CN113936065A - Remote sensing camera radiometric calibration method, system, device and medium based on fixed star source - Google Patents
Remote sensing camera radiometric calibration method, system, device and medium based on fixed star source Download PDFInfo
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Abstract
The invention discloses a method, a system, a device and a medium for radiometric calibration of a remote sensing camera based on a fixed star source, wherein the method comprises the following steps: determining a first full width half maximum of the star point image and determining a first star point target; performing radiation measurement on the first star point target by a PRF fitting measurement method and an aperture photometry method to obtain a first radiation measurement value and a second radiation measurement value; when the difference value of the first radiation measurement value and the second radiation measurement value exceeds a preset second threshold value range, a first residual image is determined according to a star image model and a star point image obtained by a PRF fitting measurement method, radiation measurement is carried out on the first residual image through an aperture photometry method to obtain a third radiation measurement value, the first radiation measurement value is corrected to obtain a first point response function, and absolute radiation calibration is carried out on a laboratory star point target and an on-orbit star point target according to the first point response function. The invention improves the accuracy and efficiency of radiometric calibration of the remote sensing camera, and can be widely applied to the technical field of radiometric calibration of remote sensing systems.
Description
Technical Field
The invention relates to the technical field of radiometric calibration of remote sensing systems, in particular to a radiometric calibration method, a radiometric calibration system, a radiometric calibration device and a radiometric calibration medium for a remote sensing camera based on a fixed star source.
Background
Radiometric calibration of an infrared remote sensing camera requires realization of non-uniformity correction (relative radiometric calibration) of infrared camera response, establishment of a relationship (absolute radiometric calibration) between a remote sensor output signal value and an input energy value, and has become a necessary link and trend of quantitative remote sensing. The former is an intermediate link of radiometric calibration, and the latter is a final target of radiometric calibration. The infrared remote sensing camera not only needs to accurately calibrate the radiation characteristic before emission (laboratory radiometric calibration), but also needs to calibrate and correct the response change of the infrared remote sensing camera caused by various factors after the on-orbit operation, which is called on-orbit radiometric calibration. On-orbit radiometric calibration generally adopts schemes such as external calibration black body radiation source, ground field calibration source or radiometric calibration based on fixed star source. Aiming at the defects of the existing calibration equipment and calibration method in radiometric calibration of a High Dynamic Range (HDR) infrared remote sensing camera, the HDR infrared remote sensing camera radiometric calibration method combining an internal calibration black body and a fixed star map becomes one of the current international new development directions.
The premise of radiometric calibration is accurate radiometry, in the prior art, usually, an aperture photometry and a Point Response Function (PRF) fitting measurement method are adopted to perform radiometry of a star source, and a system error is introduced during PRF fitting measurement, mainly an error caused by deviation of a used PRF model and a true value (model), and such an error is a dominant error in PRF fitting measurement of a bright star source, but the PRF fitting method gives consideration to radiant flux at each position of a star image, and total radiant flux of the star body is also a fitting parameter, so that the PRF fitting method can better correct the omission of radiant flux when a fitting area is small, namely, the accuracy of a dark and weak target is high. For a dark star source, in order to avoid a missing error caused by a small aperture and an image random error introduced by a large aperture as much as possible, the aperture photometry needs to finely adjust the aperture size to obtain an error similar to the PRF fitting method, which is difficult to realize in actual engineering processing, so that an error caused by star radiation flux missing can be introduced by the aperture photometry; the dominant error is usually due to the background noise of the star image, as measured by the PRF fitting method for a scotopic star source.
From the above, the existing aperture photometry has low measurement accuracy for dark and weak targets, and the PRF fitting measurement method has low measurement accuracy for bright star sources, which all affects the radiometric calibration accuracy of the remote sensing camera, and the PRF fitting measurement method requires a large number of star sources, is complex to operate, and has low efficiency.
Interpretation of terms:
PRF fitting measurement: the point response function fitting measurement method proposed by american scholarson and Ivan r.king (hereinafter referred to as a & K) is used for astronomical observation and celestial body measurement of loads such as a Wide Field Camera (WF) of a harbour telescope, a second generation Wide Field Camera (WFPC 2) of a Wide Field Camera, a scholar space telescope, and the like.
Disclosure of Invention
The present invention aims to solve at least to some extent one of the technical problems existing in the prior art.
Therefore, an object of an embodiment of the present invention is to provide an adaptive aperture point response function determining method (AA & PRF method) for radiometric calibration of a remote sensing camera based on a fixed star source, which fully utilizes respective advantages of a PRF fitting measurement method and an aperture photometry, overcomes the disadvantage that the PRF fitting measurement method requires a large number of fixed star sources for fitting calculation, and improves precision and efficiency of radiometry, thereby improving precision and efficiency of radiometry of the remote sensing camera, and providing a basis for development of a high-precision high-dynamic radiometry calibration technique of an on-orbit infrared remote sensing camera.
Another object of the embodiments of the present invention is to provide a radiometric calibration system for a remote sensing camera based on a star source.
