CN116859579A - On-orbit focusing and calibrating device and method for full-day-surface solar telescope - Google Patents

Abstract

The invention discloses an on-orbit focusing and calibrating device and method for a full-day solar telescope, which are used for solving the problems of complex structure, high weight, low reliability and high power consumption of the traditional flat-field calibrating device. The device comprises a front telescope, a first focusing calibration unit, a second focusing calibration unit, an optical filter, an imaging lens group and a detector which are sequentially arranged along the incident direction of sunlight; the first focusing calibration unit comprises a first switching rotating wheel; a focusing lens A1, a focusing lens A2, a focusing lens A3, a first standard-defining lens and a through hole are distributed on the first switching rotating wheel; the second focusing calibration unit comprises a second switching rotating wheel; a focusing lens B1, a focusing lens B2, a focusing lens B3, a second calibration lens and a baffle are distributed on the second switching rotating wheel; the optical filter is used for selecting solar observation spectral lines; the imaging lens group is used for carrying out secondary imaging on the sun and amplifying the primary imaging light spots of the sun so as to adapt to the size and the position of the target surface of the detector; the detector is used for acquiring and storing the full-sun surface image information.

Description

On-orbit focusing and calibrating device and method for full-day-surface solar telescope

Technical Field

The invention relates to an on-orbit focusing and calibrating device for a solar telescope, in particular to an on-orbit focusing and calibrating device and method for a full-day solar telescope.

Background

The full-day solar telescope can remotely detect targets such as a solar spherical layer, a color spherical layer, a solar black, a magnetic field, a flare and the like in a foundation and a space. The full-day solar telescope has higher resolution and longer focal length, and rocket launching, satellite orbit changing, temperature change and vacuum environment can all influence the focal plane position during in-orbit working. In addition, the non-uniformity of the optical elements of the instrument, the field effect of the incident light of the sun, and the non-uniformity of each pixel of the detector can cause the detection precision of the system to be reduced. Therefore, an on-orbit focusing device is required to be arranged in the telescope to ensure the best imaging quality; and the calibration of a flat field and a dark field is required, the non-uniformity of the target response is corrected, the data detection precision is improved, and an accurate target image is obtained.

When the ground and space full-day solar telescope is calibrated in a flat field, the scheme adopted generally comprises the following steps:

1. placing a full-day-surface solar telescope in a laboratory, and obtaining uniform surface targets in all directions by utilizing a stable illumination light source and an integrating sphere of the laboratory to realize uniform illumination of the target surface of the detector;

2. an additional movement mechanism is added in the light path and cuts into the dispersion screen, the dispersion screen is illuminated by utilizing sunlight or an LED light source in the telescope, and more uniform illumination is obtained on the detector;

3. adding an extra swinging mirror, taking the sun as a light source, recording a plurality of images of a solar surface by adjusting the pitching and azimuth angles of the swinging mirror, and iteratively calculating a flat field by using a least square method for the obtained images;

4. and controlling satellite attitude transformation, collecting more than nine sun-surface images with different observation angles, and calculating a flat field through image stitching and subsequent data processing.

The flat field calibration scheme is adopted, or only for flat field calibration, a stable illumination light source or a motion mechanism is additionally added, so that the design complexity and the weight of the instrument are increased, the reliability of the space full-day solar telescope is reduced, and the requirements on the power supply and the load capacity of the satellite are also improved; or put higher demands on other devices such as satellites, and the acquisition of flat-field data is more complex. The main load H alpha solar imaging spectrometer on the solar observation satellite Fund and No. adopts the 4 th flat field calibration scheme. In order to control the weight and the power consumption of the space full-day solar telescope and reduce the difficulty of flat field data acquisition, a brand new on-orbit flat field calibration scheme is required to be provided.

Disclosure of Invention

The invention aims to provide an on-orbit focusing and calibrating device and method for a full-day solar telescope, which are used for solving the technical problems of complex structure, large weight, low reliability and large power consumption of the conventional flat-field calibrating device.

