A method for precise baseline measurement of optical synthetic aperture imaging system

Abstract

The present invention discloses a method for precisely measuring the baseline of an optical synthetic aperture imaging system. Specifically, when the system does not have a combined light imaging subsystem, a movable baseline measurement telescope is used to simultaneously image the exit pupil of each baseline-changed subaperture and two reference holes with known position coordinates on a reference aperture. The two reference holes are used to determine a coordinate system, and the centroid coordinates of the exit pupil of each subaperture are calculated within the coordinate system. The entrance pupil coordinates of each subaperture are calculated based on the known structural parameters of the subaperture. When the system does have a combined light imaging subsystem, the same movable baseline measurement telescope is used to simultaneously image the entrance pupil of each baseline-changed light combining telescope and two reference holes with known position coordinates on a reference aperture. The two reference holes are used to determine a coordinate system, and the centroid coordinates of the entrance pupil of each light combining telescope are calculated within the coordinate system. The entrance pupil coordinates of the subapertures and the light combining telescope are compared with their theoretical position coordinates, and the difference is the baseline mapping error. The present invention provides a solution for measuring the baseline mapping error of an optical synthetic aperture imaging system.

Description

Technical Field

[0001] The present 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 single-aperture telescopes, 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 aperture size limitation of a single-aperture telescope. Optical synthetic aperture technology has become the inevitable path for the development of optical telescopic imaging systems.

[0003] To improve the observation efficiency of an optical synthetic aperture imaging system, the system's field of view (FOV) needs to be increased. This field of view is affected by the system's pupil mapping error. The larger the system's FOV, the stricter the requirements for pupil mapping error. This pupil mapping error can be divided into two components: baseline mapping error, which occurs when the entrance pupil baseline of the subaperture array differs from the shape of the entrance pupil baseline of the combined telescope (the system's exit pupil baseline); and subaperture magnification error, which occurs when the entrance and exit pupil sizes of each subaperture differ from the designed values ​​or differ from one subaperture to another.

[0004] An ideal Fizeau-type synthetic aperture imaging system requires strict similarity between the subaperture array's entrance pupil baseline (the distance between the subaperture entrance pupil axes; four subapertures comprise six baselines) and the combined telescope's entrance pupil baseline (the distance between the optical axes of the combined imaging beams; four combined imaging beams comprise six baselines). This similarity ratio is equal to the angular magnification of the subapertures. Therefore, precise measurement and control of the subaperture array and combined telescope entrance pupil baselines is crucial. While a Michelson-type synthetic aperture imaging system does not require this principle, precise measurement and control of the subaperture array and combined telescope entrance pupil baselines are equally important. This precise measurement and control of the baselines ensures that the actual position of the subapertures after baseline movement is consistent with the theoretically analyzed UV coverage point position, and that the combined telescope entrance pupil position is consistent with its theoretically designed position, ensuring that the interference fringes on the combined imaging camera meet the requirements for subsequent analysis.

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

[0006] 1. NASA established the Wide-Field Imaging Interferometry (WIIT) to validate wide-field interferometric imaging algorithms for space interferometer projects such as SPIRIT (infrared), SPECS (submillimeter wave), and TPF-I. The system model was established and verified. Two subtelescopes were mounted on opposite ends of a linear air-bearing stage. Each subaperture had a 25mm diameter, and the baselines of the two subtelescopes were variable between 25mm and 250mm. UV coverage was achieved through baseline adjustment and synchronous rotation of the target and detector. The position of the subapertures was obtained using feedback from a linear absolute encoder mounted on an air-bearing guide rail. This encoder only determined the position of the guide sleeve on the rail and could not determine the absolute distance between the subaperture entrance and exit pupil baselines. The paper mentions the need for well-calibrated absolute baseline metrology in the future. However, no introduction or experimental verification of absolute baseline metrology was found in subsequent papers on WIIT.

[0007] 2. The European Southern Observatory's Very Large Telescope Interferometer (VLTI) in Chile consists of four fixed 8.2-meter telescopes (UTs) and four 1.8-meter translatable auxiliary telescopes (ATs) on rails. The beams from the different telescopes are combined via an underground tunnel, ensuring that the optical path difference between the beams is less than 1 μm. The four 1.8-meter translatable auxiliary telescopes on rails can change the baseline, forming six baselines with different lengths and orientations. This yields a maximum possible resolution equivalent to that of a telescope with a diameter of 130 meters. However, no information or experiments on baseline measurement and calibration from the VLTI have been found.

