CN108507564A - A kind of star sensor method for positioning mass center based on point spread function fitting - Google Patents
A kind of star sensor method for positioning mass center based on point spread function fitting Download PDFInfo
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- CN108507564A CN108507564A CN201810698182.2A CN201810698182A CN108507564A CN 108507564 A CN108507564 A CN 108507564A CN 201810698182 A CN201810698182 A CN 201810698182A CN 108507564 A CN108507564 A CN 108507564A
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Abstract
The invention discloses it is a kind of based on point spread function fitting star sensor method for positioning mass center, the method includes：Step 1) obtains a width and refers to asterism picture, calculates the barycenter with reference to asterism picture；Step 2) obtains effective point spread function with reference to asterism picture using sinc function pairs into row interpolation, to obtain any position asterism picture resampling；After step 3) is for a width target asterism picture, a square zoning is selected centered on asterism pixel as where peak value, then by target asterism as in zoning part and step 2) in obtained resampling asterism picture carry out least square fitting, target asterism picture is estimated relative to the centroid motion with reference to asterism picture；Step 4) sums the target asterism picture that the barycenter for the reference asterism picture that step 1) obtains and step 3) obtain relative to the estimation of centroid motion and the zoning top left co-ordinate of target asterism picture for referring to asterism picture, so that it may to obtain the barycenter of target asterism picture.
Description
Technical field
The present invention relates to spacecraft attitude fields of measurement, more particularly to carry out the star sensor skill of attitude measurement based on star chart
A kind of art, and in particular to star sensor method for positioning mass center based on point spread function fitting.
Background technology
Star sensor is a kind of equipment carrying out attitude measurement as object of reference using fixed star, has precision height, without cumulative errors
Advantage, be widely used in aerospace field.In recent years, with the fast development in the fields such as earth observation, space science,
It is higher and higher to space attitude control and the required precision of attitude measurement.Therefore the measurement accuracy for improving star sensor is always sky
Between technical field lasting pursuit.
The center coordination precision for improving asterism picture is to determine the key factor of attitude measurement accuracy.Traditional centroid method has calculation
The advantages of method is simple, calculating speed is fast, strong robustness is that the asterism image quality heart most commonly seen in star sensor field at present is fixed
Position method.One defect of traditional centroid method is that its systematic error is larger, although dimensional Gaussian point spread function pair can be used
Systematic error is analyzed and compensated can reduce systematic error to a certain extent, but the defocus that general star sensor uses
The point spread function of optical system and the shape difference of dimensional Gaussian point spread function are larger, especially optical aberration compared with
Compensation effect unobvious when big.In addition, the photon numbers that the pixel of barycenter window edge detects are considerably less, traditional centroid method is but given
Their higher weights are given, this causes the noise resisting ability of traditional centroid method poor.It is not deposited then based on point spread function fitting
In above-mentioned two problems, ultimate challenge that such methods face is that the point spread function of optical system is difficult accurately to learn, at present
In star sensor field, there are no a kind of method for positioning mass center based on point spread function fitting.
Invention content
It is an object of the invention to overcome conventional star sensor method for positioning mass center measurement accuracy it is low, by optical aberration shadow
Ring big, noise resisting ability difference defect.
To achieve the goals above, the present invention proposes a kind of star sensor center coordination being fitted based on point spread function
Method, the method includes：
Step 1) obtains a width and refers to asterism picture, calculates the barycenter with reference to asterism picture；
Step 2) obtains effective point spread function with reference to asterism picture using sinc function pairs into row interpolation, arbitrary to obtain
The resampling of the asterism picture of position；
After step 3) is for a width target asterism picture, selection one is square centered on asterism pixel as where peak value
Zoning, then by target asterism as in zoning part and step 2) in obtained resampling asterism picture carry out it is minimum
Two multiply fitting, are estimated relative to the centroid motion with reference to asterism picture target asterism picture；
The target asterism picture that step 4) obtains the barycenter for the reference asterism picture that step 1) obtains and step 3) is relative to ginseng
The zoning top left co-ordinate of the estimation and target asterism picture of examining the centroid motion of asterism picture is summed, so that it may to obtain
The barycenter of target asterism picture.
