Compact imaging spectrometer based on starlight occultation technology

Abstract

The invention discloses a compact imaging spectrometer based on a 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 a light 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 invention, the absorption spectrum of oxygen molecules in the atmosphere can be obtained by utilizing a starlight occultation technology, the relatively accurate oxygen density can be measured under the high spectral resolution of 0.1 nm, and environmental information such as the atmospheric temperature and the atmospheric density can be indirectly obtained.

Description

Technical Field

[0001] The invention 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 obtain long-term and stable atmospheric composition data, which is crucial for monitoring the atmospheric environment and predicting global changes. At present, the most widely used atmospheric remote sensing method is mainly space-based remote sensing, and the remote sensing modes are mainly nadir, limb, and occultation / moon observation. However, these satellite-borne atmospheric detection methods have some shortcomings. Occultation observation can make up for these shortcomings: compared with occultation / moon technology, occultation observation has stable signals in the entire spectral band; because it is a point source, the measurement accuracy is high; compared with occultation, which can only be detected during sunrise and sunset, occultation events occur more frequently and can be observed all day long. Compared with nadir detection, occultation detection has higher vertical resolution and detection accuracy. Under normal circumstances, the vertical resolution is 2-3km and the detection height is 10-150km. Due to the observation geometry, its observation path is 60-70 times that of nadir observation and twice that of limb observation, which can greatly improve the detectability of trace gases. Therefore, starlight occultation detection technology has irreplaceable potential advantages in studying the content of atmospheric components and predicting climate change.

[0003] Imaging spectrometer is a new generation of optical remote sensing instrument developed on the basis of multi-spectral remote sensing imaging technology since the 1980s. It can obtain super-multi-spectral images of targets with high spectral resolution and is being used more and more widely in atmospheric, oceanic and land observations. China Patent Publication No. "CN117213630A", the patent name is "A Panoramic Occultation Imaging Spectrometer", which discloses a panoramic occultation imaging spectrometer, including an annular panoramic lens, a collimating lens group, a prism, an imaging lens group and a detector target surface: the first refractive surface of the annular panoramic lens refracts the 360° annular field of view into the interior of the panoramic annular lens. The problems are: 1. The spectral resolution is low, only 0.75nm, and it is not easy to measure relatively accurate oxygen density. 2. Due to the limitations of its own structure and principle, it is difficult to achieve a large effective receiving area, resulting in a low signal-to-noise ratio of the system. In the case of weak starlight signals, it is difficult to achieve high signal-to-noise ratio application requirements. Summary of the invention

[0004] In order to solve the problems of low spectral resolution and low signal-to-noise ratio in the prior art, the present invention provides a compact imaging spectrometer based on starlight occultation technology, which can measure the spectrum of starlight at high spectral resolution and high signal-to-noise ratio, so as to more accurately detect and obtain planetary atmospheric parameters such as oxygen density and temperature. And it has a compact structure and is suitable for satellite remote sensing platform applications.

[0005] The present invention adopts the following technical solution:

[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 which are sequentially arranged 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 sequentially coaxially arranged; the spectral imaging system comprises a first plane reflector, a collimator, a plane diffraction grating, a second plane reflector and a focusing mirror; an incident light beam at the slit reaches the collimator through the first plane reflector, a parallel light beam emitted from the collimator 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, reaches the focusing mirror, and a focused light beam emitted from the focusing mirror passes through the second plane reflector again to be 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, 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, with a diameter of 96 mm, and a distance from the collimator along the optical axis of -125 mm. The distance of the plane diffraction grating along the optical axis is -119.097mm, and the distance from the second plane reflector along the optical axis is -160mm; 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 -10mm in the y direction, tilted -25° around the x-axis, has a diameter of 90mm, is 159.176mm away from the focusing mirror along the optical axis, and is 139.507mm away from the CCD detector along the optical axis; the focusing mirror is tilted -1.89° around the x-axis; the CCD detector is eccentric 6.626mm 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 focal length is negative, and whose surface shape is described by the radius of curvature and the cone coefficient. The radius of curvature is -500.002 mm, with no eccentricity, no tilt, a diameter of 240 mm, and a central opening diameter of 20 mm.

[0009] Furthermore, the secondary reflector is a hyperbolic reflector with negative optical power. The surface shape is described by a curvature radius and a cone coefficient. The curvature radius is -121 mm, the cone 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 radius of curvature, the radius of curvature is 454.892 mm, and there is 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 working band is 754nm-774nm.

[0013] Furthermore, the focusing mirror is a spherical reflector, the surface shape of which is described by a radius of curvature, the radius of curvature 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 present invention are:

[0016] The spectrometer disclosed in the present invention can obtain the absorption spectrum of oxygen molecules in the atmosphere by using the starlight occultation technology, can measure relatively accurate oxygen density at a high spectral resolution of 0.1nm, and indirectly obtain environmental information such as atmospheric temperature and atmospheric density. The design of narrow slit and high line density grating has obvious advantages over the panoramic occultation imaging spectrometer disclosed in CN117213630A: the present invention can obtain a high spectral resolution of 0.1nm, and it is easier to measure relatively accurate oxygen density. The spectral resolution of the panoramic occultation imaging spectrometer can only reach 0.75nm, and the present invention is a great improvement compared with it.

