CN103175543A - Internal response difference correction method for charge coupled device (CCD) pixel - Google Patents

Abstract

The invention discloses an internal response difference correction method for a charge coupled device (CCD) pixel. The correction is realized by utilizing strong correlation between the measurement flow error of an observational star brought by the internal response difference in the CCD pixel and the normalized centric coordinates of the observational star. The two-dimensional correction map of the CCD target surface grouping is established through the actual timing sequence photometric observations, the measured data can find the corresponding two-dimensional correction map according to the observed star image central coordinate and the normalized coordinate, and the corresponding flow correction amount is obtained from the map; and finally, the correction of the photometric error brought by the internal response difference of the CCD pixel is realized, and the photometric precision is improved.

Description

The antidote of the inner response difference of a kind of CCD pixel

Technical field

The present invention relates to the antidote of the inner response difference of a kind of CCD pixel, need in astronomical sight to be applicable to carry out process because of the chronometer data that photometry flow error that the inner response difference of CCD pixel brings corrects.Be specially adapted to wide visual field, low sampling rate and front scope according to type CCD, can reduce significantly the photometry error of bringing because of the inner response difference of CCD pixel.

Background technology

Charge Coupled Device (CCD) imageing sensor (Charge Coupled Device, be called for short CCD), it uses a kind of semiconductor material of ISO to make, can be transformed into charge signal to light signal, convert digital signal to by the analog to digital converter chip, digital signal is preserved by flash memory or the built-in hard disk card of camera inside after overcompression, thereby can give computing machine data transmission easily, and by means of the processing means of computing machine, process as required image.

CCD is as using image acquisition terminal very widely in Modern Astronomical observation.It is mainly constructed with principle: CCD is a face battle array that is rearranged according to certain rules by many photosensitive pixels.Each pixel in the face battle array is exactly a mos capacitance device (mostly being greatly photodiode), when having 1 bundle ray cast to the mos capacitance device, photon passes transparency electrode and oxide layer, enters mos capacitance device substrate, last photon is converted to electronics, exports with electric signal.The efficient that photon is converted to electronics is called QE, restriction due to manufacturing process, have this species diversity of small difference for the photoelectric transformation efficiency QE of different pixels and be called as response difference between pixel, adopt the method for " flat field " to correct in the data handling procedure of Modern Astronomical, namely utilize the equal light of luminosity to beat on the CCD front, just can draw correct amount from the output charge difference of each last pixel.Simultaneously, due to the design feature of mos capacitance, CCD also exists the response difference of pixel inside, that is, if a branch of yardstick is beaten diverse location at a pixel less than the light of CCD pixel, the electron number that obtains due to the difference of photoelectric transformation efficiency is different.Due to the CCD grid cell size seldom, and the PSF (point spread function) of general astronomical sight star image all can cover the pixel of a greater number, namely sampling is good.Like this because the photometry error that the inner response difference of CCD brings generally can not considered processing much smaller than other error.But for the scope as Hubble Telescope, because PSF is very little, the sampling relative deficiency that can seem, thereby can consider the rectification of inner response difference, the method for employing is " shake " method." shake " method requires to have very high pointing accuracy, and needs all " shake " observation to be carried out repeatedly in same visual field at every turn.

The astronomy that some small-bore large visual fields have appearred in the development of the modern astronomy project of touring the heavens, its visual field can reach 14 degree * 14 degree, the sampling rate of CCD can reduce greatly like this, and the photometry error that the inner response difference of CCD brings can become very remarkable, must carry out the correction that data are processed." shake " method refers to that to telescope accuracy requirement is high, and small-bore telescope is difficult to reach, and due to the restriction of observation mode, " shake " method is not suitable for the inner response difference of the telescopical CCD of this type and corrects simultaneously.

Summary of the invention

Technology of the present invention is dealt with problems and is: the response difference of CCD pixel inside can bring the measuring error of observation starlight degree flow in astronomical sight, and this error is for more remarkable under front observation condition according to type CCD and low sampling rate.The subject matter that the present invention solves is corrects this photometric measurement error of bringing because of the inner response difference of CCD.

