Dark weak asteroid synthesis tracking method based on CMOS detector
Through the dark and weak asteroid synthesis tracking method based on CMOS detectors, the difficulty of detecting and tracking of fast moving low-brightness near-Earth asteroids in the prior art is solved, and the tracking effect of high accuracy and high signal-to-noise ratio is achieved.
Patent Information
- Application Number
- CN202411501912.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-10-25
- Publication Date
- 2025-03-25
AI Technical Summary
The prior art is difficult to detect and track fast and accurately the fast moving low-brightness near-Earth asteroids, resulting in long observation time and insufficient sensitivity.
The dark weak asteroid synthesis tracking method based on CMOS detector is adopted to obtain the single-frame star point map of the target asteroid by acquiring multiple frames of original images, subtracting the sky background, performing median filtering and velocity grid processing.
Accurate tracking of near-Earth asteroids with a fast moving magnitude of about 100 meters is achieved, improving the signal-to-noise ratio of dark and weak celestial bodies by 50 times, effectively capturing the motion position of the asteroid.
Smart Images
Figure CN119693410A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the field of space exploration and asteroids, and in particular to a synthetic tracking method for faint asteroids based on a CMOS detector. Background Art
[0002] Under existing technology, it takes about 15-20 years of observation time to find about 90% of NEOs with a diameter of 100 meters or more. In addition, for smaller NEOs (about 50-70 meters in diameter), the observation time may even take decades. The reason why it takes so long to detect these objects is that the orbits of most NEOs are highly elliptical, and each orbit will bring these NEOs into the inner solar system once. If these objects cross the Earth's orbit when the Earth is on the other side of the Sun, the facilities on the ground will not be able to detect them.
[0003] In addition, the orbits of discovered NEOs cannot be accurately determined for a variety of reasons. Small NEOs are likely to be very dim (absolute magnitude of 28-30, where magnitude indicates the brightness of a star), so they can only be observed when they are very close to the Earth (closer than 0.1AU, AU data is the average distance between the Earth and the Sun, 1AU = 149,597,870 kilometers). NEOs also move very fast in the sky, normally reaching a speed of several degrees per day, which is a big challenge for finding NEOs. Most NEOs that are about to encounter the Earth have a speed of 10km / s relative to the Earth. For an object at a distance of 0.1AU, the parallax reaches 0.14 arc seconds per second. Under a field of view of 1 arc second, the exposure time of a general celestial body for more than 7 seconds will cause tailing. Therefore, the traditional NEO survey observation has an exposure time of 30 seconds or even longer, and the sensitivity to fast-moving NEOs is significantly lower than that to slow-moving NEOs. Summary of the invention
[0004] The purpose of the present invention is to provide a synthetic tracking method for faint asteroids based on a CMOS detector, which has the advantage of accurately tracking fast-moving near-Earth small celestial bodies.
[0005] To achieve the above-mentioned purpose, the present invention provides a synthetic tracking method for faint asteroids based on a CMOS detector, the method comprising: step S1, using a CMOS detector to obtain a total of N frames of original images of the sky area where the target asteroid is located, n=1, 2...N; step S2, subtracting the sky background from the total of N frames of original images one by one, to obtain a total of N frames of images without sky background; step S3, using a median filter to compensate for pointing jitter on the total of N frames of images without sky background, to obtain a total of N frames of analysis images; step S4, performing velocity gridding processing on the total of N frames of analysis images, to obtain a total of N frames of calculation images; step S5, using a multi-vector shift and addition algorithm to process the total of N frames of calculation images frame by frame, to obtain a single-frame star point map of the target asteroid.
[0006] Preferably, the step S2 comprises: step S21, pre-selecting a star region with fewer planets and photographing the star region to estimate the sky background; step S22, subtracting the sky background from a total of N frames of original images one by one; step S23, removing pixel signals caused by cosmic rays and bad pixels in the original image after the sky background is subtracted according to a threshold search method, to obtain a total of N frames of images without sky background.
[0007] Preferably, the use of median filtering to compensate for pointing jitter in step S3 includes: any of the images without sky background is an I×J image, wherein the length is I, i=1, 2...I, and the width is J, j=1, 2...J:
[0008] I(i,j)=Med{I(im,jk),I(i-m+1,j-k+1),...,I(i+m,j+k)}
[0009] Among them, I(i,j) is the pixel grayscale value of pixel (i,j), and m and k are half of the number of data sets respectively.
