CN103776466A - Attitude adjustment and nonlinear calibration method for imaging in identical region of heterogeneous scene - Google Patents

Abstract

The invention relates to an attitude adjustment and nonlinear calibration method for imaging in the identical region of a heterogeneous scene. The attitude adjustment and nonlinear calibration method comprises the following steps: calculating an initial drift angle of satellite imaging and adjusting a satellite yaw angle, transferring into a calibration mode of imaging in the same region of the heterogeneous scene; accurately calculating an image drift size by adopting a top-down time interface step length in an imaging process of the calibration mode, controlling an accurate push-sweeping direction of imaging of a linear array CCD (Charge Coupled Device) through adjusting the satellite yaw angle to ensure that the linear array CCD can be used for sequentially imaging the identical region; and determining whether the obtained image data meets the condition of nonlinear calibration, and if being met, establishing a nonlinear calibration mapping relationship table on the basis of histogram matching histogram matching, and if not, re-determining an imaging scene to continuously execute on-tract calibration so that more image data is obtained. The attitude adjustment and nonlinear calibration method is low in requirement for a ground scene without a more uniform scene; a non-uniform scene can meet a calibration task, each track of satellite operating can realize calibration, with high calibration frequency.

Description

Attitude adjustment to the imaging of non-homogeneous scene the same area and nonlinear calibration method

Technical field

The present invention relates to attitude adjustment and nonlinear calibration method to the imaging of non-homogeneous scene the same area, belong to remote sensing satellite calibration technology field, be used in particular for attitude adjustment and the nonlinear calibration of Optical remote satellite linear array CCD camera to the imaging of non-homogeneous scene the same area.

Background technology

At present, Optical remote satellite linear array CCD camera mainly adopts push-broom type imaging mode to obtain satellite image.But, there is the problems such as heterogeneity noise and dark current noise in each ccd detector of remote sensing satellite camera and gain amplifier, cause the inconsistency of the response such as optical system and ccd detector, directly translate into the inconsistency of each pixel output gray level value, thereby cause the image obtaining to occur " band " or " striped " phenomenon.The object of relative radiometric calibration is obtained relative radiometric calibration coefficient exactly, and usage factor carries out relative radiant correction to original image, the elimination " band " of maximum possible and " striped " effect.

Conventionally there is following several method to obtain the relative radiometric calibration coefficient of Optical remote satellite.1. the Laboratory Calibration method before satellite launch, the method by experiment multiple calibration lamp in chamber view data obtains calibration coefficient, but satellite is through from being transmitted in orbit, and will there is certain variation in entrained device.2. utilize robot scaling equipment on star to calibrate in-orbit, this kind of method needs reference source on the star of standard, but because the stability of reference source is not high, therefore the application efficiency of this calibrating method is low.3. in the large-area uniform scaling of surface construction field, need to expend a large amount of financial resource and material resource and safeguard, be subject to the impact of weather condition, orbital motion etc., the cycle that calibration once expends is very long, and target is single, is difficult to realize multiple spot gamma correction.4. utilize natural even ground scenery such as lake, grassland, glacier etc., but so large-area definitely uniform scenery is little, equally also difficulty realizes high-precision nonlinear calibration.5. the statistic law in-orbit based on many rails data, is also a kind of wider method of applying at present, and the method need to be accumulated many rails view data, sets up histogram look-up table based on Histogram Matching, but the method must be guaranteed the stability of each rail data.6. the Side-slither calibrating method abroad proposing for quick satellite is (referring to Radiometric correction of RapidEye imagery using the on-orbit side-slither method, SPIE, 2011), by satellite crab angle half-twist, need to select rainforest, desert, ice sheet etc. relatively uniformly scene as reference source, therefore, to reference source require high, cause the selection to calibrating region limited, thereby affected the calibration frequency.

Summary of the invention

Technology of the present invention is dealt with problems and is: overcome the deficiencies in the prior art, a kind of and prior art distinguishing attitude adjustment and nonlinear calibration method to the imaging of non-homogeneous scene the same area in principle and implementation method is provided, the method is lower to the requirement of calibration scene, do not need ground to calibrate relatively uniformly scene, non-homogeneous scene can meet the demands, therefore, every rail of satellite transit can be realized calibration, can meet the calibration demand of high frequency time.

