Remote sensing camera radiation calibration method, system, device and medium based on star source

Abstract

The present invention discloses a remote sensing camera radiation calibration method, system, device and medium based on a star source, the method comprising: determining the first half-maximum full width of a 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 between the first radiation measurement value and the second radiation measurement 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 the PRF fitting measurement method, 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 to obtain a first point response function, and performing absolute radiation calibration on a laboratory star point target and an on-orbit star point target according to the first point response function. The present invention improves the accuracy and efficiency of remote sensing camera radiation calibration, and can be widely used in the field of remote sensing system radiation calibration technology.

Description

Technical Field

[0001] The present invention relates to the technical field of remote sensing system radiation calibration, and in particular to a remote sensing camera radiation calibration method, system, device and medium based on a star source. Background Art

[0002] The radiometric calibration of infrared remote sensing cameras requires the correction of the non-uniformity of the infrared camera response (relative radiometric calibration) and the establishment of the relationship between the output signal value of the remote sensor and the input energy value (absolute radiometric calibration), and has become an inevitable link and trend in quantitative remote sensing. The former is the intermediate link of radiometric calibration, and the latter is the ultimate goal of radiometric calibration. Infrared remote sensing cameras not only need to be accurately calibrated for their radiation characteristics before launch (laboratory radiometric calibration), but also need to be calibrated and corrected for the changes in the response of infrared remote sensing cameras caused by various factors after orbital operation, which is called on-orbit radiometric calibration. On-orbit radiometric calibration generally adopts external calibration blackbody radiation sources, ground site calibration sources, or radiometric calibration based on star sources. In view of the shortcomings of current calibration equipment and calibration methods for radiometric calibration of high dynamic range (HDR) infrared remote sensing cameras, the radiometric calibration method of HDR infrared remote sensing cameras that combines internal calibration blackbody with star maps has become one of the new development directions in the world.

[0003] The premise of radiation calibration is accurate radiation measurement. In the prior art, aperture photometry and point response function (PRF) fitting measurement methods are usually used to measure the radiation of stellar sources. Systematic errors will be introduced when performing PRF fitting measurement, which is mainly caused by the deviation of the used PRF model from the true value (model). Such errors are the dominant errors in the PRF fitting measurement of bright star sources. However, the PRF fitting method takes into account the radiation flux at various locations of the star image, and the total radiation flux of the star body is also a fitting parameter, so that the PRF fitting method can better correct the omission of radiation flux when the fitting area is small, that is, the accuracy of dim targets is high. For dark star sources, in order to avoid the omission error caused by the smaller aperture and the random error of the image introduced by the larger aperture, the aperture photometry method needs to fine-tune the aperture size to obtain an error similar to that of the PRF fitting method, which is difficult to achieve in actual engineering processing. Therefore, the use of aperture photometry will introduce errors caused by the omission of the star radiation flux; for dark star sources measured by the PRF fitting method, the main error usually comes from the background noise of the star image.

[0004] From the above, we can see that the existing aperture photometry method has low measurement accuracy for dim targets, while the PRF fitting measurement method has low measurement accuracy for bright star sources, both of which will affect the radiation calibration accuracy of the remote sensing camera. In addition, the PRF fitting measurement method requires a large number of star sources, is complex to operate, and has low efficiency.

[0005] Terminology explanation:

[0006] PRF fitting measurement method: a point response function fitting measurement method proposed by American scholars Jay Anderson and Ivan R. King (hereinafter referred to as A&K). This method is used for astronomical observations and astrometry of payloads such as the Hubble Telescope's Wide Field Camera (WF), Wide Field Planetary Camera 2 (WFPC2), and the Spitzer Space Telescope. Summary of the invention

[0007] The purpose of the present invention is to solve one of the technical problems existing in the prior art to at least a certain extent.

[0008] To this end, an object of an embodiment of the present invention is to provide an adaptive aperture point response function determination method (AA&PRF method) for radiometric calibration of a remote sensing camera based on stellar sources. This method makes full use of the respective advantages of the PRF fitting measurement method and the aperture photometry method, and makes up for the disadvantage that the PRF fitting measurement method requires a large number of stellar sources for fitting calculations, thereby improving the accuracy and efficiency of radiometric measurement, thereby improving the accuracy and efficiency of radiometric calibration of remote sensing cameras, and providing a foundation for the development of high-precision and high-dynamic radiometric calibration technology for on-orbit infrared remote sensing cameras.

[0009] Another object of an embodiment of the present invention is to provide a remote sensing camera radiation calibration system based on a stellar source.

[0010] In order to achieve the above technical objectives, the technical solutions adopted by the embodiments of the present invention include:

[0011] In a first aspect, an embodiment of the present invention provides a remote sensing camera radiation calibration method based on a star source, comprising the following steps:

[0012] Determine a first half-maximum full width of the star point image, and determine a first star point target according to the first half-maximum full width and a preset first threshold range;

[0013] Performing radiation measurement on the first star point target by a PRF fitting measurement method to obtain a first radiation measurement value, and performing radiation measurement on the first star point target by an aperture photometry method to obtain a second radiation measurement value;

[0014] When the difference between the first radiation measurement value and the second radiation measurement value exceeds a preset second threshold range, a first residual image is determined according to the star model obtained by the PRF fitting measurement method and the star point image, and then a third radiation measurement value is obtained by performing radiation measurement on the first residual image by an aperture photometry method;

[0015] The first radiation measurement value is corrected according to the third radiation measurement value to obtain a first point response function, and then absolute radiation calibration is performed on the laboratory star point target and the on-orbit star point target according to the first point response function.

