Method for precisely measuring baseline of optical synthetic aperture imaging system

Abstract

The invention discloses an optical synthetic aperture imaging system base line precision measurement method, which specifically comprises the following steps: when a light combination imaging subsystem does not exist in a system, simultaneously imaging exit pupils of sub-apertures after base line changing and two reference holes with known position coordinates on a reference diaphragm by using a movable base line measurement telescope; determining a coordinate system by using the two reference holes, respectively resolving exit pupil centroid coordinates of each sub-aperture in the coordinate system, and calculating entrance pupil coordinates of each sub-aperture according to known structure parameters of the sub-aperture; when a light combination imaging subsystem exists in the system, the same movable baseline measuring telescope is used for simultaneously imaging an entrance pupil of each baseline-changed light combination telescope and two reference holes with known position coordinates on a reference diaphragm, and the two reference holes are used for determining a coordinate system; the entrance pupil centroid coordinates of all the light combination telescopes are calculated in the coordinate system; the entrance pupil coordinate of the sub-aperture and the entrance pupil coordinate of the light combination telescope are compared with the theoretical position coordinate, and the difference value is the baseline mapping error. The invention provides a solution for measuring the baseline mapping error of the optical synthetic aperture imaging system.

Description

Technical Field

[0001] The invention relates to the technical field of astronomical observation, and in particular to a method for precisely measuring a baseline of an optical synthetic aperture imaging system. Background Art

[0002] Compared with a single-aperture telescope, optical synthetic aperture technology uses a sub-aperture array method to achieve the equivalent spatial resolution of a single large-aperture telescope, breaking through the diffraction limit caused by the limitation of aperture size of a single-aperture telescope. Optical synthetic aperture technology has become the inevitable path for the development of optical telescope imaging systems.

[0003] In order to improve the observation efficiency of the optical synthetic aperture imaging system, it is necessary to increase the system field of view. The system field of view is affected by the system pupil mapping error. The larger the system field of view, the stricter the pupil mapping error requirement. The pupil mapping error can be divided into two parts. One is the baseline mapping error, that is, there is a difference in the shape of the entrance pupil baseline of the sub-aperture array and the entrance pupil baseline of the combined telescope (system exit pupil baseline). The other is the sub-aperture magnification error, that is, the entrance pupil size / exit pupil size of each sub-aperture is different from the design value or is different between each sub-aperture.

[0004] The ideal Fizeau type optical synthetic aperture imaging system needs to follow the strict similarity of the entrance pupil baseline of the sub-aperture array (the distance between the optical axes of the entrance pupils of the sub-apertures, 4 sub-apertures contain 6 baselines) and the entrance pupil baseline of the light-combining telescope (the distance between the optical axes of the light-combining imaging beams, 4 light-combining imaging beams contain 6 baselines), and the similarity ratio is the angular magnification of the sub-aperture, so the precise measurement and control of the entrance pupil baseline of the sub-aperture array and the entrance pupil baseline of the light-combining telescope become crucial. Although the Michelson type optical synthetic aperture imaging system does not need to follow this principle, the precise measurement and control of the entrance pupil baseline of the sub-aperture array and the entrance pupil baseline of the light-combining telescope are equally significant. Through the precise measurement and control of the baseline, the actual position of the sub-aperture after the variable baseline movement can be made consistent with the UV coverage point position of its theoretical analysis, and the entrance pupil position of the light-combining telescope is consistent with its theoretical design position to ensure that the direction of the interference fringes on the light-combining imaging camera meets the requirements of the later analysis.

[0005] The existing methods and means are as follows:

[0006] 1. The Wide Field Imaging Interferometer (WIIT) established by NASA verifies the wide field interferometric imaging algorithm for space interferometer projects such as SPIRIT (infrared), SPECS (submillimeter wave), and TPF-I. The system model is established and verified. Two sub-telescopes are installed at both ends of a linear air-floating translation stage. Each sub-aperture is 25mm. The baseline of the two sub-telescopes is variable between 25mm and 250mm. UV coverage is achieved through baseline adjustment and synchronous rotation of the target and detector. The position information of the sub-aperture is obtained by feedback from the linear absolute encoder installed on the air-floating guide rail. The encoder can only obtain the position information of the guide sleeve on the guide rail, and cannot obtain the absolute distance of the sub-aperture entrance pupil and exit pupil baseline. At the end of the article, it is mentioned that well-calibrated absolute baseline measurement is needed in the future. No introduction and experimental verification of absolute baseline measurement was found in the subsequent papers on WIIT.