Technical solution of the present invention is: the attitude adjustment to the imaging of non-homogeneous scene the same area and nonlinear calibration method, realize by following steps:

(1), when satellite need to be calibrated in-orbit, calculate initial drift angle β according to the picture speed of moving ₀, and adjust satellite crab angle according to initial drift angle, the mode of adjustment is for to be rotated counterclockwise 90 °-β by satellite crab angle ₀, enter the calibration mode to the imaging of non-homogeneous scene the same area;

(2) in the imaging process of calibration mode, sweep direction by the pushing away of adjustment control line array CCD imaging to the attitude of satellite, make linear CCD array successively to the imaging of non-homogeneous scene the same area, to obtain the view data of different ccd detectors to the imaging of non-homogeneous scene the same area in linear CCD array;

(3) histogram of statistical picture data, whether the view data that judgement obtains meets the condition of carrying out nonlinear calibration, if met, utilizes histogram matching to set up nonlinear calibration mapping relations table, otherwise goes to step (4);

(4) redefine imaging scene, execution step (1), (2), obtain new view data, and new view data is formed to view data to be added up with together with view data before, execution step (3).

In described step (2), sweeping direction by pushing away of the adjustment control line array CCD imaging to the attitude of satellite realizes by following steps:

(2.1) the moment t after satellite crab angle is adjusted is as initial time, and t equals 0, and the drift angle of calculating this moment is β ₁, make stepping frequency n equal 1, continue execution step (2.2);

(2.2) calculate t and equal n × L × T _intthe drift angle in moment is β ₂, L × T _intfor time interval step-length, wherein, the length that L is line array CCD, the detector number that line array CCD comprises, T _intfor the integral time of line array CCD;

(2.3) picture that calculates two detectors of whole line array CCD first and last moves size delta d, Δ d=L × tan| β ₂-β ₁|, | .| represents to take absolute value, if Δ d is less than predetermined threshold value δ, does not need the satellite crab angle of current time to adjust, by β ₂assignment is to β ₁, stepping frequency n value adds after 1, repeating step (2.2), otherwise need to adjust satellite crab angle before the current corresponding moment of n value, satellite crab angle is adjusted time be engraved in (n-1) × L × T _int～n × L × T _intbetween, make i=1, continue the moment that step (2.4) accurate Calculation is adjusted satellite crab angle;

(2.4) for moment t _i=(n-1) × L × T _int+ i × T _int, i=1,2 ..., L, this moment t _icorresponding drift angle β ₂' obtain β by linear interpolation ₂'=β ₁+ i × (β ₂-β ₁)/L, the picture that calculates first detector of current time and i detector moves size delta d _i=i × tan| β ₂'-β ₁|, as Δ d _iwhile being less than threshold value δ, to add 1, i be the integer that is less than L to i, and repeating step (2.4), as Δ d _iwhile being greater than threshold value δ, this moment need to be adjusted satellite crab angle, restarts execution step (2.1), until it is complete to calibrate in-orbit tasks carrying after adjustment.

The whether satisfied condition of carrying out nonlinear calibration of the view data that in described step (3), judgement obtains realizes by following steps:

(1) will [0, H) gray area between be divided into three gray scale sub-ranges, be respectively sub-range [0, H/4), sub-range [H/4,3H/4] and sub-range (3H/4, H), H is number of greyscale levels;

(2) histogram of statistical picture data, the view data that calculating obtains, at the number of pixels in above-mentioned three gray scale sub-ranges, is designated as respectively M ₁, M ₂, M ₃, and calculate the number percent λ of the total number-of-pixels N that they account for obtained view data ₁, λ ₂, λ ₃, λ ₁=(M ₁/ N) × 100%, λ ₂=(M ₂/ N) × 100%, λ ₃=(M ₃/ N) × 100%;

(3) if λ ₁<10% or λ ₂<30% or λ ₃<10%, the view data obtaining under calibration mode does not meet the condition of carrying out nonlinear calibration, otherwise meets the condition of carrying out nonlinear calibration.

The present invention compared with prior art beneficial effect is:

(1) the present invention makes full use of attitude of satellite adjustment capability and calibrates, and does not need robot scaling equipment on star, and scene is as reference source relatively uniformly without special ground, and general non-homogeneous earth observation scene can meet calibration requirement.