Technical solution of the present invention is: the antidote of the inner response difference of a kind of CCD pixel, and step is as follows:

(1) according to the measuring flow error of observation star and the correlativity of the centre coordinate after the normalization of observation star, build the inner response difference two dimension of pixel rectification figure;

(2) measure flow and the center of observed object star, the center of normalization observed object star;

(3) correct figure according to the center after the normalization of observed object star by the inner response difference two dimension of interpolation pixel, calculate the flow correct amount;

(4) according to the flow correct amount, observed object star measuring flow is carried out error correction.

The inner response difference two dimension of described structure pixel rectification figure step is as follows:

(1.1) the fixing day district of selecting carried out continuous sequential photometry observation, obtain one group of seasonal effect in time series image;

(1.2) all images that observation in step (1.1) obtained carry out the removal of CCD background, flat field is corrected and the dark current Transformatin;

(1.3) all stars in the every width image j after step (1.2) processing are carried out aperture photometry, obtain the flow flux of every observation star k _kjAnd signal to noise ratio (S/N ratio) (S/N) _kjMeasure simultaneously the center (xc of every observation star _kj, yc _kj), filter out signal to noise ratio (S/N ratio) greater than 50 all observation stars;

(1.4) according to the flow flux of the observation star after step (1.3) screening _kjWith center xc _kj, yc _kj, obtain every observation star flow fluxnorm after the normalization on whole photometry time series _kj, and then obtain this group photometry seasonal effect in time series flow intermediate value fluxMedian _k, according to ratio calculation outflow ratio R atioFlux both _kjIn addition, also need to complete normalization center position coordinates (xcPixIn _kj, ycPixIn _kj) processing, computing formula is

$\left\{\begin{array}{c}{\mathrm{xcPixIn}}_{\mathrm{kj}}={\mathrm{xc}}_{\mathrm{kj}}-\mathrm{int}\left({\mathrm{xc}}_{\mathrm{kj}}\right)\\ {\mathrm{ycPixIn}}_{\mathrm{kj}}={\mathrm{yc}}_{\mathrm{kj}}\mathrm{int}\left({\mathrm{yc}}_{\mathrm{kj}}\right)\end{array}\right.;$

(1.5) actual CCD target surface is divided into groups, according to the center (xc of observation star _kj, yc _kj), obtain the respective packets of every observation star on actual CCD target surface;

(1.6) each group in step (1.5) is carried out respectively following processing:

At first, 1 pixel is divided into the grid of 10 * 10 at least, the normalization center position coordinates value (xcPixIn that obtains according to step (1.4) _kj, ycPixIn _kj), draw the observation star that normalization center position coordinates value falls into each sub-grid respective image;

Then, according to the observation star of respective image in above-mentioned definite each sub-grid, determine to fall into the flow rate ratio of all observation stars of this sub-grid; And calculate its intermediate value median (RatioFlux), and represent the value of place sub-grid with this intermediate value, namely obtain the interior response difference two dimension of the pixel rectification figure of above-mentioned grid division.

Interpolation in described step (3) adopts the cubic spline function interpolation to improve the precision of the flow correct amount that calculates.

The present invention's advantage compared with prior art is:

(1) treatment scheme operation of the present invention is more direct and convenient with realization, easily realizes.

The present invention has avoided that the complicacy of CCD pixel section response difference is measured in real chamber and to the demanding difficulty of measuring equipment.Simultaneously, there is no concrete higher requirement for pointing accuracy yet.From observation mode, as long as by selecting good weather to carry out the sequential photometry, the two dimension rectification figure of the inner response difference of construction CCD pixel can realize.

(2) two dimension by the grouping of CCD target surface of the present invention is corrected and schemed to realize correcting, and is respond well.

The centre coordinate that the present invention studies after the normalization of the measuring flow of finding the observation star (because the inner response difference of CCD pixel brings) error and observation star exists stronger correlativity, correct figure by the two dimension that builds the inner response difference of CCD pixel, realize correcting.Simultaneously, the grouping of logical CCD target surface is eliminated because the inconsistency of the distribution of PSF on the CCD target surface.Show by examples of implementation, the invention process is respond well.

