Compact imaging spectrometer based on starlight occultation technology

Abstract

The utility model discloses a compact imaging spectrometer based on starlight occultation technology. The compact imaging spectrometer comprises a front optical system, a slit, a spectral imaging system and a CCD detector which are sequentially arranged along an optical path. The front optical system comprises a primary reflector and a secondary reflector, the slit is arranged perpendicular to the horizontal direction, and the secondary reflector, the primary reflector and the slit are sequentially and coaxially arranged. According to the spectrograph disclosed by the utility model, the absorption spectrum of oxygen molecules in the atmosphere can be obtained by utilizing a starlight occultation technology, relatively accurate oxygen density can be measured under the high spectral resolution of 0.1 nm, and environmental information such as atmospheric temperature, atmospheric density and the like can be indirectly obtained.

Description

Technical Field

[0001] The utility model belongs to the technical field of optical detection, and in particular relates to a compact imaging spectrometer based on star occultation technology in this field. Background Art

[0002] Atmospheric remote sensing can provide long-term, stable atmospheric composition data, which is crucial for monitoring the atmospheric environment and predicting global change. Currently, the most widely used atmospheric remote sensing method is space-based, primarily in the nadir, limb, and occultation / lunar observation modes. However, these spaceborne atmospheric sounding methods have several limitations. Occultation observations can address these deficiencies. Compared to occultation / lunar techniques, occultation observations provide stable signals across the entire spectral band. Because they are point sources, they offer high measurement accuracy. Unlike occultation, which can only be detected during sunrise and sunset, occultation events occur more frequently, allowing for all-weather observations. Compared to nadir sounding, occultation soundings offer higher vertical resolution and detection accuracy, typically 2-3 km in vertical resolution and at detection altitudes of 10-150 km. Due to its observation geometry, its observation path is 60-70 times longer than that of nadir observations and twice that of limb observations, significantly improving the detectability of trace gases. Therefore, stellar occultation observations offer irreplaceable potential advantages for studying atmospheric composition and predicting climate change.

[0003] Imaging spectrometers are a new generation of optical remote sensing instruments developed since the 1980s based on multispectral remote sensing imaging technology. They can acquire images of targets in multiple spectral bands with high spectral resolution and are increasingly being used in atmospheric, oceanic, and terrestrial observations. Chinese Patent Publication No. CN117213630A, entitled "A Panoramic Occultation Imaging Spectrometer," discloses a panoramic occultation imaging spectrometer comprising an annular panoramic lens, a collimating lens assembly, a prism, an imaging lens assembly, and a detector target. The first refractive surface of the annular panoramic lens refracts a 360° circular field of view into the interior of the panoramic lens. However, these spectrometers suffer from the following issues: 1. The spectral resolution is low, at only 0.75 nm, making it difficult to measure oxygen density with relative accuracy. 2. Due to limitations in their structure and principle, achieving a large effective receiving area is difficult, resulting in a low signal-to-noise ratio (SNR). This makes it difficult to achieve high SNR requirements in applications where the starlight signal is weak. Summary of the Invention

[0004] To address the low spectral resolution and signal-to-noise ratio issues of existing technologies, this utility model provides a compact imaging spectrometer based on star occultation technology. This instrument can measure the spectrum of starlight at high spectral resolution and high signal-to-noise ratio, thereby more accurately detecting planetary atmospheric parameters such as oxygen density and temperature. Its compact structure makes it suitable for use on satellite remote sensing platforms.

[0005] The utility model adopts the following technical solutions:

[0006] A compact imaging spectrometer based on star occultation technology is improved in that it comprises a front optical system, a slit, a spectral imaging system and a CCD detector arranged in sequence along an optical path; the front optical system comprises a primary reflector and a secondary reflector, the slit is placed perpendicular to the horizontal direction, and the secondary reflector, the primary reflector and the slit are arranged coaxially in sequence; the spectral imaging system comprises a first plane reflector, a collimating mirror, a plane diffraction grating, a second plane reflector and a focusing mirror; an incident light beam at the slit reaches the collimating mirror via the first plane reflector, a parallel light beam emitted by the collimating mirror again passes through the first plane reflector to reach the plane diffraction grating, the light beam is dispersed by the plane diffraction grating, is folded by the first and second plane reflectors in sequence, and reaches the focusing mirror, the focused light beam emitted by the focusing mirror again passes through the second plane reflector and is finally imaged on the CCD detector.

