WO2022104992A1 - 弯曲狭缝成像光谱仪 - Google Patents

弯曲狭缝成像光谱仪 Download PDF

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WO2022104992A1
WO2022104992A1 PCT/CN2020/137813 CN2020137813W WO2022104992A1 WO 2022104992 A1 WO2022104992 A1 WO 2022104992A1 CN 2020137813 W CN2020137813 W CN 2020137813W WO 2022104992 A1 WO2022104992 A1 WO 2022104992A1
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slit
objective lens
curved slit
offner
curved
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French (fr)
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朱嘉诚
潘俏
陈新华
沈为民
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Suzhou University
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Suzhou University
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
    • G01J3/00—Spectrometry; Spectrophotometry; Monochromators; Measuring colours
    • G01J3/28—Investigating the spectrum
    • G01J3/2823—Imaging spectrometer
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
    • G01J3/00—Spectrometry; Spectrophotometry; Monochromators; Measuring colours
    • G01J3/02—Details
    • G01J3/0205—Optical elements not provided otherwise, e.g. optical manifolds, diffusers, windows
    • G01J3/021—Optical elements not provided otherwise, e.g. optical manifolds, diffusers, windows using plane or convex mirrors, parallel phase plates, or particular reflectors
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
    • G01J3/00—Spectrometry; Spectrophotometry; Monochromators; Measuring colours
    • G01J3/02—Details
    • G01J3/0205—Optical elements not provided otherwise, e.g. optical manifolds, diffusers, windows
    • G01J3/0218—Optical elements not provided otherwise, e.g. optical manifolds, diffusers, windows using optical fibers
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
    • G01J3/00—Spectrometry; Spectrophotometry; Monochromators; Measuring colours
    • G01J3/02—Details
    • G01J3/04—Slit arrangements slit adjustment
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
    • G01J3/00—Spectrometry; Spectrophotometry; Monochromators; Measuring colours
    • G01J3/12—Generating the spectrum; Monochromators
    • G01J3/18—Generating the spectrum; Monochromators using diffraction elements, e.g. grating

Definitions

  • the invention relates to the technical field of spectral imaging, and relates to a curved slit imaging spectrometer.
  • Imaging spectrometers are composed of a front objective lens and a spectroscopic device, and can be divided into dispersion type and interference type.
  • the traditional dispersive imaging spectrometer is directly imaged from the front objective lens to the slit, the slit is the object surface of the spectroscopic device, and the light passing through the slit is then split and imaged by the spectroscopic device.
  • the existing structure can well meet the requirements of the instrument index when the length of the straight slit is short, but for the long slit system that needs to meet the requirements of wide width and high spatial resolution, there is a large aberration and the spectral image is easily distorted. .
  • the field of view splicing method is usually adopted, and the long slit system is divided into multiple short and medium slit systems and spliced together, but the spliced system has a complex structure and a huge volume.
  • spaceborne imaging spectrometers generally have higher requirements on the geometrical physical quantities such as the weight and volume of the instrument. Excessive volume and weight lead to a sharp increase in the cost of production, manufacture, and launch of the instrument.
  • imaging spectrometers In the existing imaging spectrometers, most of them are short and medium slit systems, and they all use straight slits, and the slit length is all within 30mm. The increase of the slit length will rapidly increase the aberration of the optical system. To meet the application requirements of wide format and high spatial resolution, imaging spectrometers with slit lengths exceeding 100 mm are rarely reported. In the late 1980s, Wynne proposed to introduce a meniscus lens into a one-to-one imaging Offner relay system, which could compensate for spherical aberration and astigmatism with long slits and achieve better imaging quality.
  • the technical problem to be solved by the present invention is to provide a curved slit imaging spectrometer optical system with the characteristics of long slit, simple structure, compact size and excellent imaging quality, which is suitable for wide width, high spatial resolution, medium and high spectral resolution. hyperspectral remote sensing.
  • a curved slit imaging spectrometer comprising a front objective lens, an optical fiber image transmission beam, a curved slit, an Offner-type spectroscopic device, and a focal plane detector;
  • the front objective lens images the target scene, and the optical fiber image transmission beam transmits the linear image formed by the front objective lens to the curved slit.