[0007] 2. The Very Large Telescope Interferometer (VLTI) built by the European Southern Observatory in Chile consists of four fixed 8.2m telescopes (UTs) and four 1.8m auxiliary telescopes (ATs) that can move in a plane on rails. The light beams from different telescopes are combined through underground tunnels to ensure that the optical path difference between different light beams is less than 1μm. The four 1.8m auxiliary telescopes that can move in a plane on rails can change the baseline, and the UTs can form six baselines, all of which have different lengths and directions. The maximum possible resolution is equivalent to that of a telescope with a diameter of 130 meters. However, no introduction or experiments on baseline measurement and calibration in VLTI have been found so far.

[0008] 3. The National Astronomical Observatory of the Chinese Academy of Sciences designed and built a Fizeau Imaging Interferometer Test Device (FIIT), which mainly consists of a light source module for simulating infinite objects, three sub-telescopes with an aperture of 100mm in the Golay-3 distribution (equilateral triangle), three yaw / pitch correction modules and an optical path delay module, as well as three detection telescopes for phase imaging and a beam synthesis telescope. Broadband white light (400-700nm) phase imaging with a field of view of 2 arc minutes was achieved in the laboratory. The baseline length of the three sub-telescopes in FIIT is 200mm, and the baseline length of the sub-beam is 40mm, both of which cannot be changed.

[0009] The system entrance pupil baseline is determined by the aperture placed in front of the sub-telescope. The aperture has three entrance pupils that have been precisely machined and tested, which are aligned with the three sub-apertures respectively. The baseline length is strictly limited and can be used as the system entrance pupil baseline reference.

[0010] The exit pupil baseline is determined by the calibration plate, lens and camera. A precision-machined and tested calibration glass plate is placed in the path of the three sub-beams. The calibration glass plate is engraved with three circular lines distributed in an equilateral triangle. Each circular line has a cross line passing through the center of the circle. The center distance of the circular lines has been precisely tested and can be used as the exit pupil baseline test benchmark. After the sub-beam passes through the glass plate and the lens, there are six circular images on the camera, which are the images of the three sub-beams and the images of the circular lines of the three calibration plates. After identifying the coordinates of the center of the six images, the baseline of the sub-beam is calculated based on the image center of the circular lines of the calibration plate, thereby obtaining the system exit pupil baseline.

[0011] The system baseline mapping error can be obtained by combining the system entrance pupil baseline and the system exit pupil baseline.

[0012] 4. China Resources Satellite Application Center analyzed and studied the intersatellite high-precision baseline measurement and processing methods and baseline processing procedures based on the working characteristics of the distributed interferometric synthetic aperture radar satellite system GNSS, SAR and other payloads. The distributed InSAR satellite system first obtains the GNSS measurement baseline through GNSS dual-frequency carrier phase differential measurement and ground high-precision orbit solution; then, through position correction, the reference point of the baseline is converted from the satellite centroid to the SAR antenna phase center to obtain the spatial domain baseline. The experimental results show that the statistical accuracy of the InSAR baseline intercomparison results obtained by orbit determination is about 1 mm.

[0013] Disadvantages of existing technology:

[0014] (1) Currently, most existing optical synthetic aperture imaging systems at home and abroad use static methods with fixed baselines. The baseline measurement method using a reference aperture and a calibration plate is only applicable to systems with fixed baselines, and its difficulty and adaptability are inferior to the method of the present invention.

[0015] (2) At present, the baseline measurement of the existing variable baseline optical synthetic aperture imaging systems at home and abroad mostly adopts the method of installing a grating ruler on the guide rail or using a motor encoder to feedback the sub-aperture position. This method can obtain the guide sleeve position information. Due to the position difference between the guide sleeve and the sub-aperture and sub-beam, the exit pupil and entrance pupil positions of the sub-aperture and sub-beam cannot be directly obtained.

[0016] (3) Currently, the number of sub-apertures in the existing variable baseline optical synthetic aperture imaging systems at home and abroad is relatively small, mostly 2 or 3. The baseline is easy to measure, and the baseline measurement method is only applicable to the case where the number of sub-apertures is small.

[0017] (4) Currently, most existing baseline measurement methods are relative measurements, which cannot directly obtain the absolute distance between the entrance and exit pupils of each sub-aperture and sub-beam, and the accuracy cannot reach the silk level.

[0018] The information disclosed in this background technology section is only intended to deepen the understanding of the overall background technology of the present invention, and should not be regarded as acknowledging or suggesting in any form that the information constitutes the prior art already known to those skilled in the art. Summary of the invention

[0019] In view of the problems existing in the prior art, the purpose of the present invention is to provide a method for precise measurement of the baseline of an optical synthetic aperture imaging system. The method solves the high-precision absolute measurement of the sub-aperture baseline and the combined light imaging baseline in optical synthetic aperture imaging systems with variable baselines and fixed baselines, provides a solution for the measurement of the system pupil mapping error, provides a data basis for the precise control of the system pupil mapping error, and thus ensures the observation field of view of the system.

