Short-wave infrared hyperspectral imaging system and method

Abstract

The embodiment of the invention discloses a short-wave infrared hyperspectral imaging system and method, and relates to the technical field of infrared imaging. According to the scheme, a slit unit formed by splicing a plurality of short slits is arranged in the transmission direction of target light, the target light reflected by a telescope passes through the plurality of short slits to form an ultra-large view field, each short slit corresponds to an independent sub-spectrometer, the sub-spectrometers are spliced together on an image plane to form a full spectrum, and by adopting the plurality of spliced short slits, the ultra-large view field can be obtained. According to the short-wave infrared hyperspectral imaging system, the size of the short-wave infrared hyperspectral imaging system can be reduced, the image quality is guaranteed, meanwhile, the multiple sub-spectrometers are adopted, each sub-spectrometer independently controls the aberration of the sub-spectrometers, the image quality can be further improved, and image distortion is prevented.

Description

Technical Field

[0001] This application relates to the field of infrared imaging technology, and particularly to a short-wave infrared hyperspectral imaging system and method. Background Art

[0002] A short-wave infrared hyperspectral imaging spectrometer is an analytical instrument used in the fields of earth science and agronomy. The short-wave infrared technology covers the 1.0 - 2.5 μm band and has excellent penetration performance. It can penetrate obstacles such as clouds and smoke, and can also sensitively detect the material, water content and chemical properties of substances. Therefore, short-wave infrared hyperspectral imaging spectrometers are widely used in remote sensing, industry, military and other fields.

[0003] In hyperspectral related technologies, in order to accurately identify targets, it is necessary to improve the spatial resolution, and high spatial resolution requires a super-large slit field of view. Traditional short-wave infrared hyperspectral imaging spectrometers need to use an extremely long slit to achieve a super-large slit field of view, resulting in a large volume and difficult image quality control for short-wave infrared hyperspectral imaging spectrometers with extremely long slits. Summary of the Invention

[0004] Embodiments of this specification provide a short-wave infrared hyperspectral imaging system to solve the problems in the prior art that when achieving a super-large slit field of view, short-wave infrared hyperspectral imaging spectrometers with extremely long slits have a large volume and difficult image quality control.

[0005] To solve the above technical problems, the embodiments of this specification are implemented as follows:

[0006] In a first aspect, a short-wave infrared hyperspectral imaging system provided by an embodiment of this specification includes:

[0007] A telescope and a spectrometer assembly arranged in sequence along the transmission direction of the target light; the spectrometer assembly includes a slit unit and a spectrometer unit, the slit unit includes a plurality of short slits, and each short slit is used to transmit the target light reflected by the telescope;

[0008] The spectrometer unit includes a plurality of sub-spectrometers, the sub-spectrometers correspond to the short slits one by one, and each sub-spectrometer is used to receive the target light transmitted by the corresponding short slit for spectral imaging.

[0009] In a second aspect, a short-wave infrared hyperspectral imaging method provided by an embodiment of this specification is applied to a short-wave infrared hyperspectral imaging system, and the short-wave infrared hyperspectral imaging system includes a telescope and a spectrometer assembly; wherein, the spectrometer assembly includes a slit unit and a spectrometer unit, and the method may include:

[0010] Obtain the target light of the object to be imaged;

[0011] The telescope receives the target light and reflects it to the slit unit for field of view segmentation;

[0012] The segmented target light is introduced into the spectrometer assembly to obtain spectral imaging.

[0013] One embodiment of this specification achieves the following beneficial effects: A slit unit composed of multiple short slits is set in the transmission direction of the target light. The target light reflected by the telescope forms an ultra-large slit field of view through multiple short slits. Each short slit corresponds to an independent sub-spectrometer and jointly splices into a full spectrum on the image plane. By using multiple spliced short slits, the volume of the short-wave infrared hyperspectral imaging system can be reduced, the image quality can be guaranteed. At the same time, by using multiple sub-spectrometers and each sub-spectrometer independently controlling its own aberration, the image quality can be further improved and image distortion can be prevented. Description of the Drawings

[0014] To more clearly illustrate the technical solutions in the embodiments of this specification or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments recorded in this application. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0015] Figure 1 Schematic diagram of a slit unit composed of multiple short slits provided by an embodiment of this specification;