In order to achieve the technical purpose, the technical scheme adopted by the embodiment of the invention comprises the following steps:
in a first aspect, an embodiment of the present invention provides a radiometric calibration method for a remote sensing camera based on a fixed star source, including the following steps:
determining a first full width half maximum of a star point image, and determining a first star point target according to the first full width half maximum and a preset first threshold range;
carrying out radiation measurement on the first star point target by a PRF fitting measurement method to obtain a first radiation measurement value, and carrying out radiation measurement on the first star point target by an aperture photometry method to obtain a second radiation measurement value;
when the difference value of the first radiation measurement value and the second radiation measurement value exceeds a preset second threshold value range, determining a first residual image according to a star image model obtained by a PRF fitting measurement method and the star point image, and then performing radiation measurement on the first residual image by an aperture photometry method to obtain a third radiation measurement value;
and correcting the first radiation measurement value according to the third radiation measurement value to obtain a first point response function, and further performing absolute radiation calibration on a laboratory star point target and an on-orbit star point target according to the first point response function.
Further, in an embodiment of the present invention, the step of determining a first full width half maximum of the star point image, and determining a first star point target according to the first full width half maximum and a preset first threshold range specifically includes:
shooting by a remote sensing camera to obtain a star point image, and determining the first full width half maximum of the star point image;
the method comprises the steps of obtaining a preset first threshold range, and determining a star point target corresponding to a first full width half maximum which does not meet the first threshold range as a first star point target.
Further, in an embodiment of the present invention, the step of obtaining a first radiation measurement value by performing radiation measurement on the first star point target through a PRF fitting measurement method specifically includes:
determining grid points of each grid of the PRF grid point model, and determining PRF values of the grid points to obtain a PRF grid point model;
and carrying out radiation measurement on the first star point target through the PRF grid point model to obtain a first radiation measurement value.
Further, in an embodiment of the present invention, the step of obtaining a second radiation measurement value by performing radiation measurement on the first star point target through aperture photometry specifically includes:
determining a first round hole surrounding the first star point target, and measuring first brightness of each pixel in the first round hole;
determining a first circular ring area on the outer side of the first circular hole, and determining the average brightness of pixels in the first circular ring area;
and determining the second radiation measurement value according to the first brightness, the average brightness and the number of pixels in the first round hole.
Further, in an embodiment of the present invention, the step of determining a first residual image according to the star image model and the star point image obtained by the PRF fitting measurement method, and then performing a radiation measurement on the first residual image by using an aperture photometry method to obtain a third radiation measurement value specifically includes:
obtaining a star image model obtained by a PRF fitting measurement method, and deducting the star image model from the star point image to obtain a first residual image;
and determining a second round hole according to the aperture when the photometric signal-to-noise ratio is maximum, and then carrying out radiometry on the first residual image according to the second round hole by using an aperture photometry method to obtain a third radiometric value.
Further, in an embodiment of the present invention, the step of performing absolute radiometric calibration on the laboratory star point target according to the first point response function specifically includes:
carrying out non-uniform correction on the first gray level image of the laboratory star point target to obtain a second gray level image;
converting the second gray image into a first brightness image, and removing a background image of the first brightness image to obtain a second brightness image;
normalizing the first point response function, and further constructing an optimization objective function according to the normalized first point response function and the second brightness image;
and performing iterative optimization on the optimization objective function to obtain first radiance, and further determining the first irradiance of the laboratory star point target at the camera entrance pupil according to the first radiance.
Further, in an embodiment of the present invention, the step of performing absolute radiometric calibration on the on-orbit star point target according to the first point response function specifically includes:
carrying out non-uniform correction on an original star map of an on-orbit star point target to obtain a first star map;
performing radiance conversion on the first star map according to an absolute calibration coefficient obtained in a laboratory to obtain a second star map;
removing the background of the second star map to obtain a background-free target star map;
processing the background-free target star map through a point target extraction algorithm, determining a brightness value at the entrance pupil of the camera corresponding to the radiation of the standard star, and further determining a second irradiance of the standard star at the entrance pupil of the camera according to the brightness value at the entrance pupil of the camera;
determining the actual irradiance of the standard fixed star at the entrance pupil of the camera according to the distance between the standard fixed star and the remote sensing camera;
determining an on-orbit absolute calibration correction factor of the remote sensing camera according to the actual irradiance and the second irradiance;
and correcting the absolute calibration equation according to the on-orbit absolute calibration correction factor.
In a second aspect, an embodiment of the present invention provides a system for radiometric calibration of a remote sensing camera based on a fixed star source, including:
the star point target determining module is used for determining a first full width half maximum of a star point image and determining a first star point target according to the first full width half maximum and a preset first threshold range;
the first radiometric module is used for carrying out radiometric measurement on the first star point target by a PRF fitting measurement method to obtain a first radiometric value, and carrying out radiometric measurement on the first star point target by an aperture photometry method to obtain a second radiometric value;
the second radiation measurement module is used for determining a first residual image according to a star image model obtained by a PRF fitting measurement method and the star point image when the difference value of the first radiation measurement value and the second radiation measurement value exceeds a preset second threshold range, and then performing radiation measurement on the first residual image through an aperture photometry method to obtain a third radiation measurement value;
and the radiometric calibration module is used for correcting the first radiometric value according to the third radiometric value to obtain a first point response function, and further performing absolute radiometric calibration on the laboratory star point target and the on-orbit star point target according to the first point response function.
