CN105589210A

CN105589210A - Digital synthetic aperture imaging method based on pupil modulation

Info

Publication number: CN105589210A
Application number: CN201610136793.9A
Authority: CN
Inventors: 谢宗良; 马浩统; 任戈; 亓波; 史建亮; 崔占刚; 谭玉凤; 王智鹏; 何小君; 董理
Original assignee: Institute of Optics and Electronics of CAS
Current assignee: Institute of Optics and Electronics of CAS
Priority date: 2016-03-10
Filing date: 2016-03-10
Publication date: 2016-05-18
Anticipated expiration: 2036-03-10
Also published as: CN105589210B

Abstract

The invention relates to a digital synthetic aperture imaging method based on pupil modulation, which can restore the light field of the pupil, correct single aperture aberration, realize multi-aperture co-phase, and synthesize high-resolution images. The present invention uses an external diaphragm to modulate the pupil planes of each imaging subsystem, and uses Fourier stacking (FP: Fourier? ptychography) algorithm to reconstruct the light field of each pupil; use the Zernike polynomial to characterize the phase distribution of the light field, adopt the digital correction method, optimize the image quality evaluation function, correct the aberration between the single aperture itself and the multi-aperture, Based on the principle of digital imaging, each entrance pupil light field is synthesized into a high-resolution image. The invention integrates light field reconstruction, aberration correction and synthetic imaging, and has the advantages of high imaging image resolution, compact optical path, simple device, low cost and the like.

Description

A kind of digitlization synthetic aperture imaging method based on pupil modulation

Technical field

The present invention relates to a kind of synthetic aperture imaging method, particularly a kind of synthetic aperture imaging based on pupil modulation is newMethod, adopts at subsystem pupil plane and adds modulation diaphragm to realize reconstruction of optical wave field, single aperture and multiple aperture aberration correction and syntheticImaging, can reconstruct the light field of pupil, then light field is carried out to digitized processing aberration correction, realizes common phase position, sub-aperture,And synthetic high-definition picture.

Background technology

Optical synthesis aperture technology is intended to utilize the small-bore system of easy manufacture to synthesize large aperture system by optical instrument,Thereby meet high-resolution imaging requirements, solve practical application intermediate-resolution because of the limited problem of pore size. Synthetic holeFootpath imaging technique is generally divided into two kinds: baseline interference synthetic aperture technology and sparse optical synthesis aperture technology. Than baselineInterference synthetic aperture technology obtains complex degree of coherence by inverting interference fringe and carrys out imaging, and sparse optical synthesis aperture technology is profitDirectly synthesize target imaging with the multiple sub-aperture of space particular arrangement, there is sufficient flexibility, be more conducive to observation dynamicallyTarget, therefore, the correlation theory of sparse optical synthesis aperture imaging system and technical research have caused scholar's great interest in the industry,And fast development is got up in the world, it is in ground and space-based Large Telescope System, Laser Transmission, micro-imaging, three-dimensional imagingHave a wide range of applications Deng other technical field of imaging.

In order to bring into play these characteristics and advantages of sparse optical synthesis aperture system, in its application, need to realize sub-apertureBetween the key technology such as common phase, the correction of list aperture aberration. In order to break through these technical bottlenecks, scientists has proposed many solutionsCertainly method. Adaptive optical technique is the main stream approach of eliminating atmospheric turbulance impact at present, and it obtains ripple by wave front detectorFront-distortion, recycling distorting lens is proofreaied and correct. Although this method can compensate the phase distortion that atmospheric turbulance brings well,But the complexity and the cost that have increased whole system, be unfavorable for the application of synthetic aperture technique. Common phase between sub-aperture(Co-phasing), very important for sparse optical synthesis aperture imaging system, the image field of system should be each subsystemThe in-phase superposition of image field, if can not holding position synchronised between subsystem, can not reach the object of synthetic aperture, can only playImprove the effect of luminous energy acceptance rate. Realize the common phase between sub-aperture, key will detect the translation phase error between sub-aperture.The common phase Detection Techniques that scientists proposes at present have the detection technique based on position of interference fringe information, divide based on far field imageThe detection technique of analysing and utilize detection technique of special optical instrument etc., these technology can realize translation phase under certain conditionThe detection of bit error, but there is common defect, i.e. light path complexity used, system price costliness, and poor for applicability. And rightThe translation phase error detecting and the bearing calibration taked is also the machinery control based on complicated mostly, to frame for movement, systemFabrication technique and control precision have very high requirement.