As a kind of improvement of the above method, the step 1) specifically includes：
Step 1-1) allow star sensor point spread function on detector array surface along x-axis and y axis using high precision turntable
It is moved with moving step length a/M, multiframe asterism picture is acquired on the position after each movement and is averagely obtained each position
Asterism data；A is Pixel Dimensions, and M is to move step number along x-axis and y-axis both direction, amounts to mobile M × M position；
Step 1-2) to step 1-1) in the asterism data of each position that obtain pre-process, the pretreatment includes
Details in a play not acted out on stage, but told through dialogues calibration and flat field calibration, the asterism picture after being pre-processed；
Step 1-3) in the asterism picture after each pretreatment, pixel of the asterism as where peak value is found, and with asterism
A square zoning is selected centered on the pixel as where peak value；
Step 1-4) to the asterism picture of each position in step 1-3) part in the zoning of selection carries out group again
It closes, obtains a width and refer to asterism picture；
Wherein,It is asterism picture when point spread function moves along the x-axis i steps, moves along y-axis j steps in zoning
M rows the n-th row pixel value, 1≤m≤n_roi, 1≤n≤n_roi, n_roi be square zoning the length of side, m
It is positive integer with n；
Step 1-5) calculate the barycenter for referring to asterism picture：
Wherein,To refer to the barycenter of asterism picture,It is the pth of the reference asterism picture reconfigured
The value of row q row pixels, the pixel sampling interval with reference to asterism picture are a/M, 1≤p≤M × nroi, 1≤q≤M × nroi, p, q
For positive integer.
As a kind of improvement of the above method, the value range of the M is：4~10.
As a kind of improvement of the above method, the length of side n_roi of the zoning of the square is 5 or 7.
As a kind of improvement of the above method, the resampling of the step 2) is：
Wherein,It is that barycenter offsets by (Δ x relative to reference to asterism picturec,Δyc) resampling
Asterism picture.
As a kind of improvement of the above method, the centroid motion in the step 3) is estimated as：
Wherein,It is in the zoning of square of the target asterism picture centered on asterism pixel as where peak value
M rows the n-th row pixel value,It is target asterism picture and the estimated value with reference to centroid motion between asterism picture.
As a kind of improvement of the above method, the centroid estimation of target asterism picture is in the step 4)：
Wherein,It is counting for square of the target asterism picture centered on asterism pixel as where peak value
The coordinate value of the top left corner pixel in region is calculated,It is the centroid estimation of target asterism picture.
The advantage of the invention is that：
In conjunction with the modulation transfer function and image sensor pixel frequency response characteristic of optical system of star sensor, the present invention
Propose a kind of star sensor method for positioning mass center based on asterism as resampling；Not only center coordination precision is high for this method, and
And influenced by optical aberration small, it can be effectively improved in the case where not increasing existing star sensor resource requirement
The measurement accuracy of star sensor.
Description of the drawings
Fig. 1 is the flow chart for the star sensor method for positioning mass center of the present invention being fitted based on point spread function.
Specific implementation mode
In conjunction with attached drawing, the invention will be further described.
With reference to figure 1, the star sensor method for positioning mass center of the invention based on point spread function fitting includes the following steps：
Step 1) using high precision turntable allows star sensor point spread function in detector array (CCD in the lab
Or APS) surface moved along x-axis and y-axis with a fixed step size, so that moving range is covered 1 pixel, in each station acquisition
Multiframe asterism picture is averaged.
Step 2) pre-processes the asterism data of each position of acquisition in step 1), and the pretreatment includes dark
Field calibration and flat field calibration, the asterism picture after being pre-processed.
Step 3), step 2) obtain initial position pretreatment after asterism picture in, find asterism as peak value institute
Pixel, and by asterism as selecting a square zoning centered on pixel where peak value.
