CN102324098A - Relative radiation calibration method in combination with laboratory calibration and even landscape statistics - Google Patents

Abstract

The invention relates to a relative radiation calibration method in combination with laboratory calibration and even landscape statistics, which comprises steps of: 1) according to acquired laboratory calibration data, obtaining the radiance and the corresponding DN value of a lamp at each level and seeking the calibration coefficient of each pixel; 2) according to images acquired at the orbital running period of a satellite, selecting areas which are even on the whole to generate the calibration coefficient of each pixel through an even landscape statistic method; and 3) conducting joint calibration according to the step 1 and the step 2 to obtain new calibration coefficients. The method provided by the invention overcomes the defects of the prior art. In combination with the advantages of the laboratory calibration and the ground even landscape statistics, according to the characteristics of satellite running and camera response, new calibration coefficients are dynamically formed and the relative radiation calibration accuracy is ensured.

Description

A kind of relative radiometric calibration method that combines laboratory calibration and even scape statistics

Technical field

The present invention relates to a kind of remote sensing images relative radiometric calibration method.

Background technology

China succeeds in sending up China-Brazil Earth Resources Satellite (CBERS) and environment mitigation satellite (HJ-1) and changes the businessization operation in succession over to, is through with and can only relies on the history of the external remote sensing satellite data of import for a long time.CBERS and HJ-1 two big serial satellite datas have been widely used in agricultural resource investigation, crops the yield by estimation, ECOLOGICAL ENVIRONMENTAL MONITORING, city planning, survey of territorial resources and fields such as disaster monitoring and military affairs, indicate that China's spacer remote sensing application has got into a brand-new stage.

Relatively radiant correction is called that homogenising is proofreaied and correct or normalization is handled, and it is in order to proofread and correct each pixel and optical system response difference in the remote sensor the original densitometer numerical value (DN) that obtains to be carried out a kind of processing procedure that " again " quantizes.Radiant correction is as the pretreated important step of remotely-sensed data relatively, and key is to obtain effective calibration coefficient, i.e. normalized gain (NG) and biasing (B).Domestic and international main flow remote sensing satellite, for example domestic CBERS, HJ-1 and external Landsat, SPOT satellite adopt scaling method and ground statistic law to obtain calibration coefficient.Scaling method uses calibration lamp data as input, forms the calibration coefficient on basis on this basis through different algorithms.Generally speaking, the calibration lamp comprises the uniform light source of height of some different spoke brightness degrees, or when the brightness of light source spoke can not be satisfied homogeneous condition fully, the profile of its spoke brightness can accurately be measured.Because higher, so satellites transmits need the chamber of experimentizing calibration as last from calibration lamp data extract correction coefficient precision.The operation after a while of satellite warp; Certain variation will take place in the sensor performance that satellite carries; Scaling system lost efficacy or used at need in spaceborne; Statistic law is as a kind of alternative method of calibration, and through analyzing and statistics calculating calibration correction coefficient from ground image, this method is suitable for imaging form polynary and that sweep.In addition; Represent the QuickBird satellite of international remote sensing advanced level then to adopt linear array to revolve the method that turn 90 degrees, make the direction of scanning be parallel to pixel linear array direction fully, along with satellite motion; The terrain object of each pixel experience is consistent; The even scenery that this has just gathered different spoke intensity levels effectively dynamically obtains the radiation calibration coefficient, has guaranteed the precision of irradiation treatment.Because this calibration mode need rotate the focal plane, and design of satellites has been proposed higher requirement, domsat does not adopt this technology.

Because satellites transmits lift-off ascent stage inclement condition; There are bigger difference in satellite actual motion environment and surface state; And many factors such as the state after image formation state and the lift-off of camera is inconsistent during ground test; The calibration data that possibly make ground gather and analyze can not be fit to the requirement of high-precision correction fully, need carry out the follow-up improvement in ground and handle.

Summary of the invention

Technology of the present invention is dealt with problems and is: the deficiency that overcomes prior art; A kind of remote sensing images relative radiometric calibration method is provided; This method combines the even scape statistics of laboratory calibration and ground advantage; Characteristic according to satellite transit and camera response dynamically forms new calibration coefficient, guarantees relative radiant correction precision.