[0020] In order to achieve the above object, the present invention adopts the following technical solutions:

[0021] A method for precisely measuring the baseline of an optical synthetic aperture imaging system, the method specifically comprising:

[0022] When there is no light combining imaging subsystem in the system, the exit pupil of each sub-aperture after the baseline is changed and two reference holes with known position coordinates on the reference aperture are imaged simultaneously by using a movable baseline measuring telescope, a coordinate system is established through the two reference holes with known position coordinates, the coordinates of the centroid of the exit pupil of each sub-aperture are determined in the coordinate system, and the coordinates of the entrance pupil of each sub-aperture are calculated according to the structural parameters of the sub-aperture;

[0023] When there is a light-combining imaging subsystem in the system, the same movable baseline measuring telescope is used to simultaneously image the entrance pupil of each light-combining telescope after the baseline is changed and the two reference holes with known position coordinates on the reference aperture, and a coordinate system is established through the two reference holes with known position coordinates. The centroid coordinates of the entrance pupil of each light-combining telescope are determined in the coordinate system, which are also the system exit pupil coordinates.

[0024] The entrance pupil coordinates of the above sub-aperture and the system exit pupil coordinates are compared with their theoretical position coordinates, and the difference is the baseline mapping error.

[0025] Furthermore, the calculation method of the centroid coordinates of the reference aperture and the exit pupil and entrance pupil images is as follows:

[0026] The image matrix is ​​I, then the gradients of the image in the horizontal x direction and vertical y direction are:

[0027]

[0028] Then the image gradient size is:

[0029]

[0030] The gradient size G of the image is subtracted from a standard circle with undetermined parameters. When the sum of squares of the residuals is minimized, the standard circle can be regarded as the image circle, and the coordinates of the center of the image circle can be obtained.

[0031] Furthermore, the calculation method of the centroid coordinates of the exit pupil and entrance pupil space is as follows:

[0032] It is known that the center positions of the two reference hole circles 1 and 2 are position 1 and position 2 respectively, and the coordinates of their centroids on the image are [m1, n1], [m2, n2] respectively. The vector from 1 to 2 on the image is r, and the corresponding spatial positions are [x1, y1], [x2, y2] respectively. The vector from 1 to 2 in space is R; the image coordinates of the position 3 to be measured are [m, n], and the actual spatial coordinates are calculated; the tangent value of the angle between the image vector r and the spatial vector R is:

[0033]

[0034] In the formula, △m=m2-m1,△n=n2-n1,△x=x2-x1,△y=y2-y1,

[0035] The ratio of the space vector length calculated from the coordinates of the centroid of the reference hole on the reference aperture to the image vector length calculated from the coordinates of the image centroid of the reference hole is:

[0036]

[0037] Suppose the vector from position 1 to position 3 on the image is:

[0038]

[0039] The vector from position 1 to position 3 in space is:

[0040]

[0041] The space vector is equal to the image vector rotated by -θ angle, multiplied by the ratio, so the relationship between the space vector and the image vector is:

[0042]

[0043] Furthermore, the calculation method of decomposing the pupil space centroid coordinates into radial and tangential pupil mapping errors is as follows:

[0044] Facing the light source, the X axis is to the right horizontally, the Y axis is upward, and the radial and tangential directions are respectively rotated counterclockwise by an angle of α along the X axis and the Y axis; the pupil mapping error is [dx, dy] in the XY coordinate system, and [dρ, dτ] in the radial and tangential coordinate systems, then:

[0045]

[0046] Furthermore, the calculation method of the sub-aperture entrance pupil centroid coordinates is as follows:

[0047] The centroid coordinates of the entrance pupils of the four sub-apertures are calculated based on the structural dimensions of the sub-apertures:

[0048] [dρ,,dτ,]=[dρ,dτ]-[Lρ,Lτ]

[0049] Where Lρ is the length of the subaperture exit pupil and entrance pupil in the ρ direction, and Lτ is the length of the subaperture exit pupil and entrance pupil in the τ direction.

[0050] Furthermore, in Fizeau imaging mode, the baseline precision measurement method is specifically as follows:

[0051] S1. The four sub-apertures pointing in the same direction move with variable baselines driven by the air-floating motion stage. The light from the collimator passes through the long slot of the reference aperture and enters the sub-aperture, and is emitted from the rear light outlet of the sub-aperture. At this time, the exit pupil baseline of the sub-aperture is determined.

[0052] S2. At the same time, the light from the collimator passes through the reference hole of the reference aperture and propagates to the rear of the system without any obstruction;

[0053] S3, the baseline measurement telescope is moved to the rear of one of the sub-apertures, so that the exit pupil of the sub-aperture and the two reference holes around it enter the baseline measurement telescope at the same time and are imaged, and the centroid coordinates of the exit pupil of the sub-aperture are calculated according to the centroid coordinates of the two reference holes;

[0054] S4, repeat step S3 to calculate the coordinates of the exit pupil centroids of the other three sub-apertures;

[0055] S5. Calculate the entrance pupil coordinates of the four sub-apertures according to the structural dimensions of the sub-apertures. The difference between the measured coordinates and the theoretical coordinates is the system entrance pupil error.