In a third aspect, an embodiment of the present invention provides a radiometric calibration apparatus for a remote sensing camera based on a fixed star source, including:
at least one processor;
at least one memory for storing at least one program;
the at least one program, when executed by the at least one processor, causes the at least one processor to implement a method of radiometric camera based on a star source as described above.
In a fourth aspect, embodiments of the present invention also provide a computer-readable storage medium, in which a processor-executable program is stored, the processor-executable program, when executed by a processor, is configured to perform a method for radiometric calibration of a remote sensing camera based on a star source as described above.
Advantages and benefits of the present invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention:
according to the embodiment of the invention, a star source is used as a radiometric calibration standard, an aperture photometry method for measuring star light by using the physics of celestial bodies is used for reference, a star image model obtained by Point Response Function (PRF) fitting is deducted from an original star point image, a residual image is obtained, and aperture radiometry is carried out on the residual image in a central area, so that the aperture radiometry is used as correction of a PRF fitting radiometric value and is used for carrying out absolute radiometric calibration on a subsequent laboratory star point target and an on-orbit star point target. The embodiment of the invention fully utilizes the respective advantages of the PRF fitting measurement method and the aperture photometry, overcomes the defect that the PRF fitting measurement method needs a large number of fixed star sources for fitting calculation, and improves the accuracy and efficiency of radiometry, thereby improving the accuracy and efficiency of radiometric calibration of the remote sensing camera and providing a basis for the development of high-accuracy and high-dynamic radiometric calibration technology of the on-orbit infrared remote sensing camera.
Drawings
In order to more clearly illustrate the technical solution in the embodiment of the present invention, the following description is made on the drawings required to be used in the embodiment of the present invention, and it should be understood that the drawings in the following description are only for convenience and clarity of describing some embodiments in the technical solution of the present invention, and it is obvious for those skilled in the art that other drawings can be obtained according to these drawings without creative efforts.
FIG. 1 is a flowchart illustrating steps of a radiometric calibration method for a remote sensing camera based on a fixed star source according to an embodiment of the present invention;
fig. 2 is a schematic gray scale value diagram of a star point image, a star image model and a first residual image according to an embodiment of the present invention;
FIG. 3 is a specific flowchart of absolute radiometric calibration of a laboratory star target according to an embodiment of the present invention;
fig. 4 is a specific flowchart of the on-orbit star target absolute radiometric calibration provided in the embodiment of the present invention;
FIG. 5 is a block diagram of a radiometric calibration system of a remote sensing camera based on a fixed star source according to an embodiment of the present invention;
fig. 6 is a block diagram of a structure of a radiometric calibration device of a remote sensing camera based on a star source according to an embodiment of the present invention.
Detailed Description
Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like or similar reference numerals refer to the same or similar elements or elements having the same or similar function throughout. The embodiments described below with reference to the accompanying drawings are illustrative only for the purpose of explaining the present invention, and are not to be construed as limiting the present invention. The step numbers in the following embodiments are provided only for convenience of illustration, the order between the steps is not limited at all, and the execution order of each step in the embodiments can be adapted according to the understanding of those skilled in the art.
In the description of the present invention, the meaning of a plurality is two or more, if there is a description to the first and the second for the purpose of distinguishing technical features, it is not understood as indicating or implying relative importance or implicitly indicating the number of indicated technical features or implicitly indicating the precedence of the indicated technical features. Furthermore, unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art.
Referring to fig. 1, an embodiment of the present invention provides a radiometric calibration method for a remote sensing camera based on a fixed star source, which specifically includes the following steps:
s101, determining a first full width half maximum of a star point image, and determining a first star point target according to the first full width half maximum and a preset first threshold range.
Specifically, the full width at half maximum (FWHM) of a star point image is judged, a PRF fitting measurement method is still directly adopted to perform radiation measurement on a star point target with weak brightness (for example, FWHM is 2-3 pixels), and radiation measurement is performed on other star point targets by adopting the improved PRF fitting measurement method (called AA & PRF fitting method) provided by the embodiment of the invention. Step S101 specifically includes the following steps:
s1011, shooting by a remote sensing camera to obtain a star point image, and determining the first full width half maximum of the star point image;
s1012, acquiring a preset first threshold range, and determining a star point target corresponding to a first full width half maximum which does not meet the first threshold range as a first star point target.
Specifically, the first threshold range may be set to 2 to 3 pixels, a star target meeting the threshold range is directly measured by using a PRF fitting measurement method and subjected to a subsequent absolute radiometric calibration procedure, and a star target exceeding the threshold range (i.e., the first star target) is subjected to radiometric measurement by using a subsequent aperture photometry and a PRF fitting measurement method, and is corrected according to the result.
S102, carrying out radiation measurement on the first star point target through a PRF fitting measurement method to obtain a first radiation measurement value, and carrying out radiation measurement on the first star point target through an aperture photometry method to obtain a second radiation measurement value.
Specifically, the first star point target is processed by an aperture photometry method and a PRF fitting measurement method respectively, when the difference between the measurement results of the aperture photometry method and the PRF fitting measurement method exceeds a set threshold value, the AA & PRF fitting method provided by the embodiment of the invention is processed, and when the difference between the measurement results of the aperture photometry method and the PRF fitting measurement method does not exceed the set threshold value, the PRF fitting measurement method is still used for processing.
