CN112683796A - Differential absorption spectrometer optical system based on geosynchronous orbit observation - Google Patents
Differential absorption spectrometer optical system based on geosynchronous orbit observation Download PDFInfo
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Abstract
The invention discloses a differential absorption spectrometer optical system based on geosynchronous orbit observation, which comprises a scanning mirror system, a front telescopic imaging system and an Offner spectral imaging system. The scanning mirror system comprises a scanning oscillating mirror; the front telescope imaging system comprises a primary mirror, a secondary mirror and a third reflector, wherein an aperture diaphragm is arranged at the front end of the secondary mirror; the Offner spectral imaging system comprises an incident slit, an optical filter, a depolarizer, a first concave reflector, a convex grating, a second concave reflector and an area array detector; the scanning pendulum mirror introduces the nadir information detected based on the geosynchronous orbit into the front telescopic imaging system through scanning and focuses the nadir information to the entrance slit. The spectral information of the detected target object is reflected to the first concave reflector by the Offner spectral imaging system after filtering, depolarization and turning, then is split to the second concave reflector by the convex grating, and finally is focused on the area array detector, so that the detection of high spectrum and spatial resolution is completed.
Description
Technical Field
The invention belongs to the field of an optical measurement method,specifically, scattering spectrum observed at the bottom of the sky is acquired through high-resolution spectral imaging based on geosynchronous orbit, and atmospheric trace gas components such as NO in observed area are inverted2、SO2、O3Etc. vertical column concentration distribution of the species. The optical system is mainly applied to atmospheric trace gas detection based on a geosynchronous orbit satellite platform in the aerospace field, and particularly comprises a scanning mirror system, a front telescopic imaging system and an Offner spectral imaging system.
Background
The root of the influence on the atmospheric environment is the emission of pollutants, and the weather change process plays an important role in the evolution of the pollution process. Accurate air quality prediction relies on the accuracy of weather forecasts and accurate quantitative monitoring of the spatial and temporal distribution of pollutants. The problem that exists in the monitoring at present is that the main means of monitoring the pollutant is conventional foundation observation or foundation telemetering, and the requirements of air quality prediction and understanding of the cross-regional pollutant conveying process cannot be met. The solar synchronous orbit satellite can monitor the distribution and the change of global pollutants, the space coverage is enlarged, but the requirements of forecasting and real-time monitoring cannot be met by the observation frequency of 2 times at most every day. The differential absorption spectrometer based on the geosynchronous orbit can realize the observation frequency of once per hour, and is mainly used for detecting ozone and aerosol precursor SO2And NO2And the like, and simultaneously detecting optical parameters such as optical thickness, absorptive aerosol index, single scattering albedo and particle size parameters of the aerosol. The differential absorption spectrometer based on the geosynchronous orbit can partially solve the problems of insufficient data observation frequency and information quantity in the current environmental monitoring and forecasting. At present, the satellite-borne load applied to atmospheric correlation parameter inversion in China is mainly on a wind and cloud series satellite, trace gas satellite-borne monitoring is just started by utilizing an ultraviolet-visible light waveband, and no satellite-borne instrument can simultaneously monitor various polluted gases in a troposphere.
Disclosure of Invention
The technical problem to be solved by the invention is as follows: the optical system of the differential absorption spectrometer based on geosynchronous orbit observation is provided, and a differential absorption spectrum technology, an off-axis three-mirror telescopic imaging technology and an Offner spectral imaging technology are combined. The scanning mirror system and the front telescope imaging system are combined, an optical system of a differential absorption spectrometer is formed by the slit and the Offner imaging spectrometer, the detection technology of wide spectrum, high spectrum and spatial resolution based on the geosynchronous orbit is realized, and the problems of low spatial resolution, weak ultraviolet spectrum information signal, high-precision sweep technology and the like based on geosynchronous orbit observation are solved.
The technical scheme adopted by the invention for solving the technical problems is as follows: a differential absorption spectrometer optical system based on geosynchronous orbit observation comprises:
the optical system comprises a scanning mirror system, a front telescopic imaging system and an Offner spectral imaging system;
the scanning mirror system comprises a window (1) and a swinging mirror (2); detecting information of a celestial object and a bottom target object based on a geosynchronous orbit, introducing spectral information of the terrestrial object with the wavelength of 300nm-500nm into a front telescopic imaging system through a window (1) and a sweep pendulum mirror (2);
the front telescopic imaging system comprises: a primary mirror (3), an aperture diaphragm (4), a secondary mirror (5) and a third reflector (6); in the front telescope imaging system, detection light emitted by a sweep pendulum mirror (2) is reflected to a main mirror (3), enters a secondary mirror (5) through an aperture diaphragm (4), is reflected to a third reflector (6), and is finally imaged to an entrance slit (7);
the Offner spectral imaging system is matched with a front telescopic imaging system detection spectrum band of 300-500nm to form an independent spectral detection channel, and specifically comprises an incident slit (7), a light filter (8), a depolarizer (9), a plane turning mirror (10), a first concave reflector (11), a convex grating (12), a second concave reflector (13) and an area array detector (14);
the front telescope imaging system focuses and images optical information of a spectrum detection waveband of 300-500nm to an entrance slit (7), target optical information sequentially passes through the entrance slit (7), an optical filter (8) and a depolarizer (9), then passes through a plane turning mirror (10) to realize optical path turning, enters a first concave reflector (11), is subjected to dispersion and light splitting through a convex grating (12), then passes through a second concave reflector (13), and finally is focused and imaged to an area array detector (14).