(2) the present invention takes time interval step-length accurate Calculation from coarse to fine to look like to move size in the imaging process of calibration mode, sweep direction by adjusting accurately pushing away of satellite crab angle control line array CCD imaging, make linear CCD array successively to the imaging of non-homogeneous scene the same area, to obtain the view data of different ccd detectors to the imaging of non-homogeneous scene the same area in linear CCD array.

(3) the present invention's relative radiometric calibration method based on mass data statistics of comparing, do not need to accumulate many rails imaging data, less demanding to reference source, therefore guaranteeing that every rail can be realized is scaled to picture, realize the calibration of high frequency time, the calibration of same rail can meet the radiant correction demand of current rail data, really accomplishes " institute is surely used ", has avoided the insecure problem of reference source itself of bringing due to the unstable difference between different rail data.

(4) the present invention proposes to utilize the histogram probability density function of statistical picture to judge whether the image obtaining meets the requirement of setting up nonlinear calibration, guarantee the validity of calibration data, task is calibrated in formulation in-orbit flexibly, and utilize histogram matching to set up nonlinear calibration mapping relations table, overcome the nonlinear response problem between each detector causing due to camera photon noise, dark current noise etc., the error of fitting of having avoided the linear model of direct matching to bring.

Accompanying drawing explanation

Fig. 1 is the attitude adjustment of the present invention to the imaging of non-homogeneous scene the same area and the process flow diagram of nonlinear calibration;

Fig. 2 is conventional imaging pattern and calibrates in-orbit imaging pattern contrast schematic diagram;

Fig. 3 be the present invention provide by emulation calibrate in-orbit time the size that need to adjust satellite crab angle, wherein, size that to be all 0 °, different roll angle need to adjust satellite crab angle when the different latitude from the different angles of pitch (0 °, 10 °, 20 °, 30 °, 40 °) that Fig. 3 a～c is respectively three attitude angle, the size that need to adjust satellite crab angle when different roll angles and the different angle of pitch when Fig. 3 d is 40 ° of north latitude;

Fig. 4 is the schematic diagram that under calibration mode of the present invention, whole linear CCD array passes through the same area successively;

Fig. 5 is the present invention as drift angle after plane operation line array CCD length from β ₁become β ₂schematic diagram;

The shortest time that Fig. 6 adjusts satellite crab angle while being the satisfied condition to the same area imaging of the present invention, wherein, it is all the time interval that 0 °, different roll angle need to be adjusted crab angle from the different angles of pitch (0 °, 10 °, 20 °, 30 °, 40 °) that Fig. 6 a～c is respectively lower three attitude angle of different latitude, the time interval that need to adjust crab angle when different roll angles and the different angle of pitch when Fig. 6 d is 40 ° of north latitude;

Fig. 7 be output image under satellite calibration mode of the present invention with 45 ° of rotations after schematic diagram.

Embodiment

Attitude adjustment to the imaging of non-homogeneous scene the same area and nonlinear calibration method, as shown in Figure 1, the method is realized by following steps concrete steps:

1,, when satellite need to be calibrated in-orbit, calculate initial drift angle β according to the picture speed of moving ₀, and adjust satellite crab angle according to initial drift angle, the mode of adjustment is for to be rotated counterclockwise 90 °-β by satellite crab angle ₀, enter the calibration mode to the imaging of non-homogeneous scene the same area.

That the direction of linear CCD array is arranged into the mode close with satellite motion direction to the calibration mode of non-homogeneous scene the same area imaging, make linear CCD array can order the same area imaging to non-homogeneous scene, so just can obtain the mass data of different ccd detectors to the imaging of non-homogeneous scene the same area.

Linear array CCD camera in orbit during earth observation, because earth rotation causes the projection line velocity reversal of line array CCD motion inconsistent with the moving direction of the relative target subject of camera, angle is between the two drift angle.In the time carrying out calibration task, according to the parameter such as focal length of the geographic position of the attitude speed of satellite, the scenery substar of taking the photograph and height, camera, set up is that the transformation relation of P is (referring to Space Optical Remote Sensor Image Motion Velocity Vector Computational Modeling from geographic coordinate system G to image coordinates, Acta Optica, 24(12), 2004):

Move the initial drift angle β of speed and formula (3) by the derive picture that can obtain formula (2) of formula (1) ₀:

$\frac{\mathrm{dP}}{\mathrm{dt}}{|}_{t=0}=\left[\begin{array}{c}{\mathrm{dP}}_1/\mathrm{dt}\\ {\mathrm{dP}}_2/\mathrm{dt}\\ {\mathrm{dP}}_3/\mathrm{<figure-callout\; id="0"\; label="dt"\; filenames="HDA0000456890110000031.png,HDA0000456890110000042.png"\; state="\{\{state\}\}">dt</figure-callout>}\\ 0\end{array}\right]=\left[\begin{array}{c}{V}_{P_1}\\ V_{P_2}\\ V_{P_3}\\ 0\end{array}\right]---\left(2\right)$

${\mathrm{\&beta;}}_0=\arctan (V_{P_2}/V_{P_1})---\left(3\right)$

In formula, the focal length that f is line array CCD, R is earth radius, and H is satellite orbital altitude, and h is scenery Terrain Elevation, i ₀for orbit inclination; γ is illustrated in photography to start to the corresponding earth central angle of satellite: γ=γ from ascending node in the moment ₀+ Ω t, ω is earth rotation angular speed, Ω is the angular velocity that moves relative the earth's core at photography moment satellite orbit; represent driftage, pitching and the roll angle in shooting moment:

and

represent respectively initial attitude angle and angular velocity thereof.

Be illustrated in figure 2 conventional imaging pattern and calibrate in-orbit imaging pattern contrast schematic diagram, due to earth rotation cause to substar O ₁drift angle when imaging is β ₀, under calibration mode, need to be in-orbit rotated counterclockwise 90 °-β of satellite crab angle ₀.

The present invention has carried out emulation, given camera focus 2600mm, 12288 of Linear CCD Detector numbers, satellite attitude parameters to the size that need to adjust satellite crab angle in the time carrying out calibration task

be all 0, crab angle ψ is 0 ° (without driftage), pitching angle theta and roll angle

get changing value within the scope of 0 °～45 °, satellite orbital altitude 645km, 98 ° of orbit inclinations.As shown in Figure 3, provided the size that need to adjust satellite crab angle when execution is calibrated in-orbit by emulation, wherein, Fig. 3 a is the size that three attitude angle need to be adjusted satellite crab angle in different latitude while being all 0 °, can find out, equator crab angle rate of change is little, and more past two extreme direction crab angle rate of change increase, and during in latitude ± 82 °, crab angle adjustment size is 90 °.The size that need to adjust satellite crab angle in different terrestrial latitudes when Fig. 3 b is different roll angle, when rail lift, increases in Same Latitude roll angle, and crab angle adjustment size reduces; While falling rail, roll angle increases, and crab angle is adjusted size and increased; No matter rail still falls in rail lift, and during in latitude ± 82 °, crab angle adjustment size is 90 °.Fig. 3 c is the size that the different angles of pitch need to be adjusted satellite crab angle in different terrestrial latitudes, when rail lift, increases at the Same Latitude angle of pitch, and crab angle is adjusted size and increased, the adjustment minimum of crab angle when to substar imaging; While falling rail, increase at the same terrestrial latitude angle of pitch, crab angle adjustment size reduces, the adjustment maximum of crab angle when to substar imaging.The size that when Fig. 3 d is 40 °, latitude, different roll angles and the different angle of pitch need to be adjusted crab angle, along with roll angle increases, reduces crab angle adjustment size, and it is faster that the larger crab angle of the angle of pitch reduces trend.

2, in the imaging process of calibration mode, by strictly being controlled to pushing away of line array CCD imaging, the adjustment of the attitude of satellite sweeps direction, make the linear CCD array can be to the imaging of non-homogeneous scene the same area, so just can obtain the view data of different ccd detectors to the imaging of non-homogeneous scene the same area in linear CCD array.

Carry out calibration task satellite in orbit crab angle half-twist-β ₀after, the traffic direction according to satellite at track, all detectors on line array CCD can be to the same area imaging.But in scenic focal point objective point imaging process, because spacecraft orbit motion, earth rotation and attitude of flight vehicle change, all can there is the relative motion between scenery and camera picture in CCD camera, therefore need satellite crab angle constantly to adjust in imaging process.In order to make all detectors obtain the imaging data in same region, they must pass through same sampling point, one by one along path identical on landing ground.Calibration mode must have a rational control mode in-orbit, allows each detector to aim at same region, but the imaging time of each detector has corresponding a delay.