[0010] Preferably, the step S5 comprises: step S51, determining the latitude values (x t ,y t 、V x 、V y , D AU ), where x is the horizontal coordinate of the center position of the target asteroid in the nth frame of the computing image, y is the vertical coordinate of the center position of the target asteroid in the nth frame of the computing image, V x The horizontal cosmic velocity of the target asteroid at the center of the nth frame of the computational image, V y is the ordinate cosmic velocity of the target asteroid at the center of the nth frame computing image, D AU is the distance between the CMOS detector and the target asteroid, n=2, 3,...N.
[0011] Preferably, in step S5, the signal strength of the target asteroid of a single-frame star point is calculated as follows:
[0012]
[0013] Among them, (x, y) represents the center position on the COMS pixel plane, and the speed (v x ,v y ) is the two-dimensional synthesis tracking speed, n corresponds to the frame of image data, I n is the pixel intensity at coordinate (x, y) in the nth frame.
[0014] Preferably, the star point signal-to-noise ratio SNR conversion formula of the target asteroid of the single-frame star point in step S5 is as follows:
[0015]
[0016] Where T is the signal strength value of the target asteroid, is the noise intensity value of the target asteroid, Signal represents the signal intensity of the target asteroid, Noise represents the noise intensity of the target asteroid, and ∝ represents a positive correlation.
[0017] Preferably, the CMOS detector adopts an exposure time of 20 ms and an image output rate of 50 frames per second.
[0018] Preferably, the step S4 uses a 120×100 velocity grid to process the image.
[0019] Preferably, the step S4 uses FPGA technology to perform parallel processing on the images.
[0020] In summary, compared with the prior art, the synthetic tracking method for faint asteroids based on CMOS detectors provided by the present invention has the following beneficial effects:
[0021] First, the present invention can realize the tracking of fast-moving near-Earth small celestial bodies of about 100 meters with a magnitude below 20, and the signal-to-noise ratio of faint celestial bodies can be improved by 50 times.
[0022] Second, the method proposed in the present invention utilizes a new generation of high-speed CMOS camera to perform short-time, high-frame-rate exposure of a moving small near-Earth asteroid, thereby effectively capturing the position of the asteroid's movement. BRIEF DESCRIPTION OF THE DRAWINGS
[0023] Figure 1 It is a schematic diagram of the process of the present invention.
[0024] Figure 2 Schematic diagram of velocity gridding processing in an embodiment of the present invention.
[0025] Figure 3 Schematic diagram of the shift synthesis tracking technology in an embodiment of the present invention. DETAILED DESCRIPTION
[0026] The following will be combined with the attached embodiment of the present invention Figure 1 ~Attached Figure 3 , the technical solutions, structural features, objectives achieved and effects in the embodiments of the present invention are described in detail.
[0027] It should be noted that the drawings are in a very simplified form and use non-precise proportions. They are only used to conveniently and clearly assist in explaining the embodiments of the present invention, and are not used to limit the conditions for the implementation of the present invention. Therefore, they have no substantive technical significance. Any structural modification, change in proportional relationship or adjustment of size, without affecting the effects and purposes that can be achieved by the present invention, should still fall within the scope of the technical content disclosed by the present invention.
[0028] It should be noted that, in the present invention, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only the elements explicitly listed, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device.
[0029] The present invention provides a faint asteroid synthetic tracking method based on a CMOS (Complementary Metal Oxide Semiconductor) detector, which is used to accurately capture fast-moving near-Earth asteroids. Specifically, it can be used for near-Earth asteroids of about 100 meters with a magnitude below 20.
[0030] like Figure 1 As shown, the method includes:
[0031] Step S1, using a CMOS detector to acquire a total of N frames of original images of the sky region where the target asteroid is located, n=1, 2...N.
[0032] Specifically, this step requires short exposure shooting. The CMOS detector uses a CMOS camera, sets an exposure time of 20ms, an image output rate of 50 frames per second, a global shutter mode, and low readout noise. By adopting the above settings, by shooting fast-moving asteroids with short exposure, the tailing phenomenon caused by long exposure of moving celestial bodies can be avoided.
[0033] Step S2, subtracting the sky background from the N frames of original images one by one to obtain a total of N frames of images without the sky background.
[0034] The purpose of this step is to remove pixel signals caused by cosmic rays and bad pixels to prevent the influence of cosmic rays and bad pixels on asteroid observations.
[0035] Step S3, using median filtering to compensate for pointing jitter on a total of N frames of images without sky background, to obtain a total of N frames of analysis images.
[0036] The purpose of this step is to use median filtering to eliminate the impact of pointing jitter on image pixels due to pointing jitter of the detector, so that the target asteroid is aligned in each image frame. The specific method of using median filtering to compensate for pointing jitter is described below.
[0037] Step S4, performing velocity gridding processing on a total of N frames of analysis images to obtain a total of N frames of operation images.