[0056] S6, moving the light combining imaging telescope part into the system, and the light emitted from the sub-aperture enters the light combining imaging telescope part through the folding mirror;

[0057] S7. The entrance pupil mechanism of the light-combining telescope performs variable baseline movement driven by the motion platform. Its ideal baseline length / subaperture entrance pupil baseline length = subaperture angle magnification. At this time, the entrance pupil baseline of the light-combining imaging telescope is determined.

[0058] S8. At the same time, the light from the collimator passes through the reference hole of the reference aperture and propagates to the rear of the system without any obstruction;

[0059] S9, the baseline measurement telescope is moved to the rear of one of the folding axis mirrors, so that the output light of the folding axis mirror and the two reference holes around it enter the baseline measurement telescope at the same time and form an image, and the centroid coordinates of the entrance pupil of the combined light imaging telescope are calculated according to the centroid coordinates of the two reference holes;

[0060] S10, repeat step S9 to solve the coordinates of the centroids of the entrance pupils of the other three combined light imaging telescopes. The difference between the measured coordinates and the theoretical coordinates is the system exit pupil error.

[0061] S11. The dissimilarity between the geometric figure formed by the actual exit pupil of the system and the geometric figure formed by the actual entrance pupil and the geometric figure formed by the theoretical exit pupil and the geometric figure formed by the theoretical entrance pupil, or the error with the ratio of the sub-aperture angle magnification, is the baseline mapping error.

[0062] Further, in the Michelson imaging mode, the difference between the imaging mode and the Fizeau imaging mode lies in steps S7 and S11, and the other steps are consistent with the Fizeau imaging mode; wherein,

[0063] S7 is changed to: the entrance pupil mechanism of the light-combining telescope performs variable baseline motion driven by the motion stage, and its ideal baseline length / subaperture entrance pupil baseline length may not be consistent with the subaperture angle magnification, and the entrance pupil baseline of the light-combining telescope does not change subsequently with the subaperture variable baseline motion;

[0064] S11 is changed to: The inconsistency between the geometric figure formed by the actual exit pupil of the system and the geometric figure formed by the theoretical exit pupil is the system exit pupil error, and the inconsistency between the geometric figure formed by the actual entrance pupil and the geometric figure formed by the theoretical exit pupil is the system entrance pupil error.

[0065] By adopting the above technical solution, the present invention has the following beneficial effects:

[0066] 1) The technology involved is relatively mature and easy to implement. At present, the domestic processing accuracy of the roundness position accuracy of the reference hole in the meter-level reference aperture can reach the silk level, and its detection accuracy can reach the micron level, which meets the accuracy requirements of this method;

[0067] 2) Strong versatility. This method is generally applicable to optical synthetic aperture imaging systems with variable baselines and fixed baselines;

[0068] 3) Strong scalability. This method provides ideas and solutions for measuring the distance of multiple optical systems or components;

[0069] 4) High cost performance. The reference aperture, telescope and its driving mechanism used in this method are relatively mature and inexpensive. The overall structure is relatively simple, occupies little space and has high cost performance.

[0070] 5) Absolute measurement. This method is different from the traditional relative measurement that can only measure the change of the baseline. It can achieve absolute measurement of the system baseline by establishing a global coordinate system through the same reference aperture;

[0071] 6) High measurement accuracy. By optimizing the circular hole image centroid position acquisition algorithm, the baseline measurement accuracy can be achieved at the wire level;

[0072] 7) Small impact on the system. The base aperture is thin and occupies a small space. The baseline measurement telescope is located at the tail of the system and has little impact on the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0073] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0074] Figure 1 It is a structural diagram of the optical synthetic aperture imaging system baseline precision measurement device of the present invention.

[0075] Figure 2 This is a schematic diagram of the sub-aperture exit pupil measurement of the present invention.

[0076] Figure 3 Schematic diagram of the baseline of the system of the present invention.

[0077] Figure 4 This is a schematic diagram of imaging of the baseline measurement telescope of the present invention.

[0078] Figure 5 Schematic diagram of the measurement of entrance pupil error of the light combining imaging telescope of the present invention.

[0079] Figure 6 Schematic diagram of baseline mapping error of the present invention. DETAILED DESCRIPTION

[0080] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0081] The specific implementation of the present invention is described in detail below in conjunction with the accompanying drawings. It should be understood that the specific implementation described here is only used to illustrate and explain the present invention, and is not used to limit the present invention.

[0082] The present invention provides a method for precisely measuring the baseline of an optical synthetic aperture imaging system.