In order to achieve the purpose, the invention provides an on-orbit focusing and calibrating device for a full-day solar telescope, which is characterized in that: the device comprises a front telescope, a first focusing calibration unit, a second focusing calibration unit, an optical filter, an imaging lens group and a detector which are sequentially arranged along the incident direction of sunlight;

the front telescope is used for imaging the sun once and compressing the aperture and the incidence angle of the subsequent light rays;

the first focusing calibration unit comprises a first switching rotating wheel; the first switching rotating wheel is provided with a focusing lens A1, a focusing lens A2, a focusing lens A3, a first calibration lens and a through hole; the first switching rotating wheel is used for switching the focusing lens A1, the focusing lens A2, the focusing lens A3, the first calibration lens or the through hole into the light path;

the second focusing calibration unit comprises a second switching rotating wheel; the second switching rotating wheel is provided with a focusing lens B1, a focusing lens B2, a focusing lens B3, a second calibration lens and a baffle; the second switching rotating wheel is used for switching the focusing lens B1, the focusing lens B2, the focusing lens B3 and the second calibration lens or the baffle plate into the light path;

the optical filter is used for selecting solar observation spectral lines;

the imaging lens group is used for carrying out secondary imaging on the sun, and amplifying the primary imaging light spots of the sun so as to adapt to the size and the position of the target surface of the detector, and the amplification factor of the imaging lens group on the front telescope is about 1.5-2.5 times;

the detector is used for acquiring and storing the full-sun image information, converting the received sunlight signals into electric signals based on photoelectric conversion effect, storing the electric signals in single pixels of the detector in gray data, and transmitting the electric signals to the ground detection storage device.

Further, the front telescope comprises a double-layer filter window, a diaphragm, a primary mirror, a secondary mirror and three mirrors which are sequentially arranged along the incident direction of sunlight;

the double-layer filtering window is used for primarily selecting the wavelength of the solar light;

the diaphragm is used for limiting the caliber of the front telescope;

the main mirror is a plano-convex mirror, and the convex surface of the plano-convex mirror faces the diaphragm;

the secondary mirror is a concave-convex mirror, and the convex surface of the secondary mirror faces the primary mirror;

the three mirrors are biconcave lenses.

Further, the first calibration lens is a convex-concave lens, the thickness of the first calibration lens is 6mm, the material is HZF6, and the focal length of the first calibration lens is 246mm.

Further, the second calibration lens is a plano-convex lens with the thickness of 6mm, the material is HZF6, and the focal length is 211.9mm.

Further, the focusing mirror A1 is made of JGS1, and the thickness of the focusing mirror A1 is 3mm;

the focusing lens A2 is made of JGS1 and has a thickness of 6mm;

and the focusing mirror A3 is made of JGS1 and has the thickness of 9mm.

Further, the focusing mirror B1 is made of JGS1 and has a thickness of 3mm;

the focusing lens B2 is made of JGS1 and has a thickness of 4mm;

and the focusing mirror B3 is made of JGS1 and has a thickness of 5mm.

Further, the lens further comprises a first turning lens group and a second turning lens group;

the first turning mirror group is arranged on a light path between the first focusing calibration unit and the second focusing calibration unit and is used for reflecting emergent light of the first focusing calibration unit to the second focusing calibration unit;

the second turning mirror group is arranged on a light path between the second focusing calibration unit and the optical filter and is used for reflecting emergent light of the second focusing calibration unit to the optical filter, so that the optical axis of the optical filter is parallel to the optical axis of the front telescope, and the optical filter and the front telescope are positioned on the same side of the second focusing calibration unit.

Further, the device also comprises a polarization analyzer;

the polarization analyzer is arranged on an optical path between the first focusing and scaling unit and the first turning mirror group and is used for measuring the polarization of the solar magnetic field.

Further, the device also comprises a telecentric lens;

the telecentric lens is arranged between the second turning lens group and the optical filter and is used for changing the optical path passing through the second focusing calibration unit and the second turning lens group into a telecentric optical path, so that the parallelism between the principal ray and the optical axis of each view field entering the optical filter is better than 0.01 degree, and the influence of the view field effect on the full-day plane precision is avoided.

