters of the area array detector of the satellite need to be set consistently;
2) selecting a ground uniform dark target which can be covered by a plurality of satellite imaging lines, wherein the specific preferred scheme is as follows: when the satellite area-array camera images the ground once, the size of the area of one-time imaging is equal to the size of the projection area of the effective size of the detector of the satellite area-array camera on the ground, a dark target area with uniform ground is selected, the area is imaged, a calm lake or sea surface is generally selected, and the size of the area of the satellite imaging on the ground once can be covered by the selected shooting area.
3) The method comprises the steps of adjusting the attitude of a satellite under the condition that a uniform dark target can be covered by a plurality of lines of satellite imaging, rotating the yaw angle of the satellite from 0 degree to 90 degrees through attitude control, enabling the long edge direction of a satellite area array detector to be consistent with the flight direction of the satellite, imaging the ground to obtain an image of the uniform dark target, counting DN values (gray values) of the image, and taking the average DN value as a system dark signal (DN)-_Sdark；
4) The satellite keeps a posture with a yaw angle of 90 degrees, the long side direction of the satellite area array detector is consistent with the flight direction of the satellite, and under the condition, ground imaging is carried out to obtain a ground image; the yaw angle of the satellite returns to 0 degree from 90 degrees through attitude control, namely the satellite returns to the normal attitude;
5) carrying out image processing on the ground images obtained in the step 4) to enable the same ground object to be approximately on the same horizontal line;
6) performing on-orbit relative calibration on the image processed in the step 5) to obtain a correction coefficient of the responsivity of each pixel of the area array detector and a correction coefficient of a system dark signal; obtaining a calibrated image according to a correction coefficient of the responsivity of each pixel of the area array detector and a correction coefficient of a system dark signal;
7) judging whether the image after calibration obtained in the step 6) has a banding phenomenon, if so, judging whether recalibration is needed according to a banding evaluation condition, if so, returning to the step 4), otherwise, judging that the image after calibration in the step 6) meets the requirement, and finishing calibration for subsequent processing of the on-track image.
Satellite image multi-line coverage means: the length of the single side of the uniform field is greater than that of the narrow side of the area array of the satellite area array optical camera.
The imaging parameter setting of the area array detector of the satellite is consistent, and the method comprises the following steps: and setting each pixel of the area array detector to be uniform exposure time and gain.
The area array detector is preferably a full-color CCD
The uniformly dark target refers to: the uniform dark target is not overlapped with the uniform scene;
a uniform dark target, preferably comprising: ocean, calm lake surface.
The satellite area-array camera comprises an area-array detector (preferably an area-array CCD and an area-array CMOS detector), an electronic device and an optical machine main body. The area array detector is mainly responsible for light sensing and converts scenery shot by the satellite area array camera into digital signals; the electronic equipment is responsible for supplying power to the area array camera, controlling the camera, processing image information and the like; the optical machine main body consists of a structure of the area array camera and an optical lens, the optical lens is arranged on the structure of the area array camera, and the area array detector and the electronic equipment can also be arranged on the structure of the area array camera.
The area array detector is preferably rectangular, preferably 7920 × 6144 area array detector, 7920 × 6144 means that the long side of the area array is 7920 pixels, and the short side is 6144 pixels.
The strip evaluation conditions were specifically: selecting the image calibrated in the step 6) as an evaluated image, taking the column average of the evaluated image, and respectively passing the image after the column average through a 101-order median filter subjected to 25-order sampling average smoothing and a 2001-order median filter subjected to 51-order sampling average smoothing to obtain two curves, wherein the absolute value of the difference between the two curves reflects the band condition of the whole image; if the difference between the two curves meets the requirement, judging that the strip evaluation condition is met, otherwise, judging that the strip evaluation condition is not met;
step 2) selecting a ground uniform dark target which can be covered by a plurality of lines of satellite imaging, wherein the preferable scheme is as follows: when the satellite area-array camera images the ground once, the size of the area of one-time imaging is equal to the size of the projection area of the effective size of the detector of the satellite area-array camera on the ground, a dark target area with uniform ground is selected, the area is imaged, a calm lake or sea surface is generally selected, and the size of the area of the satellite imaging on the ground once can be covered by the selected shooting area.