In a word, this two dimension rectification figure by CCD target surface piecemeal of the present invention realizes the error correction of the measuring flow (because the inner response difference of pixel brings) of observation star in astronomical sight, can facilitate, effectively realize the raising of the photometry precision in astronomical sight.

Description of drawings

Fig. 1 is the inner response difference antidote of pixel of the present invention implementing procedure figure;

Fig. 2 is that sequential photometry light curve of the present invention is measured implementing procedure figure;

Fig. 3 is the process flow diagram that the star of observed image of the present invention and reference picture mates;

Fig. 4 is the interior response difference rectification figure of the pixel of embodiments of the invention;

Fig. 5 is that the typical case of embodiments of the invention corrects light curve figure;

Fig. 6 is variance comparison diagram before and after the rectification of embodiments of the invention.

Embodiment

The present invention finds by research: the centre coordinate after the normalization of the measuring flow of observation star (because CCD pixel inner response difference brings) error and observation star exists stronger correlativity.The antidote of the inner response difference of CCD pixel of the present invention utilizes this correlativity to carry out correction process just.At first, build the inner response difference two dimension of pixel rectification figure by studying this correlativity; Then, measure flow and the center of observed object star, normalization target star center, and correct figure according to the center after the normalization of observed object star by the inner response difference two dimension of cubic spline function interpolation pixel, calculate the flow correct amount; At last, realize the error correction of observed object star measuring flow (because the inner response difference of pixel brings).As shown in Figure 1, concrete implementation step is as follows:

(1) the inner response difference two dimension of CCD pixel is corrected the structure of figure;

The main observation and the processing procedure that build the inner response difference two dimension of CCD rectification figure are:

1. need to select the good and high photometry of atmospheric transparency of weather condition to observe yesterday the intensive program of a stellar field moderate sky district carry out the sequential photometry and observe, obtain one group of seasonal effect in time series image; The sequential photometry sampled point of General Requirements Continuous Observation be 500 left and right or more than, weather condition is good.

2. observe the raw data that obtains need to complete the base conditioning of ccd image, processing procedure comprises: the rectification of the removal of CCD background (BIAS), flat field and dark current Transformatin.These processing procedures use astronomical software I RAF commonly used or general astronomic graph commonly used can realize as the data processing software bag.

3. all stars in above-mentioned every width image j are carried out aperture photometry, obtain the flow flux of every observation star k _kjAnd signal to noise ratio (S/N ratio) (S/N) _kj(for example can obtain by IRAF software).Utilize simultaneously gravity model appoach to measure the center (xc of every observation star _kj, yc _kj), its computing formula is:

$\left\{\begin{array}{c}{\mathrm{xc}}_{\mathrm{kj}}=\frac{\mathrm{\Σ}{x}_i{s}_i}{\mathrm{\Σ}{s}_i}\\ {\mathrm{yc}}_{\mathrm{kj}}=\frac{\mathrm{\Σ}{y}_i{s}_i}{\mathrm{\Σ}{s}_i}\end{array}\right.----\left(1\right)$

Wherein, x _iAnd y _iX and y coordinate figure for i pixel of observation star.s _iIt is the response of i pixel starlight.Read observation time and count obstime from the file header (Fits form) of image _jAnnotate: subscript k represents k observation star in the visual field, and subscript j represents j width image.Convenience is got k and j represents in order to explain, and makes a general reference certain star and certain figure.At last, according to the signal to noise ratio (S/N ratio) of measuring, filter out signal to noise ratio (S/N ratio) and carry out the calculating of following steps greater than all observation stars of 50.