The invention also provides an on-orbit focusing and calibrating method of the full-day solar telescope, which is based on the on-orbit focusing and calibrating device of the full-day solar telescope and is characterized by comprising the following steps of;

step 1, dark field calibration:

1.1, cutting a baffle into an optical path through a second switching rotating wheel, and detecting a first reference image by a detector;

1.2, revising the detector according to a first reference image;

step 2, flat field calibration:

2.1, switching the first calibration lens into the light path through a first switching rotating wheel; switching the second calibration lens into the light path through a second switching rotating wheel; the detector acquires a second reference image;

2.2, switching the focusing mirror A1, the focusing mirror A2, the focusing mirror A3 or the through hole into the light path through the first switching rotating wheel; switching the focusing lens B1, the focusing lens B2 or the focusing lens B3 into the light path through a second switching rotating wheel; the detector respectively acquires 12 target images;

2.3, selecting the most clear target image, and revising the most clear target image through the second reference image.

The invention has the beneficial effects that:

1. the novel on-orbit focusing calibration device provided by the invention is characterized in that a first focusing calibration unit and a second focusing calibration unit are arranged behind a front telescope, namely a full-day solar telescope; the first focusing calibration unit and the second focusing calibration unit are respectively provided with the first calibration lens and the second calibration lens, and the diaphragm of the front telescope can be imaged to the target surface of the detector by cutting into the first calibration lens and the second calibration lens in the light path, the sun is utilized as a light source, no additional illumination light source or motion mechanism is added, the requirement on satellite power consumption is reduced, the reliability of equipment is improved, the loss of on-orbit calibration function caused by the damage of an external light source is avoided, and the uniform illumination of the target surface of the detector is realized.

2. The flat-field calibration light path light rays constructed by the invention are consistent with the normal imaging light path light rays in the front telescope, namely the full-day solar telescope, so that other angle light rays can be prevented from being introduced in the calibration process, and the influence of the field effect of incident light on the calibration precision is avoided.

3. According to the invention, other moving parts such as a swinging mirror or a diffusion screen are not required to be additionally introduced, the design structure is simple, the reliability is high, and higher gesture requirements on satellites or load platforms are not required, so that the subsequent calibration algorithm is simpler, and complex algorithms such as image splicing and restoration are not required.

4. According to the invention, under different use scenes, the positions and diameters of the images can be adjusted by changing the focal lengths of the first calibration lens and the second calibration lens, so that the images entering the diaphragm can cover the effective view field and focal plane position of the whole device.

Drawings

FIG. 1 is a schematic diagram of an embodiment of an on-orbit focusing calibration device for a full-day solar telescope in a calibration state, wherein an optical path is a calibration optical path;

fig. 2 is a schematic structural diagram of an embodiment of an on-orbit focusing calibration device for a full-day solar telescope, which is in a focusing imaging state, wherein an optical path is an imaging optical path.

Reference numerals:

the device comprises a 1-front telescope, a 11-double-layer filter window, a 12-diaphragm, a 13-primary mirror, a 14-secondary mirror, a 15-triple mirror, a 2-first focusing calibration unit, a 21-first calibration lens, a 3-second focusing calibration unit, a 31-second calibration lens, a 4-filter, a 5-imaging lens group, a 6-detector, a 7-first turning lens group, a 8-second turning lens group, a 9-polarization analyzer and a 10-telecentric mirror.

Detailed Description

The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to fall within the scope of the invention.

The on-orbit focusing calibration device for the full-day solar telescope is shown in combination with fig. 1 and 2, and comprises a front telescope 1, a first focusing calibration unit 2, a polarization analyzer 9, a first turning mirror group 7, a second focusing calibration unit 3, a second turning mirror group 8, a telecentric mirror 10, an optical filter 4, an imaging mirror group 5 and a detector 6 which are sequentially arranged along the incident direction of sunlight;

the front telescope 1 is used for imaging the sun once, compressing the caliber and the incidence angle of light rays entering the optical filter 4 and the imaging lens group 5 subsequently; the focal length of the front telescope 1 is 2361.98mm, and the front telescope 1 comprises a double-layer filter window 11, a diaphragm 12, a primary mirror 13, a secondary mirror 14 and a three-mirror 15 which are sequentially arranged along the incident direction of sunlight; the double-layer filter window 11 is used for primarily selecting the transmission wavelength of the full-day solar telescope and can realize the function of isolating ultraviolet and infrared radiation; the diaphragm 12 is used for limiting the caliber of the front telescope; the main mirror 13 is a plano-convex mirror, the convex surface of the plano-convex mirror faces the diaphragm 12, the thickness is 24mm, and the material HK9L; the secondary mirror 14 is a convex-concave mirror, the convex surface of the secondary mirror faces the primary mirror, the thickness of the secondary mirror is 21.7mm, and the material HLAK3 is used; the three mirrors 15 are biconcave lenses with a thickness of 21.3mm, material HZF6. Under different use scenes, the invention can compress the apertures of the subsequent optical filter 4 and the imaging component 5 by changing the focal length of the front telescope 1 and the position of the primary focal plane S2 and the size of the sun image at the primary focal plane S2.