In order to simplify the system architecture of sparse synthetic aperture imaging technology, reduce costs, reduce to realize difficulty, expand syntheticThe application of aperture imaging technology, the present invention proposes a kind of new method of the synthetic aperture imaging based on pupil modulation, passes throughPupil place at imaging len adds modulation diaphragm, rebuilds pupil light field, proofreaies and correct single aperture aberration, realizes sub-aperture common phase, goes forward side by sideRow compound imaging, this invention light harvesting field reconstruction, aberration correction and compound imaging be in one, has that image resolution ratio is high, light path is tightGather, install the advantages such as simple, with low cost.

Summary of the invention

In order to overcome the problem of prior art existence and the complexity of realization, reconstruction of optical wave field, aberration school are merged in the present inventionJust with compound imaging in one, a kind of simple and effective synthetic aperture imaging new method is provided. The present invention utilizes external lightDoor screen is modulated the pupil plane of each imaging subsystems, according to different modulation intelligences (diaphragm clear aperature position or largeLittle) and corresponding image, utilize FP algorithm to reconstruct the light field of each subsystem pupil, then light field carry out digitlization placeReason, with aberration correction, realizes common phase position, synthetic high-definition picture. This invention not only can complete relevant compound imaging, also rightIncoherent imaging has certain applicability, and light path is simply compact, is subject to hardly the restriction of frame for movement and manufacturing process.

The technical solution used in the present invention is: a kind of digitlization synthetic aperture imaging method based on pupil modulation, the partyMethod comprises following steps:

The first step, utilizes laser instrument active illumination target, and the reverberation of target enters each subsystem;

Second step, carries out identical modulation to each subsystem, utilizes diaphragm to carry out spatial modulation to the pupil of subsystem,Modulation system is lamination scanning or change pore size, and CCD records respective image;

The 3rd step, according to different modulation intelligences and corresponding different images thereof, utilizes FP Phase Retrieve Algorithm to recoverGo out the light field of each subsystem pupil; Utilize zernike polynomial to characterize the PHASE DISTRIBUTION of light field, adopt less digit correction method,Optimize image quality evaluation function, proofread and correct the aberration between single aperture itself and multiple aperture;

Finally, utilize virtual image lens by synthetic each pupil light field high-resolution image based on image-forming principle;

Wherein, FP Phase Retrieve Algorithm flow process is as follows:

1). the light field function of i aperture pupil of random initializtion

2). pupil light field obtains modulating light field after diaphragm:

U_{m, k}^{i} (x, y) = U_{i n p u t, k}^{i} (x, y) \times a_{k} (x, y) - - - (1)

A in formula_k(x, y) is the diaphragm information function while recording light intensity the k time, and it is defined as:

3). modulation light fieldScioptics are transmitted to focal plane place, obtain the optical field distribution of focal plane:

In formula, λ is imaging optical wavelength, the focal length that f is imaging subsystems, and the wave number that ko is light wave propagation,For FourierLeaf transformation,For the light field amplitude of focal plane calculating,For the light field phase place of focal plane of calculating, I_m,kBe the k time noteRecord intensity signal, so with measurement amplitudeThe amplitude that replacement is calculatedObtain the focal plane field distribution of upgrading

4). by what upgradePupil plane is changed in inversion, obtains the modulation light field of upgrading:

5). for lamination scanning modulation, by pupil light fieldPart corresponding to diaphragm clear aperature is usedAppropriate section replace, obtain new pupil light fieldFor changing pore size modulation, theWhen an iteration by pupil light fieldPart corresponding to clear aperature is usedAppropriate section replaceObtainAll the other time willUse corresponding to the logical light part of the annulus between two diaphragm clear aperaturesAppropriate section replace obtain

