High-resolution hyperspectral imager and imaging method based on field-of-view splicing

Abstract

The invention relates to high-resolution hyperspectral imaging, in particular to a high-resolution hyperspectral imager based on view field splicing and an imaging method, and aims to overcome the defects that an existing high-resolution hyperspectral spectrometer is large in spectrum bending, small in slit length, free of machining reference and low in precision, and consequently the imaging requirement cannot be met. The high-resolution hyperspectral imager based on view field splicing comprises a slit assembly, a first spectrum module and a second spectrum module. The slit assembly comprises a first slit, a second slit and a slit folding-axis reflector, wherein the first slit and the second slit are arranged in a lap joint mode, and the slit folding-axis reflector is arranged on an emergent light path of the first slit. The first spectrum module is arranged on a reflection light path of the slit folding axis reflector, and the second spectrum module is arranged on an emergent light path of the second slit. According to the imaging method, the corresponding spectrograms are obtained through the first spectrum module and the second spectrum module respectively, and then the spectrograms are spliced, so that high-resolution hyperspectral imaging is realized.

Description

Technical Field

[0001] The present invention relates to high-resolution hyperspectral imaging, and particularly to a high-resolution hyperspectral imager and an imaging method based on field-of-view stitching. Background Art

[0002] In order to achieve a large field of view and a large relative aperture design for the existing high-resolution hyperspectral spectrometers, the curved prism optical path multiplexing technology is utilized. According to the dispersion performance of different materials being mutually matched, the chromatic dispersion non-uniformity and low distortion design of the system are effectively corrected. And according to the different off-axis amounts of the curved prism, as well as the relative position and attitude of the prism in the system, the overall system aberration is optimized. Finally, the spectral performance index and the spectral sampling resolution index of the system are achieved. However, in the existing technology, for the high-resolution hyperspectral spectrometers using curved prisms, their spectral curvature is very large, the designed slit length is very small, and the machining reference surface is not considered during the design of the curved prism, resulting in no reference for the later prism machining, low machining accuracy, and inability to meet the imaging requirements. Summary of the Invention

[0003] The object of the present invention is to solve the deficiencies of the existing high-resolution hyperspectral spectrometers, such as large spectral curvature, small slit length, no machining reference, and low accuracy, which lead to the inability to meet the imaging requirements, and to provide a high-resolution hyperspectral imager and an imaging method based on field-of-view stitching.

[0004] To achieve the above object, the technical solution provided by the present invention is as follows:

[0005] A high-resolution hyperspectral imager based on field-of-view stitching, which is characterized in that it includes a slit assembly and a corresponding first spectral module and second spectral module; the slit assembly includes an optical slit and a slit anastigmat, and the optical slit includes a first slit and a second slit arranged in a lapped manner; the slit anastigmat is arranged on the outgoing light path of the first slit for deflecting the outgoing light of the first slit to avoid interference with the outgoing light of the second slit; the first spectral module is arranged on the reflected light path of the slit anastigmat, and includes a first curved prism, a second curved prism, a secondary mirror, a third curved prism, a fourth curved prism, an anastigmat and a spectral detector arranged in sequence along the deflection light path of the slit anastigmat. The deflected light of the slit anastigmat is incident on the first curved prism for primary dispersion, and the outgoing light of the first curved prism is incident on the second curved prism for secondary dispersion, and then is specularly reflected by the rear surface of the second curved prism, and then passes through the second curved prism again for tertiary dispersion, and then is incident on the first curved prism again for quaternary dispersion. The light after quaternary dispersion is reflected by the secondary mirror to the third curved prism for quinary dispersion, and then enters the fourth curved prism for senary dispersion, and then is specularly reflected by the rear surface of the fourth curved prism, and then passes through the fourth curved prism again for septenary dispersion, and then passes through the third curved prism for octonary dispersion, and finally is reflected by the anastigmat and converges on the spectral detector of the first spectral module to obtain a corresponding spectral map; the second spectral module is arranged on the outgoing light path of the second slit, and has the same structure and parameters as those of the first spectral module, and the outgoing light of the second slit passes through the second spectral module to obtain a corresponding spectral map.