[0007] Furthermore, a global rectangular coordinate system (x, y, z) is defined with the vertex of the primary reflector as the origin, where the positive direction of the z-axis is the optical axis direction of the spectrometer, the yz plane is the meridian plane of the spectrometer, and the x-axis is perpendicular to the yz plane; the distance between the primary reflector and the secondary reflector along the optical axis is -200 mm; the distance between the secondary reflector and the slit along the optical axis is 288.117 mm; the distance between the slit and the first plane reflector along the optical axis is 110 mm; the first plane reflector is eccentric -38 mm in the y direction, tilted -25° around the x-axis, has a diameter of 96 mm, and is -125 mm away from the collimator along the optical axis. The distance between the plane diffraction grating and the second plane reflector along the optical axis is -119.097 mm, and the distance between the plane diffraction grating and the second plane reflector along the optical axis is -160 mm; the collimator is tilted -45° around the x-axis; the plane diffraction grating is tilted 40.5° around the x-axis; the second plane reflector is eccentric -10 mm in the y direction, tilted -25° around the x-axis, has a diameter of 90 mm, is 159.176 mm from the focusing mirror along the optical axis, and is 139.507 mm from the CCD detector along the optical axis; the focusing mirror is tilted -1.89° around the x-axis; the CCD detector is eccentric 6.626 mm in the y direction and tilted -52° around the x-axis.

[0008] Furthermore, the main reflector is a parabolic reflector with a central opening, whose optical power is negative, and whose surface shape is described by the curvature radius and the cone coefficient. The curvature radius is -500.002mm, there is no eccentricity, no tilt, the diameter is 240mm, and the central opening diameter is 20mm.

[0009] Furthermore, the secondary reflector is a hyperbolic reflector with negative optical power. The surface shape is described by a curvature radius and a conic coefficient. The curvature radius is -121 mm, the conic coefficient is -2.016, and there is no eccentricity or tilt.

[0010] Furthermore, the slit size is 50 μm×250 μm.

[0011] Furthermore, the collimator is a spherical reflector, the surface shape of which is described by a curvature radius, which is 454.892 mm and has no eccentricity.

[0012] Furthermore, the line density of the plane diffraction grating is 1800lp / mm, the grating order is +1, the main light incident angle is 50.562°, the diffraction angle is -37.077°; there is no eccentricity, and the operating band is 754nm-774nm.

[0013] Furthermore, the focusing mirror is a spherical reflector, the surface shape of which is described by a curvature radius, the curvature radius is -597.12 mm, and there is no eccentricity.

[0014] Furthermore, the image formed on the CCD detector along the slit width direction is the spectral dimension, and along the slit length direction is the spatial dimension.

[0015] The beneficial effects of the utility model are:

[0016] The spectrometer disclosed in this utility model utilizes starlight occultation technology to obtain the absorption spectrum of oxygen molecules in the atmosphere. With a high spectral resolution of 0.1 nm, it can measure relatively accurate oxygen density and indirectly derive environmental information such as atmospheric temperature and density. Its narrow slit and high-line density grating design offers significant advantages over the panoramic occultation imaging spectrometer disclosed in CN117213630A: It can achieve a high spectral resolution of 0.1 nm, making it easier to measure relatively accurate oxygen density. This represents a significant improvement over the panoramic occultation imaging spectrometer, which only has a spectral resolution of 0.75 nm.

[0017] The spectrometer disclosed in the utility model has a coaxial telescope with a large entrance pupil diameter, small primary and secondary mirror obstruction, and an effective receiving area of ​​434cm 2 , used in conjunction with a high-diffraction-efficiency planar diffraction grating, it can achieve high signal-to-noise ratio measurements. However, due to the limitations of its own structure and principle, the panoramic occultation imaging spectrometer has difficulty in achieving a large effective receiving area, and cannot achieve high signal-to-noise ratio measurements when the starlight signal is weak.