6). repeat above 2)～5) step, until k=n obtains

7). orderRepeat above 2)～6) step, untilAmplitude and phase placeRestrain, obtain the pupil light field in i final aperture

Wherein, according to the pupil light field in i aperture of reconstructProofread and correct that this aperture brought by atmospheric turbulanceAberration and the static aberration of self, the light field PHASE DISTRIBUTION representing based on zernike polynomial, adopts digital processing method, excellentChange image quality evaluation function S (), proofread and correct the phase distortion of pupil light field, thereby obtain optimum zernike coefficientFor:

Z in formula_p(x, y) is p rank zernike polynomial, and image quality evaluation function is chosen the most frequently used S=∫ ∫ I^γ(x,y)Dxdy, the pupil light field after i aperture self aberration correction is:

U_{i n p u t c o r r}^{i} (x, y) = U_{i n p u t}^{i} (x, y) e^{j Σ_{p = 1}^{P} {\hat{w}}_{p}^{i} Z_{p} (x, y)} - - - (5)

Wherein, according to the pupil light field after single aperture aberration correctionProofread and correct the translation phase between multiple apertureBit error and slanted phase error, choose first aperture for reference to aperture, and all pupil light fields are synthesized together and carry out schoolJust, from the 1st aperture to the synthetic light field in m aperture be:

U_{c o m p}^{1 : m} (x, y) = U_{i n p u t c o r r}^{1} (x, y) + Σ_{i = 2}^{m} U_{i n p u t c o r r}^{1, i} (x, y) e^{j Σ_{p = 1}^{P} w_{p}^{i} Z_{p} (x, y)} - - - (6)

Utilize the method for optimizing image quality evaluation function, the zernike coefficient being optimizedFor:

Finally obtain each aperture light field distribution of common phase, synthetic light field is:

U_{c o m p c o r r}^{1 : m} (x, y) = U_{i n p u t c o r r}^{1} (x, y) + Σ_{i = 2}^{m} U_{i n p u t c o r r}^{1, i} (x, y) e^{j Σ_{p = 1}^{P} {\hat{w}}_{p}^{i} Z_{p} (x, y)} - - - (8)

According to synthetic light fieldUtilize image-forming principle to carry out digital imagery to it.

Wherein, the method, in the time becoming for incoherent light occasion, need to resolve into required light field multiple relevant sub-light fields,Utilize the mixed state light intensity value of this little light field and the proportionality coefficient of measurement light intensity value to upgrade light intensity, thereby realize incoherent lightSynthetic aperture imaging.

Wherein, the method both can adopt the method for lamination scanning to modulate pupil to reconstruct the optical field distribution of pupil,Also can adopt the method that changes clear aperature size to modulate pupil to reconstruct the optical field distribution of pupil.

Wherein, the method not only can be proofreaied and correct the aberration in single sub-aperture, can also proofread and correct the aberration between multiple aperture, realExisting common phase, and by the light field process digital processing compound imaging of each aperture pupil.

Wherein, the method both can adopt CCD to be placed in the light path of lens focus position, also can adopt CCD to be placed in intoThe light path at image position place, in the time adopting CCD to be placed in the light path at image space place, in FP algorithm iteration, only formula (2) needsChange the form of saving constant term phase place and amplitude factor into:

In following step, f pin coordinate is changed to l', formula (3) need to change into:

Compared with the light path that is placed in lens focus position with CCD, it is more easy to control that CCD is placed in the light path at image space place, canStrong operability.

Adopt the present invention can reach following technique effect:

1. with respect to the light channel structure of the sparse optical synthesis aperture imaging system complexity of tradition, the present invention propose based on lightThe synthetic aperture imaging new method of pupil modulation, light path used is simply compact, adopts and adds the side of modulating diaphragm at sub-aperture pupil placeMethod has completed the functions such as reconstruction of optical wave field, aberration correction, compound imaging simultaneously in conjunction with FP algorithm.