  • Spectroscopic device which is split and imaged on the focal plane detector by an Offner-type spectroscopic device.
  • the front objective lens is a transmissive objective lens, a reflective objective lens or a catadioptric objective lens.
  • the Offner-type spectroscopic device includes a concave spherical reflector and a convex spherical grating, the concave spherical reflector and the convex spherical grating are coaxially arranged, and after the light incident from the curved slit is reflected by the spherical reflector, the light converges The light beam is incident on the convex spherical grating for spectral splitting, and then the concave spherical reflecting mirror images the split optical fiber to a focal plane detector to complete spectral imaging.
  • the incident end face of the optical fiber image transmission beam is arranged in a straight line, which is overlapped with the image formed by the front objective lens, and the outgoing end face of the optical fiber image transmission beam is arranged in an arc shape, which is coincident with the bending slit.
  • the curved slit coincides with or is in the vicinity of the optimal imaging circular field of view of the Offner-type spectroscopic device, and the arc center of the curved slit is set on the optical axis or optical axis of the Offner-type spectroscopic device. near the axis.
  • the radius of the concave spherical mirror of the Offner-type spectroscopic device is R 1
  • the radius of curvature of the convex spherical grating is R 2
  • the radius of the optimal circular field of view of the Offner-type spectroscopic device is r
  • the numerical aperture of the front objective lens and the Offner type spectroscopic device are the same, and the numerical aperture of the optical fiber image transmission bundle is greater than or equal to the numerical aperture of the front objective lens; the diameter of the fiber core of the optical fiber image transmission bundle is in the range of 5-50 ⁇ m .
  • the ratio of the radius of curvature of the concave spherical reflector to the convex spherical grating is 1.9:1 to 2.2:1, and the distance between the centers of the spheres is less than 0.1R 2 .
  • the shape of the spectral line formed on the focal plane detector is consistent with the shape of the curved slit, and is transformed into a linear spectral line corresponding to the ground detection pixels through a mapping transformation algorithm, and the mapping relationship is that the arc-shaped spectral line is located equation Transform to the equation of the straight spectral line where k is a constant.
  • the present invention transmits the straight image plane of the front objective lens to the curved slit through the optical fiber image transmission beam, and does not need the front objective lens to form a curved image plane and is directly connected to the spectroscopic device, thereby reducing the complexity of the system.
  • FIG. 1 is a three-dimensional view of the optical path of the curved slit imaging spectrometer of the present invention
  • FIG. 2 is an axial view of an optical path of an Offner-type spectroscopic device in the curved slit imaging spectrometer of the present invention
  • Fig. 3 is the optimal imaging circular field of view in the 1/4 object plane of the Offner type spectroscopic device in the curved slit imaging spectrometer of the present invention
  • Fig. 4 is the curved spectral line image formed on the focal plane detector of the curved slit imaging spectrometer of the present invention and the straight spectral line image after mapping transformation;
  • FIG. 5 is a modulation transfer function curve of a curved slit imaging spectrometer provided by an embodiment of the present invention.
  • FIG. 6 is a schematic diagram of a spectral image formed by a focal plane detector of a curved slit imaging spectrometer according to an embodiment of the present invention and a range of pixels used to correct background noise and dark current noise.
  • Front objective lens 1.1, Front objective lens primary mirror, 1.2, Front objective secondary lens, 1.3, Front objective lens three mirrors, 1.4, Front objective lens folding mirror, 1.5, Front objective mirror surface; 2.
  • Optical fiber image beam 3. Bending slit; 4. Offner type beam splitting device; 4.1.
  • Concave spherical mirror 4.2. Convex spherical grating; 5.
  • Focal plane detector 6. Curved spectral line image; 7. Straight spectrum line image;
  • a curved slit imaging spectrometer includes a front objective lens, an optical fiber image transmission beam, a curved slit, an Offner-type spectroscopic device, and a focal plane detector;
  • the front objective lens images the target scene, and the optical fiber image transmission beam transmits the linear image formed by the front objective lens to the curved slit.
  • Spectroscopic device which is split and imaged on the focal plane detector by an Offner-type spectroscopic device.