Step 4), the part to the asterism picture of each position obtained in step 2) in the zoning that step 3) obtains
It is reconfigured, obtains the very low reference asterism picture in a width pixel sampling interval.
Step 5), the barycenter that the reference asterism picture obtained in step 4) is calculated using traditional centroid method.
Step 6), using the reference asterism picture obtained in step 4), accurately had into row interpolation using sinc functions
Imitate point spread function, so as to obtain any position asterism picture resampling.
Step 7), after obtaining a width target asterism picture, equally by asterism as selection one is being just centered on pixel where peak value
Rectangular zoning, then by target asterism as in zoning part and step 6) in obtained resampling asterism picture into
Row least square fitting estimates target asterism picture relative to the centroid motion with reference to asterism picture.
It is step 8), the target asterism picture obtained in the barycenter of the reference asterism picture obtained in step 5) and step 7) is opposite
It sums in the estimation of centroid motion of reference asterism picture and the zoning top left co-ordinate of target asterism picture, so that it may with
Obtain the barycenter of target asterism picture.
Each step in the method for the present invention is described further below.
In step 1), the step number that moves along x-axis and y-axis both direction is M, and moving step length a/M, wherein a are picture
Plain size amounts to mobile M × M position.The selection of M is related with camera lens F numbers, the size of defocusing amount, in order to ensure point spread function
Number reconstruction accuracy, reduces operand, generally takes 4~10.
It is related with noise of detector, background noise level etc. in the frame number of each station acquisition asterism picture in step 1),
In order to reduce the influence of noise, general frame number should be greater than 10.
In step 3), the size of square zoning, as size determination, can be 5 × 5,7 × 7 etc. according to asterism.
The selection of window size, if crossing conference influences calculating speed；And if too small, can error be generated due to signal cutout.
In step 4), mode such as following formula (1) that specific asterism picture reconfigures：
WhereinIt is asterism when point spread function moves along the x-axis i steps, moves along y-axis j steps as in zoning
The value range of the value of m rows the n-th row pixel, m, n is from 1 to n_roi, and n_roi is the size of zoning；
In step 5), it is with reference to the specific method of the asterism image quality heart using the calculating of traditional centroid method：
WhereinIt is the barycenter for the reference asterism picture being calculated,It is the reference star reconfigured
The value of the pth row q row pixels of point picture, the pixel sampling interval with reference to asterism picture is a/M, and the value range of p, q are from 1 to M*
n_roi。
Due to average by the multiframe asterism picture in step 1), the noise with reference to asterism picture is very low, so with reference to asterism picture
The random error very little of centroid calculation result.Very low additionally, due to the pixel sampling interval with reference to asterism picture, result of calculation is
Error of uniting also can be very low.
In step 6), effective point spread function is the convolution of optical system point spread function and pixel response function, star
Point seems the sampling of effective point spread function, and the sampling interval is Pixel Dimensions a.
In step 6), emulate and the experimental results showed that the high fdrequency component of effective point spread function is very low.Therefore, although
With reference to asterism as sampling interval a/M cannot meet the requirement of sampling thheorem, expanded with sinc function interpolations reconstruct available point
Dissipating the precision of function can meet the requirements.
In step 6), the method such as following formula (3) of the resampling of any position asterism picture is specifically obtained by interpolation：
In formulaIt is that barycenter offsets by (Δ x relative to reference to asterism picturec,Δyc) resampling
Asterism picture.
In step 7), the size shape of zoning and being consistent in step 3).
The specific centroid motion method of estimation such as following formula (4) in step 7)：
In formulaIt is the value of m row n-th row pixel of the target asterism picture in zoning,It is target
The estimated value of centroid motion between asterism picture and reference asterism picture.
In step 8), the method for the specific barycenter for calculating target asterism picture is as follows：
In formulaIt is the coordinate value of the zoning top left corner pixel selected in step 7),It is the centroid estimation of target asterism picture.