4. every the flow (flux that observes star that 3. filters out according to above step _kj), signal to noise ratio (S/N ratio) (S/N) _kj, center (xc _kj, yc _kj) and observation time obstime _j, complete the light curve of every observation star and measure the detailed process that to complete as shown in Figure 2.By the light curve that records, can draw every observation star flow fluxnorm after the normalization on the photometry time series _kj, calculate its intermediate value and be designated as: fluxMedian _kFor in j width figure k observation star flow rate ratio for being designated as: RatioFlux _kj, calculating formula is:

In addition, also need to complete the normalized of center, be about to all centers and normalize to a pixel intrinsic coordinates (annotating: utilized the essentially identical characteristic of the inner response difference of each pixel of CCD here).Specific formula for calculation is,

$\left\{\begin{array}{c}{\mathrm{xcPixIn}}_{\mathrm{kj}}={\mathrm{xc}}_{\mathrm{kj}}-\mathrm{int}\left({\mathrm{xc}}_{\mathrm{kj}}\right)\\ {\mathrm{ycPixIn}}_{\mathrm{kj}}={\mathrm{yc}}_{\mathrm{kj}}-\mathrm{int}\left({\mathrm{yc}}_{\mathrm{kj}}\right)\end{array}\right.---\left(2\right)$

At last, according to the centre coordinate position, every observation star is divided into groups, grouping is main according to the distribution situation of PSF on the CCD target surface, namely for the otherness of the full width at half maximum of the point spread function (PSF) of bright star (signal to noise ratio (S/N ratio) is greater than 50) in same grouping on the CCD target surface less than 10%, generally adopt 4 * 4 totally 16 groups.

5. complete the two dimension rectification figure (it is identical that each group is completed treatment step) of response difference in pixel, wherein one group of processing procedure is: 1 pixel is divided into the grid of 10 * 10, and each sub-grid represents 0.1 pixel unit.According to above measurement result, have the RatioFlux of measurement for observation stars all on all photometry time-series images _kjWith the centre coordinate (xcPixIn after the normalization of correspondence _kj, ycPixIn _kj), divide into groups by each unit sub-grid coordinate figure according to the centre coordinate after normalization, can obtain falling into one group of flow rate ratio of each sub-grid.This group flow rate ratio is got intermediate value, be median (RatioFlux), the value that represents sublattice, can obtain median (RatioFlux) value (annotate: if corresponding sublattice does not have corresponding star, the value of getting all adjacent lattice is averaged the value that represents afterwards this sublattice) of 10 * 10 sublattices by above calculating.So just obtained the flow rate ratio figure of interior 10 * 10 grid take 0.1 pixel as sublattice of 1 pixel, namely in pixel, the two dimension of response difference is corrected figure.

(2) measure flow flux and center (xc, the yc) of observed object star, the center (xcPixIn, ycPixIn) of normalization observed object star; Concrete account form is with above-mentioned observation star.

(3) correct figure according to the center after the normalization of observed object star by the inner response difference two dimension of interpolation (in order to improve the precision of calculated flow rate correct amount, can adopt the cubic spline function interpolation) pixel, obtain flow correct amount Ratioflux.

(4) according to the flow correct amount, observed object star measuring flow is carried out error correction, the flow (flux after being corrected _Corrected) be: ${\mathrm{flux}}_{\mathrm{corrected}}=\frac{\mathrm{flux}}{\mathrm{Ratioflux}}.$

As shown in Figure 2, be light curve measuring process of the present invention.Concrete steps are: 1. at first find out picture quality preferably a width be designated as reference picture.The air quality of image is main basis for estimation.2. the star of observed image and the star of reference picture are mated according to the position, namely find out corresponding same corresponding star.Record flow flux _{K, ref}, center (xc _{K, ref}, yc _{K, ref}) and observation time obstime _{K, ref}Annotate: subscript k is k star, and following table ref represents reference picture.Concrete matching process step shown in Figure 3.3. the flow rate ratio of completing between the corresponding star of coupling calculates, and formula is:

(flux _{K, ref}: the flow of k star on reference picture; Flux _{K, j}Be the flow of k star on j width image).Then can calculate the flow rate ratio intermediate value between all the corresponding stars between observed image and reference picture, namely

(k=1...N coupling star), the flow that can draw at last normalization observation star arrives with reference to stellar field, as k star, is calculated as:

4. by the processing of above step, can obtain normalizing to reference to the photometry sequence after stellar field about the photometry flow of every observation star.