[0016] Further, in one embodiment of the present invention, the step of determining a first half-maximum full width of the star point image and determining a first star point target according to the first half-maximum full width and a preset first threshold range specifically includes:

[0017] Acquire a star point image by photographing with a remote sensing camera, and determine the first half-maximum full width of the star point image;

[0018] A preset first threshold range is obtained, and a star point target corresponding to a first half-maximum full width that does not meet the first threshold range is determined as a first star point target.

[0019] Further, in one embodiment of the present invention, the step of performing radiation measurement on the first star point target by using the PRF fitting measurement method to obtain a first radiation measurement value specifically includes:

[0020] Determine the grid points of each grid of the PRF grid point model, and determine the PRF value of the grid point to obtain the PRF grid point model;

[0021] Performing radiation measurement on the first star point target through the PRF grid point model to obtain a first radiation measurement value.

[0022] Further, in one embodiment of the present invention, the step of performing radiation measurement on the first star point target by aperture photometry to obtain a second radiation measurement value specifically includes:

[0023] Determine a first circular hole surrounding the first star point target, and measure a first brightness of each pixel in the first circular hole;

[0024] Determine a first circular ring area outside the first circular hole, and determine the average brightness of the pixels in the first circular ring area;

[0025] The second radiation measurement value is determined according to the first brightness, the average brightness, and the number of pixels in the first circular hole.

[0026] Further, in one embodiment of the present invention, the step of determining a first residual image according to the star model obtained by the PRF fitting measurement method and the star point image, and then performing radiometric measurement on the first residual image by aperture photometry to obtain a third radiometric measurement value specifically includes:

[0027] Acquire a star model obtained by a PRF fitting measurement method, and deduct the star model from the star point image to obtain a first residual image;

[0028] A second circular hole is determined according to the aperture when the photometric signal-to-noise ratio is maximum, and then the first residual image is radiometrically measured using the aperture photometry method according to the second circular hole to obtain a third radiometric measurement value.

[0029] Further, in one 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:

[0030] Performing non-uniform correction on the first grayscale image of the laboratory star point target to obtain a second grayscale image;

[0031] Converting the second grayscale image into a first brightness image, and removing the background image of the first brightness image to obtain a second brightness image;

[0032] Normalizing the first point response function, and then constructing an optimization objective function according to the normalized first point response function and the second brightness image;

[0033] The optimization objective function is iteratively optimized to obtain a first radiance, and then a first irradiance of the laboratory star point target at the camera entrance pupil is determined according to the first radiance.

[0034] Further, in one 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:

[0035] Performing non-uniform correction on the original star map of the on-orbit star point target to obtain a first star map;

[0036] Performing radiance conversion on the first star map according to the absolute calibration coefficients obtained in the laboratory to obtain a second star map;

[0037] Performing background removal on the second star image to obtain a background-free target star image;

[0038] The background-free target star image is processed by a point target extraction algorithm to determine the brightness value at the camera entrance pupil corresponding to the standard star radiation, and then the second irradiance of the standard star at the camera entrance pupil is determined according to the brightness value at the camera entrance pupil;

[0039] The actual irradiance of the standard star at the camera entrance pupil is determined according to the distance between the standard star and the remote sensing camera;

[0040] Determine an on-orbit absolute calibration correction factor of a remote sensing camera according to the actual irradiance and the second irradiance;

[0041] The absolute calibration equation is corrected according to the on-orbit absolute calibration correction factor.

[0042] In a second aspect, an embodiment of the present invention provides a remote sensing camera radiation calibration system based on a star source, comprising:

[0043] A star point target determination module, used to determine a first half-maximum full width of the star point image, and determine a first star point target according to the first half-maximum full width and a preset first threshold range;

[0044] A first radiation measurement module, configured to perform radiation measurement on the first star point target by a PRF fitting measurement method to obtain a first radiation measurement value, and perform radiation measurement on the first star point target by an aperture photometry method to obtain a second radiation measurement value;

[0045] A second radiation measurement module is used to determine a first residual image according to the star model obtained by the PRF fitting measurement method and the star point image when the difference between the first radiation measurement value and the second radiation measurement value exceeds a preset second threshold range, and then perform radiation measurement on the first residual image by aperture photometry to obtain a third radiation measurement value;

[0046] The radiation calibration module is used to correct the first radiation measurement value according to the third radiation measurement value to obtain a first point response function, and then perform absolute radiation calibration on the laboratory star point target and the on-orbit star point target according to the first point response function.

[0047] In a third aspect, an embodiment of the present invention provides a remote sensing camera radiation calibration device based on a star source, comprising:

[0048] at least one processor;

[0049] at least one memory for storing at least one program;

[0050] When the at least one program is executed by the at least one processor, the at least one processor implements the above-mentioned remote sensing camera radiation calibration method based on stellar sources.

[0051] In a fourth aspect, an embodiment of the present invention further provides a computer-readable storage medium, which stores a program executable by a processor, and when the program executable by the processor is executed by the processor, it is used to execute the above-mentioned remote sensing camera radiation calibration method based on stellar sources.