[0018] The spectrometer disclosed in the utility model adopts two plane reflectors to fold the light path in the spectral imaging system, which can significantly reduce the volume of the instrument. The volume of the instrument is only 402×240×346mm. 2 , suitable for satellite remote sensing platform applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a structural schematic diagram of the spectrometer disclosed in the utility model;

[0020] Figure 2 This is a spot diagram of the spectrometer disclosed in the present utility model at the full field of view at a wavelength of 754nm;

[0021] Figure 3 This is a spot diagram of the spectrometer disclosed in the present utility model at the full field of view at a wavelength of 764nm;

[0022] Figure 4 This is a spot diagram of the spectrometer disclosed in the present utility model at the full field of view at a wavelength of 774nm;

[0023] Figure 5 This is the MTF diagram of the spectrometer disclosed in the present utility model at the full field of view at a wavelength of 754nm;

[0024] Figure 6 This is the MTF diagram of the spectrometer disclosed in the present utility model at the full field of view at a wavelength of 764nm;

[0025] Figure 7 This is the MTF diagram of the spectrometer disclosed in the utility model at the full field of view at a wavelength of 774nm.

[0026] Reference numerals: 1 - primary reflector, 2 - secondary reflector, 3 - slit, 4 - first plane reflector, 5 - collimating mirror, 6 - plane diffraction grating, 7 - second plane reflector, 8 - focusing mirror, 9 - CCD detector. DETAILED DESCRIPTION

[0027] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0028] Example 1, this embodiment discloses a compact imaging spectrometer based on star occultation technology, such as Figure 1 As shown, the telescope comprises a pre-optical system, a slit 3, a spectral imaging system, and a CCD detector 9, arranged sequentially along the optical path. The pre-optical system is a classic Cassegrain telescope system, comprising a primary reflector 1 and a secondary reflector 2, which provide a certain field of view and image distant starlight signals and their upper and lower background bands at the slit. The slit is positioned perpendicular to the horizontal direction, and the secondary reflector, primary reflector, and slit are arranged coaxially in sequence. The spectral imaging system comprises a first plane reflector 4, a collimating lens 5, a plane diffraction grating 6, a second plane reflector 7, and a focusing lens 8, which separate the starlight signals and upper and lower background bands at the slit.

[0029] The incident light beam at the slit passes through the first plane mirror to the collimator. The parallel light beam emitted by the collimator passes through the first plane mirror again to the plane diffraction grating. After being dispersed by the plane diffraction grating, the light beam is folded by the first and second plane mirrors in sequence before reaching the focusing mirror. The focused light beam emitted by the focusing mirror passes through the second plane mirror again and is finally imaged on the CCD detector. The light beams from the slit to the collimator, from the collimator to the plane diffraction grating, and from the plane diffraction grating to the focusing mirror are all folded by the first plane mirror; the light beams from the plane diffraction grating to the focusing mirror and from the focusing mirror to the CCD detector are all folded by the second plane mirror, thereby achieving system miniaturization.

[0030] In this embodiment, a global rectangular coordinate system (x, y, z) is defined with the vertex of the primary reflector as the origin, wherein the positive direction of the z-axis is the optical axis direction of the spectrometer, the yz plane is the meridian plane of the spectrometer, and the x-axis is perpendicular to the yz plane; the distance between the primary reflector and the secondary reflector along the optical axis is -200 mm; the distance between the secondary reflector and the slit along the optical axis is 288.117 mm; the distance between the slit and the first plane reflector along the optical axis is 110 mm; the first plane reflector is eccentric in the y direction by -38 mm, tilted by -25° around the x-axis, has a diameter of 96 mm, is -125 mm away from the collimator along the optical axis, and is 110 mm away from the collimator. The distance from the plane diffraction grating along the optical axis is -119.097 mm, and the distance from the second plane reflector along the optical axis is -160 mm; the collimator is tilted -45° around the x-axis; the plane diffraction grating is tilted 40.5° around the x-axis; the second plane reflector is eccentric -10 mm in the y direction, tilted -25° around the x-axis, has a diameter of 90 mm, is 159.176 mm from the focusing mirror along the optical axis, and is 139.507 mm from the CCD detector along the optical axis; the focusing mirror is tilted -1.89° around the x-axis; the CCD detector is eccentric 6.626 mm in the y direction and tilted -52° around the x-axis.