[0006] Further, the parallelism between the first slit and the second slit is better than 0.1 pixel, and the number of lapped pixels of the first slit and the second slit is 36 ± 1 pixel;

[0007] The slit lengths of the first slit and the second slit are 145 - 150 mm.

[0008] Further, the concave surfaces of the first curved prism, the second curved prism, the third curved prism and the fourth curved prism are concentrically arranged;

[0009] Both the first slit and the second slit are of double-slit structure.

[0010] Further, the refractive index nd of the material of the first curved prism is 1.5168, the Abbe number vd is 64.167, and the off-axis amount of the prism is 75.45 mm;

[0011] The refractive index nd of the material of the second curved prism is 1.7205, the Abbe number vd is 34.7, and the off-axis amount of the prism is 17.23 mm;

[0012] The refractive index nd of the material of the third curved prism is 1.5168, the Abbe number vd is 64.167, and the off-axis amount of the prism is 93.84 mm;

[0013] The refractive index nd of the material of the fourth curved prism is 1.7205, the Abbe number vd is 34.7, and the off-axis amount of the prism is 30.61 mm.

[0014] Furthermore, the secondary mirror and the slit cross-dispersion mirror are made of quartz material, and their surface form accuracy RMS is better than 1 / 50λ@632.8 nm;

[0015] The reflection angle corresponding to the slit cross-dispersion mirror is greater than or equal to 31.45°.

[0016] Furthermore, the concave surfaces of the first curved prism, the second curved prism, the third curved prism, and the fourth curved prism are all rotationally symmetric structures. Taking the concave surface as the reference plane, their convex surfaces are all off-axis with respect to the concave surface, and the surface form accuracy of the surface is better than 1 / 35λ@632.8 nm.

[0017] Furthermore, the concave surface curvature radius of the first curved prism is 600.34 mm, the convex surface curvature radius is 769.3 mm, and the central thickness is 38.5 mm;

[0018] The concave surface curvature radius of the second curved prism is 344.6 mm, the convex surface curvature radius is 545.1 mm, and the central thickness is 43 mm;

[0019] The concave surface curvature radius of the third curved prism is 602 mm, the convex surface curvature radius is 564.3 mm, and the central thickness is 67 mm;

[0020] The concave surface curvature radius of the fourth curved prism is 563.1 mm, the convex surface curvature radius is 598.6 mm, and the central thickness is 55.4 mm.

[0021] Furthermore, the slit assembly further includes an optical window provided at the exit end of the optical slit.

[0022] Meanwhile, the present invention also provides a high-resolution hyperspectral imaging method based on field-of-view stitching, which is characterized in that it includes the following steps:

[0023] Step 1, build the above-mentioned high-resolution hyperspectral imager based on field-of-view stitching;

[0024] Step 2, the incident light passes through the slit assembly and exits after passing through the first slit and the second slit respectively;

[0025] Step 3, the light exiting from the first slit is refracted by the slit cross-dispersion mirror to the first spectral module and received by the spectral detector of the first spectral module to obtain the corresponding spectral map;

[0026] The emitted light of the second slit enters the second spectral module and is received by the spectral detector of the second spectral module to obtain a corresponding spectrogram.

[0027] Step 4: Stitch the spectrogram obtained by the spectral detector of the first spectral module and the spectrogram obtained by the spectral detector of the second spectral module to achieve high-resolution hyperspectral imaging.

[0028] Advantages of the present invention:

[0029] 1. In the high-resolution hyperspectral imager based on field-of-view stitching of the present invention, the structures and parameters of the first spectral module and the second spectral module are completely the same, so that the same spectral images can be obtained. Then, through field-of-view stitching and slit stitching, two large-field spectral detectors are stitched to realize the design of an ultra-large-field high-resolution hyperspectral imager, thus meeting the usage requirements of an ultra-large field of view for the spectrometer. By setting a slit toroidal mirror, the emitted light of the first slit is refracted to avoid interference with the emitted light of the second slit, improving the imaging accuracy.