[0008] 3. The National Astronomical Observatories of the Chinese Academy of Sciences designed and built a Fizeau Imaging Interferometer Test (FIIT). This test setup primarily consists of a light source module for simulating an infinite object, three 100mm aperture sub-telescopes arranged in a Golay-3 pattern (equilateral triangle), three yaw / pitch correction modules and an optical path delay module, three detector telescopes for phase imaging, and a beam combining telescope. This setup achieved broadband white-light (400-700nm) phase imaging in the laboratory with a field of view of 2 arc minutes. The baseline lengths of the three sub-telescopes and the sub-beam baseline length are fixed at 200mm and 40mm, respectively.

[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, and 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 using a calibration plate, lens, and camera. A precisely machined and tested calibration glass plate is placed in the path of the three sub-beams. The calibration glass plate features three circular lines arranged in an equilateral triangle. Each circular line has a cross mark passing through its center. The center-to-center distance of the circular lines has been precisely measured and serves as a benchmark for exit pupil baseline testing. After the sub-beams pass through the glass plate and lens, six circular images are displayed on the camera: images of the three sub-beams and images of the three circular lines on the calibration plate. After identifying the coordinates of the centers of the six images, the baselines of the sub-beams are calculated using the centers of the circular lines on the calibration plate as a reference, 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. The China Resources Satellite Application Center analyzed and studied intersatellite high-precision baseline measurement and processing methods and workflows based on the operating characteristics of distributed interferometric synthetic aperture radar (InSAR) satellite systems, including GNSS and SAR payloads. The distributed InSAR satellite system first obtains a GNSS measurement baseline through GNSS dual-frequency carrier phase differential measurement and high-precision ground-based orbit calculation. Then, through position correction, the baseline reference point is shifted from the satellite centroid to the SAR antenna phase center, resulting in a spatial domain baseline. Experimental results demonstrate that the intercomparison of InSAR baselines obtained through orbit determination has a statistical accuracy of approximately 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) Currently, the baseline measurement of the existing variable baseline optical synthetic aperture imaging system 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 an admission or any form of suggestion that the information constitutes the prior art already known to those skilled in the art. Summary of the Invention

[0019] In response to 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. This 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, 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.

[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, a movable baseline measuring telescope is used to simultaneously image the exit pupil of each sub-aperture after baseline change 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 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 based on 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. A coordinate system is established through the two reference holes with known position coordinates. The coordinates of the centroid of the entrance pupil of each light-combining telescope are determined in the coordinate system, which is also the coordinates of the system exit pupil.

[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 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] Given that the centers of two reference hole circles 1 and 2 are at positions 1 and 2, respectively, their centroid coordinates on the image are [m1, n1] and [m2, n2], the vector from 1 to 2 on the image is r, and the corresponding spatial positions are [x1, y1] and [x2, y2], respectively, and the vector from 1 to 2 in space is R; the image coordinates of 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:

[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 centroid of the image 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 horizontal right direction is the X axis, the upward direction is the Y axis, and the radial and tangential directions are respectively rotated counterclockwise by an angle α about 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 are driven by the air-floating motion stage to perform variable baseline motion. 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. Move the baseline measurement telescope to the rear of one of the subapertures so that the exit pupil of the subaperture and the two reference holes around it enter the baseline measurement telescope at the same time and are imaged. Calculate the centroid coordinates of the exit pupil of the subaperture based on the centroid coordinates of the two reference holes.

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

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

[0056] S6. The light combining imaging telescope is moved into the system, and the light emitted from the sub-aperture enters the light combining imaging telescope through the folding mirror;

[0057] S7. The entrance pupil mechanism of the light-combining telescope performs variable baseline motion driven by the motion stage. Its ideal baseline length / sub-aperture entrance pupil baseline length = sub-aperture angle magnification. At this point, 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. Move the baseline measurement telescope to the rear of one of the folding mirrors so that the light emitted by the folding mirror and the two reference holes around it enter the baseline measurement telescope at the same time and form an image. Calculate the centroid coordinates of the entrance pupil of the combined light imaging telescope based on the centroid coordinates of the two reference holes.

[0060] S10, repeat step S9 to calculate the coordinates of the centroid of the entrance pupil of the other three light-combining 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 figures formed by the actual exit pupil and the actual entrance pupil of the system and the geometric figures formed by the theoretical exit pupil and the theoretical entrance pupil, or the error in the ratio of the sub-aperture angle magnification, is the baseline mapping error.

[0062] Furthermore, 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. 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 will not be changed 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) High versatility. This method is generally applicable to optical synthetic aperture imaging systems with variable 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 drive mechanism used in this method are relatively mature and inexpensive. The overall structure is relatively simple, occupies little space, and has a high cost performance.