[0083] When there is no light combining imaging subsystem in the system, a movable baseline measuring telescope is used to simultaneously image the exit pupil of each sub-aperture after the baseline is changed and two reference holes with known position coordinates on the reference aperture, a coordinate system is established through the two reference holes with known position coordinates, the exit pupil coordinates of each sub-aperture are determined in the coordinate system, and the entrance pupil coordinates of each sub-aperture are calculated according to the structural parameters of the sub-aperture;

[0084] When there is a light-combining imaging subsystem in the system, the same movable baseline measuring telescope is used to simultaneously image the entrance pupil of each light-combining telescope after the baseline is changed and the two reference holes with known position coordinates on the reference aperture, and a coordinate system is established through the two reference holes with known position coordinates. The entrance pupil coordinates of each light-combining telescope are determined in the coordinate system, which are also the exit pupil coordinates of the system.

[0085] The entrance pupil coordinates of the above sub-apertures and the system exit pupil coordinates are compared with their theoretical position coordinates, and these differences are the baseline mapping errors.

[0086] This method solves the problem of high-precision absolute measurement of sub-aperture baseline and combined-light imaging baseline in optical synthetic aperture imaging systems with variable baseline and fixed baseline, provides a solution for measuring the system pupil mapping error, and provides a data basis for the precise control of the system pupil mapping error, thereby ensuring the observation field of view of the system.

[0087] Combination Figure 1 As shown, the specific structure required for the method for precise measurement of the baseline of an optical synthetic aperture imaging system proposed in the present invention includes a parallel light tube 1, a reference aperture 2 with a plurality of reference holes (the line connecting the reference holes is consistent with the direction of the sub-aperture changing baseline) and long grooves (the direction of the long grooves is consistent with the direction of the sub-aperture changing baseline), a sub-aperture 3, a main delay line 4, a light combining telescope entrance pupil mechanism 5, a light combining telescope 6, a baseline measuring telescope 7, a baseline measuring telescope driving structure 8, etc.

[0088] In the present invention, a collimator 1 capable of emitting horizontal parallel light is installed at the front end of an optical synthetic aperture imaging system. A reference aperture 2 is vertically installed behind the collimator 1, and a large plane of the reference aperture 2 is perpendicular to the emitted light of the collimator 1. The long groove of the reference aperture 2 coincides with the trajectory of the entrance pupil of the sub-aperture 3 during the baseline change process, that is, during the baseline change process of the sub-aperture 3, it can be ensured that the parallel light emitted by the collimator 1 can enter the sub-aperture 3 through the long groove of the reference aperture 2. In this example, the number of sub-apertures 3 is 4, which are symmetrically arranged behind the reference aperture 2 and installed on a moving platform, and each sub-aperture 3 can perform baseline change movement. The light beam emitted by the sub-aperture 3 enters the light-combining telescope entrance pupil mechanism 5 after passing through the main delay lines 4 arranged around it. The light-combining telescope entrance pupil mechanism 5 is symmetrically arranged behind the main delay line 4 and installed on a moving platform, and the light-combining telescope entrance pupil mechanism 5 can perform baseline change movement. The light beam passing through the main delay line 4 passes through the beam splitter 6 and then the reflected light beam enters the light-combining telescope 7, and the transmitted light beam enters. In the baseline measurement telescope 8. The baseline measurement telescope 8 is installed on the baseline measurement telescope driving structure 9. When the sub-aperture 3 or the light-combining telescope entrance pupil mechanism 5 changes the baseline, the baseline measurement telescope driving structure 9 drives the baseline measurement telescope 8 to track, so that the exit pupil of the sub-aperture 3 or the entrance pupil of the light-combining telescope and at least two reference holes on the reference aperture 2 enter the field of view of the baseline measurement telescope 8 at the same time.

[0089] This method uses a movable baseline measurement telescope to simultaneously image the exit pupil of each sub-aperture after the baseline is changed or the entrance pupil of the combined light imaging telescope and two reference holes with known position coordinates on the reference aperture, and determines the coordinates of the exit pupil of each sub-aperture or the entrance pupil of the combined light imaging telescope through the two reference holes with known position coordinates. The entrance pupil coordinates of the sub-aperture are determined by their exit pupil coordinates and their structural parameters. The coordinates of each reference hole on the reference aperture have been measured in advance by 1 micron level precision three-coordinates, and each reference hole is numbered.

[0090] Calculation of the centroid coordinates of the reference hole, exit pupil, and entrance pupil images:

[0091] The image matrix is ​​I, then the gradients of the image in the x (horizontal) and y (vertical) directions are:

[0092]

[0093] Then the image gradient size is:

[0094]

[0095] The gradient size G of the image is subtracted from a standard circle with undetermined parameters. When the sum of squares of the residuals is minimized, the standard circle can be regarded as the image circle, and the coordinates of the center of the image circle can be obtained.