[0038] Because the speed of the target asteroid is unknown, such as Figure 2 As shown, velocity gridding is performed, and the image is processed using a typical velocity grid, with reference to the speed of the moon, a movement speed of 12 degrees per day, and a velocity grid of 120×100. In a preferred embodiment, due to the huge amount of data, FPGA (Field-Programmable Gate Array) technology is used to perform parallel processing on the analysis images.
[0039] Step S5, using a multi-vector shift and addition algorithm to process a total of N frames of operation images frame by frame to obtain a single-frame star point image of the target asteroid.
[0040] The purpose of this step is to use a multi-vector shift and addition algorithm to perform speed shifting and add short-exposure frames to a total of N frames of operation images frame by frame, and synthesize a long-exposure star point image.
[0041] Specifically, step S2 may be performed in the following manner:
[0042] Step S21, preselecting a star region with fewer planets, photographing the star region, and estimating the sky background;
[0043] Step S22, subtracting the sky background from the N frames of original images one by one;
[0044] Step S23, according to the threshold search method, the original image after the sky background is subtracted from the total N frames is removed one by one, and the pixel signals caused by cosmic rays and bad pixels are removed, so as to obtain a total of N frames of images without sky background.
[0045] In step S3, using median filtering to compensate for pointing jitter includes:
[0046] The image without sky background in any frame is an I×J image, wherein the length is I, i=1, 2...I, the width is J, j=1, 2...J,
[0047] I(i,j)=Med{I(im,jk),I(i-m+1,j-k+1),...,I(i+m,j+k)}
[0048] Where I(i,j) is the grayscale value of pixel (i,j), m and k are half of the number of data sets respectively; the formula Med used is a computer function that can return the median of a given value;
[0049] The step S5 comprises:
[0050] Step S51, determine the latitude values (x, y, V) of the target asteroid in the 2nd to Nth frame computing images one by one x 、V y and D AU ), where x and y are the horizontal and vertical coordinates of the center position of the target asteroid in the nth frame of the computational image, respectively, V x and V y are the horizontal and vertical cosmic velocities of the target asteroid in the nth frame of the computational image, respectively. AU is the distance between the CMOS detector and the target asteroid in the nth frame of the computational image, n = 2, 3, ... N; where x t ,y t 、V x 、V y and D AU Indicates a specific value. Although the symbol is the same in each frame, it is the value in different frames, rather than the same value.
[0051] Step S52, shifting the positions of the target asteroid in the 2nd to Nth frames of computing images to the 1st frame of computing image one by one according to the latitude values, to obtain a single-frame star point map of the target asteroid.
[0052] The principle of displacement is to accumulate the photons of the target asteroid according to the latitude value, and then obtain a long-exposure single-frame star point image.
[0053] like Figure 3 As shown, the synthesis of the first frame, the second frame, and the third frame is taken as an example, where the first frame, the second frame, and the third frame are continuous frames, and the latitude value (x, y, V x 、V y and D AU), the third frame target asteroid latitude value (x, y, V x 、V y and D AU ), using the multi-vector shift and addition algorithm, the photons of the target asteroid in the second and third frames are accumulated, because in V x and V y Under the condition that the position of the target in each subsequent frame is known (which can be obtained by the existing technology), the position of the target asteroid in the first frame is kept unchanged, thereby forming a single-frame star point image; and so on, a total of N frames are processed; the tracking of the moving target asteroid is avoided, and the tailing phenomenon causes the loss of pixels in the transmission process, thereby obtaining a more dense star point spread function (equivalent to obtaining a better target asteroid imaging).
[0054] In step S5, after obtaining a single-frame star point image of the target asteroid, a signal strength I(x, y, v x ,v y )Calculation method:
[0055]
[0056] Among them, (x, y) represents the center position on the COMS pixel plane, and the speed (v x ,v y ) is the two-dimensional synthesis tracking speed, n corresponds to the frame of image data, I n is the pixel intensity at the coordinate (x, y) in the nth frame. In this formula, round is a function that rounds the number. Here, nv x and nv y The n in represents the number of frames and serves as a positioning symbol.
[0057] In step S5, after obtaining a single-frame star point image of the target asteroid, a star point signal-to-noise ratio (SNR) conversion formula of the single-frame star point of the target asteroid is proposed as follows:
[0058]
[0059] Where T is the signal strength value of the target asteroid, which is equivalent to the aforementioned I(x, y, v x ,v y ), is the noise intensity value of the target asteroid, Signal represents the signal strength of the target asteroid, Noise represents the noise intensity of the target asteroid, and ∝ represents a positive correlation, that is, SNR is positively correlated with Signal and Noise.