[0070] 5) Absolute measurement. Unlike traditional relative measurement, which can only measure the change in baseline, this method 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, wire-level baseline measurement accuracy can be achieved;

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

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

[0074] Figure 1 This 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 entrance pupil error measurement of the light-combining imaging telescope of the present invention.

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

[0080] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0081] The following describes the specific embodiments of the present invention in detail with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present invention and are not intended to limit the present invention.

[0082] The present invention proposes 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 baseline change 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 based on 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. A coordinate system is established through the two reference holes with known position coordinates, and the coordinates of the entrance pupil of each light-combining telescope are determined within the coordinate system, which is also the coordinates of the system exit pupil.

[0085] The entrance pupil coordinates of the above sub-aperture 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 and fixed baselines, provides a solution for measuring the system's pupil mapping error, and provides a data basis for precise control of the system's pupil mapping error, thereby ensuring the system's observation field of view.

[0087] Combine Figure 1 As shown, the specific structure required for the optical synthetic aperture imaging system baseline precision measurement method 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 baseline change) and long grooves (the direction of the long grooves is consistent with the direction of the sub-aperture baseline change), a sub-aperture 3, a main delay line 4, a light combining telescope entrance pupil mechanism 5, a light combining telescope 6, a baseline measurement telescope 7, a baseline measurement telescope driving structure 8, etc.

[0088] In the present invention, a collimator 1, capable of emitting horizontally parallel light, is installed at the front end of an optical synthetic aperture imaging system. A reference aperture 2 is vertically mounted behind the collimator 1, with its large surface perpendicular to the light emitted from the collimator 1. The long slots in the reference aperture 2 coincide with the trajectory of the entrance pupil of the subaperture 3 during baseline shifting. This ensures that the parallel light emitted from the collimator 1 can pass through the long slots in the reference aperture 2 and enter the subaperture 3 during baseline shifting. In this example, there are four subapertures 3, symmetrically arranged behind the reference aperture 2 and mounted on a motion platform, allowing each subaperture 3 to undergo baseline shifting. The light beams emitted by the subapertures 3 pass through the surrounding main delay lines 4 before entering the entrance pupil mechanism 5 of the light-combining telescope. The light beams passing through the main delay lines 4 are reflected by a beam splitter 6 and enter the light-combining telescope 7, where they are then transmitted. 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 subaperture after baseline modification, or the entrance pupil of the combined-light imaging telescope, and two reference holes with known coordinates on the reference aperture. The coordinates of each subaperture's exit pupil or the combined-light imaging telescope's entrance pupil are determined using the two reference holes with known coordinates. The coordinates of the subaperture's entrance pupil are determined from its exit pupil coordinates and its structural parameters. The coordinates of each reference hole on the reference aperture have been pre-measured using 1-micron precision three-dimensional coordinate measurement, and each reference hole is numbered.

[0090] Calculation of the centroid coordinates of the reference aperture, 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 exit and entrance pupil spaces of the system based on the centroid coordinates of the image:

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

[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 horizontal right direction is the X axis, the upward direction is the Y axis, and the radial and tangential directions are respectively the X axis and the Y axis, which are rotated counterclockwise by an angle α. The pupil mapping error is [dx,dy] in the XY coordinate system and [dρ,dτ] in the radial and tangential coordinate systems, so:

[0110]

[0111] 3.4 Calculation of Subaperture 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] The working process of the present invention:

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

[0117] 1) Four subapertures 3 pointing in the same direction are driven by the air-floating motion stage 10 to perform variable baseline motion. Light from the collimator 1 passes through the long slot of the reference aperture 2 and enters the subaperture 3, and is emitted from the rear light outlet of the subaperture 3. At this time, the subaperture 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 apertures around it enter the baseline measurement telescope 8 simultaneously and form an image. A coordinate system is established based on the centroid coordinates of the two reference apertures, and the centroid coordinates of the exit pupil of the sub-aperture are calculated.

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

[0121] 5) Calculate the entrance pupil coordinates of the four sub-apertures 3 based on 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 is moved into the system, and the light emitted from the sub-aperture 3 enters the light combining imaging telescope through the folding mirror 11;

[0123] 7) The entrance pupil mechanism 5 of the light-combining telescope is driven by the motion stage 14 to perform variable baseline motion. Its ideal baseline length / sub-aperture entrance pupil baseline length = sub-aperture 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 from the two reference holes around it enter the baseline measurement telescope 8 at the same time and form an image. A coordinate system is established based on the centroid coordinates of the two reference holes, and the centroid coordinates of the entrance pupil of the combined light imaging telescope are calculated;

[0126] 10) Repeat step 9) to calculate the coordinates of the centroid of the entrance pupil of the other three combined 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 figures formed by the actual exit pupil and the actual entrance pupil of the system and the geometric figures formed by the theoretical exit pupil and the theoretical entrance pupil, or the error in the ratio of the sub-aperture angle magnification, is the baseline mapping error.