[0030] 2. The high-resolution hyperspectral imager based on field-of-view stitching of the present invention uses a curved prism optical path multiplexing system. The first curved prism, the second curved prism, the third curved prism, and the fourth curved prism are set into a concentric zero-aberration structure, correcting the chromatic dispersion non-uniformity and low distortion of the high-resolution hyperspectral imager, and effectively correcting the spectral curvature of the finally obtained imaging spectrum, improving the spectral performance of the high-resolution hyperspectral imager, enhancing its spectral recognition ability from a hardware perspective, and achieving a large field of view and a large relative aperture.

[0031] 3. In the high-resolution hyperspectral imager based on field-of-view stitching of the present invention, both the first slit and the second slit are set as double-slit structures. Using the double-slit imaging system, the signal-to-noise ratio of the image is greatly improved to meet the requirements of high-frame-rate spectral detection for the signal-to-noise ratio.

[0032] 4. The high-resolution hyperspectral imager based on field-of-view stitching of the present invention sets the first curved prism, the second curved prism, the third curved prism, and the fourth curved prism with specific parameters. By matching the dispersion properties of different materials, the high-resolution hyperspectral imager can further have higher imaging performance.

[0033] 5. The high-resolution hyperspectral imager based on field-of-view stitching of the present invention has no special requirements for the spacing and relative positions between the optical elements, and the off-axis error of each lens group is loose, making the assembly process of the high-resolution hyperspectral imager simple and easy to achieve processing.

[0034] 6. The high-resolution hyperspectral imager based on field-of-view stitching according to the present invention adjusts the off-axis amount of the curved prism, as well as the relative position and attitude of the prism in the system, to optimize the aberration, and finally achieves the spectral performance index and spectral sampling resolution index of the high-resolution hyperspectral imager. Therefore, through the off-axis amount, tilt, and decentration of the curved prism, the present invention realizes the design of the high-resolution hyperspectral imager with low distortion, large field of view, large relative aperture, high resolution, and high signal-to-noise ratio.

[0035] 7. The high-resolution hyperspectral imaging method based on field-of-view stitching according to the present invention stitches two large-field spectral detectors through a first spectral module and a second spectral module to perform imaging of an ultra-large-field high-resolution hyperspectral imager. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 is a schematic structural diagram of an embodiment of the high-resolution hyperspectral imager based on field-of-view stitching according to the present invention;

[0037] Figure 2 is a schematic structural diagram of a slit assembly in an embodiment of the high-resolution hyperspectral imager based on field-of-view stitching according to the present invention;

[0038] Figure 3 is a schematic structural diagram of the overlapping of a first slit and a second slit in an embodiment of the high-resolution hyperspectral imager based on field-of-view stitching according to the present invention;

[0039] Figure 4 is a spectral bending diagram in an embodiment of the high-resolution hyperspectral imager based on field-of-view stitching according to the present invention;

[0040] DESCRIPTION OF THE REFERENCE NUMERALS:

[0041] 1 - slit assembly, 11 - first slit, 12 - second slit, 13 - slit toroidal mirror, 14 - optical window, 2 - first curved prism, 3 - second curved prism, 4 - secondary mirror, 5 - third curved prism, 6 - fourth curved prism, 7 - toroidal mirror, 8 - spectral detector. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0042] The high-resolution hyperspectral imager based on field-of-view stitching according to the present invention includes a slit assembly 1 and corresponding first and second spectral modules, as Figure 1 shown; the slit assembly 1 includes an optical slit, an optical window 14, and a slit toroidal mirror 13, as Figure 2 shown. The optical slit includes a first slit 11 and a second slit 12 arranged in an overlapping manner. The optical window 14 is arranged corresponding to the output ends of the first slit 11 and the second slit 12. The slit toroidal mirror 13 is arranged on the optical path of the light emitted from the first slit 11, and its main function is to deflect the light emitted from the first slit 11 to avoid interference between the two spectral modules.