[0031] The main reflector is a parabolic reflector with a central opening. Its optical power is negative. The surface shape is described by the radius of curvature and the conic coefficient. The radius of curvature is -500.002mm, there is no eccentricity or tilt, the diameter is 240mm, and the diameter of the central opening is 20mm.

[0032] The secondary reflector is a hyperbolic reflector with negative optical power. Its surface shape is described by the curvature radius and the conic coefficient. The curvature radius is -121 mm, the conic coefficient is -2.016, and there is no eccentricity or tilt.

[0033] The slit size is 50 μm × 250 μm.

[0034] The collimator is a spherical reflector, and its surface shape is described by the radius of curvature, which is 454.892 mm and has no eccentricity.

[0035] The line density of the plane diffraction grating is 1800lp / mm, the grating order is +1, the main light incident angle is 50.562°, the diffraction angle is -37.077°; there is no eccentricity, and the operating band is 754nm-774nm.

[0036] The focusing mirror is a spherical reflector, the surface shape is described by the curvature radius, the curvature radius is -597.12mm, and there is no eccentricity.

[0037] The image on the CCD detector is the spectral dimension along the slit width and the spatial dimension along the slit length. The number of pixels in the CCD detector is selected based on the spectral range Δσ and the spectral resolution δσ.

[0038] The basic principle of the spectrometer disclosed in this utility model is that starlight is reflected by the primary reflector of the pre-optical system to the secondary reflector, where it is then focused at a slit, forming a single image of the distant starlight signal and its upper and lower backgrounds at the slit. Light incident from the slit is folded by a first plane reflector before reaching a collimator. The collimated beam is folded again by the first plane reflector and reaches a plane diffraction grating. Light beams of different wavelengths are reflected from the grating back to the first plane reflector at different diffraction angles. The light then passes through a second plane reflector and a focusing mirror, ultimately producing a spectral image of the starlight and its upper and lower background bands on a CCD detector.

[0039] The operating band of the spectrometer disclosed in the utility model is 754-774nm; the system F number is 7.08838, the entrance pupil diameter is 240mm, the field of view is 35μrad×175μrad; the detector pixel size is 13μm, and the equivalent pixel size after merging is 26μm 2 Spectral resolution is better than 0.1nm, limb observation altitude is 40-90km; the total system volume is 402×240×346mm 2 .

[0040] Figure 2 The spot diagram of the spectrometer disclosed in the present invention at a wavelength of 754 nm at the full field of view, wherein the maximum RMS radius of the full field of view is less than 13 μm;

[0041] Figure 3 It is a spot diagram of the spectrometer disclosed in the present invention at a wavelength of 764nm at the full field of view, and the maximum RMS radius of the full field of view is less than 14μm;

[0042] Figure 4 The spot diagram of the spectrometer disclosed in the present invention at a wavelength of 774 nm at the full field of view, wherein the maximum RMS radius of the full field of view is less than 17 μm;

[0043] Figure 5This is the MTF diagram of the spectrometer disclosed in the present invention at a wavelength of 754nm at the full field of view. The MTF value is better than 0.48 at 20lp / mm.

[0044] Figure 6 This is the MTF diagram of the spectrometer disclosed in the present invention at a wavelength of 764nm at the full field of view. The MTF value is better than 0.5 at 20lp / mm.

[0045] Figure 7 This is the MTF diagram of the spectrometer disclosed in the present invention at a wavelength of 774nm at the full field of view. The MTF value is better than 0.35 at 20lp / mm.

[0046] It can be seen that the imaging quality of the system in all bands of the entire field of view meets the index requirements.