Step 5) image processing is carried out on the ground images obtained in the step 4), so that the same ground object is on the same horizontal line, and the preferable scheme is as follows: after the satellite attitude is adjusted, each pixel of the area array detector images the same area, and the obtained image is 45 degrees (namely, 45 degrees of leveling), and the imaging relation is shown in fig. 3. The image is adjusted line by line according to the gray value DN of the first row and the first column of the image1,1Is a baseAnd correcting the images inclined by 45 degrees into the same horizontal line, so that the same ground object is approximately on the same horizontal line, as shown in the formula (1-1).
Step 6) performing on-track relative calibration on the image processed in the step 5) to obtain a correction coefficient of the responsivity of each pixel of the CCD and a correction coefficient of a system dark signal; the method specifically comprises the following steps: performing on-track relative calibration on the 45-degree leveled image in the step 5) to obtain a correction coefficient of the responsivity of each pixel of the CCD and a correction coefficient of a system dark signal; obtaining a calibrated image according to a correction coefficient of the responsivity of each pixel of the CCD and a system dark signal correction coefficient, wherein the relative calibration expression of the satellite area array camera is selected as follows:
in the formula:
in laboratory calibration, the DN value of each pixel is calculated under the same radiance, and the gray level average value of all pixels is obtained
Then, under different brightness points, the average value of the gray levels of all the pixels is calculated, and the functional relation between the average gray level value and the radiance is expressed by a least square method as follows:
in the formula:
step 3, the medium satellite images the uniform dark target (such as the sea, the calm lake surface and the like), and statistics is carried out
Taking the average value of each pixel as the on-track relative calibration dark signal value
The satellite attitude is adjusted to image the uniform target, and the radiation illumination of each pixel is consistent (the more uniform the ground object target is, the better the calibration effect is). After the gray level image output by the area array detector is converted into the incident radiance image of the satellite area array camera, the radiance L corresponding to each pixelm,nShould be consistent (collectively expressed in L), the camera input radiance inversion formula is:
the average DN value obtained by substituting formula (1-4) for formula (1-3) is expressed as follows:
in the formula:
correction coefficient of pixel responsivity
Dark signal correction factor-
Bringing the correction coefficients into equations (1-6) yields a correction function matrix for on-track relative scaling:
and (4) processing the on-orbit image by using the formula (1-7) to obtain an on-orbit relatively radiometric calibrated image.
Step 7) judging whether the image after calibration obtained in the step 6) has banding phenomenon, if so, judging whether recalibration is needed according to the banding evaluation condition, if so, returning to the step 4), otherwise, judging that the image after calibration in the step 6) meets the requirement, wherein the preferred scheme is as follows:
taking the average value of each column of the image calibrated in the step 6), changing the two-dimensional distribution of the area array image into a one-dimensional curve form, respectively passing the averaged one-dimensional curve through a 101-order median filter subjected to 25-order sampling average smoothing and a 2001-order median filter subjected to 51-order sampling average smoothing to obtain two curves, wherein the difference between the two curves forms a new curve, the absolute value of the new curve reflects the strip condition of the image calibrated, each peak of the new curve represents a strip, and if the new curve has more than 3 obvious peaks, the image calibrated in the step 6) does not meet the requirement and needs to be calibrated again.
Compared with the prior art, the invention has the advantages that:
(1) the method makes full use of the capability of adjusting the yaw attitude of the satellite platform, combines the advantages of imaging and optimizing a ground uniform scene relative calibration algorithm, and conveniently realizes the in-orbit relative radiation calibration of the satellite area array optical camera;
(2) the invention adopts the imaging mode of satellite attitude adjustment, greatly reduces the coverage area of ground imaging, ensures the uniformity of ground scene, and reduces the dependence of on-orbit relative calibration on a special calibration field;
(3) the invention adopts an optimized relative calibration algorithm, uses a matrix model, takes account of the programmability of the imaging model and the calibration algorithm of the satellite optical camera, overcomes the jump of splicing the focal plane array of the area array optical camera, and has stronger practicability to the on-orbit relative calibration of the satellite area array optical camera;
(4) the invention has the advantage of small coverage area for ground imaging, and has strong practical significance for splicing multiple detectors and on-orbit relative calibration of an optical camera with the rectangular detector;
(5) the invention ensures the calibration quality through strip evaluation, basically eliminates strips of the remote sensing image and ensures the radiation quality of the image.