[0060] The significance of introducing the signal-to-noise ratio here is that if the target asteroid displacement vector corresponds to the starry sky velocity, the photons of the target asteroid will continue to accumulate, and the background noise from the zodiac will be limited to a finite point spread function. Figure 3 When all images are added, it is equivalent to a synthetic long exposure. The photon energy of faint near-Earth asteroids will increase linearly with the increasing number of frames, while the noise will increase with the square root of the number of frames. Therefore, the star point signal-to-noise ratio will also increase with the square root of the number of frames.
[0061] Although the content of the present invention has been described in detail through the above preferred embodiments, it should be appreciated that the above description should not be considered as a limitation of the present invention. After reading the above content, it will be apparent to those skilled in the art that various modifications and substitutions of the present invention will occur. Therefore, the protection scope of the present invention should be limited by the appended claims.
Claims
1. A synthetic tracking method for faint asteroids based on CMOS detectors, characterized in that: The method comprises: Step S1, using a CMOS detector to acquire a total of N frames of original images of the sky region where the target asteroid is located; Step S2, subtracting the sky background from the N frames of original images one by one, to obtain a total of N frames of images without the sky background; Step S3, using median filtering to compensate for pointing jitter on a total of N frames of images without sky background, to obtain a total of N frames of analysis images; Step S4, performing velocity gridding processing on a total of N frames of analysis images to obtain a total of N frames of operation images; Step S5, using a multi-vector shift and addition algorithm to process a total of N frames of operation images frame by frame to obtain a single-frame star point image of the target asteroid.
2. The method for synthetically tracking faint asteroids based on CMOS detectors according to claim 1, characterized in that: The step S2 comprises: Step S21, preselecting a star region with fewer planets, photographing the star region to estimate the sky background; Step S22, subtracting the sky background from the N frames of original images one by one; Step S23, according to the threshold search method, the pixel signals caused by cosmic rays and bad pixels in the original image after the sky background is subtracted are removed to obtain a total of N frames of images without sky background.
3. The method for synthetically tracking faint asteroids based on CMOS detectors according to claim 2, characterized in that: The step S3 of using median filtering to compensate for pointing jitter includes: Any of the images without sky background is an I×J image, wherein the length is I, i=1, 2...I, and the width is J, j=1, 2...J; I(i,j)=Med{I(im,jk),I(i-m+1,j-k+1),...,I(i+m,j+k)} Among them, I(i,j) is the pixel grayscale value of pixel (i,j), and m and k are half of the number of data sets respectively.
4. The method for synthetically tracking faint asteroids based on CMOS detectors according to claim 3, characterized in that: The step S5 comprises: Step S51, determine the latitude values (x, y, V) of the target asteroid in the 2nd to Nth frame computing images one by one x 、V y , D AU ); Where x is the horizontal coordinate of the center position of the target asteroid in the nth frame computing image, y is the vertical coordinate of the center position of the target asteroid in the nth frame computing image, V x The horizontal cosmic velocity of the target asteroid at the center of the nth frame of the computational image, V y is the ordinate cosmic velocity of the target asteroid at the center of the nth frame computing image, D AU is the distance between the CMOS detector and the target asteroid, n = 2, 3, ... N; Step S52, shifting the positions of the target asteroid in the 2nd to Nth frames of computing images to the 1st frame of computing image one by one according to the latitude values, to obtain a single-frame star point map of the target asteroid.
5. The method for synthetically tracking faint asteroids based on CMOS detectors according to claim 4, characterized in that: In step S5, the signal strength of the target asteroid of a single-frame star point is calculated as follows: Among them, (x, y) represents the center position on the COMS pixel plane, and the speed (v x ,v y ) is the two-dimensional synthesis tracking speed, n corresponds to the frame of image data, I n is the pixel intensity at coordinate (x, y) in the nth frame.
6. The method for synthetically tracking faint asteroids based on CMOS detectors according to claim 5, characterized in that: The conversion formula of the star point signal-to-noise ratio (SNR) of the target asteroid of the single-frame star point in step S5 is as follows: Where T is the signal strength value of the target asteroid, is the noise intensity value of the target asteroid, Signal represents the signal intensity of the target asteroid, Noise represents the noise intensity of the target asteroid, and ∝ represents a positive correlation.
7. A method for synthetically tracking faint asteroids based on a CMOS detector according to any one of claims 1 to 6, characterized in that: The CMOS detector uses an exposure time of 20 ms and an image output rate of 50 frames per second.
8. A method for synthetically tracking faint asteroids based on a CMOS detector according to any one of claims 1 to 6, characterized in that: The step S4 processes the image using a 120×100 velocity grid.
9. A method for synthetically tracking faint asteroids based on a CMOS detector according to any one of claims 1 to 6, characterized in that: The step S4 uses FPGA technology to perform parallel processing on the images.