The first focusing calibration unit 2 comprises a first switching wheel; 3 focusing mirrors with different thicknesses, namely a focusing mirror A1, a focusing mirror A2 and a focusing mirror A3, are distributed on the first switching rotating wheel, and a first calibration lens 21 and a through hole are also distributed on the first switching rotating wheel; the first switching wheel is used for switching the focusing lens A1, the focusing lens A2, the focusing lens A3, the first calibration lens 21 or the through hole into the light path; wherein, the first calibration lens 21 is a convex-concave lens with the thickness of 6mm, the material is HZF6, the focal length is 246mm, and the function is to shorten the original primary focal plane S2 from the front end of the optical filter 4 to the position between the first refractive lens group 7 and the second focusing calibration unit 3.

The polarization analyzer 9 is used for making polarization measurements of the solar magnetic field.

The first turning mirror group 7 is arranged on the light path between the first focusing calibration unit 2 and the second focusing calibration unit 3 and is used for reflecting the emergent light of the first focusing calibration unit 2 to the second focusing calibration unit 3;

the second focusing calibration unit 3 comprises a second switching rotating wheel; 3 focusing mirrors with different thicknesses, namely a focusing mirror B1, a focusing mirror B2 and a focusing mirror B3, are distributed on the second switching rotating wheel, and a second calibration lens 31 and a baffle are also distributed; the second switching wheel is used for switching the focusing lens B1, the focusing lens B2, the focusing lens B3, the second calibration lens 31 or the baffle plate into the light path; the second calibration lens 31 is a plano-convex lens with a thickness of 6mm, a material of HZF6 and a focal length of 211.9mm, and is used for imaging the diaphragm 12 of the front telescope 1 at the original primary focal plane S2, performing secondary imaging through the optical filter 4 and the imaging lens group 5, and finally imaging the entrance pupil of the full-day solar telescope to the target plane S1 of the detector 6, thereby realizing the uniform illumination requirement of the detector required during flat field calibration.

Under different use scenes, the magnification of the front telescope 1 and the position and diameter of the entrance pupil image can be adjusted by changing the focal length and the position of the first calibration lens 21 and the second calibration lens 31, so that the position and the diameter of the entrance pupil image on the detector 6 are consistent with those of the solar imaging light spots, and the fact that other field light rays are not introduced to cause additional calibration errors is ensured.

Through the cutting-in of the baffle, the dark field calibration of the full-day solar telescope can be realized.

Through switching the focusing mirrors with different thicknesses in the first switching rotating wheel and the second switching rotating wheel and matching with the use of through holes, namely the focusing mirror A1, the focusing mirror A2, the focusing mirror A3, the focusing mirror B1, the focusing mirror B2, the focusing mirror B3 and the through holes work cooperatively, 12 groups of equidistant focusing at a focal plane can be realized, the focusing quantity of each group of focusing mirrors can cover 1/2-1.5 times of the focal depth, and specific focusing mirror parameters and focusing schemes are shown in the following table:

in addition, dark field calibration of the detector 6 can be achieved by cutting into the optical path a baffle; the entrance pupil of the front telescope 1 can be imaged to the target surface of the detector 6 by cutting into the first calibration lens 21 and the second calibration lens 31, the diaphragm is uniformly illuminated by sunlight, no additional illumination light source or motion mechanism is added, the entrance pupil image is imaged to the target surface of the detector 6, and the target surface of the detector 6 can be illuminated by stable and uniform light. The focusing and flat field calibration device has the advantages of adjustable primary image plane, adjustable target image position and size, and common imaging and calibration light path.