(6) The invention is based on the concept of on-orbit relative calibration of satellite attitude adjustment, and thus a uniform target is generated for an area array optical camera which acquires earth surface information from an orbit. The purpose of generating a uniform target is that each detector element of the area array optical camera can receive the same radiance. After the satellite attitude is adjusted, each detection pixel of the satellite area-array optical camera images the same ground target by rotating the satellite, and the on-orbit relative calibration can be carried out as long as the ground has a small uniform field without using a special ground calibration field. The technique improves the conventional scaling method to reduce banding in the image, resulting in an image superior to the non-uniformity correction, which can be used as a criterion for calculating relative gain.
Drawings
FIG. 1 is a flow chart of in-orbit relative radiometric calibration based on satellite attitude adjustment;
FIG. 2 is a schematic projection diagram of a focal plane of a detector on the ground before and after satellite attitude adjustment;
FIG. 3 is a schematic diagram of the arrangement of detector pixels before and after satellite attitude adjustment;
Detailed Description
The invention is described in further detail below with reference to the figures and specific embodiments.
The invention relates to an in-orbit relative radiation calibration method of an area-array camera based on satellite attitude adjustment.A CCD imaging parameter of a focal plane of a satellite needs to be set consistently before the satellite performs attitude adjustment and ground imaging; selecting a ground uniform dark target, wherein the uniform dark target can be covered by a plurality of lines of satellite imaging; under the condition that the uniform dark target can be covered by multiple satellite imaging lines, adjusting the satellite to a normal posture to obtain an image of the uniform dark target, counting DN values of the image, and taking the average DN value as a system dark signal; the satellite performs attitude adjustment to enable the long side direction of the satellite CCD area array to be consistent with the flight direction of the satellite, then the ground is imaged to obtain a ground image, and the satellite returns to the normal attitude of the satellite; and carrying out image processing on the ground image, carrying out in-orbit relative calibration on the processed image, dynamically acquiring a relative radiometric calibration coefficient according to the satellite operation and the response consistency of the area array optical camera, and ensuring the in-orbit relative calibration precision.
The method is used for on-orbit relative calibration of the area-array optical camera, and the calibrated image obviously eliminates image noise through image inversion, thereby improving the imaging effect. The original on-orbit relative calibration needs to use a special ground calibration field which requires uniform ground objects and good diffuse reflection characteristic so as to simulate indoor calibration and generate a uniform surface light field. However, it is difficult to shoot a uniform ground object with an on-orbit optical camera because it is difficult to have a plurality of uniform targets with uniform radiation characteristics in a typical imaging area (tens to hundreds of kilometers) on the ground. The deep space is a good homogeneous field but is only suitable for measuring the bias level, and a certain radiance is needed for calculating the relative gain. In the solar illumination area, the ocean is an ideal uniform field but has insufficient brightness, and the whole dynamic range of the equipment cannot be well calibrated. There are many relatively uniform desert targets in north, but the ground uniform terrain area is not large enough for most optical camera on-track relative scaling. The method is based on an in-orbit relative calibration concept of satellite attitude adjustment, and each detection pixel of an area array optical camera detector scans the same ground target through a rotating satellite so as to finish the generation of a uniform field. The technology does not need to select a special ground calibration field, and can carry out on-orbit relative calibration as long as the ground is a small uniform field. The technique improves the conventional scaling method to reduce banding in the image, resulting in an image superior to the non-uniformity correction, which can be used as a criterion for calculating relative gain. By using the technology, the relative calibration of the orbit satellite can be developed into a calibration mode of business normalization from one time or a few times in the past year.
