CN100510662C - Spatial modulation and interference type computed tomography imaging spectrometer - Google Patents

Abstract

The invention relates to a space modulation interference-type calculating chromatography image spectrometer in the field of devising technology of the image spectrometer. It is mainly formed by a front telescopic system, a rotating projector, an interfering optics system, a two-dimension focus plane detector and a data collecting and processing system. The interfering optics system adopts heavy caliber projection space modulation interfering structure, which is Markesan-type interference and can generate the interfering strip with the same thickness. It uses column lens to do projecting expansion. The incident light becomes an aligning light beam after the aligning lens; the rotating projector aims to the light beam to rotate so as to obtain the image with various angles; the interference optics system makes the light beam from the rotating projector to interfere, project and focus; the data collecting and processing system changes the outputted data from vacuum site to frequency site to obtain the spectrum distribution of the image and the spectrum image data cube by rebuilding the calculating chromatography projection.

Description

Spatial modulation and interference type computed tomography imaging spectrometer

Technical field the present invention relates to a kind of interference type computed tomography imaging spectrometer, belongs to the technology that the designs and produces category of imaging spectrometer in the remote sensing technology field; Be particularly related to the design of Optical System of spatial modulation and interference type computed tomography imaging spectrometer.

Background technology computed tomography imaging spectrometer (computed-tomography imaging spectrometer) is called for short CTIS, is the novel imaging spectrometer technology paid attention to of people extremely in recent years.With the current another kind of high spectral resolution imaging spectrometer technology that is subjected to generally paying attention to is that Fourier transform imaging spectrometer is compared, and the optical system of CTIS has higher luminous flux, therefore is easier to be made into highly sensitive imaging spectrum system.

The thought that computed tomography (CT) is applied to the imaging spectrometer field was just proposed by Japan and Muscovite scholar as far back as phase early 1990s.After this, the countries in the world scientific worker who comprises China on this direction, conduct a research one after another [.The ultimate principle of present normally used CT imaging spectrometer may be summarized to be: the multispectral image data cube along three-dimensional distribution (two-dimensional space and one dimension spectrum), can compress or project into along the multispectral optical imagery sequence of two-dimensional directional distribution (one-dimensional space and one dimension spectrum); The multispectral optical imagery sequence of these compressed two dimensions is received by one or more two-dimentional focal plane array detectors; The two-dimentional multispectral optical imagery sequence that adopts the CT reconstruction algorithm to compress is redeveloped into the spectral image data cube of original object.

Up to now, in the world the implementation of the CT imaging spectrometer of Gong Buing have multiple, for example: the whole rotation mode of scenery rotation mode, optical prism or dispersive component rotation mode, instrument and Nitride Binary-Phase plane grating (or one dimension combination grating) beam splitting projection pattern or the like.Wherein, the common feature that adopts the CTIS of rotating and projection mode is to adopt a cover one dimension dispersion element and an optical slot in light path, so their spectral resolution is subjected to the restriction of slit width.Though the another kind of CTIS of binary plane raster beam-splitting projection structure that adopts does not need optical slot, but also there are other fatal defectives in it: there are the blind area in its projection angle limited amount and projection angle, promptly so-called " awl loses " (missing cones) phenomenon, therefore the spectrum and the spatial resolution of this type systematic are very limited, only are suitable for the use of certain special occasions.

Patent aspect at home, Chinese patent № 01213109, № 01213108, and № 99256129, and № 99256131, and № 99115953, and № 99115952 is the interference type imaging spectrometer of non-chromatography type; № 00261470, and № 99256128 is chromatic dispersion formula computed tomography imaging spectrometer, does not belong to interference type imaging spectrometer category.

Patent aspect abroad, U.S. Pat 2004021934, US5260767 is a total-reflection type color dispersion-type imaging spectrometer.US6519040, US4523846 are the interference type imaging spectrometer of non-calculating computed tomography.Said system is not a calculating computed tomography formula imaging spectrometer.US6522403 does not belong to the interfere type category for adopting the color dispersion-type CT imaging spectrometer of two-dimensional grating.

In a word, the precedent that in present employed imaging spectrometer, spatial modulation and interference technology and computed tomography technology is not used in combination.

List of references

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Summary of the invention the present invention is a kind of novel imaging spectrometer---spatial modulation and interference type computed tomography imaging spectrometer [CTII (computed-tomography imaging interferometer)].It has used spatial modulation and interference technology and computed tomography technology to ingenious the combining of principle of the principle of traditional spatial modulation formula Fourier transform imaging spectrometer and computed tomography imaging spectrometer simultaneously in optical texture design and Data Management Analysis process.Have the characteristics of high light flux, high spectral resolution, high spatial resolution and high s/n ratio, and be easy to realize.

