CN108896039B - Moon stray light inhibition method applied to star sensor - Google Patents
Moon stray light inhibition method applied to star sensor Download PDFInfo
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Abstract
A method for suppressing moonlight stray light applied to a star sensor relates to the technical field of astronomical navigation, and solves the problem that after moonlight and other star body stray light enter a star sensor field of view, bright light spots appear after imaging of a detector, influences on threshold calculation, centroid extraction and incapability of outputting real-time star sensor postures of the star sensor are caused, the star sensor images an actual star map through the detector, a data processor performs four-blocking on the collected star map, extracts star point data larger than the threshold of star map subblocks in each subblock, generates four sample data and performs screening, FIFO1 is adopted to perform line caching on the sample data of each line sampling period, the sample data are stored through FIFO2 according to set conditions, the data processor is adopted to process calculation, and finally a star point structural body is sent to a star map matching module to perform star map identification and posture calculation. The method reduces the image processing time occupied by the large light spot, ensures normal extraction and further ensures the attitude output precision of the star sensor, and greatly improves the applicability of the star sensor.
Description
Technical Field
The invention relates to the technical field of astronomical navigation, in particular to a moon stray light suppression method applicable to a star sensor.
Background
The star sensor is a high-precision attitude sensitive measuring instrument, determines the attitude of a carrier by detecting fixed stars at different positions on a celestial sphere, and is the most widely applied attitude measuring equipment in the field of aerospace at present. After the stray light of the star bodies such as the sun, the moon and the like enters the view field of the star sensor, bright light spots can appear after the detector images, the threshold value of the star map is greatly increased, and the influence is as follows: 1. the gray value of the star after imaging in the detector imaging system is low, so that the gray value of the star point after threshold segmentation can be used as the background, a star point target cannot be extracted, and in severe cases, the star sensor cannot output a real-time posture, so that the star sensor enters a space 'lost' state. 2. Bright light spots in the star map can be taken as targets to be sent to a star sensor target extraction module after being subjected to threshold segmentation, so that a large amount of hardware processing time is occupied, and the real-time property of star sensor attitude output is influenced. The traditional star sensor avoids the stray light of the stars, such as the sun, the moon and the like, through the light shield, but the light shield can only avoid the stray light of the stars, such as the sun, the moon and the like, with a fixed angle, and the attitude is usually difficult to output in real time after the moon completely enters the field of view of the star sensor, so that the space equipment is lost in space.
Disclosure of Invention
The invention provides a moon stray light suppression method applied to a star sensor, aiming at solving the influence of moon, earth and other star stray light on star sensor attitude output.
A moon veiling glare inhibition method applied to a star sensor is realized by the following steps:
the method comprises the following steps that firstly, a star sensor images an actual star atlas through a detector, a data processor conducts four-blocking on the collected star atlas to obtain four image sub-blocks, meanwhile, self-adaptive threshold value calculation is conducted on each image sub-block, threshold value segmentation is conducted according to the threshold value of each image sub-block, star point data which are larger than the threshold value of the star atlas sub-block in each image sub-block are extracted, and four sample data are generated;
step two, screening the four sample data generated in the step one, adopting FIFO1 to cache the sample data of each line sampling period, counting the number T of continuous y columns of each line, and when T is less than or equal to a threshold value ThThen, storing the target data into a memory FIFO2, and counting the x rows in sequence to obtain a target data set of the x rows;
step three, a target extraction module in the data processor reads the target data set in the FIFO2 in the step two, star point connectivity analysis and centroid calculation are carried out, and the size of the target is obtained
Mean gray scale
And the order of stars and dotsCentroid coordinates marked on star map coordinate system
Deleting target sizes
Target of isolated points or random noise less than 4, target size deleted
Bright spots or halos larger than 50 to obtain a final star point structural body;
and step four, sending the final star point structural body obtained in the step three to a star map matching module for star map recognition and attitude calculation, and realizing the suppression of moonlight.
The invention has the beneficial effects that: the moon stray light inhibition method applied to the star sensor can not only filter moon stray light, but also inhibit large spots and halos formed by earth gas stray light on star images; according to the star sensor attitude information output method, when moonlight enters the star sensor field of view, star sensor attitude information can still be stably output; the invention is easy to realize by a hardware platform, has simple, reliable and effective method and can greatly improve the applicability of the star sensor.
Drawings
FIG. 1 is a schematic block diagram of a method for suppressing moonlight for a star sensor according to the present invention;
FIG. 2 is a schematic diagram illustrating an eight-connectivity analysis principle of a star point target in the method for suppressing moonlight stray of a star sensor according to the present invention;
FIG. 3 is an imaging star map of the moon flare in the method for suppressing the moon flare applied to the star sensor according to the present invention, when the moon flare is at the upper left corner of the target surface of the detector;
fig. 4 shows a real-time attitude output result of the star sensor after moon blooming suppression in the moon blooming suppression method applied to the star sensor according to the present invention. Fig. 4a is a simulated star map of star point centroid results output by the star sensor after moon flare is removed, and fig. 4b is attitude data and star point centroid results output by the star sensor in real time.
Detailed Description
In the first embodiment, the present embodiment is described with reference to fig. 1 to 4, and a method for suppressing moonlight stray light applied to a star sensor is implemented by the following steps:
step one, the star sensor images an actual star map under the background of moonlight through a detector, the imaging result is shown as 3, a data processor of the star sensor conducts four-block division on the collected image, and threshold calculation is conducted on each image sub-block. Adopting an adaptive threshold value calculation method, wherein the calculation formula is as follows:
Timage＝v+aσ
in the formula, v is the mean value of the grey scale of the star map, a is a scale factor, and sigma is the standard deviation of the star map. And taking 3 according to the property of normal distribution and the reference test result a.