The invention is described in detail below with reference to the accompanying drawings, and the specific steps are as follows:
1. and selecting a uniform earth surface, and ensuring that the unilateral length of a uniform scene is greater than the projection N of the satellite area array optical camera on the ground as shown in figure 2. If the detector of the satellite area array optical camera consists of two area array rectangular detectors, the size of the rectangular detector is 7800 pixels multiplied by 5400 pixels, the long sides of the two detectors are spliced to form an area array focal plane with 15600 pixels multiplied by 5400 pixels, and the single-time ground imaging area is 15.6km multiplied by 5.4km on a 500km track. When the area-array camera is relatively calibrated on the orbit, the length of a single side of a uniform scene on the ground is more than 5.4 km.
2. Selecting a ground uniform dark target which can be covered by a plurality of satellite imaging lines, wherein the preferable scheme is as follows: when the satellite area-array camera images the ground once, the size of the area of one-time imaging is equal to the size of the projection area of the effective size of the detector of the satellite area-array camera on the ground, a dark target area with uniform ground is selected, the area is imaged, a calm lake or sea surface is generally selected, and the size of the area of the satellite imaging on the ground once can be covered by the selected shooting area. The single-time ground imaging area of the area-array camera is 15.6km multiplied by 5.4km, and a target with the lake surface larger than 5.4km is selected as a uniform dark target.
3. The method comprises the steps that a satellite performs attitude adjustment under the condition that a uniform dark target can be covered by multiple lines of satellite imaging, a satellite yaw angle is rotated to 90 degrees from 0 degrees through attitude control, the pixel (long edge) direction of a satellite area array detector 15600 is consistent with the satellite flight direction, imaging is performed on the ground, an image of the uniform dark target is obtained, the DN value (gray value) of the image is counted, and the average DN value is taken as a system dark signal (DN) - _ Sdark;
4. the satellite keeps a yaw angle of 90 degrees, the pixel (long side) direction of a satellite area array detector 15600 is consistent with the flight direction of the satellite, and under the condition, ground imaging is carried out to obtain a ground image; the yaw angle of the satellite returns to 0 degree from 90 degrees through attitude control, namely the satellite returns to the normal attitude;
5. and (3) carrying out image processing on the ground image obtained in the step (4) to enable the same ground object to be approximately on the same horizontal line, after the satellite attitude is adjusted, imaging the same area by each pixel of the area array detector, wherein the obtained image is 45 degrees, and the imaging relation is shown in figure 3. The image is adjusted line by line according to the gray value DN of the first row and the first column of the image1,1For reference, the images inclined by 45 ° are corrected to be the same horizontal line, so that the same ground object is approximately on the same horizontal line, as shown in equation (1-1).
In this case, m is 15600 and n is 5400
6. Performing on-track relative calibration on the 45-degree leveled image in the step 5) to obtain a correction coefficient of the responsivity of each pixel of the CCD and a correction coefficient of a system dark signal; obtaining a calibrated image according to the correction coefficient of the responsivity of each pixel of the CCD and the correction coefficient of the system dark signal, wherein the relative calibration expression of the satellite area-array camera is as follows:
in laboratory calibration, the DN value of each pixel is calculated under the same radiance, and the gray level average value of all pixels is obtained
Then, under different brightness points, the average value of the gray levels of all the pixels is calculated, and the functional relation between the average gray level value and the radiance is expressed by a least square method as follows:
in the formula:
step 3, the medium satellite images the uniform dark target (such as the sea, the calm lake surface and the like), and statistics is carried out
Taking the average value of each pixel as the on-track relative calibration dark signal value
The satellite attitude is adjusted to image the uniform target, and the radiation illumination of each pixel is consistent (the more uniform the ground object target is, the better the calibration effect is). After the gray level image output by the area array detector is converted into the incident radiance image of the satellite area array camera, the radiance L corresponding to each pixelm,nShould be consistent (collectively expressed in L), the camera input radiance inversion formula is:
the average DN value obtained by substituting formula (1-4) for formula (1-3) is expressed as follows:
in the formula:
correction coefficient of pixel responsivity
Dark signal correction factor-
Bringing the correction coefficients into equations (1-6) yields a correction function matrix for on-track relative scaling:
and (4) processing the on-orbit image by using the formula (1-7) to obtain an on-orbit relatively radiometric calibrated image.