As a further optional implementation manner, the step of obtaining the first radiation measurement value by performing radiation measurement on the first star point target by using a PRF fitting measurement method specifically includes:
a1, determining grid points of each grid of the PRF grid point model, and determining PRF values of the grid points to obtain a PRF grid point model;
a2, carrying out radiation measurement on the first star point target through the PRF grid point model to obtain a first radiation measurement value.
Specifically, the process of establishing the PRF grid point model is as follows: on the premise of knowing the initial values of the point target position and the flux, sampling is carried out according to the central position of 25 (namely 5 multiplied by 5) pixels of the sampling point, a rectangular coordinate system is reestablished on the assumption that the central point of the point target is taken as the origin, the gray data obtained by 25 sampling points are established into a numerical relationship based on a new coordinate system, so that 25 PRF numerical values can be obtained, and a two-dimensional PRF model is established by using the new coordinate system.
In order to obtain a more accurate PRF grid point model, the data processing will adopt a method of "sampling grid + PRF iteration". The grid is further subdivided, for example by subdividing each grid into 4 equal divisions of 21 x 21 grid points. In order to avoid errors caused by other factors such as cosmic rays and the like, an iterative method is adopted to solve the PRF value of the grid point and establish a PRF grid point model. This procedure of establishing mesh points can be summarized as:
1) for each grid point, a set of all sample points within a square range centered on the grid point and having r in the vertical and horizontal directions is obtained. And taking the average value of the PRF values of all the sampling points in the set as the PRF value of the grid point.
2) And for a set of sampling points near each grid point, solving the residual error of the numerical value of each sampling point in the set and the numerical value of the current PRF grid point of the sampling point, and eliminating the sampling points with the variance larger than 2.5 times relative to the average residual error. The iterative process ends until there are no sample points to cull for all grid points.
After obtaining the PRF mesh model, the grid point values in the model are smoothed, and unlike the empirical value smoothing template based on the star source adopted by WFPC2, the embodiment of the present invention adopts the gaussian template as the smoothing template. If the infrared remote sensing system corresponds to a target through actual measurement and a smooth template measured by the system is obtained, the Gaussian template can be replaced.
As a further optional implementation manner, the step of performing radiation measurement on the first star point target by using aperture photometry to obtain a second radiation measurement value specifically includes:
b1, determining a first round hole surrounding the first star point target, and measuring the first brightness of each pixel in the first round hole;
b2, determining a first circular ring area at the outer side of the first circular hole, and determining the average brightness of the picture elements in the first circular ring area;
and B3, determining a second radiation measurement value according to the first brightness, the average brightness and the number of the pixels in the first round hole.
In particular, aperture photometry (aperture photometry) is still widely applied to current astronomical physical research as a classical photometry method in astronomy, and a lot of results are obtained. When one star is an isolated star or is in an evacuated star field and appears to be completely separated from other celestial bodies in the image (e.g., stars in an evacuated constellation), an aperture photometry method can be used. The basic principle of aperture photometry is: taking an aperture on the formed star image to surround a star source image, wherein the aperture center (star image center) is given by astronomy measurement based on a celestial coordinate system, the aperture is larger than a point spread function of an infrared remote sensing camera, and the brightness or output data of all pixels in the aperture is measured; if it is notIf there is no other object outside the aperture, a circular area is taken outside the aperture, and the average brightness of the pixels is measured as the background radiation brightness LB. The total brightness L in the circular apertureAMinus the number of pixels in the circle NAWith background radiance LBThe product of the two is the output L of the corresponding starS. The correlation formula is as follows:
LS≡LA-NA×LB
s103, when the difference value of the first radiometric value and the second radiometric value exceeds a preset second threshold range, determining a first residual image according to a star image model and a star point image obtained by a PRF fitting measurement method, and then performing radiometric measurement on the first residual image by an aperture photometry method to obtain a third radiometric value.
As a further optional implementation manner, the method includes the steps of determining a first residual image according to a star image model and a star point image obtained by a PRF fitting measurement method, and then performing radiation measurement on the first residual image by using an aperture photometry method to obtain a third radiation measurement value, and specifically includes:
c1, obtaining a star image model obtained by a PRF fitting measurement method, and deducting the star image model from the star point image to obtain a first residual image;
and C2, determining a second round hole according to the aperture when the photometric signal-to-noise ratio is maximum, and then performing radiometry on the first residual image according to the second round hole by using an aperture photometry method to obtain a third radiometry value.
Specifically, the AA & PRF fitting method of the embodiment of the present invention specifically is: the method comprises the steps of firstly obtaining a PRF fitting radiometric value of a fixed star source based on a PRF fitting measurement method, then deducting a star image model obtained through fitting from an original image to obtain a residual image (namely a first residual image), carrying out radiation measurement based on an aperture photometry on the residual image in the star central area by using a smaller self-adaptive aperture, and using the value as the correction of the PRF fitting photometric value. As shown in fig. 2, which is a schematic diagram of gray values of a star point image, a star image model, and a first residual image provided in the embodiment of the present invention, it can be understood that after the star image model is obtained by fitting, gray values of pixel points corresponding to the star image model are subtracted from an original star point image, so as to obtain gray values of the first residual image. In practical operation, the aperture photometry method selects the aperture with the largest photometry signal-to-noise ratio as the best aperture for measurement, and the adaptive window in the embodiment of the present invention selects the same size as the FWHM, because the FWHM value is initially calculated in the embodiment of the present invention, the aperture size can be dynamically changed adaptively according to the target FWHM parameters.