[0016] Figure 2 Optical path schematic diagram of a single sub-spectrometer provided by an embodiment of this specification;

[0017] Figure 3 Optical path schematic diagram of a short-wave infrared hyperspectral imaging system provided by an embodiment of this specification;

[0018] Figure 4 Schematic diagram of the modulation transfer function at the central wavelength of a short-wave infrared hyperspectral imaging system provided by an embodiment of this specification;

[0019] Figure 5 Schematic diagram of the modulation transfer function at the central wavelength of a single spectrometer of a short-wave infrared hyperspectral imaging system provided by an embodiment of this specification.

[0020] Description of the Drawings: 1 - Telescope; 2 - Spectrometer assembly; 3 - Slit unit; 4 - Mirror M1; 5 - Convex grating M2; 6 - Mirror M3; 7 - Image plane. Detailed Embodiments

[0021] To make the objectives, technical solutions, and advantages of one or more embodiments of this specification clearer, the following will clearly and completely describe the technical solutions of one or more embodiments of this specification in combination with specific embodiments of this specification and the corresponding drawings. Obviously, the described embodiments are only a part of the embodiments of this specification, rather than all of the embodiments. Based on the embodiments in this specification, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope protected by one or more embodiments of this specification.

[0022] The following will detail the technical solutions provided by each embodiment of this specification in combination with the drawings.

[0023] To address the deficiencies in the prior art, the following embodiments are provided in this solution:

[0024] A specific description will be given of a short-wave infrared hyperspectral imaging system provided by an embodiment of the specification in combination with the drawings.

[0025] The short-wave infrared hyperspectral imaging system in an embodiment of this specification may include:

[0026] A telescope and a spectrometer assembly arranged in sequence along the target light transmission direction; the spectrometer assembly includes a slit unit and a spectrometer unit, the slit unit includes a plurality of short slits, and each short slit is used to transmit the target light reflected by the telescope;

[0027] The spectrometer unit includes a plurality of sub-spectrometers, the sub-spectrometers correspond to the short slits one by one, and each sub-spectrometer is used to receive the target light transmitted by the corresponding short slit for spectral imaging.

[0028] In an embodiment of this specification, the telescope is the front-end component of the system, arranged along the target light transmission direction, and can capture and focus the target light. The spectrometer assembly is located behind the telescope and can split and image the target light focused by the telescope. The spectrometer assembly includes a slit unit and a spectrometer unit. Among them, the slit unit is located at the front end of the spectrometer assembly and can include a plurality of short slits. Specifically, the slit unit can include 10 short slits to form a large field of view of an ultra-long slit. Each short slit is carefully designed to ensure the effective transmission of light and the quality of spectral imaging.

[0029] The spectrometer unit can include a plurality of sub-spectrometers, and one sub-spectrometer corresponds to one short slit. A plurality of spectrometers are stitched together in the field of view to form the spectrometer unit. The sub-spectrometer can receive the target light transmitted by the corresponding short slit and perform spectral imaging.

[0030] Due to the particularity of field stitching, as long as the front telescope has a sufficiently long image plane, the slit field of view can be infinitely enlarged. For multiple short slits, if a single spectrometer design is adopted, once the field of view continues to increase, it will become increasingly difficult for the single spectrometer design. The volume of the single spectrometer increases sharply, and the ability to correct aberrations is limited. By adopting the form of multi-spectrometer stitching, each spectrometer independently controls its own aberration. In contrast, the volume will be further reduced and it is not restricted by the continuous increase of the field of view.

[0031] In practical applications, the number of short slits and sub-spectrometers can be increased according to needs. On the basis of ensuring image quality, the field of view can be infinitely enlarged.

[0032] It should be understood that the order of some steps of the method described in one or more embodiments of this specification can be mutually exchanged according to actual needs, or some of the steps can also be omitted or deleted.

[0033] In the embodiments of this specification, a slit unit spliced by multiple short slits is arranged in the target light transmission direction. The target light reflected by the telescope forms an ultra-large field of view through multiple short slits. Each short slit corresponds to an independent sub-spectrometer and is jointly spliced into a full spectrum on the image plane. By adopting multiple spliced short slits, the volume of the short-wave infrared hyperspectral imaging system can be reduced, the image quality can be guaranteed. At the same time, by adopting multiple sub-spectrometers, each sub-spectrometer independently controls its own aberration, which can further improve the image quality and prevent image distortion.