After obtaining the threshold value of the image sub-block, extracting the value greater than the threshold value TimageThe navigation star point in the star map has three data of x rows, y columns and z gray value, and four data samples are generated.
The significance of the four blocks of the star map is two: 1. the star sensor can process the four image subblocks simultaneously, so that the hardware processing time is shortened, and the real-time performance of a star sensor system is improved; 2. the occupied areas of the star stray light in the star map are different, the threshold value of each star map is different, and the existence of large light spots and false targets can be more intelligently and effectively distinguished by respectively carrying out threshold segmentation on the block images, so that intelligent elimination is carried out.
Step two, intelligently screening the four sample data generated in the step one, adopting FIFO1 to perform line delay on star map line data, because the star map is divided into four blocks, each line of data of each sub-block is 512 pixels, the data depth of FIFO1 is 512, for each line sampling period, calculating the number T of continuous y columns of each line, and when the value of T is less than or equal to a threshold value ThWhen target data is written into target data memory FIFO2, and conversely, when the value of T is greater than threshold ThWhen it is stated that the line contains large spots, halos, etc. of lightThe target disturbance, which is a block of samples that are deleted from being written into the target data memory FIFO2, prevents the incoming star target fetch module from using hardware processing resources. Since the star flare is imaged as a quasi-circular target in the star map, the embodiment is verified by multiple tests, ThWhen the set value is 20, the effect of suppressing flare is best.
And step three, the target data in the target data memory FIFO2 in the step two is sent to a target extraction module, the target extraction module adopts an eight-communication connectivity analysis method, the principle of the eight-communication connectivity analysis method is shown in fig. 2, the star target of the star sensor is a light spot which is defocused by the image surface, and the star target is a convex target, so that an eight-communication criterion and a related processing method are mainly adopted in the embodiment. And after the connectivity analysis, the number of the targets in the image and the area of each target are obtained, and finally, the centroid calculation of the star point targets in the image is carried out.
The embodiment adopts a gray-weighted centroid calculation method, and the formula is as follows:
where (x, y) represents the pixel position in the image belonging to a certain object S, f (x, y) is the gray scale value of the pixel (x, y) position, TimageIs the threshold value of the star map subblock.
And deleting the generated target structure again, wherein the size of a punctiform target formed by the 5.5Mv fixed star on the star sensor imaging device is usually more than 2 × 2 and less than 7 × 7 by the aid of defocused imaging of the star sensor optical system and by reference to design parameters and results of the star sensor optical system, so that false targets such as isolated points and random noise with the number of pixels of less than 4 occupied by the target and large targets such as bright spots and halos with the number of pixels of more than 50 occupied by the target are deleted, and through the step, the star sensor completes suppression of veiling glare such as moon and earth atmosphere and achieves continuous and correct output of a centroid result of the star point target.
And step four, sending the final target structure generated in the step three to a star map matching module for star map recognition and attitude calculation, and realizing the suppression of moonlight stray light. The recognition result is shown in fig. 4, the method solves the influence of moonlight on the attitude output of the star sensor, and improves the application range of the star sensor. Fig. 4a is a simulated star map of star point centroid results output by the star sensor after moon flare is removed, and fig. 4b is attitude data and star point centroid results output by the star sensor in real time.
The method for inhibiting the moonlight stray light applied to the star sensor solves the problem that the moonlight, the earth gas and other stray light have influence on the system attitude output, and greatly improves the applicability of the star sensor. When the moon enters the view field of the star sensor, the interference area and the size of the interference target can be judged in a self-adaptive manner, so that stray light is intelligently filtered and enters the star sensor target extraction module, the image processing time occupied by large light spots is reduced, and the normal extraction of star point targets is ensured, thereby ensuring the attitude output precision of the star sensor.
Claims (3)
1. The method for inhibiting the moonlight stray light of the star sensor is characterized by comprising the following steps of:
the method comprises the following steps that firstly, a star sensor images an actual star atlas through a detector, a data processor conducts four-blocking on the collected star atlas to obtain four image sub-blocks, meanwhile, self-adaptive threshold value calculation is conducted on each image sub-block, threshold value segmentation is conducted according to the threshold value of each image sub-block, star point data which are larger than the threshold value of the star atlas sub-block in each image sub-block are extracted, and four sample data are generated;
step two, screening the four sample data generated in the step one, adopting FIFO1 to cache the sample data of each line sampling period, counting the number T of continuous y columns of each line, and when T is less than or equal to a threshold value ThThen, storing the target data into a memory FIFO2, and counting the x rows in sequence to obtain a target data set of the x rows;
step three, a target extraction module in the data processor reads the target data set in the FIFO2 in the step two, star point connectivity analysis and centroid calculation are carried out, and the size of the target is obtained
Mean gray scale
And the centroid coordinate of the star point target in the star map coordinate system
Deleting target sizes
Deleting the target size of isolated points or random noise targets smaller than 4 pixels
Bright light spots or halos larger than 50 pixels to obtain a final star point structural body;
and step four, sending the final star point structural body obtained in the step three to a star map matching module for star map recognition and attitude calculation, and realizing the suppression of moonlight.
2. The method for suppressing the veiling glare of moon on the star sensor as claimed in claim 1, wherein in the first step, the star point data greater than the threshold value in each image sub-block is extracted, and the star point data comprises three data of the x row, the y column and the gray value f (x, y).
3. The method for suppressing the veiling glare of moon applied to the star sensor as claimed in claim 1, wherein in the first step, the method for calculating the threshold of the star map sub-block is as follows:
Timage＝v+aσ
in the formula, v is the mean value of the grey scale of the star map, a is a scale factor, and sigma is the standard deviation of the star map.
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