S104, correcting the first radiation measurement value according to the third radiation measurement value to obtain a first point response function, and further performing absolute radiation calibration on the laboratory star point target and the on-orbit star point target according to the first point response function.
Specifically, the radiometric method is generally used for star photometric measurement, for example, a photometric method for astronomical physics is used for researching stars in a star constellation, and is commonly used for platforms such as an astronomical telescope or a space astronomical telescope.
As a further optional implementation manner, the step of performing absolute radiometric calibration on the laboratory star point target according to the first point response function specifically includes:
d1, carrying out non-uniform correction on the first gray level image of the laboratory star point target to obtain a second gray level image;
d2, converting the second gray image into a first brightness image, and removing a background image of the first brightness image to obtain a second brightness image;
d3, performing normalization processing on the first point response function, and further constructing an optimization objective function according to the first point response function and the second brightness image after the normalization processing;
d4, performing iterative optimization on the optimization objective function to obtain first radiance, and further determining the first irradiance of the laboratory star point target at the camera entrance pupil according to the first radiance.
Specifically, in order to implement the absolute radiometric calibration of the remote sensing camera based on the fixed star source, a test experiment process needs to be designed in advance, and as shown in fig. 3, a specific flowchart of the absolute radiometric calibration of the laboratory star target provided by the embodiment of the present invention, that is, a flow of extracting response of the laboratory star target irradiance is specifically as follows:
1) and aligning the camera to the extended flat light source module through the channel switching module, performing corresponding absolute radiometric calibration according to the determined relative radiometric calibration method, and turning to the step 2) if a relative radiometric calibration method of two-point correction is adopted, or turning to the step 3) if a relative radiometric calibration method of sectional correction is adopted.
2) The two-point calibration requires two temperature calibration points to determine the absolute radiometric calibration coefficient of the camera, and the absolute radiometric calibration equation is obtained by solving the absolute radiometric calibration coefficient:
3) for the sectional correction scheme, the number of sections of absolute radiometric calibration of the infrared remote sensing camera and the selection of the sectional calibration points are completely the same as those of relative radiometric calibration, and the radiance absolute radiometric calibration is carried out on each section by using the formula.
4) For the absolute radiometric calibration coefficient of the infrared remote sensing camera obtained in the steps 2) and 3), the conversion from radiance absolute radiometric calibration to irradiance absolute radiometric calibration is realized through an AA & PRF fitting method based on a star point target: the obtained point response function is first normalized, i.e. satisfies the following equation:
In the above formula, HaIs a measured PRF function, H'aIs a normalized PRF function; then, converting the gray level image into a brightness image by using the absolute calibration result of the radiance, and carrying out background removal and candidate point target judgment; finally, H 'is used'aAn optimization objective function is constructed for the image (brightness image for short) after the background is removed:
in the above formula, x2Representing the optimization objective function, djRepresents the corresponding luminance value on the luminance image, σ represents the noise estimate in the vicinity of the point target, (x)i,yi) Representing the point object to be extracted. Solving and making the equation of the Chi through an optimization method2Minimizing the corresponding star target center position (ε, η) and the radiance L after actual solid angle normalizationaFurther according to AA&The self-adaptive aperture range of the PRF fitting method corrects the measured radiance value, and finally the irradiance of the star point target at the entrance pupil can be obtained by calculation:
the absolute radiometric calibration of the infrared remote sensing camera of the laboratory star point target can be completed.
As a further optional implementation manner, the step of performing absolute radiometric calibration on the on-orbit star point target according to the first point response function specifically includes:
e1, carrying out non-uniform correction on the original star map of the on-orbit star point target to obtain a first star map;
e2, performing radiance conversion on the first star map according to the absolute calibration coefficient obtained in the laboratory to obtain a second star map;
e3, removing the background of the second star map to obtain a background-free target star map;
e4, processing the background-free target star map through a point target extraction algorithm, determining a brightness value at the entrance pupil of the camera corresponding to the radiation of the standard star, and further determining a second irradiance of the standard star at the entrance pupil of the camera according to the brightness value at the entrance pupil of the camera;
e5, determining the actual irradiance of the standard stars at the entrance pupil of the camera according to the distance between the standard stars and the remote sensing camera;
e6, determining an on-orbit absolute calibration correction factor of the remote sensing camera according to the actual irradiance and the second irradiance;
and E7, correcting the absolute scaling equation according to the on-track absolute scaling correction factor.