[0052] The advantages and beneficial effects of the present invention will be partly given in the following description, partly become apparent from the following description, or be understood through the practice of the present invention:

[0053] The embodiment of the present invention uses star sources as a radiation calibration benchmark, draws on the aperture photometry method for measuring starlight in astrophysics, deducts the star image model obtained by fitting the point response function (PRF) from the original star point image and obtains a residual image, performs aperture method radiation measurement on the residual image in the central area, and uses this as a correction to the PRF fitting radiation measurement value, and is used for subsequent absolute radiation calibration of laboratory star point targets and on-orbit star point targets. The embodiment of the present invention fully utilizes the respective advantages of the PRF fitting measurement method and the aperture photometry method, makes up for the disadvantage that the PRF fitting measurement method requires a large number of star sources for fitting calculations, improves the accuracy and efficiency of radiation measurement, and thus improves the accuracy and efficiency of remote sensing camera radiation calibration, and provides a foundation for the development of high-precision and high-dynamic radiation calibration technology for on-orbit infrared remote sensing cameras. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] In order to more clearly illustrate the technical solution in the embodiments of the present invention, the following introduction is made to the drawings required for use in the embodiments of the present invention. It should be understood that the drawings introduced below are only for the convenience of clearly describing some embodiments of the technical solution of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative work.

[0055] Figure 1 A flow chart of the steps of a remote sensing camera radiation calibration method based on a star source provided by an embodiment of the present invention;

[0056] Figure 2 A schematic diagram of grayscale values ​​of a star point image, a star model and a first residual image provided by an embodiment of the present invention;

[0057] Figure 3 A specific flow chart of absolute radiation calibration of laboratory star point targets provided by an embodiment of the present invention;

[0058] Figure 4 A specific flow chart of absolute radiation calibration of on-orbit star point targets provided by an embodiment of the present invention;

[0059] Figure 5 A structural block diagram of a remote sensing camera radiation calibration system based on a star source provided by an embodiment of the present invention;

[0060] Figure 6 A structural block diagram of a remote sensing camera radiation calibration device based on a star source provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0061] The embodiments of the present invention are described in detail below, and examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and are not to be construed as limitations of the present invention. For the step numbers in the following embodiments, they are only provided for the convenience of explanation, and the order between the steps is not limited in any way, and the execution order of each step in the embodiment can be adaptively adjusted according to the understanding of those skilled in the art.

[0062] In the description of the present invention, the meaning of "a plurality" is two or more than two. If there is a description of "a first" or "a second", it is only used for the purpose of distinguishing technical features, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features or implicitly indicating the order of the indicated technical features. In addition, unless otherwise defined, all technical and scientific terms used in this document have the same meaning as those commonly understood by those skilled in the art.

[0063] Reference Figure 1 The embodiment of the present invention provides a remote sensing camera radiation calibration method based on a star source, which specifically includes the following steps:

[0064] S101 , determining a first half-maximum full width of a star point image, and determining a first star point target according to the first half-maximum full width and a preset first threshold range.

[0065] Specifically, the full width at half maximum (FWHM) of the star point image is first determined, and the star point target with weaker brightness (such as FWHM of 2 to 3 pixels) is still directly measured by the PRF fitting measurement method, and other star point targets will be measured by the improved PRF fitting measurement method (called AA&PRF fitting method) provided in the embodiment of the present invention. Step S101 specifically includes the following steps:

[0066] S1011, acquiring a star point image by photographing with a remote sensing camera, and determining the first half-maximum full width of the star point image;

[0067] S1012: Obtain a preset first threshold range, and determine that a star point target corresponding to a first half-maximum full width that does not meet the first threshold range is a first star point target.

[0068] Specifically, the first threshold range can be set to 2 to 3 pixels. The star point targets that meet the threshold range are directly measured using the PRF fitting measurement method and the subsequent absolute radiation calibration process is carried out. The star point targets that exceed the threshold range (i.e., the first star point targets) will be measured for radiation through subsequent aperture photometry and PRF fitting measurement methods, and corrections will be made based on the results.

[0069] S102 . Performing radiation measurement on the first star point target by using a PRF fitting measurement method to obtain a first radiation measurement value, and performing radiation measurement on the first star point target by using an aperture photometry method to obtain a second radiation measurement value.

[0070] Specifically, the first star point target is processed by the aperture photometry method and the PRF fitting measurement method respectively. When the difference between the two measurement results exceeds the set threshold, the AA&PRF fitting method proposed in the embodiment of the present invention is used for processing. When the difference between the two measurement results does not exceed the set threshold, the PRF fitting measurement method is still used for processing.

[0071] Further as an optional implementation manner, the step of performing radiation measurement on the first star point target by the PRF fitting measurement method to obtain the first radiation measurement value specifically includes:

[0072] A1. Determine the grid points of each grid of the PRF grid point model, and determine the PRF value of the grid point to obtain the PRF grid point model;

[0073] A2. Perform radiation measurement on the first star point target using the PRF grid point model to obtain a first radiation measurement value.

[0074] Specifically, the process of establishing the PRF grid point model is as follows: under the premise of knowing the point target position and the initial value of the flux, sampling is performed at the center position of 25 (i.e., 5×5) pixels, and the rectangular coordinate system is re-established assuming that the center point of the point target is taken as the origin. The grayscale data obtained from the 25 sampling points are numerically related based on the new coordinate system, which can obtain 25 PRF values ​​and establish a two-dimensional PRF model with the new coordinate system.