  • the present invention transmits the straight image plane of the front objective lens to the curved slit through the optical fiber image transmission beam, and does not need the front objective lens to form a curved image plane and is directly connected to the spectroscopic device, thereby reducing the complexity of the system.
  • the invention meets the requirements of a wide-width and high-spatial-resolution spaceborne imaging spectrometer, and breaks through the limitation of the short length of the straight slit in the existing imaging spectrometer.
  • the imaging length of the front objective lens is the same as the arc length of the curved slit.
  • the front objective lens is a transmissive objective lens, a reflective objective lens or a catadioptric objective lens.
  • the front objective lens is an off-axis three-mirror telescopic objective lens, which includes a front objective lens primary mirror, a front objective lens secondary mirror, a front objective lens three mirrors, a front objective lens folding mirror, and a front objective mirror surface, and the imaging of the target scene passes through in sequence.
  • the main mirror of the front objective lens, the secondary mirror of the front objective lens, the third mirror of the front objective lens, and the folding mirror of the front objective lens are finally transmitted to the optical fiber image transmission beam through the mirror surface of the front objective lens.
  • the Offner-type spectroscopic device includes a concave spherical reflector and a convex spherical grating.
  • the concave spherical reflector and the convex spherical grating are coaxially arranged. After the light incident from the curved slit is reflected by the spherical reflector, the light is incident as a convergent beam.
  • Spectral spectroscopy is performed on the convex spherical grating, and then the concave spherical reflection mirror images the optical fiber after the spectroscopy to a focal plane detector to complete the spectral imaging.
  • the Offner-type spectroscopic device is composed of a concave spherical reflector and a convex spherical grating coaxially;
  • the curved slit coincides with or is in the vicinity of the optimal imaging circular field of view of the Offner-type spectroscopic device, and the arc center of the curved slit is set on or near the optical axis of the Offner-type spectroscopic device
  • the convex spherical grating After the light incident from the curved slit is reflected by the spherical mirror, it is incident on the convex spherical grating in the form of a converging beam; after diffracting by the convex spherical grating, the spectral splitting is realized, and the condensing beam is changed into a diverging beam at the same time;
  • the concave spherical reflector images the split beam to the focal plane detector to realize spectral imaging.
  • the formed spectral image is in a curved shape, and the focal plane detector is not filled.
  • the focal plane detector has the spectral image position pixel gray value IS minus the non-spectral image position pixel gray mean IN, and corrects background noise and dark current. Noise to get denoised spectral data.
  • pixels on the focal plane detector of the imaging spectrometer that cannot receive spectral images. These pixels can be used to correct background noise and dark current noise to obtain denoised hyperspectral data and improve data fidelity.
  • the incident end face of the optical fiber image transmission beam is arranged in a straight line, which is overlapped with the image formed by the front objective lens, and the outgoing end face of the optical fiber image transmission beam is arranged in an arc shape, which is coincident with the bending slit.
  • the radius of the concave spherical mirror of the Offner type beam splitter is R 1
  • the curvature radius of the convex spherical grating is R 2
  • the radius of the optimal circular field of view of the Offner type beam splitter is r
  • the numerical aperture of the front objective lens and the Offner type spectroscopic device is the same, and the numerical aperture of the optical fiber image transmission bundle is greater than or equal to the numerical aperture of the front objective lens; the optical fiber core diameter of the optical fiber image transmission bundle is in the range of 5 to 50 ⁇ m.
  • the ratio of the curvature radius of the concave spherical reflector to the convex spherical grating is 1.9:1 ⁇ 2.2:1, and the distance between the centers of the spheres is less than 0.1R 2 .
  • the shape of the spectral line formed on the focal plane detector is consistent with the shape of the curved slit, and is transformed into a linear spectral line corresponding to the ground detection pixels through a mapping transformation algorithm.
  • the mapping relationship is the equation where the circular arc spectral line is located. Transform to the equation of the straight spectral line where k is a constant.
  • FIG. 2 it is an axial view of the optical path of the Offner-type spectroscopic device in the curved slit imaging spectrometer of the present invention.