[0034] The embodiments of this specification also provide some specific implementation schemes of this method, which will be described below.

[0035] Optionally, in the embodiments of this specification, multiple short slits are spliced alternately in the length direction and the width direction. The size of each short slit is 40mm×20μm. The interval between two adjacent short slits in the width direction is 0.6mm, and two adjacent short slits overlap by 10 pixels in the length direction.

[0036] In the embodiments of this specification, multiple short slits are spliced alternately in the length direction and the width direction, in a pyramid shape. Multiple short slits are spliced to form an ultra-long slit, improving the imaging efficiency of the system. Through staggered splicing, the imaging ability of each slit can be fully utilized, reducing light loss and ensuring that the light can evenly cover the entire slit unit.

[0037] Figure 1 It is a schematic diagram of a slit unit spliced by multiple short slits provided by the embodiments of this specification.

[0038] Such as Figure 1As shown, based on the requirements of the short-wave infrared hyperspectral imaging system for resolution and sensitivity, the size of each short slit can be 40 mm × 20 μm. The 40-mm length can ensure that the slit can cover a wide enough target area, improving the imaging efficiency of the system, and the 20-μm width can ensure the spectral resolution.

[0039] The slits are arranged in sequence in the length direction. In the width direction, there is a certain interval between adjacent slits. This design not only ensures the independence between the slits, avoiding interference of light between the slits, but also ensures the continuity of light and the consistency of imaging through the overlapping pixels.

[0040] Specifically, based on the requirements of the short-wave infrared hyperspectral imaging system for light transmission efficiency and imaging quality, the interval between two adjacent short slits in the width direction is 0.6 mm, which also ensures the reasonable layout of the spectrometer unit. At the same time, 10 pixels overlap between two adjacent short slits in the length direction, which can ensure the continuity of light and the consistency of imaging. The overlapping pixels can serve as a transition area between adjacent slits, helping to smooth the transmission of light between the slits, ensuring the integrity of the image, reducing light loss and imaging distortion.

[0041] By splicing multiple short slits, a large field of view of an ultra-long slit is formed, improving the imaging efficiency of the system. By optimizing the splicing method and interval of the slits, light loss and imaging distortion are reduced, and the image quality performance of the system is improved.

[0042] Optionally, in the embodiments of this specification, each of the sub-spectrometers includes a mirror M1, a convex grating M2, and a mirror M3; the mirror M1, the convex grating M2, and the mirror M3 are all even aspheres.

[0043] In the embodiments of this specification, the sub-spectrometer may include a mirror M1, a convex grating M2, and a mirror M3, all of which are even aspheres and made of aluminum metal material with a reflective film coated on the surface.

[0044] Among them, the convex grating has both spectral splitting and optical focusing functions. Compared with prism splitting, it has higher spectral resolution, compactness, and flexibility. Prisms rely on the material dispersion characteristics, and the dispersion ability of short-wavelength light is relatively low, while the convex grating uses the diffraction principle and can maintain relatively uniform dispersion throughout the spectral range, especially suitable for high-precision spectral analysis in a wide spectral range (ultraviolet to infrared). In addition, the convex grating can replace the lens system for focus adjustment, reducing the number of optical elements, making the system more compact and with less light loss, while the prism system often requires an additional focusing lens to compensate for dispersion, resulting in an increase in volume and loss. Therefore, the convex grating has more advantages in the fields of hyperspectral imaging, space remote sensing, precision spectral measurement, etc.

[0045] The sub-spectrometer can be an Offner-type spectrometer.

[0046] Figure 2 This is the optical path schematic diagram of a single sub - spectrometer provided by the embodiments of this specification.

[0047] As Figure 2 shown, the mirror M1 is the first optical element of the sub - spectrometer. It is located behind the slit and can receive the target light from the slit and reflect it to the convex grating M2 for spectral splitting.

[0048] The convex grating M2 is located behind the mirror M1 and can disperse the light according to the wavelength.