Technical solution of the present invention is: a kind of relative radiometric calibration method that combines laboratory calibration and even scape statistics, and step is following:

(1) according to the laboratory calibration data of gathering, obtains the spoke brightness and corresponding DN value of every grade of lamp, and ask for the calibration coefficient of each pixel;

(2) image of gathering in orbit according to satellite is chosen overall zone uniformly, generates the calibration coefficient of each pixel through even scape statistic law;

(3) result according to step (1), (2) unites calibration, and detailed process is following:

(3.1) associating pixel design: be combined into an associating pixel to m pixel, promptly array is made up of the associating pixel, and each associating pixel is on average obtained by m pixel, to the push-scanning image pattern, and 50＜m＜200;

(3.2), ask for the response coefficient LNG of laboratory associating pixel according to the result of calculation of step (1) _j

(3.3), ask for the response coefficient HNG of the even scape associating in ground pixel according to the result of calculation of step (3) _j

(3.4) ask for associating pixel correction factor COR _j, COR _j=LGN _j/ HGN _j

(3.5) correction factor equation model: with associating pixel sequence number is horizontal ordinate, and correction factor is an ordinate, adopts second-degree parabola equation model correction factor curve;

(3.6) insert in the correction factor: the correction factor curve to above-mentioned match disperses, and obtains one group of correction factor cor to single pixel _i

(3.7) new calibration coefficient nNG _i: adopt the result of calculation of step (1) or step (2) to be in correction factor, can obtain the new calibration coefficient of this array.

At first adopt even scape statistic law, histogram equalization method, three kinds of methods of least square method to ask for the calibration coefficient of each pixel in the said step (1), choose the result of calculation of the result of calculation of three kinds of optimal algorithms in the algorithm then as step (1).

The first-selection of choosing of said optimal algorithm is chosen homogeneous area big as far as possible in the image, and the gray average that calculates the heading image and this regional gray average calculate the error of above-mentioned two gray averages, when error hour, this algorithm is optimal algorithm.

The present invention compared with prior art beneficial effect is:

(1) the inventive method has been eliminated aberration between remote sensing images sheet intra-striate and sheet basically, has guaranteed the radiation quality of image preferably, has solved large format remote sensing images radiant correction problem, to the data processing of other earth observation satellite reference is provided.

(2) the present invention unites a kind of effective ways of bringing into play laboratory calibration and even scape statistics comprehensive advantage of calibration.The laboratory calibration has guaranteed the stationarity of image local transition in the trimming process; And evenly the scape statistics has overcome the jumping characteristic that array splices.

(3) laboratory calibration of the present invention adopts three kinds of methods to handle, and through broad sense noise rating, preferred calibration coefficient, as basic data, is the subsequent treatment service.

Description of drawings

Fig. 1 is an overview flow chart of the present invention;

Fig. 2 is an algorithm flow chart of the present invention;

Fig. 3 unites the pixel mapping graph for the present invention.

Embodiment

Unite the pixel design drawing in conjunction with accompanying drawing 1 overview flow chart, Fig. 2 algorithm flow chart and Fig. 3, below specific embodiments of the invention do following the description:

Step 1: laboratory calibration

(1.1) read level B at the bottom of the i pixel _i

(1.2) calculated product bulb separation k level spoke brightness L _k

$L_k=\frac{{\∫}_0^{\∞}{R}_k\left(\mathrm{\λ}\right)\·S\left(\mathrm{\λ}\right)\mathrm{d\λ}}{{\∫}_0^{\∞}S\left(\mathrm{\λ}\right)\mathrm{d\λ}}$ ②

Wherein, S (λ) is the camera spectral response functions, R _k(λ) be light source light spectrum spoke luminance function, λ is a wavelength.

(1.3) read the DN value Q of i pixel under the brightness of k level spoke _{I, k}

(1.4) use even scape statistic law to calculate i pixel calibration coefficient lNG _i

${\mathrm{DN}}_i=\frac{1}{n}\underset{k=1}{\overset{n}{\mathrm{\Σ}}}(Q_{i,k}-B_i)$ ③

${\mathrm{lNG}}_i=\frac{{\mathrm{DN}}_i}{\frac{1}{N}\underset{j=1}{\overset{N}{\mathrm{\Σ}}}{\mathrm{DN}}_j}$ ④

Wherein, n is calibration lamp spoke brightness progression, and N is the pixel sum.

(1.5) use the histogram equalization method to calculate i pixel calibration coefficient lNG _i

Calculate the standard deviation of i pixel image DN value _i

Calculate the mean value σ of entire image standard deviation _R

${\mathrm{\σ}}_R=\frac{1}{N}\underset{i=1}{\overset{n}{\mathrm{\Σ}}}{\mathrm{\σ}}_i$ ⑤

lNG _i＝σ _i/σ _R ⑥

Wherein, N is the pixel sum.