  • the concave spherical mirror and the convex spherical grating are coaxial
  • the axis is the optical axis of the Offner-type spectroscopic device
  • the arc center of the curved slit is near the optical axis
  • the vicinity of the optical axis refers to the optical axis in the
  • the optical axis is within a radius of 2-5 cm from the center of the circle.
  • the optimal imaging circular field of view in the object plane of the Offner type spectroscopic device the position of the curved slit in the object plane coincides with the optimal imaging circular field of view.
  • the imaging magnification ratio of the Offner-type spectroscopic device is 1:1, and the curved spectral line image formed on the focal plane detector is consistent with the shape of the curved slit.
  • a straight spectral line image is obtained, and the curved spectral line
  • the spectral line arc length of the image is the same as the spectral line length of the straight spectral line image, and the spectral lines of different wavelengths in the curved spectral line image are the same as the spectral lines of different wavelengths in the straight spectral line image, and the spectral lines of different wavelengths in the straight spectral line image are mutually parallel.
  • the relevant indicators of the provided curved slit imaging spectrometer are:
  • Slit length 100mm
  • Image plane dispersion width 6mm;
  • each optical element in this embodiment The specific optical parameters of each optical element in this embodiment are shown in Table 1.
  • surface type represents the name of each optical surface
  • curvature radius represents the radius of curvature of each optical surface
  • distance represents the vertex of the optical surface to the next The lateral distance of the apex of the optical surface.