[0075] In order to obtain a more accurate PRF grid point model, the data processing will adopt the method of "sampling grid + PRF iteration". The grid is further subdivided, for example, each grid is subdivided into 4 equal parts, with a total of 21×21 grid points. In order to avoid errors caused by other factors such as cosmic rays, an iterative method is required to obtain the PRF value of the grid point and establish the PRF grid point model. The process of establishing the grid point can be summarized as follows:

[0076] 1) For each grid point, obtain a set of all sampling points within a square range of r in the vertical and horizontal directions with the grid point as the center. Take the average of the PRF values ​​of all sampling points in the set as the PRF value of the grid point.

[0077] 2) For each set of sampling points near each grid point, calculate the residual between the value of each sampling point in the set and the current PRF grid point value of the sampling point, and remove the sampling points whose variance is greater than 2.5 times the average residual. The iterative process ends when there are no sampling points to be removed for all grid points.

[0078] After obtaining the PRF grid model, the grid point values ​​in the model are smoothed. Different from the empirical value smoothing template based on the star source adopted by WFPC2, the embodiment of the present invention adopts a Gaussian template as the smoothing template. If the corresponding target of the infrared remote sensing system is actually measured and a smoothing template of the system measurement is obtained, the Gaussian template can be replaced.

[0079] Further as an optional implementation manner, the step of performing radiation measurement on the first star point target by aperture photometry to obtain a second radiation measurement value specifically includes:

[0080] B1, determining a first circular hole surrounding a first star point target, and measuring a first brightness of each pixel in the first circular hole;

[0081] B2, determining a first circular ring area outside the first circular hole, and determining the average brightness of the pixels in the first circular ring area;

[0082] B3. Determine a second radiation measurement value according to the first brightness, the average brightness, and the number of pixels in the first circular hole.

[0083] Specifically, aperture photometry, as a classic photometry method in astronomy, is still widely used in current astrophysical research and has achieved many results. When a star is an isolated star or is in an open star field and appears to be completely separated from other celestial bodies in the image (such as stars in an open star cluster), aperture photometry can be used. The basic principle of aperture photometry is: take an aperture on the star image formed to surround the stellar source image, the aperture center (star image center) is given by astrometry based on the celestial coordinate system, the aperture is larger than the point spread function of the infrared remote sensing camera, and the brightness or output data of all pixels in the aperture is measured; if there are no other targets outside the aperture, take a circular area outside this aperture and measure the average brightness of the pixels therein as the background radiation brightness L B . The total brightness L within the circular aperture A Subtract the number of pixels in the circle N A and background radiation brightness L B The product of the corresponding star output L S The relevant formula is as follows:

[0084] L S ≡L A -N A ×L B

[0085] S103. When the difference between the first radiation measurement value and the second radiation measurement value exceeds a preset second threshold range, a first residual image is determined based on the star model and the star point image obtained by the PRF fitting measurement method, and then a third radiation measurement value is obtained by performing radiation measurement on the first residual image through the aperture photometry method.

[0086] As an optional implementation, the step of determining the first residual image according to the star model and the star point image obtained by the PRF fitting measurement method, and then performing radiometric measurement on the first residual image by the aperture photometry method to obtain a third radiometric measurement value specifically includes:

[0087] C1. Obtaining a star model obtained by a PRF fitting measurement method, and deducting the star model from the star point image to obtain a first residual image;

[0088] C2. Determine a second circular aperture according to the aperture when the photometry signal-to-noise ratio is maximum, and then perform radiation measurement on the first residual image using aperture photometry according to the second circular aperture to obtain a third radiation measurement value.

[0089] Specifically, the AA&PRF fitting method of the embodiment of the present invention is as follows: first, based on the PRF fitting measurement method, the PRF fitting radiation measurement value of the star source is obtained, then the star image model obtained by fitting is deducted from the original image to obtain a residual image (i.e., the first residual image), and a smaller adaptive aperture is used to perform a radiation measurement based on the aperture photometry method on the residual image in the center area of ​​the star image, and this value is used as a correction to the PRF fitting photometry value. Figure 2 The figure shows a schematic diagram of the grayscale values ​​of the star point image, the star model and the first residual image provided by the embodiment of the present invention. It can be understood that after the star model is fitted, the grayscale value of the pixel corresponding to the star model is subtracted from the original star point image to obtain the grayscale value of the first residual image. In actual operation, the aperture photometry method selects the aperture when the photometry signal-to-noise ratio is the largest as the optimal aperture for measurement. The adaptive window of the embodiment of the present invention selects the same size as the FWHM. Since the embodiment of the present invention initially calculates the value of the FWHM, the aperture size can be adaptively and dynamically changed according to the FWHM parameter of the target.

[0090] S104: Correct the first radiation measurement value according to the third radiation measurement value to obtain a first point response function, and then perform absolute radiation calibration on the laboratory star point target and the on-orbit star point target according to the first point response function.