As shown in Figure 3, the process flow diagram that mates for the star of observed image of the present invention and reference picture.1. take j width figure as example, matching process is: respectively select respectively the coupling that 500 the brightest stars carry out star catalogue from j width figure and reference picture.The algorithm of coupling adopts widely used triangle map algorithm in astronomy, namely utilizes the triangle of the star structure in two stellar fields, and then carries out the coupling of similar triangles, finds out at last corresponding coupling star.Be output as one after Matching of star atlas is completed and mate in twos the list of broadcasting TV programs by satellite: the 1st, 2 classifies (xc as _kj, yc _kj) the 3rd, 4 classify (xc as _{K, ref}, yc _{K, ref}).2. utilize 4 rank 2-d polynomials to come match (xc _{K, ref}, yc _{K, ref}) and (xc _kj, yc _kj) Relations Among.Fitting formula can be written as:

$\left\{\begin{array}{c}{\mathrm{xc}}_{k,\mathrm{ref}}=a_1{a}_2{\mathrm{xc}}_{\mathrm{kj}}+a_3{\mathrm{xc}}_{\mathrm{kj}}^2+a_4{\mathrm{<figure-callout\; id="3"\; label="xc\; kj"\; filenames="DEST\_PATH\_HDA00003134480000031.png,DEST\_PATH\_HDA00003134480000032.png"\; state="\{\{state\}\}">xc</figure-callout>}}_{\mathrm{kj}}^{}+a_5{\mathrm{yc}}_{\mathrm{kj}}+a_6{\mathrm{yc}}_{\mathrm{kj}}^2+a_7{\mathrm{<figure-callout\; id="3"\; label="yc\; kj"\; filenames="DEST\_PATH\_HDA00003134480000031.png,DEST\_PATH\_HDA00003134480000032.png"\; state="\{\{state\}\}">yc</figure-callout>}}_{\mathrm{kj}}^{}\\ +a_8{\mathrm{xc}}_{\mathrm{kj}}{\mathrm{yc}}_{\mathrm{kj}}+a_9{\mathrm{xc}}_{\mathrm{kj}}^2{\mathrm{yc}}_{\mathrm{kj}}+a_{10}{\mathrm{<figure-callout\; id="3"\; label="xc\; kj"\; filenames="DEST\_PATH\_HDA00003134480000031.png,DEST\_PATH\_HDA00003134480000032.png"\; state="\{\{state\}\}">xc</figure-callout>}}_{\mathrm{kj}}^{}{\mathrm{yc}}_{\mathrm{kj}}\\ +a_{11}{\mathrm{xc}}_{\mathrm{kj}}{\mathrm{yc}}_{\mathrm{kj}}^2+a_{12}{\mathrm{xc}}_{\mathrm{kj}}^2{\mathrm{yc}}_{\mathrm{kj}}^2+a_{13}{\mathrm{<figure-callout\; id="3"\; label="xc\; kj"\; filenames="DEST\_PATH\_HDA00003134480000031.png,DEST\_PATH\_HDA00003134480000032.png"\; state="\{\{state\}\}">xc</figure-callout>}}_{\mathrm{kj}}^{}{\mathrm{yc}}_{\mathrm{kj}}^2\\ +a_{14}{\mathrm{xc}}_{\mathrm{<figure-callout\; id="3"\; label="kj\; yc\; kj"\; filenames="DEST\_PATH\_HDA00003134480000031.png,DEST\_PATH\_HDA00003134480000032.png"\; state="\{\{state\}\}">kj</figure-callout>}}{\mathrm{yc}}_{\mathrm{kj}}^{}{}_3^{}+a_{15}{\mathrm{xc}}_{\mathrm{kj}}^2{\mathrm{<figure-callout\; id="3"\; label="yc\; kj"\; filenames="DEST\_PATH\_HDA00003134480000031.png,DEST\_PATH\_HDA00003134480000032.png"\; state="\{\{state\}\}">yc</figure-callout>}}_{\mathrm{kj}}^{}+a_{16}{\mathrm{<figure-callout\; id="3"\; label="xc\; kj"\; filenames="DEST\_PATH\_HDA00003134480000031.png,DEST\_PATH\_HDA00003134480000032.png"\; state="\{\{state\}\}">xc</figure-callout>}}_{\mathrm{kj}}^{}{\mathrm{<figure-callout\; id="3"\; label="yc\; kj"\; filenames="DEST\_PATH\_HDA00003134480000031.png,DEST\_PATH\_HDA00003134480000032.png"\; state="\{\{state\}\}">yc</figure-callout>}}_{\mathrm{kj}}^{}\\ {\mathrm{yc}}_{k,\mathrm{ref}}=b_1+b_2{\mathrm{xc}}_{\mathrm{kj}}+{\mathrm{<figure-callout\; id="3"\; label="b"\; filenames="DEST\_PATH\_HDA00003134480000031.png,DEST\_PATH\_HDA00003134480000032.png"\; state="\{\{state\}\}">b</figure-callout>}}_3{\mathrm{xc}}_{\mathrm{kj}}^2+b_4{\mathrm{<figure-callout\; id="3"\; label="xc\; kj"\; filenames="DEST\_PATH\_HDA00003134480000031.png,DEST\_PATH\_HDA00003134480000032.png"\; state="\{\{state\}\}">xc</figure-callout>}}_{\mathrm{kj}}^{}+b_5{\mathrm{yc}}_{\mathrm{kj}}+b_6{\mathrm{yc}}_{\mathrm{kj}}^2+b_7{\mathrm{<figure-callout\; id="3"\; label="yc\; kj"\; filenames="DEST\_PATH\_HDA00003134480000031.png,DEST\_PATH\_HDA00003134480000032.png"\; state="\{\{state\}\}">yc</figure-callout>}}_{\mathrm{kj}}^{}\\ +{\mathrm{<figure-callout\; id="8"\; label="b"\; filenames="DEST\_PATH\_HDA00003134480000032.png"\; state="\{\{state\}\}">b</figure-callout>}}_8{\mathrm{xc}}_{\mathrm{kj}}{\mathrm{yc}}_{\mathrm{kj}}+{\mathrm{<figure-callout\; id="9"\; label="b"\; filenames="DEST\_PATH\_HDA00003134480000032.png"\; state="\{\{state\}\}">b</figure-callout>}}_9{\mathrm{xc}}_{\mathrm{kj}}^2{\mathrm{yc}}_{\mathrm{kj}}+{\mathrm{<figure-callout\; id="10"\; label="b"\; filenames="DEST\_PATH\_HDA00003134480000032.png"\; state="\{\{state\}\}">b</figure-callout>}}_{10}{\mathrm{<figure-callout\; id="3"\; label="xc\; kj"\; filenames="DEST\_PATH\_HDA00003134480000031.png,DEST\_PATH\_HDA00003134480000032.png"\; state="\{\{state\}\}">xc</figure-callout>}}_{\mathrm{kj}}^{}{\mathrm{yc}}_{\mathrm{kj}}\\ +{\mathrm{<figure-callout\; id="11"\; label="b"\; filenames="DEST\_PATH\_HDA00003134480000032.png"\; state="\{\{state\}\}">b</figure-callout>}}_{11}{\mathrm{xc}}_{\mathrm{kj}}{\mathrm{yc}}_{\mathrm{kj}}^2+{\mathrm{<figure-callout\; id="12"\; label="b"\; filenames="DEST\_PATH\_HDA00003134480000032.png"\; state="\{\{state\}\}">b</figure-callout>}}_{12}{\mathrm{xc}}_{\mathrm{kj}}^2{\mathrm{yc}}_{\mathrm{kj}}^2+{\mathrm{<figure-callout\; id="13"\; label="b"\; filenames="DEST\_PATH\_HDA00003134480000032.png"\; state="\{\{state\}\}">b</figure-callout>}}_{13}{\mathrm{<figure-callout\; id="3"\; label="xc\; kj"\; filenames="DEST\_PATH\_HDA00003134480000031.png,DEST\_PATH\_HDA00003134480000032.png"\; state="\{\{state\}\}">xc</figure-callout>}}_{\mathrm{kj}}^{}{\mathrm{yc}}_{\mathrm{kj}}^2\\ +{\mathrm{<figure-callout\; id="14"\; label="b"\; filenames="DEST\_PATH\_HDA00003134480000032.png"\; state="\{\{state\}\}">b</figure-callout>}}_{14}{\mathrm{xc}}_{\mathrm{<figure-callout\; id="3"\; label="kj\; yc\; kj"\; filenames="DEST\_PATH\_HDA00003134480000031.png,DEST\_PATH\_HDA00003134480000032.png"\; state="\{\{state\}\}">kj</figure-callout>}}{\mathrm{yc}}_{\mathrm{kj}}^{}{}_3^{}+{\mathrm{<figure-callout\; id="15"\; label="b"\; filenames="DEST\_PATH\_HDA00003134480000032.png"\; state="\{\{state\}\}">b</figure-callout>}}_{15}{\mathrm{xc}}_{\mathrm{kj}}^2{\mathrm{<figure-callout\; id="3"\; label="yc\; kj"\; filenames="DEST\_PATH\_HDA00003134480000031.png,DEST\_PATH\_HDA00003134480000032.png"\; state="\{\{state\}\}">yc</figure-callout>}}_{\mathrm{kj}}^{}+b_{16}{\mathrm{<figure-callout\; id="3"\; label="xc\; kj"\; filenames="DEST\_PATH\_HDA00003134480000031.png,DEST\_PATH\_HDA00003134480000032.png"\; state="\{\{state\}\}">xc</figure-callout>}}_{\mathrm{kj}}^{}{\mathrm{yc}}_{\mathrm{kj}}^3\end{array}---\left(3\right)\right.$