[0017] The spectrometer disclosed in the present invention uses 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 plane diffraction grating, can achieve high signal-to-noise ratio measurements. However, due to the limitations of its own structure and principle, it is difficult for the panoramic occultation imaging spectrometer to achieve a large effective receiving area, and it is impossible to achieve high signal-to-noise ratio measurements when the starlight signal is weak.

[0018] The spectrometer disclosed in the present invention adopts two plane reflectors to fold the optical 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 present invention;

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

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

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

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

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

[0025] Figure 7 It is the MTF diagram of the spectrometer disclosed in the present invention at the full field of view at a wavelength of 774nm.

[0026] Figure 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 solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with 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] Embodiment 1, this embodiment discloses a compact imaging spectrometer based on star occultation technology, such as Figure 1 As shown, it includes a front optical system, a slit 3, a spectral imaging system and a CCD detector 9 arranged in sequence along the optical path; the front optical system is a classic Cassegrain telescope system, including a primary reflector 1 and a secondary reflector 2, which are used to provide a certain field of view and image distant starlight signals and their upper and lower background bands at the slit. The slit is placed perpendicular to the horizontal direction, and the secondary reflector, the primary reflector and the slit are coaxially arranged in sequence; the spectral imaging system includes a first plane reflector 4, a collimator 5, a plane diffraction grating 6, a second plane reflector 7, and a focusing mirror 8, which are used to split the starlight signals at the slit and the upper and lower background bands.

[0029] The incident light beam at the slit reaches the collimator through the first plane reflector. The parallel light beam emitted from the collimator reaches the plane diffraction grating through the first plane reflector again. After being dispersed by the plane diffraction grating, the light beam is folded through the first and second plane reflectors in sequence and reaches the focusing mirror. The focused light beam emitted from the focusing mirror passes through the second plane reflector 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 through the first plane reflector; the light beams from the plane diffraction grating to the focusing mirror, and from the focusing mirror to the CCD detector are all folded through the second plane reflector, thereby realizing the miniaturization of the system.

[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, with a diameter of 96 mm, a distance from the collimator along the optical axis by -125 mm, and a distance from the collimator along the optical axis by 10 mm. The distance from the plane diffraction grating along the optical axis is -119.097mm, and the distance from the second plane reflector along the optical axis is -160mm; 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 -10mm in the y direction, tilted -25° around the x-axis, has a diameter of 90mm, is 159.176mm away from the focusing mirror along the optical axis, and is 139.507mm away from the CCD detector along the optical axis; the focusing mirror is tilted -1.89° around the x-axis; the CCD detector is eccentric 6.626mm in the y direction and tilted -52° around the x-axis.

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

[0032] The secondary reflector is a hyperbolic reflector with negative optical power. The surface shape is described by the radius of curvature and the cone coefficient. The radius of curvature is -121 mm, the cone 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 the 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 working band is 754nm-774nm.

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

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

[0038] The basic principle of the spectrometer disclosed in the present invention is that starlight is reflected by the primary reflector of the front optical system to the secondary reflector, and then focused at the slit, so that the distant starlight signal and its upper and lower backgrounds are imaged at the slit at one time. The light incident from the slit is folded by the first plane reflector and reaches the collimator, and the collimated light beam is folded again by the first plane reflector to reach the plane diffraction grating, and light beams of different wavelengths are reflected from the grating back to the first plane reflector at different diffraction angles. Then it passes through the second plane reflector and the focusing mirror in sequence, and finally the spectral image of the starlight and its upper and lower background bands is obtained on the CCD detector.

[0039] The working band of the spectrometer disclosed in the present invention 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, edge observation altitude is 40~90km; The volume of the whole system is 402×240×346mm 2 .

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

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

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

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

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

[0045] Figure 7 It is the MTF diagram of the spectrometer disclosed in the present invention at the full field of view at a wavelength of 774nm, and 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 full field of view meets the index requirements.

Claims

1. A compact imaging spectrometer based on star occultation technology, characterized by: The invention comprises a front optical system, a slit, a spectral imaging system and a CCD detector which are arranged in sequence along the 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 arranged coaxially in sequence; the spectral imaging system comprises a first plane reflector, a collimator, a plane diffraction grating, a second plane reflector and a focusing mirror; the incident light beam at the slit reaches the collimator through the first plane reflector, the parallel light beam emitted by the collimator 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 to be 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 eccentric in the y direction by -38 mm, tilted by -25° around the x-axis, with a diameter of 96 mm, a distance from the collimator along the optical axis by -125 mm, and a distance from the plane The distance of the diffraction grating along the optical axis is -119.097mm, and the distance from the second plane reflector along the optical axis is -160mm; 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 -10mm in the y direction, tilted -25° around the x-axis, has a diameter of 90mm, is 159.176mm away from the focusing mirror along the optical axis, and is 139.507mm away from the CCD detector along the optical axis; the focusing mirror is tilted -1.89° around the x-axis; the CCD detector is eccentric 6.626mm 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, whose optical power is negative and whose surface shape is described by the radius of curvature and the cone coefficient. The radius of curvature is -500.002mm, with no eccentricity or tilt, a diameter of 240mm, and a central opening diameter of 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. The surface shape is described by the radius of curvature and the cone coefficient. The radius of curvature is -121 mm, the cone 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 the 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 working 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 radius of curvature, the radius of curvature 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.

Images