2. the synthetic aperture imaging new method based on pupil modulation that the present invention proposes, utilizes modulation diaphragm information and institute to rememberThe light field of the image reconstruction pupil of record, is not used any wave front detector, has reduced complexity and the cost of system, and favourableIn by this technology to multi-field popularization. The FP algorithm adopting, utilizes the restriction of lamination, has solved well traditional GS algorithm onlyThe poor shortcoming of one property.

3. carry out aberration correction with respect to conventional distorting lens in the sparse optical synthesis aperture imaging system of tradition, the present invention proposesThe synthetic aperture imaging new method based on pupil modulation, utilize the method for image sharpness digital processing to proofread and correct atmospheric turbulance bandThe aberration coming and the static aberration in aperture self, greatly simplified system, reduced cost.

With respect in the sparse optical synthesis aperture imaging system of tradition, adopt based on position of interference fringe information and spyThe common phase Detection Techniques of different optical instrument, the synthetic aperture imaging new method based on pupil modulation that invention proposes, utilizes picture clearThe method of clear number of degrees word processing has been proofreaied and correct each the aberration between sub-aperture, has realized common phase position, sub-aperture, without complex hardwareStructure, is conducive to applying of technology.

Brief description of the drawings

Fig. 1 is total system schematic diagram of the present invention;

Fig. 2 is the demonstration graph of scanning diaphragm control in system;

Fig. 3 is the demonstration graph of iris diaphgram control in system.

Detailed description of the invention

Further illustrate the present invention below in conjunction with accompanying drawing and detailed description of the invention.

The present invention proposes a kind of digitlization synthetic aperture imaging method based on pupil modulation, and concrete steps are as follows:

1.. according to different modulation intelligence (clear aperature position or size) and corresponding different images thereof, utilize FP to calculateMethod recovers the light field of each aperture pupil. FP Phase Retrieve Algorithm flow process is as follows:

1). the light field function of i aperture pupil of random initializtion

2). pupil light field obtains modulating light field after diaphragm:

U_{m, k}^{i} (x, y) = U_{i n p u t, k}^{i} (x, y) \times a_{k} (x, y) - - - (1)

6). repeat above 2)～5) step, until k=n obtains

2.. according to the pupil light field in i aperture of reconstructProofread and correct the picture that this aperture is brought by atmospheric turbulanceDifference and the static aberration of self, the light field PHASE DISTRIBUTION representing based on zernike polynomial, adopts digital processing method, optimizesImage quality evaluation function S (), proofreaies and correct the phase distortion of pupil light field, thereby obtains optimum zernike coefficientFor:

U_{i n p u t c o r r}^{i} (x, y) = U_{i n p u t}^{i} (x, y) e^{j Σ_{p = 1}^{P} {\hat{w}}_{p}^{i} Z_{p} (x, y)} - - - (5)

3.. according to the pupil light field after single aperture aberration correctionProofread and correct the translation phase place between multiple apertureError and slanted phase error, choose first aperture for reference to aperture, and all pupil light fields are synthesized together and proofread and correct,From the 1st aperture to the synthetic light field in m aperture be:

U_{c o m p}^{1 : m} (x, y) = U_{i n p u t c o r r}^{1} (x, y) + Σ_{i = 2}^{m} U_{i n p u t c o r r}^{1, i} (x, y) e^{j Σ_{p = 1}^{P} w_{p}^{i} Z_{p} (x, y)} - - - (6)

U_{c o m p c o r r}^{1 : m} (x, y) = U_{i n p u t c o r r}^{1} (x, y) + Σ_{i = 2}^{m} U_{i n p u t c o r r}^{1, i} (x, y) e^{j Σ_{p = 1}^{P} {\hat{w}}_{p}^{i} Z_{p} (x, y)} - - - (8)

4.. according to synthetic light fieldUtilize image-forming principle to carry out digital imagery to it.