Wherein, and ai (i=1 ..16) and bi (i=1 ... 16) be fitting parameter, these 32 fitting parameters can be drawn by the match to the star on the coupling in twos in above 500 ludcidas.Then utilize (3) formula (relational expression that this match obtains) with the coordinate (xc of all the observation stars in j width figure _kj, yc _kj) be converted into coordinate under the reference picture coordinate system (xc ' _kj, yc ' _kj).3. the distance between star in twos of calculating observation star and all reference picture culminant stars under the reference picture coordinate system, distance (d) computing formula are under rectangular coordinate system apart from computing formula, i.e. distance

((xc wherein _ref, yc _ref) coordinate of all stars in the expression reference picture).Can select a reference star the shortest with observing the star distance according to the calculating of above distance (d), and the distance between them is also eligible, namely (error radius is generally got 1.5 pixels less than error radius, according to equipment and observation condition, this parameter can be done suitable adjustment), think that this reference star and observation star are to mate in twos star, the coordinate that can remember this reference star is (xc _{K, ref}, yc _{K, ref}).Annotate: every width image is all completed the processing procedure of above j width figure, can be realized star in all observed images and the coupling of reference picture culminant star.

Embodiment

(1) scope: the bore of telescope lens is 7 centimetres, and the CCD model is: before ALTA U9000, according to 3056 * 3056 pixels of type, each pixel is corresponding to 12.6 rads.The full width at half maximum (FWHM) of the point spread function of star image (PSF) is 1.2 pixels (corresponding 1.5 rads).