[0091] Specifically, radiation measurement methods are commonly used for star point photometry. For example, photometry methods are used in astrophysics to study stars in star clusters, and are often used in platforms such as observatory telescopes or space astronomical telescopes. The embodiments of the present invention are based on an improved radiation measurement method (AA&PRF fitting method) and apply it to absolute radiation calibration of high-orbit infrared remote sensing cameras (which belong to earth remote sensing, and the detection targets are different from astronomical telescopes, etc.). An absolute radiation calibration method for infrared remote sensing cameras of laboratory (before launch) star point targets based on the AA&PRF fitting method and an absolute radiation calibration method for on-orbit (after launch) star point targets are proposed.

[0092] As an optional implementation, the step of performing absolute radiation calibration on the laboratory star point target according to the first point response function specifically includes:

[0093] D1, performing non-uniform correction on the first grayscale image of the laboratory star point target to obtain a second grayscale image;

[0094] D2, converting the second grayscale image into the first brightness image, and removing the background image of the first brightness image to obtain the second brightness image;

[0095] D3, normalizing the first point response function, and then constructing an optimization objective function according to the normalized first point response function and the second brightness image;

[0096] D4. Iteratively optimize the optimization objective function to obtain the first radiance, and then determine the first irradiance of the laboratory star point target at the camera entrance pupil according to the first radiance.

[0097] Specifically, in order to achieve absolute radiometric calibration of remote sensing cameras based on stellar sources, it is necessary to design the test experimental process in advance, such as Figure 3 The figure shows a specific flow chart of absolute radiation calibration of laboratory star point targets provided by an embodiment of the present invention, that is, a process of extracting irradiance response of laboratory star point targets, which is specifically as follows:

[0098] 1) Aim the camera at the extended flat-panel light source module through the channel switching module, and perform the corresponding absolute radiation calibration according to the determined relative radiation calibration method. If the relative radiation calibration method of two-point correction is adopted, go to step 2); if the relative radiation calibration method of segmented correction is adopted, go to step 3).

[0099] 2) Two-point calibration requires two temperature calibration points to determine the absolute radiation calibration coefficient of the camera. By solving the absolute radiation calibration coefficient, the absolute radiation calibration equation is obtained:

[0100]

[0101] 3) For the segmented correction scheme, the number of segments and the selection of segmented calibration points for absolute radiation calibration of infrared remote sensing cameras are exactly the same as those for relative radiation calibration. The above formula is used to perform absolute radiation calibration of radiance for each segment.

[0102] 4) For the absolute radiometric calibration coefficients of the infrared remote sensing camera obtained in steps 2) and 3), the conversion from absolute radiometric calibration of radiance to absolute radiometric calibration of irradiance is realized by the AA&PRF fitting method based on the star point target: first, the obtained point response function is normalized to satisfy the following formula:

[0103] or

[0104] In the above formula, H a is the measured PRF function, H' a is the normalized PRF function; then the grayscale image is converted into a brightness image using the radiance absolute calibration result, and background removal and candidate point target judgment are performed; finally, H' a Construct an optimization objective function for the image after background removal (referred to as brightness image):

[0105]

[0106] In the above formula, χ 2 represents the optimization objective function, d j represents the corresponding brightness value on the brightness image, σ represents the noise estimation near the point target, (x i ,y i ) represents the point target to be extracted. Through the optimization method, the solution is obtained so that χ in the above formula 2 Minimize the radiance L of the corresponding star point target center position (ε,η) and the actual solid angle normalized a , and then the measured radiance value is corrected according to the adaptive aperture range of the AA&PRF fitting method, and finally the irradiance of the star point target at the entrance pupil can be calculated as:

[0107]

[0108] The above can complete the absolute radiation calibration of the infrared remote sensing camera of the laboratory star point target.

[0109] As an optional implementation, the step of performing absolute radiation calibration on the on-orbit star point target according to the first point response function specifically includes:

[0110] E1. Perform non-uniform correction on the original star map of the on-orbit star point target to obtain a first star map;

[0111] E2, converting the radiance of the first star map according to the absolute calibration coefficient obtained in the laboratory to obtain a second star map;

[0112] E3, removing the background of the second star image to obtain a background-free target star image;

[0113] E4. Process the background-free target star map by using a point target extraction algorithm to determine the brightness value at the camera entrance pupil corresponding to the standard star radiation, and then determine the second irradiance of the standard star at the camera entrance pupil according to the brightness value at the camera entrance pupil;

[0114] E5. Determine the actual irradiance of the standard star at the camera entrance pupil based on the distance between the standard star and the remote sensing camera;

[0115] E6. Determine the on-orbit absolute calibration correction factor of the remote sensing camera based on the actual irradiance and the second irradiance;

[0116] E7. Correct the absolute calibration equation according to the on-orbit absolute calibration correction factor.