(1.6) use the histogram equalization method to calculate i pixel calibration coefficient B _i

Calculate the average μ of i pixel image DN value _i

Calculate the average μ of entire image DN value _R

${\mathrm{\μ}}_R=\frac{1}{n}\underset{i=1}{\overset{n}{\mathrm{\Σ}}}{\mathrm{\μ}}_i$ ⑦

$B_i={\mathrm{\μ}}_i-\frac{{\mathrm{\σ}}_i\·{\mathrm{\μ}}_R}{{\mathrm{\σ}}_R}$ ⑧

(1.7) use least square method to calculate i pixel calibration coefficient lNG _i

$G_i=\frac{\underset{k=1}{\overset{n}{\mathrm{\&Sigma;}}}(Q_{i,k}-B_i)L_k}{\underset{k=1}{\overset{\mathrm{<figure-callout\; id="2"\; label="n\; L\; k"\; filenames="HSA00000562069200022.png"\; state="\{\{state\}\}">n</figure-callout>}}{\mathrm{\&Sigma;}}}{L}_k^{}{}_2^{}}$ ⑨

${\mathrm{lNG}}_i=\frac{G_i}{\frac{1}{N}\underset{j=1}{\overset{N}{\mathrm{\&Sigma;}}}{G}_j}$ ⑩

(1.8) through the performance of the above-mentioned three kinds of algorithms of broad sense noise rating, preferred optimal algorithm.

Its algorithm can reduce: choose big as far as possible homogeneous area, calculate the gray average and this regional gray average of every row (heading) image, calculate both errors.When error hour, this algorithm is optimal algorithm.

Step 2: evenly scape calibration

(2.1) read level B at the bottom of the i pixel _i

(2.2) read the DN value Q of the even scape of k width of cloth i pixel _{I, k}

(2.3) use even scape statistic law to calculate i pixel calibration coefficient hNG _i

${\mathrm{DN}}_i=\frac{1}{n}\underset{k=1}{\overset{n}{\mathrm{\&Sigma;}}}(Q_{i,k}-B_i)$

${\mathrm{hNG}}_i=\frac{{\mathrm{DN}}_i}{\frac{1}{N}\underset{j=1}{\overset{N}{\mathrm{\&Sigma;}}}{\mathrm{DN}}_j}$

(2.4) the even scape of evaluating and optimizing

Based on result, increase and decrease even scape, through visual interpretation, preferred selected even scenery reaches the purpose that improves calibration precision.

Step 3: unite calibration

(3.1) associating pixel design

As shown in Figure 3, be combined into an associating pixel to m pixel, promptly array is made up of the associating pixel, and each associating pixel is on average obtained by m pixel, guarantees the uniform properties of scenery between the associating pixel on this basis.Consider present push-scanning image system, the pixel sum is generally thousands of more than tens thousand of, takes into account the consistance that atural object homogeneity and adjacent picture elements respond, the span of m: 50＜m＜200.

(3.2) ask for the response coefficient LNG that pixel is united in the laboratory _j

${\mathrm{LGN}}_j=\frac{1}{m}\underset{i=1}{\overset{m}{\mathrm{\&Sigma;}}}{\mathrm{lGN}}_{j*m+i}$

(3.3) ask for the even scape in ground and unite the response coefficient HNG of pixel _j

${\mathrm{HGN}}_j=\frac{1}{m}\underset{i=1}{\overset{m}{\mathrm{\&Sigma;}}}{\mathrm{hGN}}_{j*m+i}$

(3.4) ask for associating pixel correction factor COR _j

COR _j＝LGN _j/HGN _j

(3.5) match of correction factor equation;

With associating pixel sequence number is horizontal ordinate, and correction factor is an ordinate, adopts second-degree parabola equation model correction factor curve.