(2) choose the observation that the good observation of weather builds the inner response difference two dimension of pixel rectification figure night, concrete data acquisition and processing (DAP) requirement and process are undertaken by the requirement described in " embodiment " of the present invention.Obtain at last 4 * 4 the inner response difference two dimension of totally 16 groups of pixels correct figure as shown in Figure 4:

(3) choose other photometry observation constantly, according to treatment step of the present invention, utilize above rectification figure to correct, obtain typical rectification effect as shown in Figure 5,1. light curve is the data after correcting; 2. be correct amount; 3. be raw data.The figure shows the present invention and can eliminate preferably the photometry style (error) that brings because of the inner response difference of CCD pixel.A collection of observation star is improved fore-and-aft survey variance (error) Statistical Comparison of processing, as shown in Figure 6.In upper figure a in Fig. 6, dotted line represents variance and the magnitude relation before correction process, and solid line represents variance after correction process and the relation of magnitude.B represents the reduction of variance and the graph of a relation of magnitude.This figure shows the star for high s/n ratio, and measuring error can reduce by 50% left and right.

The unspecified part of the present invention belongs to general knowledge as well known to those skilled in the art.

Claims (3)

1. the antidote of the inner response difference of a CCD pixel is characterized in that step is as follows:

(1) according to the measuring flow error of observation star and the correlativity of the centre coordinate after the normalization of observation star, build the inner response difference two dimension of pixel rectification figure;

(2) measure flow and the center of observed object star, the center of normalization observed object star;

(3) correct figure according to the center after the normalization of observed object star by the inner response difference two dimension of interpolation pixel, calculate the flow correct amount;

(4) according to the flow correct amount, observed object star measuring flow is carried out error correction.

2. the antidote of the inner response difference of a kind of CCD pixel according to claim 1 is characterized in that: it is as follows that the inner response difference two dimension of described structure pixel is corrected the figure step:

(1.1) the fixing day district of selecting carried out continuous sequential photometry observation, obtain one group of seasonal effect in time series image;

(1.2) all images that observation in step (1.1) obtained carry out the removal of CCD background, flat field is corrected and the dark current Transformatin;

(1.3) all stars in the every width image j after step (1.2) processing are carried out aperture photometry, obtain the flow flux of every observation star k _kjAnd signal to noise ratio (S/N ratio) (S/N) _kjMeasure simultaneously the center (xc of every observation star _kj, yc _kj), filter out signal to noise ratio (S/N ratio) greater than 50 all observation stars;

(1.4) according to the flow flux of the observation star after step (1.3) screening _kjWith center xc _kj, yck _j, obtain every observation star flow fluxnorm after the normalization on whole photometry time series _kj, and then obtain this group photometry seasonal effect in time series flow intermediate value fluxMedian _k, according to ratio calculation outflow ratio R atioFlux both _kjIn addition, also need to complete normalization center position coordinates (xcPixIn _kj, ycPixIn _kj) processing, computing formula is

$\left\{\begin{array}{c}{\mathrm{xcPixIn}}_{\mathrm{kj}}={\mathrm{xc}}_{\mathrm{kj}}-\mathrm{int}\left({\mathrm{xc}}_{\mathrm{kj}}\right)\\ {\mathrm{ycPixIn}}_{\mathrm{kj}}={\mathrm{yc}}_{\mathrm{kj}}-\mathrm{int}\left({\mathrm{yc}}_{\mathrm{kj}}\right)\end{array}\right.;$

(1.5) actual CCD target surface is divided into groups, according to the center (xc of observation star _kj, yc _kj), obtain the respective packets of every observation star on actual CCD target surface;

(1.6) each group in step (1.5) is carried out respectively following processing:

At first, 1 pixel is divided into the grid of 10 * 10 at least, the normalization center position coordinates value (xcPixIn that obtains according to step (1.4) _kj, ycPixIn _kj), draw the observation star that normalization center position coordinates value falls into each sub-grid respective image;

Then, according to the observation star of respective image in above-mentioned definite each sub-grid, determine to fall into the flow rate ratio of all observation stars of this sub-grid; And calculate its intermediate value median (RatioFlux), and represent the value of place sub-grid with this intermediate value, namely obtain the interior response difference two dimension of the pixel rectification figure of above-mentioned grid division.

3. the antidote of the inner response difference of a kind of CCD pixel according to claim 1, it is characterized in that: the interpolation in described step (3) adopts the cubic spline function interpolation to improve the precision of the flow correct amount that calculates.

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