The present invention is mainly by preposition telescopic system, rotating and projection device, interference optics, two-dimentional focus planardetector, compositions such as data acquisition processing system.Interference optics adopts heavy caliber projection spatial modulation and interference structure, and concrete form is the Michelson formula interferometer of generation equal thick interference fringe, and carries out project extended with the post lens combination.Optical slot common in the conventional interference light path need not be adopted in the light path, therefore luminous energy can be utilized fully.Preposition telescope object observing, incident ray becomes collimated light beam after the collimating mirror effect; The light image of rotating and projection device collimation is rotated with a fixed step size, obtain different angles image this revolve and adopt Dove prism or other to revolve the camera structure as process to realize; Interference optics make from the collimated light beam of rotating and projection device outgoing interfere, projection and focusing, on the focal plane, picture side of focus lamp, can obtain projected image and interference fringe clearly simultaneously; Adopting spectral response range respectively is the two-dimentional focus planardetector collection interference projection image signal of visible light and near infrared (0.4～1 μ m), short-wave infrared (1～5 μ m) and LONG WAVE INFRARED (8～14 μ m), realizes the collection of wide frequency domain interference data for projection sequence.Data acquisition processing system is a core with intelligentized microprocessor, signal to focus planardetector output is gathered and is handled, finish by the conversion of spatial domain, obtain the spectral distribution of image, can obtain spectrum pattern data cube behind the chromatography backprojection reconstruction as calculated simultaneously to frequency domain.The algorithm of the common CTIS of backprojection reconstruction algorithm is identical.

Compare with common computed tomography imaging spectrometer, CTII adopts interference structure to replace chromatic dispersion structure commonly used, with Fourier transform interference figure is transformed into the spectrum pattern in computation process.Compare with traditional Fourier transform imaging spectrometer, the imaging link has adopted advanced computed tomography technology.

The present invention has the characteristics of high sensitivity, high spectral resolution, high spatial resolution and high s/n ratio, is particularly suitable for the Hyperspectral imager in Aero-Space remote sensing field.

Description of drawings

The system light path signal of Fig. 1 interference type computed tomography imaging spectrometer of the present invention.

The structural representation of Fig. 2 heavy caliber projection of the present invention spatial modulation and interference.

Target rotation and projection signal in Fig. 3 target process of reconstruction.

Fig. 4 implements schematic diagram.

Primary structure is among the figure: the preposition telescope of 1-, 2-collimating mirror, 3-rotating and projection device, 4-interfere beam splitter, 5-focus lamp system, 6-post lens combination, 7-two dimension focus planardetector, 8-data acquisition processing system.

The spatial modulation and interference type computed tomography imaging spectrometer of embodiment the present invention's narration, be characterized in: in optical texture design and Data Management Analysis process, adopt interference modulations technology and computed tomography technology simultaneously, and, be a kind of imaging spectrometer of innovating formula interfering link to use heavy caliber projection spatial modulation and interference structure.Now in conjunction with Fig. 1, Fig. 2, Fig. 3 and Fig. 4 describe its principle.

As shown in Figure 1, the present invention is by preposition telescopic system, rotating and projection device (3), interference optics, and two-dimentional focus planardetector (7) and data acquisition process (8) system etc. partly form.Comprise target observation, the projection pattern data sequence is interfered in target image rotating and projection, optical interference projection imaging, collection, obtains the spectroscopic data sequence through Fourier transform, by processes such as CT backprojection reconstruction data cubes.

Preposition telescopic system is made up of preposition telescope (1) and collimating mirror (2), can adopt reflective or the transmission-type structure, and its focal length, aperture, visual field, aberration and spectral bandwidth etc. should design according to the general requirement of imaging spectral instrument system.Preposition telescope object observing, incident ray need not pass through traditional optical slot in light path, therefore can reduce the target light loss of energy, these high-throughout characteristics of the present invention just.Incident ray becomes collimated light beam after the collimating mirror effect.Rotating and projection device (3) collimation light image is rotated with a fixed step size, obtains the image of different angles.Step-length=anglec of rotation/images acquired number is chosen for 1 ° in implementation example.This revolves and adopts Dove prism or other to revolve the camera structure as process to realize.In implementation example, adopt Dove prism.Interference optics make from the collimated light beam of rotating and projection device outgoing interfere, projection and focusing, on the focal plane, picture side of focus lamp (5), receive with detector (7), obtain projected image and interference fringe clearly.Interference optics adopts heavy caliber projection spatial modulation and interference structure.Concrete form is that Michelson is interfered beam splitter (4), and adopts post lens combination (6) to carry out the project extended (see figure 2).It produces interference fringe is equal thickness fringes.This interference structure can make full use of the luminous energy of target, and can produce desirable picture on focus planardetector, is a desirable interference projection imaging system.Interference surface is on the conjugate plane of plane mirror, and imaging surface is on the focal plane of focus lamp.The interference figure stripe direction is parallel to post lens combination bus.Interference device will be introduced in the back.Projection image signal is interfered in the two-dimentional focus planardetector collection of adopting spectral response range to be respectively visible light and near infrared (0.4～μ m), short-wave infrared (1～5 μ m) and LONG WAVE INFRARED (8～14 μ m) respectively, realizes the collection (wherein infrared part adopts the infrared interference measurement device) of wide frequency domain interference data for projection sequence.Data acquisition processing system (8) is a core with intelligentized microprocessor, signal to detector output is gathered and is handled, finish by the conversion of spatial domain, obtain the spectral distribution of image, behind the CT backprojection reconstruction, can obtain spectrum pattern data cube simultaneously to frequency domain.The backprojection reconstruction algorithm is identical with the algorithm of common CTIS, will be introduced in the back.