[0049] The mirror M3 is located behind the convex grating M2 and can reflect and converge the dispersed light onto the image plane for imaging.

[0050] The even - order aspheric design provides more design freedoms, making the design of the spectrometer more flexible, capable of meeting different application requirements, and at the same time improving the spectral splitting efficiency and sensitivity of the spectrometer.

[0051] Optionally, in the embodiments of this specification, the radius of curvature of the mirror M1 can be 120.90 mm, the radius of curvature of the convex grating M2 can be 62.08 mm, the radius of curvature of the mirror M3 can be 123.66 mm, and the number of rulings of the convex grating M2 can be 12 rulings / mm.

[0052] In the embodiments of this specification, the spectrometer assembly realizes high resolution, high sensitivity, and excellent image quality performance by optimizing parameters such as the radius of curvature of the mirror M1, the convex grating M2, and the mirror M3, as well as the number of rulings of the convex grating M2.

[0053] Optionally, in the embodiments of this specification, the telescope includes a primary mirror, a secondary mirror, and a tertiary mirror; both the primary mirror and the tertiary mirror are free - form surfaces, and the secondary mirror is an even - order aspheric surface.

[0054] In the embodiments of this specification, the telescope can include a primary mirror, a secondary mirror, and a tertiary mirror. Among them, the primary mirror and the tertiary mirror adopt free - form surface designs, and the secondary mirror adopts an even - order aspheric surface design. This can improve the imaging quality of the telescope, reduce aberration, and increase design freedoms.

[0055] Specifically, the telescope can be an off-axis three-mirror telescope, a reflecting telescope, a refracting telescope, a catadioptric telescope, etc. Among them, the off-axis three-mirror telescope (TMA) has the advantages of a large field of view, high resolution, and no central obstruction, which can effectively reduce the diffraction effect and improve the imaging quality. The off-axis design avoids the problem of central obstruction of the primary mirror, improves the light throughput and contrast of the system, and makes it particularly suitable for high-precision remote sensing imaging, astronomical observation, and space exploration. In addition, the three-mirror structure can optimize the aberration through free-form surfaces and achieve large-field distortion correction, thereby improving the imaging uniformity and target recognition ability of the detection system.

[0056] The off-axis three-mirror telescope is calculated according to the third-order aberration correction theory, and free-form surfaces and even aspheres are introduced and optimized in optical software.

[0057] Optionally, in the embodiments of this specification, the radius of curvature of the primary mirror can be -5437.23 mm, the radius of curvature of the secondary mirror can be 27749.60 mm, and the radius of curvature of the tertiary mirror can be -811.63 mm.

[0058] In the embodiments of this specification, by optimizing the radius of curvature and surface shape of the primary mirror, secondary mirror, and tertiary mirror, the aberration is effectively reduced and the imaging quality is improved.

[0059] In the embodiments of this specification, the parameters of each optical component in the telescope and the sub-spectrometer are shown in Table 1.

[0060] Table 1

[0061]

[0062]

[0063] The sag equation of the free-form surface is used to describe the free-form surface shape, and the sag equation of the even asphere is used to describe the even asphere surface shape.

[0064] The sag equation of the free-form surface for z is:

[0065]

[0066] where r is the radius of curvature of the mirror, c is the curvature, k is the conic constant, N is the total number of polynomial coefficients in the series, and A i is the coefficient of the i-th extended polynomial.

[0067] The sag equation of the even asphere for z is:

[0068]

[0069] Among them, r is the radius of curvature of the mirror, c is the curvature, k is the conic coefficient, and a1 to a6 are the coefficients of each term respectively.

[0070] In the embodiments of this specification, the coefficients of each surface mirror are shown in Table 2.

[0071] Table 2

[0072]

[0073]

[0074] Optionally, in the embodiments of this specification, the telescope may have an image-space telecentric optical path, the along-track field of view may be ±4.25°, the across-track field of view may be ±1.0°, the entrance pupil diameter may be 100 mm, and the focal length may be 500 mm.

[0075] In the embodiments of this specification, the image plane is rectangular. By adopting designs such as an image-space telecentric optical path, optimizing the field of view and optical parameters, high-quality imaging, a large observation range, strong light-gathering ability, and high resolution are achieved.