[0096] Calculate the centroid coordinates of the system exit pupil and entrance pupil space according to the image centroid coordinates:

[0097] It is known that the center positions of the two reference hole circles 1 and 2 are position 1 and position 2 respectively, and the coordinates of their centroids on the image are [m1,n1], [m2,n2] respectively. The vector from 1 to 2 on the image is r, and the corresponding spatial positions are [x1,y1], [x2,y2] respectively. The vector from 1 to 2 in space is R. The image coordinates of the position 3 to be measured are [m,n]. Find the actual spatial coordinates. The tangent value of the angle between the image vector r and the spatial vector R is:

[0098]

[0099] In the formula, △m=m2-m1,△n=n2-n1,△x=x2-x1,△y=y2-y1,

[0100] The ratio of the space vector length (calculated from the coordinates of the centroid of the reference hole on the reference aperture) to the image vector length (calculated from the coordinates of the image centroid of the reference hole):

[0101]

[0102] Suppose the vector from position 1 to position 3 on the image is:

[0103]

[0104] The vector from position 1 to position 3 in space is:

[0105]

[0106] The space vector is equal to the image vector rotated by -θ angle, multiplied by the ratio, so the relationship between the space vector and the image vector is:

[0107]

[0108] The pupil space centroid coordinates are decomposed into radial and tangential pupil mapping errors:

[0109] Facing the light source, the X axis is to the right horizontally, the Y axis is upward, and the radial and tangential directions are respectively X axis and Y axis rotated counterclockwise by an angle of α. The pupil mapping error is [dx, dy] in the XY coordinate system and [dρ, dτ] in the radial and tangential coordinate systems, then:

[0110]

[0111] 3.4 Calculation of sub-aperture entrance pupil centroid coordinates

[0112] The centroid coordinates of the entrance pupils of the four sub-apertures are calculated based on the structural dimensions of the sub-apertures:

[0113] [dρ,,dτ,]=[dρ,dτ]-[Lρ,Lτ]

[0114] Where Lρ is the length of the subaperture exit pupil and entrance pupil in the ρ direction, and Lτ is the length of the subaperture exit pupil and entrance pupil in the τ direction.

[0115] Working process of the present invention:

[0116] Combination Figure 2-6 As shown, in Fizeau imaging mode:

[0117] 1) The four sub-apertures 3 pointing in the same direction are driven by the air-floating motion stage 10 to perform variable baseline motion. The light from the collimator 1 enters the sub-aperture 3 after passing through the long groove of the reference aperture 2 and is emitted from the rear light outlet of the sub-aperture 3. At this time, the sub-aperture exit pupil baseline 12 is determined;

[0118] 2) At the same time, the light from the collimator 1 passes through the reference hole of the reference aperture 2 and propagates to the rear of the system without any obstruction;

[0119] 3) The baseline measurement telescope 8 is moved to the rear of one of the sub-apertures, so that the light from the exit pupil of the sub-aperture 3 and the two reference holes around it enter the baseline measurement telescope 8 at the same time and form an image. The coordinate system is established according to the centroid coordinates of the two reference holes, and the centroid coordinates of the exit pupil of the sub-aperture are calculated;

[0120] 4) Repeat step 3) to calculate the centroid coordinates of the other three sub-apertures;

[0121] 5) The entrance pupil coordinates of the four sub-apertures 3 are calculated according to the structural dimensions of the sub-aperture 3. The difference between the measured coordinates and the theoretical coordinates is the system entrance pupil error;

[0122] 6) The light combining imaging telescope part is moved into the system, and the light emitted from the sub-aperture 3 enters the light combining imaging telescope part through the folding mirror 11;

[0123] 7) The entrance pupil mechanism 5 of the light-combining telescope performs variable baseline movement driven by the motion platform 14, and its ideal baseline length / subaperture entrance pupil baseline length=subaperture angle magnification. At this time, the entrance pupil baseline 13 of the light-combining imaging telescope is determined;

[0124] 8) At the same time, the light from the collimator 1 passes through the reference hole of the reference aperture 2 and propagates to the rear of the system without any obstruction;

[0125] 9) The baseline measurement telescope 8 is moved to the rear of one of the folding mirrors 11, so that the light emitted by the folding mirror 11 and the light of the two reference holes around it simultaneously enter the baseline measurement telescope 8 and form an image. After the coordinate system is established according to the centroid coordinates of the two reference holes, the centroid coordinates of the entrance pupil of the combined light imaging telescope are calculated;

[0126] 10) Repeat step 9) to calculate the centroid coordinates of the entrance pupils of the other three combined light imaging telescopes. The difference between the measured coordinates and the theoretical coordinates is the system exit pupil error.