Furthermore, the spectral detection wavelength band of the optical system is 300nm-500nm, in the Offner spectral imaging system, the positions of a first concave reflector (11), a convex grating (12) and a second concave reflector (13) are set to enable the imaging of the three elements to conform to a Rowland circle, the first concave reflector (11) and the second concave reflector (13) are distributed up and down symmetrically according to the convex grating (12), and the curvature radiuses of the first concave reflector (11) and the second concave reflector (13) are the same or within a preset threshold value.
Furthermore, the front telescope imaging system is designed as an off-axis three-mirror telescope and comprises three aspheric reflectors; wherein the primary mirror (3), the secondary mirror (5) and the third reflector (6) are designed by quadric surfaces; the aperture diaphragm (4) is inclined in a preset manner, so that no central blocking is realized; an aperture diaphragm (4) is arranged on the secondary mirror (5), the central view field is inclined, and the diaphragm (4) is not off-axis.
Furthermore, the sweep pendulum mirror (2) sweeps the east-west direction of the observation of the nadir, the optical information detected by the nadir is introduced into the front telescopic imaging system, and the concrete material of the sweep pendulum mirror (2) is silicon carbide or beryllium.
Further, the front telescopic imaging system is designed to meet the following requirements: firstly, an image space telecentric structure is provided; and the numerical aperture of the imaging system is matched with the numerical aperture of a convex grating light splitting system of the rear-end Offner spectral imaging system.
Furthermore, the incident slit (7), the optical filter (8) and the depolarizer (9) are sequentially arranged on one component, the optical filter is coated with a band-pass optical filter film, and the thickness of the depolarizer is controlled to be 1-2 mm, so that the spatial resolution detection is not influenced.
Furthermore, the first concave reflector, (11) and the second concave reflector (13) are made of ULE optical glass and are respectively plated with metal dielectric films, and the optical efficiency is improved.
The scanning mirror system of the optical system performs swinging scanning in the east-west direction and staring imaging in the north-south direction aiming at the bottom-of-the-day observation. The detected optical information is introduced into a front telescopic imaging system, and preferably, the specific material of the swing mirror is silicon carbide and is subjected to light weight treatment.
Preferably, the front telescopic imaging system of the optical system adopts a three-aspheric-surface reflector design, wherein the main reflector adopts a hyperboloid design, and the secondary reflector and the third reflector adopt an ellipsoidal design. Through the proper inclination of the aperture diaphragm, the non-center blocking is realized, and the device has the advantages of high resolution, small volume, flat image field and the like. The aperture diaphragm is arranged on the secondary mirror, the central view field is inclined, and the diaphragm is not off-axis. The lens material of the off-axis three-mirror telescopic system is made of a material with an ultralow thermal expansion coefficient, and is microcrystalline glass or ULE material. The front telescope imaging system lens is plated with a metal dielectric film to realize high-efficiency reflection of ultraviolet and visible wave bands.
The Offner spectral imaging system of the optical system is provided with the depolarizer at the rear end of the incident slit, so that the system is not sensitive to the polarization of incident light, the central thickness of the depolarizer is reduced as much as possible in consideration of the imaging quality of the front telescopic system, and the thickness of the central thickness of the depolarizer is controlled to be (1-2) mm. The concave mirror in the Offner imaging spectrometer can be one or two and has different curvature radius. The invention is designed according to two. The convex grating may be a convex Rowland grating or a convex aberration-correcting grating. These specific parameters will depend on the aberration correction required by the optical system. The convex grating Offner structure imaging spectrometer has better resolution in both space and spectral directions, and is widely used in low-dispersion and large-field-of-view image spectrometers. Here, the-1 order of diffraction is chosen for imaging.
The scanning mirror system introduces observation information of the nadir into an instrument (staring in the north-south direction and swinging in the east-west direction) through one-dimensional swinging, and mainly comprises a swinging mirror assembly. The front telescope imaging system mainly comprises an off-axis three-mirror telescope and an aperture diaphragm. The light of the detection target object passes through the sweep mirror and the off-axis three-mirror telescope and passes through the independent spectral channel (300-. The image quality entering the entrance slit of the Offner imaging spectrometer is optimized by controlling the curvature radius of the off-axis three-mirror telescope, the distance and the angle among the primary mirror, the secondary mirror and the third reflector and the aspheric coefficients of the primary mirror, the secondary mirror and the third reflector. The light for detecting the spectral information enters from an incidence slit of the Offner spectral imaging system, passes through the optical filter and the depolarizer, is converted by the plane turning mirror, is reflected by the first concave reflector to the convex grating for light splitting, and is focused on the area array detector by the second concave reflector.