(3.6) the interior of correction factor inserted;

In order to accomplish of the mapping of associating pixel to single pixel, need disperse to this continuous para-curve, obtain one group of correction factor cor to single pixel _i

(3.7) new calibration coefficient nNG _i

If divided by correction factor, can obtain the new calibration coefficient of this array with the laboratory calibration coefficient.

nNG _i＝lNG _i/cor _i

Embodiment

CBERS satellite useful load comprises cameras such as CCD and WFI.The CCD camera resolution is 19.5 meters, and fabric width is 113 kilometers, between resolution and fabric width, has sought compromise, and this image user uses the most extensive; The WFI camera resolution is 258 meters, and fabric width reaches 890 kilometers, realizes heavily visiting fast target easily.In order to guarantee to observe the visual field, CCD and WFI camera have adopted the optics splicing.No matter the CBERS-02 satellite in the process, adopts the calibration of the still even scape statistics of laboratory calibration in orbit, and there are certain problem in WFI and ccd image calibration result, tone transition vestige occurs in the array jointing positions especially, influence visual effect.Calibrate and even scape statistics in conjunction with the laboratory, promptly adopt the calibration of uniting of laboratory and even scape statistics, generate new calibration coefficient, use this adjustment of data original image, picture quality obtains bigger improvement, has satisfied the remote sensing application demand.

The CBERS-02 satellite WFI calibration data of at first utilizing the laboratory to gather are carried out relative radiant correction to the WFI image, and correcting result shows that there is tangible aberration in WFI two chip arrays at overlap, but the aberration transition of image is better in the array chip.When adopting even scape statistical method,, choose overall uniform many scapes WFI image, generate one group of calibration coefficient in order to guarantee the uniform properties of atural object.Use this coefficient that the WFI image is carried out relative radiant correction, correcting result shows that two array lap-joint aberration of WFI eliminate fully, but there is comparatively serious longitudinal stripe in image in some position in the array chip.The uniformity index that the WFI image is described is difficult to satisfy the calibration requirement, has error equally based on the calibration data of even scape method.

Adopt method of the present invention to proofread and correct; Correcting result shows that the inner striped of pattern matrix disappears basically; The aberration and the striped of left and right sides array are eliminated fully, and the image radiation correction mass is greatly improved, and solve large format remote sensing images radiant correction problem preferably.

There is the problem of light and shade transition in CCD camera B4 band image, and through the inventive method, the problems referred to above are equally effectively solved, and after revising the calibration coefficient profile, is difficult to find image light and shade transient.

Above-mentioned is to be the explanation that example is carried out with CBERS satellite WFI and CCD camera, and the inventive method extends to other satellites or sensor.

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

Claims (3)

1. one kind combines the relative radiometric calibration method that calibrate in the laboratory and even scape is added up, and it is characterized in that step is following:

(1) according to the laboratory calibration data of gathering, obtains the spoke brightness and corresponding DN value of every grade of lamp, and ask for the calibration coefficient of each pixel;

(2) image of gathering in orbit according to satellite is chosen overall zone uniformly, generates the calibration coefficient of each pixel through even scape statistic law;

(3) result according to step (1), (2) unites calibration, and detailed process is following:

(3.1) associating pixel design: be combined into an associating pixel to m pixel, promptly array is made up of the associating pixel, and each associating pixel is on average obtained by m pixel, to the push-scanning image pattern, and 50＜m＜200;

(3.2), ask for the response coefficient LNG of laboratory associating pixel according to the result of calculation of step (1) _j

(3.3), ask for the response coefficient HNG of the even scape associating in ground pixel according to the result of calculation of step (3) _j

(3.4) ask for associating pixel correction factor COR _j, COR _j=LGN _j/ HGN _j

(3.5) correction factor equation model: with associating pixel sequence number is horizontal ordinate, and correction factor is an ordinate, adopts second-degree parabola equation model correction factor curve;

(3.6) insert in the correction factor: the correction factor curve to above-mentioned match disperses, and obtains one group of correction factor cor to single pixel _i

(3.7) new calibration coefficient nNG _i: adopt the result of calculation of step (1) or step (2) to be in correction factor, can obtain the new calibration coefficient of this array.

2. a kind of relative radiometric calibration method that combines laboratory calibration and even scape statistics according to claim 1; It is characterized in that: at first adopt even scape statistic law, histogram equalization method, three kinds of methods of least square method to ask for the calibration coefficient of each pixel in the said step (1), choose the result of calculation of the result of calculation of three kinds of optimal algorithms in the algorithm then as step (1).

3. a kind of relative radiometric calibration method that combines laboratory calibration and even scape statistics according to claim 2; It is characterized in that: the first-selection of choosing of said optimal algorithm is chosen homogeneous area big as far as possible in the image; Calculate the gray average and this regional gray average of heading image; Calculate the error of above-mentioned two gray averages, when error hour, this algorithm is optimal algorithm.

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