Specifically, on-orbit star point target absolute radiometric calibration provides key data support for on-orbit target detection and measurement and other star point target radiometric measurement methods, and provides diagnostic data for long-time scale system load on-orbit state monitoring. Fig. 4 is a specific flowchart of the on-orbit star target absolute radiometric calibration provided in the embodiment of the present invention, and the specific flowchart is as follows:
(1) according to a system instruction, the camera enters an absolute radiometric calibration state, and a pointing mechanism is controlled to enable the camera to be tested to be aligned to a target starry sky (an area where a calibration fixed star is located is screened);
(2) detecting the working temperature state of each device to enable the working temperature state to meet the normal working requirement value, and recording;
(3) judging whether the target starry sky is aligned or not, acquiring an image of the target starry sky, and recording an output signal value of a detector;
(4) correcting the detector output signal value obtained in step (3) using the obtained relative calibration result;
(5) performing radiance conversion on the corrected detector output signal by using a laboratory absolute calibration result to obtain a radiance numerical image containing a target star point, wherein the image pixel value unit is the same as the radiance unit;
(6) performing background removal operation on the brightness numerical value image to obtain a background-free target star map;
(7) extracting the calibration fixed star by using a point target extraction algorithm to obtain the radiance value of the calibration fixed star at the entrance pupil (namely, carrying out template matching on a point response function obtained by a laboratory or an on-orbit actually measured point response function and a background-free target star map to extract a candidate star point target);
(8) calculating the product of the effective solid angle of the detector unit calibrated by the laboratory and the radiance to obtain the irradiance E of the standard star at the entrance pupil of the cameratest；
(9) Repeating the steps (1) to (8), carrying out n times of repeated measurement on the standard star, and calculating the evaluation value of the n times of repeated measurement
(10) Obtaining the actual irradiance E of the calibration fixed star at the entrance pupil of the camera according to the distance between the calibration fixed star and the camera to be measuredtrue；
(11) Calculating on-orbit absolute calibration correction factor of camera
(12) Absolute calibration equation of correction camera as Lcorrect＝k·Le＝k(aVc+b)。
The absolute radiometric calibration of the infrared remote sensing camera of the on-orbit star point target can be completed.
It should be realized that there are differences between the detection target, the orbit working state, etc. of the space astronomical telescope system and the infrared remote sensing camera, and the on-orbit radiation calibration method applied to the high orbit infrared remote sensing camera cannot directly use the space astronomical telescope to process the light measuring method for observing fixed stars, and the embodiment of the invention carries out targeted improvement on the method: the method provides a self-adaptive aperture point response function method (AA & PRF fitting method), fully utilizes the respective advantages of a PRF fitting measurement method and an aperture photometry, overcomes the defect that the PRF fitting measurement method needs a large number of fixed star sources for fitting calculation, and improves the accuracy and efficiency of radiometric measurement, thereby improving the accuracy and efficiency of radiometric calibration of the remote sensing camera, and providing a foundation for the development of high-accuracy and high-dynamic radiometric calibration technology of the on-orbit infrared remote sensing camera. In addition, the existing relative radiometric calibration and absolute radiometric calibration are combined, absolute radiometric calibration of all pixels can be realized, an accurate mapping relation of target image gray scale and target entrance pupil irradiance covering the dynamic range of the whole detector is established, and a technical basis is provided for a point target detection inversion technology of the space-based infrared remote sensing camera.
The two existing radiation measurement methods are all calibrated by utilizing star point sources, the detection target is also a star point target, but the high-orbit infrared remote sensing cameras are different, the AA & PRF method provided by the embodiment of the invention can be adopted to observe a near-earth space target, absolute calibration parameters are corrected, a space target detection point response model under the actual detection condition is optimized and established, and the method has more practical significance to a space target infrared remote sensing system.
Referring to fig. 5, an embodiment of the present invention provides a system for radiometric calibration of a remote sensing camera based on a fixed star source, including:
the star point target determining module is used for determining a first full width half maximum of a star point image and determining a first star point target according to the first full width half maximum and a preset first threshold range;
the first radiometric module is used for carrying out radiometric measurement on the first star point target by a PRF fitting measurement method to obtain a first radiometric value, and carrying out radiometric measurement on the first star point target by an aperture photometry method to obtain a second radiometric value;
the second radiation measurement module is used for determining a first residual image according to a star image model and a star point image obtained by a PRF fitting measurement method when the difference value of the first radiation measurement value and the second radiation measurement value exceeds a preset second threshold range, and then performing radiation measurement on the first residual image through an aperture photometry method to obtain a third radiation measurement value;
and the radiometric calibration module is used for correcting the first radiometric value according to the third radiometric value to obtain a first point response function, and further performing absolute radiometric calibration on the laboratory star point target and the on-orbit star point target according to the first point response function.
The contents in the above method embodiments are all applicable to the present system embodiment, the functions specifically implemented by the present system embodiment are the same as those in the above method embodiment, and the beneficial effects achieved by the present system embodiment are also the same as those achieved by the above method embodiment.
Referring to fig. 6, an embodiment of the present invention provides a radiometric calibration apparatus for a remote sensing camera based on a fixed star source, including:
at least one processor;
at least one memory for storing at least one program;
when executed by the at least one processor, the at least one program causes the at least one processor to implement a method for radiometric calibration of a remote sensing camera based on a star source as described above.
The contents in the above method embodiments are all applicable to the present apparatus embodiment, the functions specifically implemented by the present apparatus embodiment are the same as those in the above method embodiments, and the advantageous effects achieved by the present apparatus embodiment are also the same as those achieved by the above method embodiments.
Embodiments of the present invention also provide a computer-readable storage medium, in which a program executable by a processor is stored, and the program executable by the processor is used for executing the above-mentioned radiometric calibration method for a remote sensing camera based on a star source.