Fig. 2 is the signal of heavy caliber projection spatial modulation and interference structure.Two level crossings of beam splitter are not 90 degree, but level crossing bias angle theta slightly wherein.Incident ray is through the half-reflection and half-transmission beam-splitting board and after flat mirror reflects, because of the existence at θ angle produces optical path difference, therefore interferes.The type that produces striped is an equal thick interference fringe.At this moment, when on the focal plane, picture side of detector, obtaining projected image, also obtain the interference fringe picture, just need the focal length and the position of suitable selection post lens combination.On whole focus planardetector, we just can obtain a complete interference between projections figure of tested two dimension target like this.The post lens combination is between focus lamp and focus planardetector in the present invention, and bus is parallel to interferes beam splitter two plane mirrors.

The power spectrum density in hypothetical target source be S ' (v), when the identical and optical path difference of relevant light intensity differed to Δ, the intensity of interference field was:

$I\left(\mathrm{\Δ}\right)=C\′\underset{0}{\overset{+\∞}{\∫}}S\′\left(v\right)[1+\cos \left(2\mathrm{\π}\frac{v}{c}\mathrm{\Δ}\right)]\mathrm{dv}$

Wherein C ' is a constant.Because we only are concerned about the variable part of interference image, therefore can remove dc operation to the interference image on the detector, the interferogram function that obtains at last is:

$G\left(\mathrm{\Δ}\right)=C\′\underset{0}{\overset{+\∞}{\∫}}S\′\left(v\right)\cos \left(2\mathrm{\π}\frac{v}{c}\mathrm{\Δ}\right)\mathrm{dv}$

G (Δ) is measurable, is called " interferogram ".G (Δ) is done contrary Fourier cosine transform, just can try to achieve S ' (v).In order to adopt ready-made Fourier transform program, often it is rewritten into the Fourier transform form:

$G\left(\mathrm{\&Delta;}\right)=\frac{C\&prime;}{2}\underset{-\&infin;}{\overset{+\&infin;}{\&Integral;}}S\&prime;\left(v\right)\exp (-\mathrm{<figure-callout\; id="2"\; label="j"\; filenames="C200510130308E00091.png"\; state="\{\{state\}\}">j</figure-callout>}2\mathrm{\&pi;}\frac{v}{c}\mathrm{\&Delta;})\mathrm{dv}$

Or

$S\&prime;\left(v\right)=\frac{2}{\mathrm{cC}\&prime;}\underset{-\&infin;}{\overset{+\&infin;}{\&Integral;}}G\left(\mathrm{\&Delta;}\right)\exp \left(\mathrm{<figure-callout\; id="2"\; label="j"\; filenames="C200510130308E00091.png"\; state="\{\{state\}\}">j</figure-callout>}2\mathrm{\&pi;}\frac{v}{c}\mathrm{\&Delta;}\right)\mathrm{d\&Delta;}$

Its frequency spectrum resolution characteristic only depends on the maximum variable quantity of Δ, and this amount is big more, and (" frequency " that v) may occur is just high more, and its resolving power is just big more for S '.In the present invention, the resolution of the tiltangle of the plane mirror of the size of Δ and the medium dip of interference beam splitter and focus planardetector is closely related.θ is big more, and Δ is also big more thereupon.But the upper limit of Δ is limited by detector resolution.Δ L is a maximum optical path difference, and D is a clear aperature, Δ L=2 x D x tan θ. θ is less than 1 ° usually.In implementation example, adopt 0.16 °

Difficult point in the enforcement is how to realize the coaxial rotation of target.Adopt Dove prism, running accuracy is had relatively high expectations.On the imaging dimension, detector is positioned on the conjugate plane of measured target just, therefore can produce desirable picture.This device is a desirable interference between projections imaging system.

In conjunction with Fig. 3, we illustrate image reconstruction process of the present invention.The method of rebuilding has a variety of, can adopt direct FFT invert method, filtering (convolution) back projection's method and algebraic reconstruction technique (ART).We adopt the direct FFT method of inverting.