[0043] The light passes through the first slit 11 and the second slit 12 of the slit assembly 1, forming two beams of light, respectively denoted as the first outgoing light and the second outgoing light. After the first outgoing light is deflected by the slit declinator mirror 13, it enters the first spectral module. Specifically, after being deflected, the first outgoing light is incident on the first curved prism 2 for the first dispersion. The light emitted from the first curved prism 2 is incident on the second curved prism 3 for the second dispersion, and then after being specularly reflected by the rear surface of the second curved prism 3, it passes through the second curved prism 3 again for the third dispersion, and then is incident on the first curved prism 2 again for the fourth dispersion. The light after the fourth dispersion is reflected by the secondary mirror 4 to the third curved prism 5 for the fifth dispersion, and then enters the fourth curved prism 6 for the sixth dispersion. The light after the sixth dispersion is specularly reflected by the rear surface of the fourth curved prism 6 and then passes through the fourth curved prism 6 again for the seventh dispersion. The light after the seventh dispersion passes through the third curved prism 5 again for the eighth dispersion and then is reflected by the declinator mirror 7 and converges on the spectral detector 8 of the first spectral module. The second outgoing light passes through the second spectral module and converges on its corresponding spectral detector 8.

[0044] The concave surfaces of the first curved prism 2, the second curved prism 3, the third curved prism 5, and the fourth curved prism 6 are set to a concentric zero aberration structure, correcting the dispersion non-uniformity and low distortion of the high-resolution hyperspectral imager. At the same time, the first curved prism 2, the second curved prism 3, the third curved prism 5, and the fourth curved prism 6 are all set with tilt and decentration.

[0045] The second spectral module is arranged on the outgoing light path of the second slit 12. The structures and parameters of the second spectral module and the first spectral module are exactly the same, and its corresponding spectral detector 8 is used to receive the second outgoing light that has undergone multiple scatterings and reflections.

[0046] In this embodiment, the parameters of each optical element are as follows:

[0047] For the first curved prism 2, the refractive index of the material nd = 1.5168, the Abbe number vd = 64.167, and the decentration of the prism is 75.45 mm; the radius of curvature of the concave surface is 600.34 mm, the radius of curvature of the convex surface is 769.3 mm, and the central thickness is 38.5 mm;

[0048] For the second curved prism 3, the refractive index of the material nd = 1.7205, the Abbe number vd = 34.7, and the decentration of the prism is 17.23 mm; the radius of curvature of the concave surface is 344.6 mm, the radius of curvature of the convex surface is 545.1 mm, and the central thickness is 43 mm;

[0049] The third curved surface prism 5, with a refractive index of the material nd = 1.5168 and an Abbe number vd = 64.167, has an off-axis amount of the prism of 93.84 mm; the concave surface has a curvature radius of 602 mm, the convex surface has a curvature radius of 564.3 mm, and the central thickness is 67 mm;

[0050] The fourth curved surface prism 6, with a refractive index of the material nd = 1.7205 and an Abbe number vd = 34.7, has an off-axis amount of the prism of 30.61 mm; the concave surface has a curvature radius of 563.1 mm, the convex surface has a curvature radius of 598.6 mm, and the central thickness is 55.4 mm;

[0051] The secondary mirror 4 and the coudé mirror are made of quartz material, and the surface form accuracy RMS requirement is better than 1 / 50λ@632.8 nm;

[0052] The first curved surface prism 2, the second curved surface prism 3, the third curved surface prism 5, and the fourth curved surface prism 6 are all curved surface prisms with the concave surface as the reference surface and the convex surface having a certain off-axis relative to the concave surface. The surface form accuracy of all their surfaces is better than 1 / 35λ@632.8 nm, and the concave surfaces are all rotationally symmetric structures.