The computer-readable storage medium of the embodiment of the invention can execute the radiometric calibration method of the remote sensing camera based on the fixed star source provided by the embodiment of the method of the invention, can execute any combination implementation steps of the embodiment of the method, and has corresponding functions and beneficial effects of the method.
The embodiment of the invention also discloses a computer program product or a computer program, which comprises computer instructions, and the computer instructions are stored in a computer readable storage medium. The computer instructions may be read by a processor of a computer device from a computer-readable storage medium, and executed by the processor to cause the computer device to perform the method illustrated in fig. 1.
In alternative embodiments, the functions/acts noted in the block diagrams may occur out of the order noted in the operational illustrations. For example, two blocks shown in succession may, in fact, be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order, depending upon the functionality/acts involved. Furthermore, the embodiments presented and described in the flow charts of the present invention are provided by way of example in order to provide a more thorough understanding of the technology. The disclosed methods are not limited to the operations and logic flows presented herein. Alternative embodiments are contemplated in which the order of various operations is changed and in which sub-operations described as part of larger operations are performed independently.
Furthermore, although the present invention is described in the context of functional modules, it should be understood that, unless otherwise stated to the contrary, one or more of the above-described functions and/or features may be integrated in a single physical device and/or software module, or one or more of the functions and/or features may be implemented in a separate physical device or software module. It will also be appreciated that a detailed discussion of the actual implementation of each module is not necessary for an understanding of the present invention. Rather, the actual implementation of the various functional modules in the apparatus disclosed herein will be understood within the ordinary skill of an engineer, given the nature, function, and internal relationship of the modules. Accordingly, those skilled in the art can, using ordinary skill, practice the invention as set forth in the claims without undue experimentation. It is also to be understood that the specific concepts disclosed are merely illustrative of and not intended to limit the scope of the invention, which is defined by the appended claims and their full scope of equivalents.
The above functions, if implemented in the form of software functional units and sold or used as a separate product, may be stored in a computer-readable storage medium. Based on such understanding, the technical solution of the present invention may be embodied in the form of a software product, which is stored in a storage medium and includes instructions for causing a computer device (which may be a personal computer, a server, or a network device) to execute all or part of the steps of the above method according to the embodiments of the present invention. And the aforementioned storage medium includes: a U-disk, a removable hard disk, a Read-Only Memory (ROM), a Random Access Memory (RAM), a magnetic disk or an optical disk, and other various media capable of storing program codes.
The logic and/or steps represented in the flowcharts or otherwise described herein, e.g., an ordered listing of executable instructions that can be considered to implement logical functions, can be embodied in any computer-readable medium for use by or in connection with an instruction execution system, apparatus, or device, such as a computer-based system, processor-containing system, or other system that can fetch the instructions from the instruction execution system, apparatus, or device and execute the instructions. For the purposes of this description, a "computer-readable medium" can be any means that can contain, store, communicate, propagate, or transport the program for use by or in connection with the instruction execution system, apparatus, or device.
More specific examples (a non-exhaustive list) of the computer-readable medium would include the following: an electrical connection (electronic device) having one or more wires, a portable computer diskette (magnetic device), a Random Access Memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), an optical fiber device, and a portable compact disc read-only memory (CDROM). Further, the computer readable medium could even be paper or another suitable medium upon which the above described program is printed, as the program can be electronically captured, via for instance optical scanning of the paper or other medium, then compiled, interpreted or otherwise processed in a suitable manner if necessary, and then stored in a computer memory.
It should be understood that portions of the present invention may be implemented in hardware, software, firmware, or a combination thereof. In the above embodiments, the various steps or methods may be implemented in software or firmware stored in memory and executed by a suitable instruction execution system. For example, if implemented in hardware, as in another embodiment, any one or combination of the following techniques, which are known in the art, may be used: a discrete logic circuit having a logic gate circuit for implementing a logic function on a data signal, an application specific integrated circuit having an appropriate combinational logic gate circuit, a Programmable Gate Array (PGA), a Field Programmable Gate Array (FPGA), or the like.
In the foregoing description of the specification, reference to the description of "one embodiment/example," "another embodiment/example," or "certain embodiments/examples," etc., means that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, schematic representations of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.
While embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art that: various changes, modifications, substitutions and alterations can be made to the embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.
While the preferred embodiments of the present invention have been illustrated and described, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.
Claims (10)
1. A radiometric calibration method of a remote sensing camera based on a fixed star source is characterized by comprising the following steps:
determining a first full width half maximum of a star point image, and determining a first star point target according to the first full width half maximum and a preset first threshold range;
carrying out radiation measurement on the first star point target by a PRF fitting measurement method to obtain a first radiation measurement value, and carrying out radiation measurement on the first star point target by an aperture photometry method to obtain a second radiation measurement value;
when the difference value of the first radiation measurement value and the second radiation measurement value exceeds a preset second threshold value range, determining a first residual image according to a star image model obtained by a PRF fitting measurement method and the star point image, and then performing radiation measurement on the first residual image by an aperture photometry method to obtain a third radiation measurement value;
and correcting the first radiation measurement value according to the third radiation measurement value to obtain a first point response function, and further performing absolute radiation calibration on a laboratory star point target and an on-orbit star point target according to the first point response function.