As shown in Figure 4, satellite adopts conventional imaging pattern at position A, after adjusting crab angle, adopt calibration imaging pattern at position B, position C is the scenery of ground resolution size, therefore, conditional request of the present invention is that whole line array CCD must can be to C imaging in order, and all ccd detectors are successively through position C.

For guaranteeing in-orbit under calibration mode, to the same area imaging, need to constantly to take a drift, and constantly adjust pushing away of satellite crab angle control line array CCD according to drift angle and sweep direction.First detector in requirement line array CCD and the picture of last detector move deviation and are no more than threshold value δ, and 1～2 pixel of δ value, if exceed threshold value δ, needs satellite crab angle to adjust, otherwise do not adjust.Below under calibration imaging pattern, provide and judge whether the concrete steps that need to adjust satellite crab angle:

(1) the moment t after satellite crab angle is adjusted is as initial time, and t equals 0, and the drift angle of calculating this moment is β ₁, make stepping frequency n equal 1, continue execution step (2);

(2) calculate t and equal n × L × T _intthe drift angle in moment is β ₂, L × T _intfor time interval step-length, wherein, the length that L is line array CCD, the detector number that line array CCD comprises, T _intfor the integral time of line array CCD;

(3) picture that calculates two detectors of whole line array CCD first and last moves size delta d, Δ d=L × tan| β ₂-β ₁|, | .| represents to take absolute value, if Δ d is less than predetermined threshold value δ, does not need the satellite crab angle of current time to adjust, by β ₂assignment is to β ₁, stepping frequency n value adds after 1, repeating step (2), otherwise need to adjust satellite crab angle before the current corresponding moment of n value, satellite crab angle is adjusted time be engraved in (n-1) × L × T _int～n × L × T _intbetween, make i=1, continue the moment that step (4) accurate Calculation is adjusted satellite crab angle;

(4) for moment t _i=(n-1) × L × T _int+ i × T _int, this moment t _icorresponding drift angle β ₂' obtain β by linear interpolation ₂'=β ₁+ i × (β ₂-β ₁)/L, the picture that calculates first detector of current time and i detector moves size delta d _i=i × tan| β ₂'-β ₁|, as Δ d _iwhile being less than threshold value δ, to add 1, i be the integer that is less than L to i, and repeating step (4), as Δ d _iwhile being greater than threshold value δ, this moment need to be adjusted satellite crab angle, restarts execution step (1), until it is complete to calibrate in-orbit tasks carrying after adjustment.

T integral time is got in emulation of the present invention in the time realizing _intequal 0.32ms, line array CCD length L is 12288 pixels, and threshold value δ gets 1 pixel.

Be illustrated in figure 5 running time T _intafter × L, as drift angle after plane operation line array CCD length from β ₁become β ₂schematic diagram, require during this period of time in all detectors of line array CCD all to the same area imaging.

For meeting the relative radiometric calibration in-orbit of the inventive method, need 12288 detectors the same area through non-linear scenes, according to the set-up procedure of above-mentioned crab angle, pitching angle theta and roll angle when emulation provides satellite and falls rail operation as shown in Figure 6

get the adjustment time interval (accompanying drawing has provided simulation result when rail operation falls in satellite) of crab angle corresponding to variation within the scope of 0 °～45 °.Wherein, Fig. 6 a is the time interval that three attitude angle need to be adjusted crab angle in different latitude while being all 0 °, long to the adjustment interval of satellite crab angle near can finding out under the line, the frequency is low, more past low latitude region therebetween every shorter, the frequency is relatively high.Fig. 6 b is the time interval that need to adjust crab angle in the time of the different roll angle of different latitude, can find out in same latitude region, and the larger adjustment time interval of roll angle is longer.Fig. 6 c is the time interval that need to adjust crab angle in the time of the different angle of pitch of different latitude, can find out in same latitude region, and the larger adjustment time interval of the angle of pitch is less.Fig. 6 d is 40 ° of north latitude, in the time interval that need to adjust crab angle, can find out along with the increase of satellite roll angle is longer to the adjustment interval of crab angle, the frequency is lower when different roll angles and the different angle of pitch; In identical roll angle, the larger adjustment time interval of the angle of pitch is less, the frequency is relatively high.

3, obtain line array CCD to the view data of non-homogeneous scene the same area imaging after, whether the view data that judgement obtains meets the condition of carrying out nonlinear calibration, if meet, utilize histogram matching to set up nonlinear calibration mapping relations table, otherwise go to step 4.