The second refractive lens group 8 is disposed on the optical path between the second focusing calibration unit 3 and the optical filter 4, and is configured to reflect the outgoing light of the second focusing calibration unit 3 to the optical filter 4, where the first refractive lens group 7 and the second refractive lens group 8 cooperate to make the optical axis of the optical filter 4 parallel to the optical axis of the front telescope 1, and make the optical filter 4 and the front telescope 1 located on the same side of the second focusing calibration unit 3. The first turning mirror group 7 and the second turning mirror group 8 can further shorten the length of the full-day solar telescope, and save resources such as satellite platform envelope, weight and the like to the greatest extent.

The telecentric lens 10 is arranged between the second turning lens group 8 and the optical filter 4, the telecentric lens 10 is a biconvex lens with the thickness of 8mm, and the material is JGS1 and is used for converting the light path into a telecentric light path, so that the parallelism between the principal ray and the optical axis of each view field is better than 0.01 degree, and the influence of the view field effect on the full-day surface precision is avoided.

The optical filter 4 is used for selecting solar observation spectral lines, for example, fe I magnetic sensitive spectral lines correspond to 532.4nm of wavelength, H alpha spectral lines correspond to 656.3nm of wavelength, and the selection of different spectral lines corresponds to the observation requirements of different levels (color sphere layers, light sphere layers and the like) and different targets (magnetic fields, flare and the like) of the sun;

the imaging lens group 5 is used for carrying out secondary imaging on the sun and amplifying the primary imaging light spots of the sun so as to adapt to the size and the position of the target surface of the detector 6;

the detector 6 is used for acquiring and storing the full-sun image information, converts the received sunlight signals into electric signals based on photoelectric conversion effect, stores the electric signals in single pixels in gray data, and transmits the electric signals to the ground detection storage device.

An on-orbit focusing and calibrating method for a full-day solar telescope is based on the on-orbit focusing and calibrating device for the full-day solar telescope, and specifically comprises the following steps of;

step 1, dark field calibration:

1.1, cutting a baffle into an optical path through a second switching rotating wheel, and detecting a first reference image by a detector 6;

1.2, revising the detector 6 according to the first reference image;

step 2, flat field calibration:

2.1, as shown in fig. 1, switching the first calibration lens 21 into the optical path by a first switching wheel; and switching the second scaling lens 31 into the optical path by the second switching wheel; the detector 6 acquires a second reference image;

2.2, as shown in fig. 2, switching the focusing lens A1, the focusing lens A2, the focusing lens A3 or the through hole into the light path through the first switching rotating wheel; switching the focusing lens B1, the focusing lens B2 or the focusing lens B3 into the light path through a second switching rotating wheel; the detector 6 respectively acquires 12 target images;

2.3, selecting the most clear target image, and revising the most clear target image through the second reference image.

The foregoing is merely illustrative of specific embodiments of the present invention, and the scope of the present invention is not limited thereto, but any changes or substitutions within the technical scope of the present invention should be covered by the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.

Claims (10)

1. An on-orbit focusing calibration device of a full-day solar telescope is characterized in that: the device comprises a front telescope (1), a first focusing calibration unit (2), a second focusing calibration unit (3), an optical filter (4), an imaging lens group (5) and a detector (6) which are sequentially arranged along the incident direction of sunlight;

the front telescope (1) is used for imaging the sun once and compressing the subsequent light caliber and incidence angle;

the first focusing calibration unit (2) comprises a first switching rotating wheel; the first switching rotating wheel is provided with a focusing lens A1, a focusing lens A2, a focusing lens A3, a first calibration lens (21) and a through hole; the first switching rotating wheel is used for switching the focusing lens A1, the focusing lens A2, the focusing lens A3, the first calibration lens (21) or the through hole into the light path;

the second focusing calibration unit (3) comprises a second switching rotating wheel; a focusing lens B1, a focusing lens B2, a focusing lens B3, a second calibration lens (31) and a baffle are distributed on the second switching rotating wheel; the second switching rotating wheel is used for switching the focusing lens B1, the focusing lens B2, the focusing lens B3, the second calibration lens (31) or the baffle plate into the light path;

the optical filter (4) is used for selecting solar observation spectral lines;

the imaging lens group (5) is used for carrying out secondary imaging on the sun and amplifying the primary imaging light spots of the sun so as to adapt to the size and the position of the target surface of the detector (6);

the detector (6) is used for acquiring and storing the full-sun surface image information.