2. The method for radiometric calibration of remote sensing cameras based on star sources as claimed in claim 1, wherein said step of determining a first full width half maximum of a star point image, and determining a first star point target based on said first full width half maximum and a preset first threshold range specifically comprises:
shooting by a remote sensing camera to obtain a star point image, and determining the first full width half maximum of the star point image;
the method comprises the steps of obtaining a preset first threshold range, and determining a star point target corresponding to a first full width half maximum which does not meet the first threshold range as a first star point target.
3. The method for radiometric calibration of a fixed star source based remote sensing camera as claimed in claim 1, wherein said step of radiometric measurement of said first star point target by PRF fitting measurement to obtain a first radiometric value specifically comprises:
determining grid points of each grid of the PRF grid point model, and determining PRF values of the grid points to obtain a PRF grid point model;
and carrying out radiation measurement on the first star point target through the PRF grid point model to obtain a first radiation measurement value.
4. The radiometric calibration method for the remote sensing camera based on the star source as claimed in claim 1, wherein the step of radiometrically measuring the first star point target by aperture photometry to obtain the second radiometric value specifically comprises:
determining a first round hole surrounding the first star point target, and measuring first brightness of each pixel in the first round hole;
determining a first circular ring area on the outer side of the first circular hole, and determining the average brightness of pixels in the first circular ring area;
and determining the second radiation measurement value according to the first brightness, the average brightness and the number of pixels in the first round hole.
5. The method according to claim 1, wherein the step of determining a first residual image according to the star image and the star image obtained by the PRF fitting measurement method, and then performing radiometry on the first residual image by an aperture photometry method to obtain a third radiometric value specifically comprises:
obtaining a star image model obtained by a PRF fitting measurement method, and deducting the star image model from the star point image to obtain a first residual image;
and determining a second round hole according to the aperture when the photometric signal-to-noise ratio is maximum, and then carrying out radiometry on the first residual image according to the second round hole by using an aperture photometry method to obtain a third radiometric value.
6. The method for radiometric calibration of remote sensing cameras based on fixed star sources according to any of claims 1 to 5, wherein the step of absolute radiometric calibration of laboratory star targets according to said first point response function specifically comprises:
carrying out non-uniform correction on the first gray level image of the laboratory star point target to obtain a second gray level image;
converting the second gray image into a first brightness image, and removing a background image of the first brightness image to obtain a second brightness image;
normalizing the first point response function, and further constructing an optimization objective function according to the normalized first point response function and the second brightness image;
and performing iterative optimization on the optimization objective function to obtain first radiance, and further determining the first irradiance of the laboratory star point target at the camera entrance pupil according to the first radiance.
7. The method for radiometric calibration of remote sensing cameras based on fixed star sources according to claim 6, wherein the step of absolute radiometric calibration of on-orbit star point targets according to said first point response function specifically comprises:
carrying out non-uniform correction on an original star map of an on-orbit star point target to obtain a first star map;
performing radiance conversion on the first star map according to an absolute calibration coefficient obtained in a laboratory to obtain a second star map;
removing the background of the second star map to obtain a background-free target star map;
processing the background-free target star map through a point target extraction algorithm, determining a brightness value at the entrance pupil of the camera corresponding to the radiation of the standard star, and further determining a second irradiance of the standard star at the entrance pupil of the camera according to the brightness value at the entrance pupil of the camera;
determining the actual irradiance of the standard fixed star at the entrance pupil of the camera according to the distance between the standard fixed star and the remote sensing camera;
determining an on-orbit absolute calibration correction factor of the remote sensing camera according to the actual irradiance and the second irradiance;
and correcting the absolute calibration equation according to the on-orbit absolute calibration correction factor.
8. A remote sensing camera radiometric calibration system based on a fixed star source is characterized by comprising:
the star point target determining module is used for determining a first full width half maximum of a star point image and determining a first star point target according to the first full width half maximum and a preset first threshold range;
the first radiometric module is used for carrying out radiometric measurement on the first star point target by a PRF fitting measurement method to obtain a first radiometric value, and carrying out radiometric measurement on the first star point target by an aperture photometry method to obtain a second radiometric value;
the second radiation measurement module is used for determining a first residual image according to a star image model obtained by a PRF fitting measurement method and the star point image when the difference value of the first radiation measurement value and the second radiation measurement value exceeds a preset second threshold range, and then performing radiation measurement on the first residual image through an aperture photometry method to obtain a third radiation measurement value;
and the radiometric calibration module is used for correcting the first radiometric value according to the third radiometric value to obtain a first point response function, and further performing absolute radiometric calibration on the laboratory star point target and the on-orbit star point target according to the first point response function.
9. A remote sensing camera radiometric calibration device based on a fixed star source is characterized by comprising:
at least one processor;
at least one memory for storing at least one program;
when executed by the at least one processor, cause the at least one processor to implement a method for radiometric calibration of a remote sensing camera based on a fixed-star source as claimed in any one of claims 1 to 7.
10. A computer readable storage medium having stored therein a processor executable program, wherein the processor executable program when executed by a processor is for performing a method of radiometric calibration of a remote sensing camera based on a star source as claimed in any one of claims 1 to 7.
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