Same detector is usually expressed as non-linear to the response under different light degree, particularly illuminance lower region, and nonlinear characteristic is more obvious.Adopt the method for Histogram Matching to carry out nonlinear calibration, can solve on the one hand the feature of CCD nonlinearity, relative linear scaled model on the other hand, it is relatively uniform that employing no longer requires the selection of ground calibration scene, but a natural scene heterogeneous can meet calibration requirement.

Whether the view data that 3.1, judgement obtains meets the condition of carrying out nonlinear calibration.

Between some gray area by avoiding in acquisition view data, do not have data or data very few, and therefore the nonlinear calibration mapping relations table that impact is set up, need to be analyzed the intensity profile situation of obtained view data.

(1) will [0, H) gray area between be divided into three gray scale sub-ranges, be respectively sub-range [0, H/4), sub-range [H/4,3H/4] and sub-range (3H/4, H), H is number of greyscale levels;

(2) histogram of statistical picture data, the view data that calculating obtains, at the number of pixels in above-mentioned three gray scale sub-ranges, is respectively M ₁, M ₂, M ₃, and calculate the number percent λ of the total number-of-pixels N that they account for obtained view data ₁, λ ₂, λ ₃, λ ₁=(M ₁/ N) × 100%, λ ₂=(M ₂/ N) × 100%, λ ₃=(M ₃/ N) × 100%;

(3) if λ ₁<10% or λ ₂<30% or λ ₃<10%, the view data obtaining under calibration mode does not meet the condition of carrying out nonlinear calibration, goes to step 4, otherwise meets the condition of carrying out nonlinear calibration, continues following step 3.2.

3.2, utilize histogram matching to set up nonlinear calibration mapping relations table.

(1) output image under calibration mode is carried out to 45 ° of rotations, the imaging of all detectors of same behavior of its image rotating to the same area.

The imaging data of each detector shows as a column data on output image, and because all detectors of line array CCD are to the same area successively imaging successively, and causing the data on 45 ° of diagonal line of output image is the imagings of different detectors to the same area.Schematic diagram after being illustrated in figure 7 the output image under calibration imaging pattern and rotating 45 °, after rotation, each row vector represents the response of different pixels to basic identical input, each column vector represents the response results of same detector to different scenes.

(2) calculate histogram probability density function p (the l)=N of whole image _l/ N, expects histogram as target, wherein, l=0,1 ..., L-1, L is number of greyscale levels, N _lbe that gray-scale value is the number of pixels of l, N is total number-of-pixels, expects that cumulative probability density corresponding to Gray Histogram value l is:

(3) calculate the histogram probability density function of each detector image, as original histogram, the probability density function that in the histogram of h detector, the gray-scale value of pixel is k is:

wherein, k=0,1 ..., L-1, L is number of greyscale levels,

be the number of pixels that in h detector, gray-scale value is k, M is total number-of-pixels.The cumulative probability density corresponding to Gray Histogram value k of h detector is: $C_h\left(k\right)=\underset{i=0}{\overset{k}{\mathrm{\&Sigma;}}}{p}_h\left(i\right)=\underset{i=0}{\overset{k}{\mathrm{\&Sigma;}}}(M_i^h/M).$

(4) set up original histogram based on Histogram Matching and target is expected histogrammic Histogram Mapping relation, obtain the nonlinear calibration mapping relations table of this detector.Concerning the view data of i detector gray-scale value k, expecting can to find a l on histogram, make C (l)≤C _h(k)≤C (l+1), if | C (l)-C _h(k) |≤| C _h(k)-C (l+1) |, replace k with l, if | C (l)-C _h(k) | >|C _h(k)-C (l+1) |, replace k with l+1.

(5) repeating step (3) and (4), use the same method and process all detectors, just can obtain the nonlinear calibration mapping relations table of all detectors.

4, redefine imaging scene, execution step 1,2, obtains new view data, and new view data is formed to view data to be added up with together with view data before, execution step 3.For example,, if the λ in step 3 ₁do not meet the demands, the data that lack low half-tone information are described, need to select the low brightness area such as ocean, vegetation to be scaled to picture; If the λ in step 3 ₃do not meet the demands, the data that lack high half-tone information are described, need to select the high-brightness regions such as desert to be scaled to picture.