If 5.. target scattering light is incoherent light, the stack form that visual this incoherent light is multiple coherent light, instituteCan not directly carry out light intensity replacement in the light intensity renewal process of above algorithm, but need to required light field be resolved into manyIndividual relevant sub-light field, utilizes the mixed state light intensity value of this little light field and the proportionality coefficient of measurement light intensity value to upgrade light intensity, fromAnd realize the reconstruction of optical wave field of incoherent light.

Embodiment:

The whole synthesis aperture imaging system based on pupil modulation is by multiple sub-imaging systems, modulation diaphragm, CCD camera andData processing terminal (generally adopting PC) composition, the operation principle of whole system as shown in Figure 1:

Its concrete course of work is:

1. for every sub-aperture system, in the time adopting lamination scanning modulation, control as shown in Figure 2 diaphragm clear aperature,Corresponding image under CCD cameras record; In the time adopting the modulation of change pore size, control as shown in Figure 3 diaphragm clear aperature,CCD records corresponding image.

2. according to the image of modulation intelligence (position of clear aperature or size) and institute's corresponding record, at data processing terminalUtilize FP algorithm to reconstruct pupil light field.

3. the light field of pair every sub-aperture pupil is carried out digital processing, proofreaies and correct aberration that atmospheric turbulance brings and self is quietState aberration, then puts sub-aperture light field together and proofreaies and correct the aberration between multiple aperture, realizes the common phase position in sub-aperture.

4. according to image-forming principle, utilize virtual lens that each sub-aperture light occasion is become to full resolution pricture.

Claims

1. A digital synthetic aperture imaging method based on pupil modulation, characterized in that the method comprises the following steps:

In the first step, the laser (1) is used to actively illuminate the target, and the reflected light of the target enters each subsystem;

The second step is to carry out the same modulation on each subsystem, using the diaphragm (3) to spatially modulate the pupil of the subsystem (2), the modulation method is stack scanning or changing the aperture size, and the CCD (4) records the corresponding image;

The third step is to use the FP phase recovery algorithm to restore the light field of the pupil of each subsystem according to different modulation information and the corresponding different images; use the Zernike polynomial to characterize the phase distribution of the light field, and use the digital correction method, Optimize the image quality evaluation function and correct the aberrations between the single aperture itself and the multiple apertures;

Finally, based on the imaging principle, the virtual imaging lens is used to synthesize the high-resolution image of each pupil light field;

Among them, the FP phase recovery algorithm flow is as follows:

1). Randomly initialize the light field function of the i-th aperture pupil

2). After the pupil light field passes through the diaphragm, the modulated light field is obtained:

{U u}_{m m,, k k}^{i i} ((x x,, y the y)) = = {U u}_{i i n no p p u u t t,, k k}^{i i} ((x x,, y the y)) \times \times {a a}_{k k} ((x x,, y the y)) - - - - - - ((11))

where a _k (x, y) is the aperture information function when the light intensity is recorded for the kth time, and it is defined as:

3). Modulated light field Propagate to the focal plane through the lens, and obtain the light field distribution of the focal plane:

where λ is the wavelength of the imaging light wave, f is the focal length of the imaging subsystem, ko is the wave number of the light wave propagation, is the Fourier transform, is the calculated light field amplitude at the focal plane, is the calculated phase of the light field at the focal plane, I _m,k is the light intensity information recorded for the kth time, so the measured amplitude Amplitude calculated by substitution Get updated focal plane field distribution

4). Will update the Inverse transform to the pupil plane to get the updated modulated light field:

5). For stack scan modulation, the pupil light field The part corresponding to the aperture of the diaphragm is used Replace the corresponding part of , and get the new pupil light field For varying aperture size modulation, the pupil light field The part corresponding to the clear aperture is used Replace the corresponding part of the rest of the time will Corresponding to the ring clear part between the clear apertures of the two diaphragms Replace the corresponding part of

6). Repeat steps 2) to 5) above until k=n to obtain

7). Order Repeat steps 2) to 6) above until Amplitude and phase converge to get the final i-th pupil light field

where, according to the reconstructed pupil light field of the ith aperture Correct the aberration caused by the atmospheric turbulence and the static aberration of the aperture, based on the phase distribution of the light field expressed by the Zernike polynomial, use digital processing methods to optimize the image quality evaluation function S( ), and correct the pupil light field phase distortion, so as to obtain the optimal Zernike coefficient for:

In the formula, Z _p (x, y) is the p-th order Zernike polynomial, and the image quality evaluation function selects the most commonly used S=∫∫I ^γ (x, y)dxdy, then the i-th aperture’s own aberration-corrected light The pupil light field is:

{U u}_{i i n no p p u u t t c c o o r r r r}^{i i} ((x x,, y the y)) = = {U u}_{i i n no p p u u t t}^{i i} ((x x,, y the y)) {e e}^{j j {Σ Σ}_{p p = = 11}^{P P} {\overset{^^}{w w}}_{p p}^{i i} {Z Z}_{p p} ((x x,, y the y))} - - - - - - ((55))

Among them, according to the pupil light field corrected by the single aperture aberration Correct the translation phase error and tilt phase error between multiple apertures, select the first aperture as the reference aperture, and combine all the pupil light fields together for correction. The synthetic light field from the first aperture to the mth aperture is :

{U u}_{c c o o m m p p}^{11 : : m m} ((x x,, y the y)) = = {U u}_{i i n no p p u u t t c c o o r r r r}^{11} ((x x,, y the y)) + + {Σ Σ}_{i i = = 22}^{m m} {U u}_{i i n no p p u u t t c c o o r r r r}^{11,, i i} ((x x,, y the y)) {e e}^{j j {Σ Σ}_{p p = = 11}^{P P} {w w}_{p p}^{i i} {Z Z}_{p p} ((x x,, y the y))} - - - - - - ((66))

Using the method of optimizing the image quality evaluation function, the optimized Zernike coefficient is obtained for:

Finally, the light field distribution of each aperture of the common phase is obtained, and the synthesized light field is:

{U u}_{c c o o m m p p c c o o r r r r}^{11 : : m m} ((x x,, y the y)) = = {U u}_{i i n no p p u u t t c c o o r r r r}^{11} ((x x,, y the y)) + + {Σ Σ}_{i i = = 22}^{m m} {U u}_{i i n no p p u u t t c c o o r r r r}^{11,, i i} ((x x,, y the y)) {e e}^{j j {Σ Σ}_{p p = = 11}^{P P} {\overset{^^}{w w}}_{p p}^{i i} {Z Z}_{p p} ((x x,, y the y))} - - - - - - ((88))

According to the synthetic light field It is digitally imaged using imaging principles.

2. The digital synthetic aperture imaging method based on pupil modulation according to claim 1, characterized in that, when the method is used for incoherent light field synthesis, the required light field needs to be decomposed into a plurality of coherent sub-light fields , using the mixed-state light intensity values of these sub-light fields and the proportional coefficient of the measured light intensity values to update the light intensity, so as to realize the synthetic aperture imaging of incoherent light.

3. the digital synthetic aperture imaging method based on pupil modulation according to claim 1, is characterized in that, this method both can adopt the method for stack scanning to modulate pupil to reconstruct the light field distribution of exit pupil, also can The method of changing the size of the clear aperture is used to modulate the pupil to reconstruct the light field distribution of the exit pupil.

4. The new method of digital synthetic aperture imaging based on pupil modulation according to claim 1, characterized in that the method can not only correct the aberration of a single sub-aperture, but also can correct the aberration between multiple apertures to achieve a common phase, and digitally process the light fields of each aperture pupil into an image.

5. the digital synthetic aperture imaging method based on pupil modulation according to claim 1, is characterized in that, this method both can adopt the optical path that CCD is placed at lens focus position, also can adopt the optical path that CCD is placed at imaging position , when using the optical path where the CCD is placed at the imaging position, in the iteration of the FP algorithm, only the formula (2) needs to be changed to the form that omits the constant term phase and amplitude factor:

In the next step, the coordinates of foot f are changed to l', and the formula (3) needs to be changed to:

Compared with the optical path where the CCD is placed at the focal point of the lens, the optical path where the CCD is placed at the imaging position is easier to control and has strong operability.