  • the density of convex spherical grating lines is 89Lp/mm; the fiber core diameter is 20 ⁇ m, one fiber corresponds to one detector pixel, a total of 5000 fibers are used, and the fiber length is 20cm; the arc radius of the bending slit is 53.8mm, The arc length is 100mm, the off-axis amount of the curved slit is 55.2mm; the off-axis amount of the focal plane detector is 36.5mm;
  • FIG. 5 it is the modulation transfer function curve of a curved slit imaging spectrometer provided in this embodiment.
  • the modulation transfer function of the spectroscopic device at the detector Nyquist frequency of 25Lp/mm is greater than 0.91, which is very close to the diffraction limit. , the imaging quality is excellent, and the performance of the transfer function at different fields of view is consistent, indicating the consistency of the spectral response function.
  • FIG. 6 it is a schematic diagram of a spectral image formed by a focal plane detector of a curved slit imaging spectrometer provided in this embodiment and a range of pixels used to correct background noise and dark current noise.
  • the gray value IS of each pixel in the spectral image position is compared with the average gray value I N of the pixel at the position without spectral image, and the background noise and dark current noise are removed to obtain the denoised spectral data IS -IN .

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Abstract

一种弯曲狭缝成像光谱仪，涉及光谱成像技术领域。通过光纤传像束将前置物镜的直像面传递至弯曲狭缝，不需要前置物镜成弯曲像面与分光装置直接对接，降低了系统复杂程度，同时前置物镜与分光装置结构简单；通过圆弧或近圆弧形的弯曲狭缝，与Offner型分光装置最佳成像圆匹配，实现超长狭缝，沿弧线方向的狭缝比经典Offner型分光装置的直狭缝增长5～10倍，在体积紧凑的情况下狭缝长度能够突破100mm；同时在不同视场具有一致的光谱响应函数，成像质量优，适用于宽幅、高空间分辨率、中高光谱分辨率的高光谱遥感。

Description

弯曲狭缝成像光谱仪 技术领域
本发明涉及光谱成像技术领域，涉及一种弯曲狭缝成像光谱仪。
背景技术
上世纪80年代，随着对地观测应用的发展需要，成像光谱技术兴起。它是综合了空间成像技术和光谱成像技术的新兴领域，极大地拓宽了人们在航天遥感领域、农林资源探测、矿物资源与地质勘探、军事侦测、生物医疗等方面的应用范围。
成像光谱仪由前置物镜和分光装置构成，可分为色散型、干涉型等。传统的色散型成像光谱仪由前置物镜直接成像至狭缝，狭缝是分光装置物面，经过狭缝的光线再由分光装置分光成像。现有结构在直狭缝长度较短时能够很好的满足仪器指标要求，但是对于需满足宽幅、高空间分辨率要求的长狭缝系统而言，存在较大像差且光谱图像易失真。
为实现宽幅，通常采用视场拼接的方式，将长狭缝系统分为多个中短狭缝系统拼接而成，但拼接后的系统结构复杂，体积庞大。而星载成像光谱仪一般对仪器的重量、体积等几何物理量要求较高，过大的体积和重量导致仪器的生产、制造、发射等成本急剧增加。