[0053] The present invention splices the first spectral module and the second spectral module, realizing the use requirement of a super-large field of view for the spectrometer. The field of view size can reach 148 mm. As Figure 3 shown in Figure 2 the right side cross-sectional view of the optical slit in, the field of view splicing accuracy requirement of the present invention in the spatial direction is that the number of overlapping pixels of the first slit 11 and the second slit 12 is 36 ± 1 pixel, and in the spectral dimension, the field of view splicing requires that the parallelism of the first slit 11 and the second slit 12 is better than 0.1 pixel, which is converted to an angle of 1″. In this embodiment, the number of overlapping pixels is 36, and the overlapping field of view angle is 0.004°. In order to prevent the two instruments from interfering with each other, the positive direction field of view corresponding to the first spectral module is folded by a specific angle using the slit coudé mirror 13. In this embodiment, the reflection angle of the slit coudé mirror 13 is set to 31.45°, so that the first spectral module and the second spectral module do not interfere with each other to achieve the effect of field of view splicing. In other embodiments of the present invention, the reflection angle can also be greater than 31.45° to ensure that the first spectral module and the second spectral module do not interfere.

[0054] The high-resolution hyperspectral imaging method based on field of view splicing of the present invention, through the spectral detectors 8 of the first spectral module and the second spectral module in the above-mentioned high-resolution hyperspectral imager respectively receiving the corresponding spectral images, and then performing field of view splicing to achieve high-resolution hyperspectral imaging. The field of view splicing can adopt the existing L-shaped image splicing method.

[0055] In this embodiment, at an ambient temperature of 20 ± 1°C, the incident light wavelength range of the slit assembly 1 is 0.4 - 0.9 μm, its spectral sampling resolution is better than 10 nm, the slit lengths of the first slit 11 and the second slit 12 are both 148 mm, and both adopt a double-slit structure to perform high-resolution hyperspectral imaging to obtain a corresponding spectral image, and the analysis results in a spectral bending diagram as shown in Figure 4 . In the diagram, the abscissa is the slit length, and the ordinate is the deviation of the same wavelength relative to the 0 field of view in different fields of view. It can be seen that the spectral bending of this embodiment < 0.2 pixels, meeting the international high-resolution requirements. In this embodiment, the slit length reaches 148 mm. In other embodiments, it can be set to 145 - 150 mm. Since the longer the slit length, the higher the ground element resolution during ground observation, the larger the imaging swath, and the finer the observation target, but the greater the design difficulty of the imaging system. Therefore, through the mutual cooperation of the parameters of each optical element, the present invention realizes a longer slit length design, effectively improves the ground element resolution, and at the same time realizes ground observation with a larger field of view.

Claims

1. A high-resolution hyperspectral imager based on field-of-view stitching, characterized in that: It includes a slit assembly (1) and a corresponding first spectral module and a second spectral module; The slit assembly (1) includes an optical slit and a slit anastigmat (13), and the optical slit includes a first slit (11) and a second slit (12) arranged in an overlapping manner; The slit anastigmat (13) is arranged on the outgoing light path of the first slit (11) for deflecting the outgoing light of the first slit (11) to avoid interference with the outgoing light of the second slit (12); The first spectral module is arranged on the reflected light path of the slit anastigmat (13), and includes a first curved prism (2), a second curved prism (3), a secondary mirror (4), a third curved prism (5), a fourth curved prism (6), an anastigmat (7) and a spectral detector (8) arranged in sequence along the deflection light path of the slit anastigmat (13). The deflected light of the slit anastigmat (13) is incident on the first curved prism (2) for primary dispersion. After the outgoing light of the first curved prism (2) is incident on the second curved prism (3) for secondary dispersion, it is specularly reflected by the rear surface of the second curved prism (3) and then passes through the second curved prism (3) again for tertiary dispersion, and then is incident on the first curved prism (2) again for quaternary dispersion. The light after quaternary dispersion is reflected by the secondary mirror (4) to the third curved prism (5) for quinary dispersion, then enters the fourth curved prism (6) for senary dispersion, and then is specularly reflected by the rear surface of the fourth curved prism (6) and then passes through the fourth curved prism (6) again for septenary dispersion, then passes through the third curved prism (5) for octal dispersion, and finally is reflected by the anastigmat (7) and converges on the spectral detector (8) of the first spectral module to obtain a corresponding spectral map; The second spectral module is arranged on the outgoing light path of the second slit (12), and has the same structure and parameters as those of the first spectral module respectively. The outgoing light of the second slit (12) passes through the second spectral module to obtain a corresponding spectral map.