7. Taking the average value of each column of the image calibrated in the step 6), changing the two-dimensional distribution of the area array image into a one-dimensional curve form, respectively passing the averaged one-dimensional curve through a 101-order median filter subjected to 25-order sampling average smoothing and a 2001-order median filter subjected to 51-order sampling average smoothing to obtain two curves, wherein the difference between the two curves forms a new curve, the absolute value of the new curve reflects the strip condition of the image calibrated, each peak of the new curve represents a strip, and if the new curve has more than 3 obvious peaks, the image calibrated in the step 6) does not meet the requirement and needs to be calibrated again.
Based on the concept of on-orbit relative scaling of satellite attitude adjustment, a uniform target is generated for an area array optical camera acquiring earth surface information from an orbit. The purpose of generating a uniform target is that each detector element of the area array optical camera can receive the same radiance. After the satellite attitude is adjusted, each detection pixel of the satellite area-array optical camera images the same ground target by rotating the satellite, and the on-orbit relative calibration can be carried out as long as the ground has a small uniform field without using a special ground calibration field. The technique improves the conventional scaling method to reduce banding in the image, resulting in an image superior to the non-uniformity correction, which can be used as a criterion for calculating relative gain.
The method makes full use of the capability of adjusting the yaw attitude of the satellite platform, and conveniently realizes the in-orbit relative radiation calibration of the satellite area array optical camera; the invention adopts the imaging mode of satellite attitude adjustment, greatly reduces the coverage area of ground imaging, ensures the uniformity of ground scenes, and reduces the dependence of on-orbit relative calibration on a special calibration field;
the invention adopts an optimized relative calibration algorithm, uses a matrix model, takes account of the programmability of the imaging model and the calibration algorithm of the satellite optical camera, overcomes the jump of splicing the focal plane array of the area array optical camera, and has stronger practicability to the on-orbit relative calibration of the satellite area array optical camera; the invention can make the relative calibration of the orbit satellite develop from the previous one year or several times into the calibration mode (once per week or twice per month) of the business normalization.
The invention selects a uniform earth surface as shown in fig. 1, and ensures that the unilateral length of a uniform scene is greater than the projection N of a satellite area array optical camera on the ground as shown in fig. 2. Imaging parameter setting, wherein before satellite attitude adjustment, the imaging parameter setting of all detectors of a focal plane is required to be consistent, and if a full-color CCD is set to be uniform exposure time and gain; the satellite images the uniform dark target (such as the sea, a calm lake surface and the like), the DN value (gray value) of the image is counted, and the average DN value is taken as the dark signal of the system
And adjusting the satellite attitude to enable the projection of the detector of the optical area array optical camera on the ground to rotate by 90 degrees, as shown in figure 2, so that the long side direction of the detector is consistent with the flight direction. On the ground after attitude adjustmentThe projection length N is far less than M, when the uniform earth surface is selected for the on-orbit relative calibration test, all pixels of the area array optical camera can be covered by a small ground scene, and the method is particularly favorable for the wide-view-field space optical camera.