Claims

1. A compact imaging spectrometer based on star occultation technology, characterized by: The optical system comprises a front optical system, a slit, a spectral imaging system and a CCD detector which are sequentially arranged along the optical path; the front optical system comprises a primary reflector and a secondary reflector, the slit is placed perpendicular to the horizontal direction, and the secondary reflector, the primary reflector and the slit are sequentially coaxially arranged; the spectral imaging system comprises a first plane reflector, a collimating mirror, a plane diffraction grating, a second plane reflector and a focusing mirror; the incident light beam at the slit reaches the collimating mirror via the first plane reflector, the parallel light beam emitted by the collimating mirror passes through the first plane reflector again to reach the plane diffraction grating, the light beam is dispersed by the plane diffraction grating, is folded by the first and second plane reflectors in sequence, and reaches the focusing mirror, the focused light beam emitted by the focusing mirror passes through the second plane reflector again and is finally imaged on the CCD detector.

2. The compact imaging spectrometer based on star occultation technology according to claim 1, characterized in that: With the vertex of the primary reflector as the origin, a global rectangular coordinate system (x, y, z) is defined, where the positive direction of the z-axis is the optical axis direction of the spectrometer, the yz plane is the meridian plane of the spectrometer, and the x-axis is perpendicular to the yz plane; the distance between the primary reflector and the secondary reflector along the optical axis is -200 mm; the distance between the secondary reflector and the slit along the optical axis is 288.117 mm; the distance between the slit and the first plane reflector along the optical axis is 110 mm; the first plane reflector is -38 mm eccentric in the y direction, tilted -25° around the x-axis, has a diameter of 96 mm, is -125 mm away from the collimator along the optical axis, and is 110 mm away from the plane reflector. The distance between the diffraction grating and the second plane reflector along the optical axis is -119.097 mm, and the distance between the diffraction grating and the second plane reflector along the optical axis is -160 mm; the collimator is tilted -45° around the x-axis; the plane diffraction grating is tilted 40.5° around the x-axis; the second plane reflector is eccentric -10 mm in the y direction, tilted -25° around the x-axis, has a diameter of 90 mm, is 159.176 mm from the focusing mirror along the optical axis, and is 139.507 mm from the CCD detector along the optical axis; the focusing mirror is tilted -1.89° around the x-axis; the CCD detector is eccentric 6.626 mm in the y direction and tilted -52° around the x-axis.

3. The compact imaging spectrometer based on star occultation technology according to claim 1, characterized in that: The main reflector is a parabolic reflector with a central opening. Its optical power is negative. The surface shape is described by the radius of curvature and the conic coefficient. The radius of curvature is -500.002mm, there is no eccentricity or tilt, the diameter is 240mm, and the diameter of the central opening is 20mm.

4. The compact imaging spectrometer based on star occultation technology according to claim 1, characterized in that: The secondary reflector is a hyperbolic reflector with negative optical power. Its surface shape is described by the curvature radius and the conic coefficient. The curvature radius is -121 mm, the conic coefficient is -2.016, and there is no eccentricity or tilt.

5. The compact imaging spectrometer based on star occultation technology according to claim 1, characterized in that: The slit size is 50 μm × 250 μm.

6. The compact imaging spectrometer based on star occultation technology according to claim 1, characterized in that: The collimator is a spherical reflector, and its surface shape is described by the radius of curvature, which is 454.892 mm and has no eccentricity.

7. The compact imaging spectrometer based on star occultation technology according to claim 1, characterized in that: The line density of the plane diffraction grating is 1800lp / mm, the grating order is +1, the main light incident angle is 50.562°, the diffraction angle is -37.077°; there is no eccentricity, and the operating band is 754nm-774nm.

8. The compact imaging spectrometer based on star occultation technology according to claim 1, characterized in that: The focusing mirror is a spherical reflector, the surface shape is described by the curvature radius, the curvature radius is -597.12mm, and there is no eccentricity.

9. The compact imaging spectrometer based on star occultation technology according to claim 1, characterized in that: The image on the CCD detector is the spectral dimension along the slit width direction and the spatial dimension along the slit length direction.

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