现有的成像光谱仪中，多为中短狭缝系统，均采用直狭缝，狭缝长度都在30mm以内，狭缝长度的增加会使光学系统像差迅速增大，仅凭单台分光系统难以满足宽幅和高空间分辨率的应用需求，狭缝长度超过100mm的成像光谱仪鲜有报道。上世纪80年代末，Wynne提出在一比一成像的Offner中继系统中引 入弯月形透镜，可补偿长狭缝时的球差和像散，实现较好的成像质量。在开启对Offner型成像光谱仪的研究之后，不少学者又进一步发展和完善了Offner-Wynne型成像光谱仪的理论，它能够获得比经典Offner分光装置长的狭缝。但弯月镜的引入带来的新问题是，在弯月镜表面制作光栅成本高；弯月镜表面入射角大，会使成像光谱仪产生偏振。因此亟需提出一种结构简单、体积紧凑、狭缝长的成像光谱仪以满足航天遥感应用中对宽幅、高空间分辨率的需求。
发明内容
本发明要解决的技术问题是提供一种同时具备狭缝长、结构简单、体积紧凑、成像质量优等特点的弯曲狭缝成像光谱仪光学系统，适用于宽幅、高空间分辨率、中高光谱分辨率的高光谱遥感。
为了解决上述技术问题，本发明解决其技术问题所采用的技术方案是：
一种弯曲狭缝成像光谱仪，包括前置物镜、光纤传像束、弯曲狭缝、Offner型分光装置、焦平面探测器；
前置物镜对目标场景成像，光纤传像束将前置物镜所成直线形像传递至弯曲狭缝，所述弯曲狭缝形状为圆弧或近圆弧形，光线经弯曲狭缝进入Offner型分光装置，由Offner型分光装置分光成像至焦平面探测器上。
优选的，所述前置物镜为透射式物镜、反射式物镜或折反式物镜。
优选的，所述Offner型分光装置包括凹球面反射镜和凸球面光栅，所述凹球面反射镜和凸球面光栅同轴设置，从弯曲狭缝入射的光线经球面反射镜反射后，光线以会聚光束入射到所述凸球面光栅上进行光谱分光，再由所述凹球面反射镜将分光后的光纤成像至焦平面探测器完成光谱成像。
优选的，所述光纤传像束入射端面排列为直线形，与前置物镜所成像重合， 所述光纤传像束出射端面排列为圆弧形，与弯曲狭缝重合。
优选的，所述弯曲狭缝在与Offner型分光装置的最佳成像圆视场重合或在其附近，所述弯曲狭缝的圆弧圆心设置在所述Offner型分光装置的光轴上或光轴附近。
优选的，当Offner型分光装置凹球面反射镜半径为R 1，凸球面光栅曲率半径为R 2，Offner型分光装置最佳圆视场半径为r，
Figure PCTCN2020137813-appb-000001
所述弯曲狭缝为半径为r s的圆弧或为处于半径为r 1和r 2两段圆弧之间的近圆弧曲线，其中r 1＝0.8r，r 2＝1.2r，r 1≤r s≤r 2。
优选的，所述前置物镜和Offner型分光装置的数值孔径相同，光纤传像束的数值孔径大于等于前置物镜的数值孔径；所述光纤传像束的光纤纤芯直径范围为5～50μm。
优选的，所述凹球面反射镜与凸球面光栅的曲率半径之比为1.9:1～2.2:1，球心间距小于0.1R 2。
优选的，在焦平面探测器上所成谱线形状与弯曲狭缝形状一致，通过映射变换算法将其变换为与地面探测像素对应的直线形谱线，映射关系为将圆弧形谱线所在方程
Figure PCTCN2020137813-appb-000002
变换至直谱线所在方程
Figure PCTCN2020137813-appb-000003
其中，k为常数。
本发明的有益效果：
本发明通过光纤传像束将前置物镜的直像面传递至弯曲狭缝，不需要前置物镜成弯曲像面与分光装置直接对接，降低了系统复杂程度，同时前置物镜与分光装置结构简单；通过圆弧或近圆弧形的弯曲狭缝，与Offner型分光装置最 佳成像圆匹配，实现超长狭缝，沿弧线方向的狭缝可比经典Offner型分光装置的直狭缝增长5～10倍，在体积紧凑的情况下狭缝长度能够突破100mm；同时在不同视场具有一致的光谱响应函数，成像质量优，适用于宽幅、高空间分辨率、中高光谱分辨率的高光谱遥感。
附图说明
图1是本发明的弯曲狭缝成像光谱仪光路三维视图；
图2是本发明的弯曲狭缝成像光谱仪中Offner型分光装置的光路轴向视图；
图3是本发明的弯曲狭缝成像光谱仪中Offner型分光装置1/4物面内的最佳成像圆视场；
图4是本发明的弯曲狭缝成像光谱仪焦平面探测器上所成的弯曲谱线图像与映射变换后的直谱线图像；
图5是本发明实施例提供的一种弯曲狭缝成像光谱仪的调制传递函数曲线。
图6是本发明实施例提供的一种弯曲狭缝成像光谱仪的焦平面探测器所成光谱像与用于校正背景噪声和暗电流噪声的像元范围示意图。
图中标号说明：1、前置物镜、1.1、前置物镜主镜、1.2、前置物镜次镜、1.3、前置物镜三镜、1.4、前置物镜折叠镜、1.5、前置物镜像面；2、光纤传像束；3、弯曲狭缝；4、Offner型分光装置；4.1、凹球面反射镜4.2、凸球面光栅；5、焦平面探测器；6、弯曲谱线图像；7、直谱线图像；
具体实施方式