2. The full-face solar telescope on-orbit focusing calibration device according to claim 1, wherein: the front telescope (1) comprises a double-layer filter window (11), a diaphragm (12), a primary mirror (13), a secondary mirror (14) and a three-mirror (15) which are sequentially arranged along the incident direction of sunlight;

the double-layer filter window (11) is used for primarily selecting the wavelength of the solar light;

the diaphragm (12) is used for limiting the caliber of the front telescope (1);

the main mirror (13) is a plano-convex mirror, and the convex surface of the plano-convex mirror faces the diaphragm (12);

the secondary mirror (14) is a concave-convex mirror, and the convex surface of the secondary mirror faces the primary mirror (13);

the three mirrors (15) are biconcave lenses.

3. The full-face solar telescope on-orbit focusing calibration device according to claim 1 or 2, wherein: the first calibration lens (21) is a convex-concave lens, the thickness of the first calibration lens is 6mm, the material is HZF6, and the focal length of the first calibration lens is 246mm.

4. The on-orbit focusing and scaling device for the full-day solar telescope according to claim 3, wherein: the second calibration lens (31) is a plano-convex lens, the thickness of the plano-convex lens is 6mm, the material is HZF6, and the focal length of the plano-convex lens is 211.9mm.

5. The on-orbit focusing and scaling device for the full-day solar telescope according to claim 4, wherein: the focusing lens A1 is made of JGS1 and has a thickness of 3mm;

the focusing lens A2 is made of JGS1 and has a thickness of 6mm;

and the focusing mirror A3 is made of JGS1 and has the thickness of 9mm.

6. The on-orbit focusing and scaling device for the full-day solar telescope according to claim 5, wherein: the focusing lens B1 is made of JGS1 and has a thickness of 3mm;

the focusing lens B2 is made of JGS1 and has a thickness of 4mm;

and the focusing mirror B3 is made of JGS1 and has a thickness of 5mm.

7. The full-face solar telescope on-orbit focusing calibration device according to claim 6, wherein: the device also comprises a first turning mirror group (7) and a second turning mirror group (8);

the first turning mirror group (7) is arranged on a light path between the first focusing calibration unit (2) and the second focusing calibration unit (3) and is used for reflecting emergent light of the first focusing calibration unit (2) to the second focusing calibration unit (3);

the second turning mirror group (8) is arranged on a light path between the second focusing calibration unit (3) and the optical filter (4) and is used for reflecting emergent light of the second focusing calibration unit (3) to the optical filter (4), so that the optical axis of the optical filter (4) is parallel to the optical axis of the front telescope (1), and the optical filter (4) and the front telescope (1) are positioned on the same side of the second focusing calibration unit (3).

8. The full-face solar telescope on-orbit focusing calibration device according to claim 7, wherein: also comprises a polarization analyzer (9);

the polarization analyzer (9) is arranged on the light path between the first focusing and scaling unit (2) and the first turning mirror group (7) and is used for measuring the polarization of the solar magnetic field.

9. The full-face solar telescope on-orbit focusing calibration device according to claim 7, wherein: further comprising a telecentric lens (10);

the telecentric lens (10) is arranged between the second turning lens group (8) and the optical filter (4) and is used for converting the optical path into a telecentric optical path.

10. An on-orbit focusing and calibrating method for a full-day solar telescope is based on the on-orbit focusing and calibrating device for the full-day solar telescope, which is characterized by comprising the following steps of;

step 1, dark field calibration:

1.1, cutting a baffle into an optical path through a second switching rotating wheel, and detecting a first reference image by a detector (6);

1.2 revising the detector (6) according to a first reference image;

step 2, flat field calibration:

2.1, switching the first calibration lens (21) into the light path through a first switching rotating wheel; and switching the second scaling lens (31) into the optical path by means of a second switching wheel; the detector (6) acquires a second reference image;

2.2, switching the focusing mirror A1, the focusing mirror A2, the focusing mirror A3 or the through hole into the light path through the first switching rotating wheel; switching the focusing lens B1, the focusing lens B2 or the focusing lens B3 into the light path through a second switching rotating wheel; the detector (6) respectively acquires 12 target images;

2.3, selecting the most clear target image, and revising the most clear target image through the second reference image.