[0117] Specifically, the absolute radiation calibration of on-orbit star point targets will provide key data support for on-orbit target detection and measurement and other star point target radiation measurement methods, and provide diagnostic data for long-term on-orbit status monitoring of system payloads. Figure 4 The figure shows a specific flow chart of absolute radiation calibration of on-orbit star point targets provided by an embodiment of the present invention. The specific process is as follows:

[0118] (1) According to the system instructions, the camera enters the absolute radiation calibration state, and controls the pointing mechanism so that the camera to be tested is aimed at the target starry sky (the area where the calibration stars are located);

[0119] (2) Check the operating temperature of each device to ensure that it meets the required value for normal operation and record it;

[0120] (3) Determine whether the target starry sky has been aligned, obtain an image of the target starry sky, and record the detector output signal value;

[0121] (4) using the obtained relative calibration result to calibrate the detector output signal value obtained in step (3);

[0122] (5) Using the laboratory absolute calibration result, the corrected detector output signal is converted into radiance to obtain a radiance numerical image containing the target star point, that is, the image pixel value unit is the same as the radiance unit;

[0123] (6) performing background removal operation on the brightness numerical image to obtain a background-free target star image;

[0124] (7) Use the point target extraction algorithm to extract the calibration stars and obtain their radiance values ​​at the entrance pupil (i.e., use the point response function obtained in the laboratory or the point response function measured in orbit to perform template matching with the background-free target star map to extract candidate star point targets. Then, use the optimization algorithm that minimizes the solution error, i.e., the AA&PRF fitting method, to simultaneously obtain the point target position coordinates and the point target radiance value at the entrance pupil);

[0125] (8) Calculate the product of the effective solid angle of the detector unit calibrated in the laboratory and the above radiance to obtain the irradiance E of the standard star at the camera entrance pupil test ;

[0126] (9) Repeat steps (1) to (8) to perform n repeated measurements on the standard star and calculate the evaluation value of n repeated measurements.

[0127] (10) According to the distance between the calibration star and the camera to be tested, the actual irradiance E of the calibration star at the camera entrance pupil is obtained. true ;

[0128] (11) Calculate the camera’s on-orbit absolute calibration correction factor

[0129] (12) The corrected camera absolute calibration equation is L correct = k·L e = k(aV c +b).

[0130] The above can complete the absolute radiation calibration of the infrared remote sensing camera of the on-orbit star point target.

[0131] It should be recognized that there are differences in the detection targets, orbital working conditions, etc. between the space astronomical telescope system and the infrared remote sensing camera. 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 photometry method of observing stars. The embodiment of the present invention has made targeted improvements to this: an adaptive aperture point response function method (AA&PRF fitting method) is proposed, which fully utilizes the respective advantages of the PRF fitting measurement method and the aperture photometry method, overcomes the disadvantage that the PRF fitting measurement method requires a large number of star sources for fitting calculation, improves the accuracy and efficiency of radiation measurement, and thus improves the accuracy and efficiency of remote sensing camera radiation calibration, providing a basis for the development of high-precision and high-dynamic radiation calibration technology for on-orbit infrared remote sensing cameras. In addition, combining the existing relative radiation calibration with the absolute radiation calibration can achieve absolute radiation calibration of all pixels, establish an accurate mapping relationship between the target image grayscale and the target entrance pupil irradiance covering the entire detector dynamic range, and provide a technical basis for the point target detection inversion technology of space-based infrared remote sensing cameras.

[0132] The two existing radiation measurement methods both use star point sources for calibration, and the detection targets are also star point targets. However, high-orbit infrared remote sensing cameras are different. The AA&PRF method proposed in the embodiment of the present invention can be used to observe near-Earth space targets, correct absolute calibration parameters, optimize and establish a space target detection point response model under actual detection conditions, which is more practical for space target infrared remote sensing systems.

[0133] Reference Figure 5 The embodiment of the present invention provides a remote sensing camera radiation calibration system based on a star source, comprising:

[0134] A star point target determination module, used to determine a first half-maximum full width of the star point image, and determine a first star point target according to the first half-maximum full width and a preset first threshold range;

[0135] A first radiation measurement module is used to perform radiation measurement on the first star point target by a PRF fitting measurement method to obtain a first radiation measurement value, and to perform radiation measurement on the first star point target by an aperture photometry method to obtain a second radiation measurement value;

[0136] A second radiation measurement module is used to determine a first residual image according to the star model and the star point image obtained by the PRF fitting measurement method when the difference between the first radiation measurement value and the second radiation measurement value exceeds a preset second threshold range, and then perform radiation measurement on the first residual image by the aperture photometry method to obtain a third radiation measurement value;

[0137] The radiation calibration module is used to correct the first radiation measurement value according to the third radiation measurement value to obtain a first point response function, and then perform absolute radiation calibration on the laboratory star point target and the on-orbit star point target according to the first point response function.

[0138] The contents of the above method embodiments are all applicable to the present system embodiments. The functions specifically implemented by the present system embodiments are the same as those of the above method embodiments, and the beneficial effects achieved are also the same as those achieved by the above method embodiments.

[0139] Reference Figure 6 The embodiment of the present invention provides a remote sensing camera radiation calibration device based on a star source, comprising:

[0140] at least one processor;

[0141] at least one memory for storing at least one program;

[0142] When the at least one program is executed by the at least one processor, the at least one processor implements the above-mentioned remote sensing camera radiation calibration method based on star sources.

[0143] The contents of the above method embodiments are all applicable to the present device embodiments. The functions specifically implemented by the present device embodiments are the same as those of the above method embodiments, and the beneficial effects achieved are also the same as those achieved by the above method embodiments.

[0144] An embodiment of the present invention further provides a computer-readable storage medium, in which a program executable by a processor is stored. When the program executable by the processor is executed by the processor, it is used to execute the above-mentioned remote sensing camera radiation calibration method based on a stellar source.

[0145] A computer-readable storage medium of an embodiment of the present invention can execute a remote sensing camera radiation calibration method based on a stellar source provided by a method embodiment of the present invention, can execute any combination of implementation steps of the method embodiment, and has the corresponding functions and beneficial effects of the method.