下面结合附图和具体实施例对本发明作进一步说明，以使本领域的技术人员可以更好地理解本发明并能予以实施，但所举实施例不作为对本发明的限定。
参照图1-6所示，一种弯曲狭缝成像光谱仪，包括前置物镜、光纤传像束、弯曲狭缝、Offner型分光装置、焦平面探测器；
前置物镜对目标场景成像，光纤传像束将前置物镜所成直线形像传递至弯曲狭缝，所述弯曲狭缝形状为圆弧或近圆弧形，光线经弯曲狭缝进入Offner型分光装置，由Offner型分光装置分光成像至焦平面探测器上。
本发明通过光纤传像束将前置物镜的直像面传递至弯曲狭缝，不需要前置物镜成弯曲像面与分光装置直接对接，降低了系统复杂程度，同时前置物镜与分光装置结构简单；通过圆弧或近圆弧形的弯曲狭缝，与Offner型分光装置最佳成像圆匹配，实现超长狭缝，沿弧线方向的狭缝可比经典Offner型分光装置的直狭缝增长5～10倍，在体积紧凑的情况下狭缝长度能够突破100mm；同时在不同视场具有一致的光谱响应函数，成像质量优，适用于宽幅、高空间分辨率、中高光谱分辨率的高光谱遥感。
本发明满足宽幅、高空间分辨率星载成像光谱仪的需求，突破现有成像光谱仪中直狭缝长度短的局限。
其中，前置物镜所成像长度与弯曲狭缝弧长相同。
所述前置物镜为透射式物镜、反射式物镜或折反式物镜。
所述前置物镜为离轴三反望远物镜，其包括前置物镜主镜、前置物镜次镜、前置物镜三镜、前置物镜折叠镜、前置物镜像面，目标场景成像依次经过前置物镜主镜、前置物镜次镜、前置物镜三镜、前置物镜折叠镜，最后经过前置物镜像面传递至光纤传像束。
所述Offner型分光装置包括凹球面反射镜和凸球面光栅，所述凹球面反射镜和凸球面光栅同轴设置，从弯曲狭缝入射的光线经球面反射镜反射后，光线以会聚光束入射到所述凸球面光栅上进行光谱分光，再由所述凹球面反射镜将 分光后的光纤成像至焦平面探测器完成光谱成像。
具体的，所述Offner型分光装置由一块凹球面反射镜和一块凸球面光栅同轴构成；
所述弯曲狭缝在与Offner型分光装置的最佳成像圆视场重合或在其附近，所述弯曲狭缝的圆弧圆心设置在所述Offner型分光装置的光轴上或光轴附近
从弯曲狭缝入射的光线经球面反射镜反射后，以会聚光束的形式入射到所述凸球面光栅上；经过凸球面光栅衍射后实现光谱分光，同时将会聚光束变为发散光束；最后由所述凹球面反射镜将分光后的光束成像至焦平面探测器，实现光谱成像。
所成光谱像为弯曲形状，未充满焦平面探测器，焦平面探测器上有光谱像位置像元灰度值I S减去无光谱像位置像元灰度均值IN，校正背景噪声和暗电流噪声，用以得到降噪的光谱数据。
该成像光谱仪焦平面探测器上存在接收不到光谱像的像元，可利用这部分像元校正背景噪声和暗电流噪声，获得降噪处理的高光谱数据，提高数据保真度。
所述光纤传像束入射端面排列为直线形，与前置物镜所成像重合，所述光纤传像束出射端面排列为圆弧形，与弯曲狭缝重合。
当Offner型分光装置凹球面反射镜半径为R 1，凸球面光栅曲率半径为R 2，Offner型分光装置最佳圆视场半径为r，
Figure PCTCN2020137813-appb-000004
所述弯曲狭缝为半径为r s的圆弧或为处于半径为r 1和r 2两段圆弧之间的近圆弧曲线，其中r 1＝0.8r，r 2＝1.2r，r 1≤r s≤r 2。
所述前置物镜和Offner型分光装置的数值孔径相同，光纤传像束的数值孔 径大于等于前置物镜的数值孔径；所述光纤传像束的光纤纤芯直径范围为5～50μm。
所述凹球面反射镜与凸球面光栅的曲率半径之比为1.9:1～2.2:1，球心间距小于0.1R 2。
在焦平面探测器上所成谱线形状与弯曲狭缝形状一致，通过映射变换算法将其变换为与地面探测像素对应的直线形谱线，映射关系为将圆弧形谱线所在方程
Figure PCTCN2020137813-appb-000005
变换至直谱线所在方程
Figure PCTCN2020137813-appb-000006
其中，k为常数。
参阅图2，是本发明的弯曲狭缝成像光谱仪中Offner型分光装置的光路轴向视图。由图可以看出，凹球面反射镜与凸球面光栅同轴，轴线即为Offner型分光装置的光轴，弯曲狭缝的圆弧圆心在该光轴附近，该光轴的附近是指在以光轴为圆心2-5厘米半径范围内。
参阅图3，Offner型分光装置物面内的最佳成像圆视场，弯曲狭缝在物面内的位置与该最佳成像圆视场重合。
参阅图4，Offner型分光装置的成像放大率为1:1，在焦平面探测器上所成弯曲谱线图像与弯曲狭缝的形状一致，进行映射变换后获得直谱线图像，弯曲谱线图像的谱线弧长与直谱线图像的谱线长度相同，弯曲谱线图像中不同波长谱线间隔与直谱线图像中不同波长谱线间隔相同，直谱线图像中不同波长谱线相互平行。
在一个实施例中，参考图1，所提供的弯曲狭缝成像光谱仪相关指标为：