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

Claims (3)

1. attitude adjustment and the nonlinear calibration method of pair non-homogeneous scene the same area imaging, is characterized in that, realizes by following steps:

(1), when satellite need to be calibrated in-orbit, calculate initial drift angle β according to the picture speed of moving ₀, and adjust satellite crab angle according to initial drift angle, the mode of adjustment is for to be rotated counterclockwise 90 °-β by satellite crab angle ₀, enter the calibration mode to the imaging of non-homogeneous scene the same area;

(2) in the imaging process of calibration mode, sweep direction by the pushing away of adjustment control line array CCD imaging to the attitude of satellite, make linear CCD array successively to the imaging of non-homogeneous scene the same area, to obtain the view data of different ccd detectors to the imaging of non-homogeneous scene the same area in linear CCD array;

(3) histogram of statistical picture data, whether the view data that judgement obtains meets the condition of carrying out nonlinear calibration, if met, utilizes histogram matching to set up nonlinear calibration mapping relations table, otherwise goes to step (4);

(4) redefine imaging scene, execution step (1), (2), obtain new view data, and new view data is formed to view data to be added up with together with view data before, execution step (3).

2. attitude adjustment and the nonlinear calibration method to the imaging of non-homogeneous scene the same area according to claim 1, is characterized in that: in described step (2), sweep direction by pushing away of the adjustment control line array CCD imaging to the attitude of satellite and realize by following steps:

(2.1) the moment t after satellite crab angle is adjusted is as initial time, and t equals 0, and the drift angle of calculating this moment is β ₁, make stepping frequency n equal 1, continue execution step (2.2);

(2.2) calculate t and equal n × L × T _intthe drift angle in moment is β ₂, L × T _intfor time interval step-length, wherein, the length that L is line array CCD, the detector number that line array CCD comprises, T _intfor the integral time of line array CCD;

(2.3) picture that calculates two detectors of whole line array CCD first and last moves size delta d, Δ d=L × tan| β ₂-β ₁|, | .| represents to take absolute value, if Δ d is less than predetermined threshold value δ, does not need the satellite crab angle of current time to adjust, by β ₂assignment is to β ₁, stepping frequency n value adds after 1, repeating step (2.2), otherwise need to adjust satellite crab angle before the current corresponding moment of n value, satellite crab angle is adjusted time be engraved in (n-1) × L × T _int～n × L × T _intbetween, make i=1, continue the moment that step (2.4) accurate Calculation is adjusted satellite crab angle;

(2.4) for moment t _i=(n-1) × L × T _int+ i × T _int, i=1,2 ..., L, this moment t _icorresponding drift angle β ₂' obtain β by linear interpolation ₂'=β ₁+ i × (β ₂-β ₁)/L, the picture that calculates first detector of current time and i detector moves size delta d _i=i × tan| β ₂'-β ₁|, as Δ d _iwhile being less than threshold value δ, to add 1, i be the integer that is less than L to i, and repeating step (2.4), as Δ d _iwhile being greater than threshold value δ, this moment need to be adjusted satellite crab angle, restarts execution step (2.1), until it is complete to calibrate in-orbit tasks carrying after adjustment.

3. attitude adjustment and the nonlinear calibration method to the imaging of non-homogeneous scene the same area according to claim 1, is characterized in that: the whether satisfied condition of carrying out nonlinear calibration of the view data that in described step (3), judgement obtains realizes by following steps:

(1) will [0, H) gray area between be divided into three gray scale sub-ranges, be respectively sub-range [0, H/4), sub-range [H/4,3H/4] and sub-range (3H/4, H), H is number of greyscale levels;

(2) histogram of statistical picture data, the view data that calculating obtains, at the number of pixels in above-mentioned three gray scale sub-ranges, is designated as respectively M ₁, M ₂, M ₃, and calculate the number percent λ of the total number-of-pixels N that they account for obtained view data ₁, λ ₂, λ ₃, λ ₁=(M ₁/ N) × 100%, λ ₂=(M ₂/ N) × 100%, λ ₃=(M ₃/ N) × 100%;

(3) if λ ₁<10% or λ ₂<30% or λ ₃<10%, the view data obtaining under calibration mode does not meet the condition of carrying out nonlinear calibration, otherwise meets the condition of carrying out nonlinear calibration.

Images