[0146] The embodiment of the present invention also discloses a computer program product or a computer program, wherein the computer program product or the computer program includes computer instructions, and the computer instructions are stored in a computer-readable storage medium. A processor of a computer device can read the computer instructions from the computer-readable storage medium, and the processor executes the computer instructions, so that the computer device executes Figure 1 The method shown.

[0147] In some selectable embodiments, the function / operation mentioned in the block diagram may not occur in the order mentioned in the operation diagram. For example, depending on the function / operation involved, the two boxes shown in succession can actually be executed substantially simultaneously or the above-mentioned boxes can sometimes be executed in reverse order. In addition, the embodiment presented and described in the flow chart of the present invention is provided by way of example, for the purpose of providing a more comprehensive understanding of technology. The disclosed method is not limited to the operation and logic flow presented herein. Selectable embodiments are expected, wherein the order of various operations is changed and the sub-operation of a part for which is described as a larger operation is performed independently.

[0148] In addition, although the present invention is described in the context of functional modules, it should be understood that, unless otherwise specified to the contrary, one or more of the above-mentioned functions and / or features can be integrated into a single physical device and / or software module, or one or more functions and / or features can be implemented in a separate physical device or software module. It is also understood that a detailed discussion of the actual implementation of each module is unnecessary for understanding the present invention. More specifically, in view of the properties, functions and internal relationships of the various functional modules in the device disclosed herein, the actual implementation of the module will be understood within the conventional skills of the engineer. Therefore, those skilled in the art can implement the present invention set forth in the claims without excessive experimentation using ordinary techniques. It is also understood that the specific concepts disclosed are merely illustrative and are not intended to limit the scope of the present invention, which is determined by the full scope of the appended claims and their equivalents.

[0149] If the above functions are implemented in the form of software functional units and sold or used as independent products, they can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, or the part that contributes to the prior art or the part of the technical solution, can be embodied in the form of a software product. The computer software product is stored in a storage medium, including several instructions for a computer device (which can be a personal computer, a server, or a network device, etc.) to perform all or part of the steps of the above methods of each embodiment of the present invention. The aforementioned storage medium includes: U disk, mobile hard disk, read-only memory (ROM, Read-Only Memory), random access memory (RAM, Random Access Memory), disk or optical disk and other media that can store program codes.

[0150] The logic and / or steps represented in the flowchart or otherwise described herein, for example, can be considered as an ordered list of executable instructions for implementing logical functions, and can be embodied in any computer-readable medium for use by an instruction execution system, device or apparatus (such as a computer-based system, a system including a processor, or other system that can fetch instructions from an instruction execution system, device or apparatus and execute instructions), or in conjunction with such instruction execution systems, devices or apparatuses. For the purposes of this specification, "computer-readable medium" can be any device that can contain, store, communicate, propagate or transmit a program for use by an instruction execution system, device or apparatus, or in conjunction with such instruction execution systems, devices or apparatuses.

[0151] More specific examples of computer-readable media (a non-exhaustive list) include the following: an electrical connection with one or more wires (electronic device), a portable computer disk case (magnetic device), a random access memory (RAM), a read-only memory (ROM), an erasable and editable read-only memory (EPROM or flash memory), an optical fiber device, and a portable compact disk read-only memory (CDROM). In addition, the computer-readable medium may even be a paper or other suitable medium on which the above-mentioned program is printed, since the above-mentioned program can be obtained electronically, for example, by optically scanning the paper or other medium, followed by editing, deciphering or processing in other suitable ways as necessary, and then stored in a computer memory.

[0152] It should be understood that the various parts of the present invention can be implemented by hardware, software, firmware or a combination thereof. In the above-mentioned embodiments, a plurality of steps or methods can be implemented by software or firmware stored in a memory and executed by a suitable instruction execution system. For example, if implemented by hardware, as in another embodiment, it can be implemented by any one of the following technologies known in the art or their combination: a discrete logic circuit having a logic gate circuit for implementing a logic function for a data signal, a dedicated integrated circuit having a suitable combination of logic gate circuits, a programmable gate array (PGA), a field programmable gate array (FPGA), etc.

[0153] In the above description of this specification, the description with reference to the terms "one embodiment / example", "another embodiment / example" or "certain embodiments / examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner.

[0154] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the claims and their equivalents.

[0155] The above is a specific description of the preferred implementation of the present invention, but the present invention is not limited to the above embodiments. Those skilled in the art may make various equivalent modifications or substitutions without violating the spirit of the present invention. These equivalent modifications or substitutions are all included in the scope defined by the claims of this application.

Claims

1. A radiometric calibration method for a remote sensing camera based on a stellar source, characterized in that: The following steps are involved: Determine a first half-maximum full width of the star point image, and determine a first star point target according to the first half-maximum full width and a preset first threshold range; Performing radiation measurement on the first star point target by a point response function fitting measurement method to obtain a first radiation measurement value, and performing radiation measurement on the first star point target by an aperture photometry method to obtain a second radiation measurement value; When the difference between the first radiation measurement value and the second radiation measurement value exceeds a preset second threshold range, a first residual image is determined according to the star model obtained by the point response function fitting measurement method and the star point image, and then a third radiation measurement value is obtained by performing radiation measurement on the first residual image by an aperture photometry method; The first radiation measurement value is corrected according to the third radiation measurement value to obtain a first point response function, and then absolute radiation calibration is performed on the laboratory star point target and the on-orbit star point target according to the first point response function.