If CTII system input image information be f (x, y, λ).X wherein, y presentation video plane, perpendicular to optical axis direction, λ is that the spectrum dimension of image distributes, perpendicular to x, the y plane.The image projection direction of establishing the CTII system again is parallel to the y axle, and (λ) one dimension on the x direction is projected as (regard λ as preset parameter this moment) to then two-dimentional input picture f for x, y

$p(x,\mathrm{\&lambda;})=\underset{-\&infin;}{\overset{+\&infin;}{\&Integral;}}f(x,y,\mathrm{\&lambda;})\mathrm{dy}---\left(1\right)$

Establish the anglec of rotation that θ is an image again, then any being projected as of θ angle image rotating (as shown in Figure 3)

$p_{\mathrm{\&theta;}}(x,\mathrm{\&lambda;})=\underset{-\&infin;}{\overset{+\&infin;}{\&Integral;}}{f}_{\mathrm{\&theta;}}(x,y,\mathrm{\&lambda;})\mathrm{dy}---\left(2\right)$

F wherein _θ(x, y, λ)=f (xcos θ-ysin θ, xsin θ+ycos θ, λ) (3)

Make θ in 0～π scope, rotate n angle, so in CTII, can collect corresponding to p with the equal angles spacing _θ(x, n group interference figure λ) is established this interference figure and is distributed as I _θ(x, r), wherein on behalf of projection, the x direction still distribute, and the r direction reflects that then fringe intensity changes.According to Fourier transform spectrometer principle, to I _θ(x, r) pattern sequence carries out along the one dimensional fourier transform of r direction, just can revert to the p of projection pattern _θ(x, λ) sequence.

According to center section theorem (being projection theorem), image rotating f _θ(x, y is λ) along the axial projection p of y _θ(x, one dimensional fourier transform λ) (x is a variable) is designated as P _θ(ρ, λ), provide original image f (x, y, two-dimension fourier transform F λ) (ξ, η, section λ), the angle of this section and ξ axle is θ, and passes through true origin.

Therefore, the key of problem be how to construct two-dimension fourier transform F (ξ, η, λ).For the discrete sampling situation of this paper, can be the P of n different θ angular projections ₀(ρ, λ) data are arranged along rectilinear direction separately in the η coordinate plane at ξ, and the angle of cut of these straight lines and x axle is θ, and all crosses true origin.Generally speaking, n P _θ(ρ, λ) sequence can't be with ξ, and the η coordinate plane fills up, and can partly fill up vacancy this moment with interpolation method.

To the F that constructs (ξ, η λ) carry out two dimension discrete fourier transform, then revert to f (x, y, λ), promptly required spectral image data cube.

Implementation example

With the black and white square shape pattern among Fig. 4 is target, throw light on the ordinary incandescent lamp light source, and use the area array CCD imaging, obtained the interference between projections pattern of 0 °, 45 °, 90 ° three typical angles, the result as shown in Figure 4, this figure is a kind of sampled result of collection of illustrative plates unification, and wherein horizontal direction performance interference fringe distributes, the intensity profile of vertical direction performance projection pattern.Therefrom as can be seen: (1) 0 °, 45 °, 90 ° projection gray level distributes and the projection of Fig. 4 on three directions coincide, the projection gray level distribution in the horizontal direction of each width of cloth pattern all is consistent with ideal situation, and the projection gray level distribution effect of this experimental provision has reached extraordinary effect.(2) interference fringe is symmetrical distribution with the center of pattern, and its degree of modulation is maximum in the center, decays rapidly along the right and left, and the interference rule of this and white light fits like a glove; If carry out the one dimensional fourier transform of horizontal direction, just can obtain the spectral distribution of each position on the vertical direction.

Through the CT backprojection reconstruction, can see that picture and the target after the recovery is in full accord substantially.

Claims (1)

1. a spatial modulation and interference type computed tomography imaging spectrometer comprises optical system structure, focus planardetector (7) and data acquisition processing system (8); It is characterized in that: adopted heavy caliber projection spatial modulation and interference structure in optical system, whole interference optics structure is made up of preposition telescope (1), collimating mirror (2), rotating and projection device (3), interference beam splitter (4), focus lamp system (5), post lens combination (6); Wherein rotating and projection device (3) adopts Dove prism or other to revolve the picture structure; Interfere the two-face mirror out of plumb of beam splitter (4), but have certain angle, this angle is greater than 90 ⁰And less than 91 ⁰Post lens combination (6) is positioned between focus lamp system (5) and the two-dimentional focus planardetector (7), and bus is parallel to two plane mirrors of interfering beam splitter (4); Two dimension focus planardetector (7) is positioned at picture side's focal plane position of focus lamp system (5).

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