[0127] 11) The dissimilarity between the geometric figure formed by the actual exit pupil of the system and the geometric figure formed by the actual entrance pupil to the geometric figure formed by the theoretical exit pupil and the geometric figure formed by the theoretical entrance pupil, or the error with the ratio of the sub-aperture angle magnification, is the baseline mapping error.

[0128] In Michelson imaging mode:

[0129] The difference between the Michelson imaging mode and the Fizeau imaging mode lies in steps 7) and 11). In this mode, step 7) is changed to the light combining telescope entrance pupil mechanism 5 being driven by the motion stage 14 to perform variable baseline movement, and its ideal baseline length / sub-aperture entrance pupil baseline length may not be consistent with the sub-aperture angle magnification and the light combining telescope entrance pupil baseline is not subsequently changed with the variable baseline movement of the sub-aperture 3. In this mode, step 11) is changed to the inconsistency between the geometric figure formed by the actual exit pupil of the system and the geometric figure formed by the theoretical exit pupil, which is the system exit pupil error. The inconsistency between the geometric figure formed by the actual entrance pupil and the geometric figure formed by the theoretical exit pupil is the system entrance pupil error.

[0130] Compared with the prior art, the present invention has the following outstanding technical effects:

[0131] 1) This method uses a movable baseline measurement telescope and an aperture with a reference hole of known position coordinates to accurately measure the exit pupil of the sub-aperture of the variable baseline and the entrance pupil position of the variable baseline of the light-combining telescope through image measurement. The accuracy can reach the silk level, less equipment is used, the space occupied is small, there is no interference with the imaging system, and the cost is low.

[0132] 2) This method is applicable to Fizeau and Michelson type optical synthetic aperture imaging systems, and can perform baseline measurement on both variable baseline and fixed baseline optical synthetic aperture imaging systems;

[0133] 3) This method can be applied to an optical synthetic aperture imaging system containing 2, 3, 4 or even more sub-apertures by changing the layout of the reference holes on the reference aperture;

[0134] 4) The baseline measurement telescope, subaperture and beam after subaperture shrinkage involved in this method can be driven by an inclined or horizontal or vertical motion stage, which can be composed of an air-floating guide rail, a mechanical guide rail, a linear motor, a stepper motor, a lead screw, etc.

[0135] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for precise baseline measurement of an optical synthetic aperture imaging system, characterized in that: The method is specifically as follows: When there is no light-combining imaging subsystem in the system, a movable baseline measuring telescope is used to simultaneously image the exit pupil of each sub-aperture after the baseline is changed and two reference holes with known position coordinates on the reference aperture, and a coordinate system is established through the two reference holes with known position coordinates. The coordinates of the centroid of the exit pupil of each sub-aperture are determined in the coordinate system, and the entrance pupil coordinates of each sub-aperture are calculated according to the structural parameters of the sub-aperture, which are the entrance pupil coordinates of the system; When there is a light-combining imaging subsystem in the system, the same movable baseline measuring telescope is used to simultaneously image the entrance pupil of each light-combining telescope after the baseline is changed and the two reference holes with known position coordinates on the reference aperture, and a coordinate system is established through the two reference holes with known position coordinates. The centroid coordinates of the entrance pupil of each light-combining telescope are determined in the coordinate system, which are the exit pupil coordinates of the system; The above system entrance pupil coordinates and system exit pupil coordinates are compared with their theoretical position coordinates, and the difference is the baseline mapping error.

2. The optical synthetic aperture imaging system baseline precision measurement method according to claim 1, characterized in that: The calculation method of the centroid coordinates of the reference hole and the exit pupil and entrance pupil images is as follows: The image matrix is ​​I, then the gradients of the image in the horizontal x direction and vertical y direction are: Then the image gradient size is: The gradient size G of the image is subtracted from a standard circle with undetermined parameters. When the sum of squares of the residuals is minimized, the standard circle can be regarded as the image circle, and the coordinates of the center of the image circle can be obtained.

3. The method for precise baseline measurement of an optical synthetic aperture imaging system according to claim 2, characterized in that: The calculation method of the centroid coordinates of the exit pupil and entrance pupil space is as follows: It is known that the center positions of the two reference hole circles 1 and 2 are position 1 and position 2 respectively, and the coordinates of their centroids on the image are [m1, n1], [m2, n2] respectively. The vector from 1 to 2 on the image is r, and the corresponding spatial positions are [x1, y1], [x2, y2] respectively. The vector from 1 to 2 in space is R; the image coordinates of the position 3 to be measured are [m, n], and the actual spatial coordinates are calculated; the tangent value of the angle between the image vector r and the spatial vector R is: In the formula, △m=m2-m1,△n=n2-n1,△x=x2-x1,△y=y2-y1, The ratio of the space vector length calculated from the coordinates of the centroid of the reference hole on the reference aperture to the image vector length calculated from the coordinates of the image centroid of the reference hole is: Suppose the vector from position 1 to position 3 on the image is: The vector from position 1 to position 3 in space is: The space vector is equal to the image vector rotated by -θ angle, multiplied by the ratio, so the relationship between the space vector and the image vector is:

4. The optical synthetic aperture imaging system baseline precision measurement method according to claim 3, characterized in that: The calculation method of decomposing the pupil space centroid coordinates into radial and tangential pupil mapping errors is as follows: Facing the light source, the X axis is to the right horizontally, the Y axis is upward, and the radial and tangential directions are respectively rotated counterclockwise by an angle of α along the X axis and the Y axis; the pupil mapping error is [dx, dy] in the XY coordinate system, and [dρ, dτ] in the radial and tangential coordinate systems, then:

5. The optical synthetic aperture imaging system baseline precision measurement method according to claim 4, characterized in that: The calculation method of the sub-aperture entrance pupil centroid coordinates is as follows: The centroid coordinates of the entrance pupils of the four sub-apertures are calculated based on the structural dimensions of the sub-apertures: [dρ,,dτ,]=[dρ,dτ]-[Lρ,Lτ] Where Lρ is the length of the subaperture exit pupil and entrance pupil in the ρ direction, and Lτ is the length of the subaperture exit pupil and entrance pupil in the τ direction.

6. The method for precise baseline measurement of an optical synthetic aperture imaging system according to claim 5, characterized in that: In Fizeau imaging mode, the precise baseline measurement method is as follows: S1. The four sub-apertures pointing in the same direction move with variable baselines driven by the air-floating motion stage. The light from the collimator passes through the long slot of the reference aperture and enters the sub-aperture, and is emitted from the rear light outlet of the sub-aperture. At this time, the exit pupil baseline of the sub-aperture is determined. S2. At the same time, the light from the collimator passes through the reference hole of the reference aperture and propagates to the rear of the system without any obstruction; S3, the baseline measurement telescope is moved to the rear of one of the sub-apertures, so that the light from the exit pupil of the sub-aperture and the two reference holes around it enters the baseline measurement telescope at the same time and forms an image, and the coordinate system is established according to the centroid coordinates of the two reference holes to calculate the centroid coordinates of the exit pupil of the sub-aperture; S4, repeat step S3 to calculate the coordinates of the exit pupil centroids of the other three sub-apertures; S5. Calculate the entrance pupil coordinates of the four sub-apertures according to the structural dimensions of the sub-apertures. The difference between the measured coordinates and the theoretical coordinates is the system entrance pupil error. S6, moving the light combining imaging telescope part into the system, and the light emitted from the sub-aperture enters the light combining imaging telescope part through the folding mirror; S7. The entrance pupil mechanism of the light-combining telescope performs variable baseline movement driven by the motion platform. Its ideal baseline length / subaperture entrance pupil baseline length = subaperture angle magnification. At this time, the entrance pupil baseline of the light-combining imaging telescope is determined. S8. At the same time, the light from the collimator passes through the reference hole of the reference aperture and propagates to the rear of the system without any obstruction; S9, the baseline measurement telescope is moved to the rear of one of the folding axis mirrors, so that the light emitted by the folding axis mirror and the light of the two reference holes around it enter the baseline measurement telescope at the same time and form an image, and the coordinate system is established according to the centroid coordinates of the two reference holes to calculate the centroid coordinates of the entrance pupil of the combined light imaging telescope; S10, repeat step S9 to solve the coordinates of the centroids of the entrance pupils of the other three combined light imaging telescopes. The difference between the measured coordinates and the theoretical coordinates is the system exit pupil error. S11. The dissimilarity between the geometric figure formed by the actual exit pupil of the system and the geometric figure formed by the actual entrance pupil and the geometric figure formed by the theoretical exit pupil and the geometric figure formed by the theoretical entrance pupil, or the error with the ratio of the sub-aperture angle magnification, is the baseline mapping error.

7. The method for precise baseline measurement of an optical synthetic aperture imaging system according to claim 6, characterized in that: In the Michelson imaging mode, the difference between the imaging mode and the Fizeau imaging mode lies in steps S7 and S11, and the other steps are consistent with the Fizeau imaging mode; wherein, S7 is changed to: the entrance pupil mechanism of the light-combining telescope performs variable baseline motion driven by the motion stage, and its ideal baseline length / subaperture entrance pupil baseline length may not be consistent with the subaperture angle magnification, and the entrance pupil baseline of the light-combining telescope does not change subsequently with the subaperture variable baseline motion; S11 is changed to: The inconsistency between the geometric figure formed by the actual exit pupil of the system and the geometric figure formed by the theoretical exit pupil is the system exit pupil error, and the inconsistency between the geometric figure formed by the actual entrance pupil and the geometric figure formed by the theoretical exit pupil is the system entrance pupil error.

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