2. The method for calibrating a remote sensing camera based on a stellar source according to claim 1, characterized in that: The step of determining a first half-maximum full width of the star point image and determining a first star point target according to the first half-maximum full width and a preset first threshold range specifically includes: Acquire a star point image by photographing with a remote sensing camera, and determine the first half-maximum full width of the star point image; A preset first threshold range is obtained, and a star point target corresponding to a first half-maximum full width that does not meet the first threshold range is determined as a first star point target.

3. The method for calibrating a remote sensing camera radiation based on a stellar source according to claim 1, characterized in that: The step of performing radiation measurement on the first star point target by using the point response function fitting measurement method to obtain a first radiation measurement value specifically includes: Determine the grid points of each grid of the point response function grid point model, and determine the point response function values ​​of the grid points to obtain the point response function grid point model; The first star point target is subjected to radiation measurement through the point response function grid point model to obtain a first radiation measurement value.

4. The method for calibrating a remote sensing camera radiation based on a stellar source according to claim 1, characterized in that: The step of performing radiation measurement on the first star point target by aperture photometry to obtain a second radiation measurement value specifically includes: Determine a first circular hole surrounding the first star point target, and measure a first brightness of each pixel in the first circular hole; Determine a first circular ring area outside the first circular hole, and determine the average brightness of the pixels in the first circular ring area; The second radiation measurement value is determined according to the first brightness, the average brightness, and the number of pixels in the first circular hole.

5. The method for calibrating a remote sensing camera radiation based on a stellar source according to claim 1, characterized in that: The step of determining a first residual image according to the star model obtained by the point response function fitting measurement method and the star point image, and then performing radiometric measurement on the first residual image by aperture photometry to obtain a third radiometric measurement value specifically includes: Acquire a star model obtained by a point response function fitting measurement method, and deduct the star model from the star point image to obtain a first residual image; A second circular hole is determined according to the aperture when the photometric signal-to-noise ratio is maximum, and then the first residual image is radiometrically measured using the aperture photometry method according to the second circular hole to obtain a third radiometric measurement value.

6. A remote sensing camera radiation calibration method based on a stellar source according to any one of claims 1 to 5, characterized in that: The step of performing absolute radiation calibration on the laboratory star point target according to the first point response function specifically includes: Performing non-uniform correction on the first grayscale image of the laboratory star point target to obtain a second grayscale image; Converting the second grayscale image into a first brightness image, and removing the background image of the first brightness image to obtain a second brightness image; Normalizing the first point response function, and then constructing an optimization objective function according to the normalized first point response function and the second brightness image; The optimization objective function is iteratively optimized to obtain a first radiance, and then a first irradiance of the laboratory star point target at the camera entrance pupil is determined according to the first radiance.

7. The method for calibrating a remote sensing camera radiation based on a stellar source according to claim 6, characterized in that: The step of performing absolute radiation calibration on the on-orbit star point target according to the first point response function specifically includes: Performing non-uniform correction on the original star map of the on-orbit star point target to obtain a first star map; Performing radiance conversion on the first star map according to the absolute calibration coefficients obtained in the laboratory to obtain a second star map; Performing background removal on the second star image to obtain a background-free target star image; The background-free target star image is processed by a point target extraction algorithm to determine the brightness value at the camera entrance pupil corresponding to the standard star radiation, and then the second irradiance of the standard star at the camera entrance pupil is determined according to the brightness value at the camera entrance pupil; The actual irradiance of the standard star at the camera entrance pupil is determined according to the distance between the standard star and the remote sensing camera; Determine an on-orbit absolute calibration correction factor of a remote sensing camera according to the actual irradiance and the second irradiance; The absolute calibration equation is corrected according to the on-orbit absolute calibration correction factor.

8. A remote sensing camera radiation calibration system based on star sources, characterized in that: include: A star point target determination module, used to determine a first half-maximum full width of the star point image, and determine a first star point target according to the first half-maximum full width and a preset first threshold range; A first radiation measurement module, configured to perform radiation measurement on the first star point target by a point response function fitting measurement method to obtain a first radiation measurement value, and perform radiation measurement on the first star point target by an aperture photometry method to obtain a second radiation measurement value; A second radiation measurement module is used to determine a first residual image according to the star model obtained by the point response function fitting measurement method and the star point image when the difference between the first radiation measurement value and the second radiation measurement value exceeds a preset second threshold range, and then perform radiation measurement on the first residual image by aperture photometry to obtain a third radiation measurement value; The radiation calibration module is used to correct the first radiation measurement value according to the third radiation measurement value to obtain a first point response function, and then perform absolute radiation 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 radiation calibration device based on a star source, characterized in that: include: at least one processor; at least one memory for storing at least one program; When the at least one program is executed by the at least one processor, the at least one processor implements a remote sensing camera radiation calibration method based on a stellar source as described in any one of claims 1 to 7.

10. A computer-readable storage medium storing a program executable by a processor, characterized in that: The processor-executable program is used to execute a remote sensing camera radiation calibration method based on a stellar source as described in any one of claims 1 to 7 when executed by the processor.

Images