After the satellite attitude is adjusted, each pixel of the detector sequentially images the same ground object, the obtained image is 45 degrees, and the imaging relation is shown in figure 3. Because the posture adjustment imaging time period is short, the gray values of the same ground object in different probe cells are considered to be the result of the inconsistency of the probe cell response;
image processing after posture adjustment, wherein in order to obtain the imaging of the detector under the same ground object, the image is adjusted line by line and the gray value DN of the first line and the first column of image is used1,1For reference, correcting the images inclined by 45 degrees into the same horizontal line, so that the same ground object is approximately on the same horizontal line, as shown in formula (1-1);
relative calibration, namely performing on-track relative calibration processing on the 45-degree leveled image, processing according to formulas (1-2) to (1-7), calculating to obtain a correction coefficient of the responsivity of each pixel and a dark signal correction value, and performing on-track relative calibration correction on each pixel;
the relative scaling expression of the satellite area array optical camera is as follows:
in the formula:
in laboratory calibration, the DN value of each pixel is calculated under the same radiance, and the gray level average value of all pixels is obtained
Then, under different brightness points, the gray average value of all CCD pixels is calculated, and the functional relation between the average gray value and the radiance is expressed by a least square method as follows:
in the formula:
step 3, the medium satellite images the uniform dark target (such as the sea, the calm lake surface and the like), and statistics is carried out
Taking the average value of each pixel as the on-track relative calibration dark signal value
The satellite attitude is adjusted to image the uniform target, and the radiation illumination of each pixel is consistent (the more uniform the ground object target is, the better the calibration effect is). After the gray level image output by the detector is converted into the incident radiance image of the satellite area array optical camera, the radiance L corresponding to each pixelm,nShould be consistent (collectively expressed in L), the camera input radiance inversion formula is:
the average DN value obtained by substituting formula (1-4) for formula (1-3) is expressed as follows:
in the formula:
correction coefficient of pixel responsivity
Dark signal correction factor-
Bringing the correction coefficients into equations (1-6) yields a correction function matrix for on-track relative scaling:
and (4) processing the on-orbit image by using the formula (1-7) to obtain an on-orbit relatively radiometric calibrated image.
The pixel responsivity correction coefficient and the dark signal correction coefficient obtained by the calibration method can not adapt to all ground scene processing, and banding phenomenon can be clearly observed from images when uniform scenes such as water with low radiation value, rainforest with medium radiation value and desert, snow and cloud layer with high radiation value are imaged. Relative radiation correction evaluation needs to be carried out on the image after calibration processing, the condition of strips of the image after calibration is counted, and whether the pixel response and the dark signal correction value of the satellite detector need to be recalibrated or not is determined according to the counting result of the strips;
in the strip evaluation of the invention, the row average of the selected evaluation image is selected, and the averaged image respectively passes through a 101-order median filter which is subjected to 25-order sampling average smoothing and a 2001-order median filter which is subjected to 51-order sampling average smoothing to obtain two curves. The latter filter removes spikes and streaks in the image. The absolute value of the difference between the two curves reflects the banding of the entire image, where the peak of the curve represents an individual band. The band evaluation values of the entire image are averaged over all individual bands.
And the evaluated pixel responsivity correction coefficient and the evaluated dark signal correction coefficient are used as on-track relative radiation correction coefficients for subsequent on-track image processing, and the on-track image processing needs to be subjected to strip evaluation again without strip evaluation to meet strip evaluation conditions, so that radiometric calibration is finally realized.
The invention has not been described in detail in part of the common general knowledge of those skilled in the art.
Claims (10)
1. An in-orbit relative radiation calibration method of an area-array camera based on satellite attitude adjustment is characterized by comprising the following steps:
1) before the attitude adjustment of the satellite is carried out on the ground imaging, the imaging parameters of the area array detector of the satellite need to be set consistently;
2) selecting a ground uniform dark target which can be covered by a plurality of lines of satellite imaging;
3) the method comprises the steps that a satellite performs attitude adjustment under the condition that a uniform dark target can be covered by multiple satellite imaging lines, the satellite turns a satellite yaw angle from 0 degree to 90 degrees through attitude control, the long edge direction of a satellite area array detector is consistent with the satellite flight direction, imaging is performed on the ground, an image of the uniform dark target is obtained, the DN value of the image is counted, and the average DN value is taken as a system dark signal
A value of (d); DN value is gray value;
4) the satellite keeps a posture with a yaw angle of 90 degrees, the long side direction of the satellite area array detector is consistent with the flight direction of the satellite, and under the condition, ground imaging is carried out to obtain a ground image; the yaw angle of the satellite returns to 0 degree from 90 degrees through attitude control, namely the satellite returns to the normal attitude;
5) carrying out image processing on the ground images obtained in the step 4) to enable the same ground object to be on the same horizontal line;
6) performing on-orbit relative calibration on the image processed in the step 5) to obtain a correction coefficient of the responsivity of each pixel of the area array detector and a correction coefficient of a system dark signal; obtaining a calibrated image according to a correction coefficient of the responsivity of each pixel of the area array detector and a correction coefficient of a system dark signal;
7) judging whether the image after calibration obtained in the step 6) has banding phenomenon, if so, judging whether recalibration is needed according to set banding evaluation conditions, if so, returning to the step 4), and otherwise, judging that the image after calibration in the step 6) meets the requirements.