[0076] Optionally, in the embodiments of this specification, the length of the short slit is 40 mm, and the numerical aperture of the sub-spectrometer is 0.13.

[0077] Specifically, the length of the slit unit is closely related to the resolution of the telescope. A longer slit unit helps improve the resolution of the system. The length and numerical aperture of the short slit jointly determine the overall performance of the spectrometer, including resolution, sensitivity, and imaging quality, etc.

[0078] Figure 3 It is a schematic optical path diagram of a short-wave infrared hyperspectral imaging system provided by the embodiments of this specification.

[0079] As Figure 3 shown, the target light enters the primary mirror of the telescope and is reflected to the secondary mirror of the telescope, then reflected by the secondary mirror to the tertiary mirror of the telescope. There are 10 short slits, and the corresponding sub-spectrometers are also 10. In order to obtain a reasonably arranged spectrometer unit, the multiple sub-spectrometers are divided into two parts, and 5 sub-spectrometers are respectively arranged above and below in the width direction of the slit. The target light passes through the short slits that are alternately spliced in the width direction and enters the mirror M1 of the sub-spectrometer corresponding to the short slit, is reflected by the mirror M1 to the convex grating M2 of the sub-spectrometer for spectral splitting, is reflected by the convex grating M2 to the mirror M3 of the sub-spectrometer, and is reflected by the mirror M3 and converges onto the image plane for spectral imaging.

[0080] Specifically, the short-wave infrared hyperspectral imaging system further includes a detector. The target light is first imaged at the slit unit by the telescope, then enters the spectrometer unit through the slit unit for spectral splitting, and finally enters the large image plane of the detector for spectral imaging. Further, a multi-channel detector can be used to achieve high-resolution imaging of the complete spectrum.

[0081] Figure 4 Schematic diagram of the modulation transfer function at the central wavelength of a short-wave infrared hyperspectral imaging system provided by an embodiment of this specification;

[0082] The modulation transfer function (MTF) is used to characterize the system's ability to transfer signals of different spatial frequencies and is an important indicator for measuring the spatial resolution and imaging quality of an imaging system. MTF describes how the system attenuates and phase-shifts the image contrast of different frequencies, comprehensively reflecting the influence of optical systems, sensors, signal processing, etc. on image sharpness. A higher MTF value means the system can resolve details more clearly.

[0083] As Figure 4 shown, the full-field MTF at the Nyquist sampling frequency of 25 lp / mm is better than 0.70, meeting the requirements for high-quality imaging.

[0084] Figure 5 Schematic diagram of the modulation transfer function at the central wavelength of a single spectrometer of a short-wave infrared hyperspectral imaging system provided by an embodiment of this specification;

[0085] As Figure 5 shown, the full-field MTF at the Nyquist sampling frequency of 25 lp / mm is better than 0.78, meeting the requirements for high-quality spectral imaging.

[0086] The short-wave infrared hyperspectral imaging method in the embodiments of this specification is applied to a short-wave infrared hyperspectral imaging system. The short-wave infrared hyperspectral imaging system includes a telescope and a spectrometer assembly; wherein, the spectrometer assembly includes a slit unit and a spectrometer unit, and the method may include:

[0087] Obtain the target light of the object to be imaged;

[0088] The telescope receives the target light and reflects it to the slit unit for splitting;

[0089] Import the split target light into the spectrometer assembly to obtain spectral imaging.

[0090] In the embodiments of this specification, the short-wave infrared hyperspectral imaging system obtains the target light of the object to be imaged. The telescope, as the front-end optical component of the system, can receive the light from the target and reflect it to the slit unit for further processing.

[0091] The slit unit is used to limit the range of light entering the spectrometer, thereby defining the field of view and resolution of the spectrometer. The slit unit divides the received target light so that the light can enter the spectrometer unit in a suitable manner.

[0092] The spectrometer unit is used to disperse the divided target light. Through the processing of the spectrometer unit, spectral imaging of the target object can be obtained, thereby achieving the purpose of hyperspectral imaging.

[0093] Optionally, in the embodiments of this specification, the slit unit may include a plurality of short slits, and the spectrometer unit may include a plurality of sub-spectrometers, and the sub-spectrometers correspond to the short slits one by one.