It should be noted last that the above examples are only used to illustrate the technical scheme of the present invention and are not limiting.Although ginseng
It is described the invention in detail according to embodiment, it will be understood by those of ordinary skill in the art that, to the technical side of the present invention
Case is modified or replaced equivalently, and without departure from the spirit and scope of technical solution of the present invention, should all be covered in the present invention
Right in.
Claims (7)
1. a kind of star sensor method for positioning mass center based on point spread function fitting, the method includes：
Step 1) obtains a width and refers to asterism picture, calculates the barycenter with reference to asterism picture；
Step 2) obtains effective point spread function with reference to asterism picture using sinc function pairs into row interpolation, to obtain any position
Asterism picture resampling；
After step 3) is for a width target asterism picture, a square calculating is selected centered on asterism pixel as where peak value
Region, then by target asterism as in zoning part and step 2) in obtained resampling asterism picture carry out least square
Target asterism picture is estimated in fitting relative to the centroid motion with reference to asterism picture；
The target asterism picture that step 4) obtains the barycenter for the reference asterism picture that step 1) obtains and step 3) is relative to reference star
The estimation of centroid motion of point picture and the zoning top left co-ordinate of target asterism picture are summed, so that it may to obtain target
The barycenter of asterism picture.
2. the star sensor method for positioning mass center according to claim 1 based on point spread function fitting, which is characterized in that
The step 1) specifically includes：
Step 1-1) using high precision turntable allow star sensor point spread function on detector array surface along x-axis and y-axis to move
Dynamic step-length a/M is moved, and the star that multiframe asterism picture is averagely obtained each position is acquired on the position after each movement
Point data；A is Pixel Dimensions, and M is to move step number along x-axis and y-axis both direction, amounts to mobile M × M position；
Step 1-2) to step 1-1) in the asterism data of each position that obtain pre-process, the pretreatment includes details in a play not acted out on stage, but told through dialogues
Calibration and flat field calibration, the asterism picture after being pre-processed；
Step 1-3) in the asterism picture after each pretreatment, pixel of the asterism as where peak value is found, and with asterism as peak
A square zoning is selected centered on pixel where value；
Step 1-4) to the asterism picture of each position in step 1-3) part in the zoning of selection reconfigures, obtains
Asterism picture is referred to a width；
Wherein,It is that point spread function moves along the x-axis i steps, moves m of the asterism picture in zoning when j is walked along y-axis
The value of row the n-th row pixel, 1≤m≤n_roi, 1≤n≤n_roi, n_roi are the length of sides of the zoning of square, and m and n are
Positive integer；
Step 1-5) calculate the barycenter for referring to asterism picture：
Wherein,To refer to the barycenter of asterism picture,It is the pth row q of the reference asterism picture reconfigured
The value of row pixel, the pixel sampling interval with reference to asterism picture are a/M, 1≤p≤M × nroi, 1≤q≤M × nroi, p, q are just whole
Number.
3. the star sensor method for positioning mass center according to claim 2 based on point spread function fitting, which is characterized in that
The value range of the M is：4~10.
4. the star sensor method for positioning mass center according to claim 2 or 3 based on point spread function fitting, feature exist
In the length of side n_roi of the zoning of the square is 5 or 7.
5. the star sensor method for positioning mass center according to claim 4 based on point spread function fitting, which is characterized in that
The resampling of the step 2) is：
Wherein,It is that barycenter offsets by (Δ x relative to reference to asterism picturec, Δ yc) resampling asterism
Picture.
6. the star sensor method for positioning mass center according to claim 5 based on point spread function fitting, which is characterized in that
Centroid motion in the step 3) is estimated as：
Wherein,It is the m in the zoning of square of the target asterism picture centered on asterism pixel as where peak value
The value of row the n-th row pixel,It is target asterism picture and the estimated value with reference to centroid motion between asterism picture.
7. the star sensor method for positioning mass center according to claim 6 based on point spread function fitting, which is characterized in that
The centroid estimation of target asterism picture is in the step 4)：
Wherein,It is the calculating area of square of the target asterism picture centered on asterism pixel as where peak value
The coordinate value of the top left corner pixel in domain,It is the centroid estimation of target asterism picture.
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