光谱范围：400～1000nm；
系统F数：3；
视场角：10.22°；
焦距：560mm；
狭缝长度：100mm；
光谱分辨率：2nm；
像平面色散宽度：6mm；
探测器像元大小：20μm×20μm；
探测器规模：2560×1280。
该实施例中各光学元件的具体光学参数参见表1，表中“面型”表示各光学面名称；“曲率半径”表示各光学表面曲率半径大小；“距离”表示该光学面顶点到下一个光学面顶点的横向距离。其中凸球面光栅刻线密度为89Lp/mm；光纤纤芯直径为20μm，1根光纤对应一个探测器像元，共采用5000根光纤，光纤长度为20cm；弯曲狭缝弧形半径为53.8mm，弧长为100mm，弯曲狭缝离轴量为55.2mm；焦平面探测器离轴量为36.5mm；。
表1弯曲狭缝成像光谱仪光学参数
Figure PCTCN2020137813-appb-000007
Figure PCTCN2020137813-appb-000008
参见图5，它是本实施例供的一种弯曲狭缝成像光谱仪的调制传递函数曲线，该分光装置在探测器奈奎斯特频率25Lp/mm处的调制传递函数大于0.91，十分接近衍射极限，成像质量优良，且不同视场处传函表现一致，表明光谱响应函数的一致性。
参考图6，它是本实施例供的一种弯曲狭缝成像光谱仪的焦平面探测器所成光谱像与用于校正背景噪声和暗电流噪声的像元范围示意图。光谱像位置的每个像元灰度值I S与无光谱像位置的像元灰度均值I N作差，去除背景噪声和暗电流噪声，获得降噪的光谱数据I S-I N。
以上所述实施例仅是为充分说明本发明而所举的较佳的实施例，本发明的保护范围不限于此。本技术领域的技术人员在本发明基础上所作的等同替代或变换，均在本发明的保护范围之内。本发明的保护范围以权利要求书为准。

Claims (9)

  1. 一种弯曲狭缝成像光谱仪，其特征在于，包括前置物镜、光纤传像束、弯曲狭缝、Offner型分光装置、焦平面探测器；
    前置物镜对目标场景成像，光纤传像束将前置物镜所成直线形像传递至弯曲狭缝，所述弯曲狭缝形状为圆弧或近圆弧形，光线经弯曲狭缝进入Offner型分光装置，由Offner型分光装置分光成像至焦平面探测器上。
  2. 如权利要求1所述的弯曲狭缝成像光谱仪，其特征在于，所述前置物镜为透射式物镜、反射式物镜或折反式物镜。
  3. 如权利要求1所述的弯曲狭缝成像光谱仪，其特征在于，所述Offner型分光装置包括凹球面反射镜和凸球面光栅，所述凹球面反射镜和凸球面光栅同轴设置，从弯曲狭缝入射的光线经球面反射镜反射后，光线以会聚光束入射到所述凸球面光栅上进行光谱分光，再由所述凹球面反射镜将分光后的光纤成像至焦平面探测器完成光谱成像。
  4. 如权利要求1所述的弯曲狭缝成像光谱仪，其特征在于，所述光纤传像束入射端面排列为直线形，与前置物镜所成像重合，所述光纤传像束出射端面排列为圆弧形，与弯曲狭缝重合。
  5. 如权利要求4所述的弯曲狭缝成像光谱仪，其特征在于，所述弯曲狭缝在与Offner型分光装置的最佳成像圆视场重合或在其附近，所述弯曲狭缝的圆弧圆心设置在所述Offner型分光装置的光轴上或光轴附近。
  6. 如权利要求4所述的弯曲狭缝成像光谱仪，其特征在于，当Offner型分光装置凹球面反射镜半径为R 1，凸球面光栅曲率半径为R 2，Offner型分光装置最佳圆视场半径为r，
    Figure PCTCN2020137813-appb-100001
    所述弯曲狭缝为半径为r s的圆弧或为处于半径为r 1和r 2两段圆弧之间的近圆弧曲线，其中r 1＝0.8r，r 2＝1.2r，r 1≤r s≤r 2。
  7. 如权利要求1所述的弯曲狭缝成像光谱仪，其特征在于，所述前置物镜和Offner型分光装置的数值孔径相同，光纤传像束的数值孔径大于等于前置物镜的数值孔径；所述光纤传像束的光纤纤芯直径范围为5～50μm。
  8. 如权利要求7所述的弯曲狭缝成像光谱仪，其特征在于，所述凹球面反射镜与凸球面光栅的曲率半径之比为1.9:1～2.2:1，球心间距小于0.1R 2。
  9. 如权利要求7所述的弯曲狭缝成像光谱仪，其特征在于，在焦平面探测器上所成谱线形状与弯曲狭缝形状一致，通过映射变换算法将其变换为与地面探测像素对应的直线形谱线，映射关系为将圆弧形谱线所在方程
    Figure PCTCN2020137813-appb-100002
    变换至直谱线所在方程
    Figure PCTCN2020137813-appb-100003
    其中，k为常数。
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