2. The in-orbit relative radiation calibration method for the area-array camera based on satellite attitude adjustment, according to claim 1, is characterized in that: satellite image multi-line coverage means: the length of the single side of the uniform field is greater than that of the narrow side of the area array of the satellite area array optical camera.
3. The in-orbit relative radiation calibration method for the area-array camera based on satellite attitude adjustment, according to claim 1, is characterized in that: the imaging parameter setting of the area array detector of the satellite is consistent, and the method comprises the following steps: and setting each pixel of the area array detector to be uniform exposure time and gain.
4. The in-orbit relative radiation calibration method for the area-array camera based on satellite attitude adjustment, according to claim 1, is characterized in that: the area array detector is a full-color CCD.
5. The in-orbit relative radiation calibration method for the area-array camera based on satellite attitude adjustment, according to claim 1, is characterized in that: the uniform dark targets are specifically: the uniform dark objects do not overlap with the uniform scene.
6. The in-orbit relative radiation calibration method for the area-array camera based on satellite attitude adjustment, according to claim 1, is characterized in that: a uniform dark target comprising: ocean, calm lake surface.
7. The in-orbit relative radiation calibration method for the area-array camera based on satellite attitude adjustment, according to claim 1, is characterized in that: the area array camera of the satellite comprises an area array detector, electronic equipment and an optical machine main body, wherein the area array detector can sense light and convert scenery shot by the area array camera of the satellite into a digital signal; the electronic equipment is used for supplying power to the area array camera, controlling the camera and processing image information; the optical machine main body consists of the structure of the area-array camera and an optical lens.
8. The in-orbit relative radiation calibration method for the area-array camera based on satellite attitude adjustment, according to claim 1, is characterized in that: the area array detector is rectangular, the rectangle is 7920 multiplied by 6144, 7920 multiplied by 6144 shows that the long side of the area array is 7920 pixel, and the short side of the area array is 6144 pixel.
9. The in-orbit relative radiation calibration method for the area-array camera based on satellite attitude adjustment, according to claim 1, is characterized in that: the strip evaluation conditions were specifically: selecting the image calibrated in the step 6) as an evaluated image, taking the column average of the evaluated image, and respectively passing the image after the column average through a 101-order median filter subjected to 25-order sampling average smoothing and a 2001-order median filter subjected to 51-order sampling average smoothing to obtain two curves, wherein the absolute value of the difference between the two curves reflects the band condition of the whole image; and if the difference between the two curves meets the requirement, judging that the strip evaluation condition is met, otherwise, judging that the strip evaluation condition is not met.
10. The in-orbit relative radiation calibration method for the area-array camera based on satellite attitude adjustment, according to claim 1, is characterized in that: step 2) selecting a ground uniform dark target which can be covered by a plurality of lines of satellite imaging, and specifically comprises the following steps: when the satellite area-array camera images the ground once, the size of the area of primary imaging is equal to the size of the projection area of the effective size of the detector of the satellite area-array camera on the ground, a dark target area with uniform ground is selected, the area is imaged, calm lake water or sea surface is selected, and the size of the area of the satellite imaging on the ground once can be covered by the selected shooting area.
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| CN111397730A (en) * | 2019-12-31 | 2020-07-10 | 中国科学院合肥物质科学研究院 | Optical camera wide-spectrum relative radiation calibration method based on L ED light source |
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| CN112150555B (en) * | 2020-08-27 | 2024-02-09 | 北京空间机电研究所 | On-orbit relative radiation calibration method for geosynchronous orbit area array camera |
| CN112529810A (en) * | 2020-12-15 | 2021-03-19 | 北京空间机电研究所 | Detection signal-to-noise ratio improving method of area array staring camera |
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