[0128] In Michelson imaging mode:

[0129] The Michelson imaging mode differs from the Fizeau imaging mode 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 a variable baseline motion. Its ideal baseline length / subaperture entrance pupil baseline length may not be consistent with the subaperture angular magnification, and the subsequent variable baseline motion of the subaperture 3 does not change the light-combining telescope entrance pupil baseline. In this mode, step 11) is changed to the system exit pupil error. The inconsistency between the actual and theoretical exit pupil geometry 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 known position coordinate of a reference hole to accurately measure the exit pupil of the variable baseline subaperture 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 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 optical synthetic aperture imaging systems containing 2, 3, 4 or even more sub-apertures by changing the layout of the reference holes on the reference diaphragm;

[0134] 4) The baseline measurement telescope, subaperture, and beam after subaperture shrinkage involved in this method can be driven by an inclined, 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 above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above 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. 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. According to the structural parameters of the sub-aperture, the coordinates of the entrance pupil of each sub-aperture are calculated, which are the entrance pupil coordinates of the system. When there is a light-combining imaging subsystem in the system, the same movable baseline measurement 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. A coordinate system is established through the two reference holes with known position coordinates. The coordinates of the centroid of the entrance pupil of each light-combining telescope are determined in the coordinate system, which is the exit pupil coordinate 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 aperture, 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, wherein: The calculation method of the centroid coordinates of the exit pupil and entrance pupil space of the image is as follows: Given that the centers of two reference hole circles 1 and 2 are at positions 1 and 2, respectively, their centroid coordinates on the image are [m1, n1] and [m2, n2], the vector from 1 to 2 on the image is r, and the corresponding spatial positions are [x1, y1] and [x2, y2], respectively, and the vector from 1 to 2 in space is R; the image coordinates of 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: 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 centroid of the image 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 method for precise baseline measurement of an optical synthetic aperture imaging system according to claim 3, wherein: 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 horizontal right direction is the X axis, the upward direction is the Y axis, and the radial and tangential directions are respectively rotated counterclockwise by an angle α about 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 method for precise baseline measurement of an optical synthetic aperture imaging system according to claim 4, wherein: 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 optical synthetic aperture imaging system baseline precision measurement method according to claim 5, characterized in that: In Fizeau imaging mode, the baseline precision measurement method is as follows: S1. The four sub-apertures pointing in the same direction are driven by the air-floating motion stage to perform variable baseline motion. 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. Move the baseline measurement telescope to the rear of one of the subapertures so that light from the exit pupil of the subaperture and the two reference apertures surrounding it enter the baseline measurement telescope simultaneously and form an image. A coordinate system is established based on the centroid coordinates of the two reference apertures, and the centroid coordinates of the exit pupil of the subaperture are calculated. 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 based on their structural dimensions. The difference between the measured coordinates and the theoretical coordinates is the system entrance pupil error. S6. The light combining imaging telescope is moved into the system, and the light emitted from the sub-aperture passes through the folding mirror and enters the light combining imaging telescope. S7. The entrance pupil mechanism of the light-combining telescope performs variable baseline motion driven by the motion stage. Its ideal baseline length / sub-aperture entrance pupil baseline length = sub-aperture angle magnification. At this point, 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. Move the baseline measurement telescope to the rear of one of the folding mirrors so that the light emitted by the folding mirror and the light from the two reference holes around it simultaneously enter the baseline measurement telescope and form an image. After establishing a coordinate system based on the centroid coordinates of the two reference holes, calculate the centroid coordinates of the entrance pupil of the combined light imaging telescope. S10, repeat step S9 to calculate the coordinates of the centroids of the entrance pupils of the other three combined imaging telescopes. The difference between the measured coordinates and the theoretical coordinates is the system exit pupil error; S11. The dissimilarity between the geometric figures formed by the actual exit pupil and the actual entrance pupil of the system and the geometric figures formed by the theoretical exit pupil and the theoretical entrance pupil, or the error in 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, wherein: 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 the same as those in the Fizeau imaging mode; S7 is changed to: The entrance pupil mechanism of the light-combining telescope performs variable baseline motion driven by the motion stage. 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 will not be changed 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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