[0094] The above describes specific embodiments of this specification, and other embodiments are within the scope of the appended claims. In some cases, the actions or steps recited in the claims may be performed in a different order than in the embodiments and still achieve the desired result. Additionally, the processes depicted in the drawings do not necessarily have to be performed in the specific order or consecutive order shown to achieve the desired result. Each embodiment in this specification is described in a progressive manner, and the same or similar parts between each embodiment can be referred to each other. Each embodiment focuses on the differences from other embodiments.

[0095] It should also be noted that the term "including", "comprising" or any other variant thereof is intended to cover non-exclusive inclusion, such that a process, method, commodity or device including a series of elements not only includes those elements but also includes other elements not explicitly listed, or further includes elements inherent to such process, method, commodity or device. Without further limitation, an element defined by the statement "including one..." does not exclude the existence of another identical element in the process, method, commodity or device including the said element.

[0096] The above is only for the embodiments of this specification and is not used to limit this application. For those skilled in the art, various changes and modifications can be made to this application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of this application shall be included within the scope of the claims of this application.

Claims

1. A short-wave infrared hyperspectral imaging system, characterized in that, Comprising: A telescope and a spectrometer assembly arranged in sequence along the transmission direction of the target light; the spectrometer assembly includes a slit unit and a spectrometer unit, the slit unit includes a plurality of short slits, and each short slit is used to transmit the target light reflected by the telescope; The spectrometer unit includes a plurality of sub-spectrometers, the sub-spectrometers correspond to the short slits one by one, and each sub-spectrometer is used to receive the target light transmitted by the corresponding short slit for spectral imaging.

2. The short-wave infrared hyperspectral imaging system according to claim 1, wherein The plurality of short slits are spliced alternately in the length direction and the width direction, the size of each short slit is 40mm×20μm, the interval between two adjacent short slits in the width direction is 0.6mm, and two adjacent short slits overlap by 10 pixels in the length direction.

3. The short-wave infrared hyperspectral imaging system according to claim 1, characterized in that, Each sub-spectrometer includes a mirror M1, a convex grating M2 and a mirror M3; both the mirror M1 and the mirror M3 are even aspheres.

4. The short-wave infrared hyperspectral imaging system according to claim 3, wherein The radius of curvature of the mirror M1 is 120.90mm, the radius of curvature of the convex grating M2 is 62.08mm, the radius of curvature of the mirror M3 is 123.66mm, and the number of rulings of the convex grating M2 is 12 rulings / mm.

5. The short-wave infrared hyperspectral imaging system according to claim 1, wherein The telescope includes a primary mirror, a secondary mirror and a tertiary mirror; both the primary mirror and the tertiary mirror are free-form surfaces, and the secondary mirror is an even aspherical surface.

6. The short-wave infrared hyperspectral imaging system according to claim 5, wherein The radius of curvature of the primary mirror is -5437.23mm, the radius of curvature of the secondary mirror is 27749.60mm, and the radius of curvature of the tertiary mirror is -811.63mm.

7. The short-wave infrared hyperspectral imaging system according to claim 1, wherein The telescope is an image-space telecentric optical path, the along-track field angle is ±4.25°, the across-track field angle is ±1.0°, the entrance pupil diameter is 100mm, and the focal length is 500mm.

8. The short-wave infrared hyperspectral imaging system according to any one of claims 1-7, characterized in that, The length of the short slit is 40mm, and the numerical aperture of the sub-spectrometer is 0.

13.

9. A short-wave infrared hyperspectral imaging method, characterized in that Applied to a short-wave infrared hyperspectral imaging system, the short-wave infrared hyperspectral imaging system includes a telescope and a spectrometer assembly; wherein, the spectrometer assembly includes a slit unit and a spectrometer unit, and the method includes: Obtaining the target light of the object to be imaged; The telescope receives the target light and reflects it to the slit unit for splitting; Importing the split target light into the spectrometer assembly to obtain spectral imaging.

10. The short-wave infrared hyperspectral imaging method according to claim 9, wherein The slit unit includes a plurality of short slits, the spectrometer unit includes a plurality of sub-spectrometers, and the sub-spectrometers correspond to the short slits one by one.

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