2. The high-resolution hyperspectral imager based on field-of-view stitching according to claim 1, characterized in that: The parallelism between the first slit (11) and the second slit (12) is better than 0.1 pixel, and the number of overlapping pixels of the first slit (11) and the second slit (12) is 36 ± 1 pixel; The slit lengths of the first slit (11) and the second slit (12) are 145 - 150 mm.

3. The high-resolution hyperspectral imager based on field-of-view stitching according to claim 2, characterized in that: The concave surfaces of the first curved prism (2), the second curved prism (3), the third curved prism (5), and the fourth curved prism (6) are concentrically arranged; Both the first slit (11) and the second slit (12) are of double-slit structure.

4. The high-resolution hyperspectral imager based on field-of-view stitching according to any one of claims 1 to 3, characterized in that: The refractive index nd of the material of the first curved prism (2) is 1.5168, the Abbe number vd is 64.167, and the off-axis amount of the prism is 75.45 mm; The refractive index nd of the material of the second curved prism (3) is 1.7205, the Abbe number vd is 34.7, and the off-axis amount of the prism is 17.23 mm; The refractive index nd of the material of the third curved prism (5) is 1.5168, the Abbe number vd is 64.167, and the off-axis amount of the prism is 93.84 mm; The refractive index nd of the material of the fourth curved prism (6) is 1.7205, the Abbe number vd is 34.7, and the off-axis amount of the prism is 30.61 mm.

5. The high-resolution hyperspectral imager based on field stitching according to claim 4, characterized in that: The secondary mirror (4) and the slit anastigmat (13) are made of quartz material, and the surface form accuracy RMS is better than 1 / 50λ@632.8 nm; The reflection angle corresponding to the slit anastigmat (13) is greater than or equal to 31.45°.

6. The high-resolution hyperspectral imager based on field stitching according to claim 5, characterized in that: The concave surfaces of the first curved prism (2), the second curved prism (3), the third curved prism (5), and the fourth curved prism (6) are all rotationally symmetric structures. Taking the concave surface as the reference surface, their convex surfaces are all off-axis with respect to the concave surface, and the surface form accuracy of the surface is better than 1 / 35λ@632.8 nm.

7. The high-resolution hyperspectral imager based on field stitching according to claim 6, characterized in that: The concave surface curvature radius of the first curved prism (2) is 600.34 mm, the convex surface curvature radius is 769.3 mm, and the central thickness is 38.5 mm; The concave surface curvature radius of the second curved prism (3) is 344.6 mm, the convex surface curvature radius is 545.1 mm, and the central thickness is 43 mm; The concave surface curvature radius of the third curved prism (5) is 602 mm, the convex surface curvature radius is 564.3 mm, and the central thickness is 67 mm; The concave surface curvature radius of the fourth curved prism (6) is 563.1 mm, the convex surface curvature radius is 598.6 mm, and the central thickness is 55.4 mm.

8. The high-resolution hyperspectral imager based on field stitching according to claim 7, characterized in that: The slit assembly (1) further includes an optical window (14) provided at the optical slit exit end.

9. A high-resolution hyperspectral imaging method based on field-of-view stitching, characterized in that, Including the following steps: Step 1, build the high-resolution hyperspectral imager based on field stitching according to any one of claims 1-8; Step 2, the incident light passes through the slit assembly (1), and exits after passing through the first slit (11) and the second slit (12) respectively; Step 3, the light exiting from the first slit (11) is refracted by the slit anastigmat (13) to the first spectral module and received by the spectral detector (8) of the first spectral module to obtain the corresponding spectral map; The light exiting from the second slit (12) enters the second spectral module and is received by the spectral detector (8) of the second spectral module to obtain the corresponding spectral map; Step 4, splice the spectrogram obtained by the spectral detector (8) of the first spectral module and the spectrogram obtained by the spectral detector (8) of the second spectral module to achieve high-resolution hyperspectral imaging.

Images