Compared with the prior art, the invention has the advantages that:
(1) the optical system of the present invention has a high transfer function (MTF). The invention utilizes the sweep pendulum mirror to introduce optical information into the instrument, and the spectral imaging detection is carried out by combining the Offner imaging spectrometer through the front telescope imaging system. The optical system has stronger light collecting capacity. Because the bandwidth and the energy received by the detector pixel are weak, the relative aperture of the optical system is enlarged as much as possible to improve the energy collection capability of the optical system on the premise that the system performance, the instrument volume and the quality meet the technical requirements. The invention has good resolution and contrast ratio in a certain spatial frequency range, thereby improving the detection resolution of the system and ensuring the accuracy of measurement. The optical system of the differential absorption spectrometer based on geosynchronous orbit observation can obtain good spectral resolution and spatial resolution within a certain field range and within a detected (300-500) nm wave band.
(2) The optical system of the invention has higher signal-to-noise ratio. Under the same condition of geosynchronous orbit, the received energy is more than three thousand times weaker than that of low orbit, and the inversion of atmospheric trace gas puts higher requirements on the signal-to-noise ratio of the instrument. The Offner spectral imaging system is based on a convex grating light splitting system, which is the core part of the optical system of the present invention and directly determines the spectral characteristics of the imaging spectrometer. Because the ultraviolet band signal is weak, for a high-resolution imaging spectrometer and a spectral instrument for detecting weak spectral signals, a higher signal-to-noise ratio is important, and the main way of improving the signal-to-noise ratio is to increase the luminous flux of the spectrometer and reduce noise. The spectrometer adopts an Offner light splitting system, and the Offner spectral imaging system realizes high luminous flux and high diffraction efficiency of the holographic grating and has the characteristics of high spectrum and high spatial resolution. The small F-number (F # -3) design of the front telescopic imaging system also ensures that a high signal-to-noise ratio of the optical system is achieved.
(3) The front telescope imaging system adopts an off-axis three-mirror telescope, is particularly set to be in a field of view off-axis mode, places a diaphragm on a secondary mirror, is similar to a classic Cooke three-piece system, has symmetrical structure, easy adjustment, stronger aberration correction capability, large field of view and good imaging quality, and is easy to realize an image space telecentric structural form and matched with the pupil of an Offner spectral imaging system. The off-axis three-mirror telescope system inherits the free variable of the on-axis three-mirror telescope system, additionally increases the inclination and eccentricity of the reflector, and can better correct aberration while meeting the structural requirements of the system. In the optimization process, optical design software is firstly utilized to optimize the coaxial three-mirror system to achieve ideal image quality, then the inclination and the eccentricity of each mirror surface are set as variables to carry out man-machine interactive optimization, the light path is gradually avoided from being blocked, and the technical index requirements of the system are achieved. The light diaphragm off-axis avoids the shielding, the spherical aberration, the coma aberration and the astigmatism are corrected by the aspherization of the main mirror, the field of view is enlarged, and the aberration balance is carried out by the aspherization and the inclination of the third mirror.
(4) The invention has good stray light inhibition performance. A window protective glass (fused quartz material) is added at the front end of the swing mirror, so that on one hand, a front telescopic imaging system is prevented from pollution, and on the other hand, a broadband filter coating is plated on the surface of the window; meanwhile, an optical filter is additionally arranged at an incidence slit of the Offner imaging spectrometer, and the coated optical filter film controls the out-of-band spectrum to enter the inside of the spectrometer. The grating of the spectrometer adopts a convex grating, and has the characteristics of no ghost line and signal-to-noise ratio improvement when the astigmatism correction is carried out.
(5) The surface of the microcrystalline glass material (Zerodur) or ULE glass material with better structural performance and thermal performance for the reflector in the front telescope imaging system and the Offner spectral imaging system is plated with the dielectric film, so that the spectral range of the lens (300-500nm) is ensured to have the reflectivity of more than 98 percent.
Drawings
FIG. 1 is a schematic diagram of an optical system of a differential absorption spectrometer based on geosynchronous orbit observation according to the invention;
FIG. 2 is a schematic diagram of the Offner imaging spectrometer optical system of the present invention;
FIG. 3 is a schematic diagram of the components of the entrance slit, the filter and the depolarizer of the present invention;
FIG. 4 is a plot of wavelength points for a system according to an embodiment of the present invention; (a) a wavelength of 300 nm; (b) a wavelength of 400 nm; (c) a wavelength of 500 nm;
FIG. 5 is a graph of MTF curves at various wavelengths for the system Offner imaging spectrometer of an embodiment of the present invention; (a) a wavelength of 300 nm; (b) a wavelength of 400 nm; (c) the wavelength is 500 nm.
In the figure: the optical system comprises a window 1, a sweep pendulum mirror 2, a primary mirror 3, an aperture diaphragm 4, a secondary mirror 5, a third reflector 6, an incident slit 7, an optical filter 8, a depolarizer 9, a plane turning mirror 10, a first concave reflector 11, a convex grating 12, a second concave reflector 13 and an area array detector 14.
Detailed Description
The technical solutions in the embodiments of the present invention will be described clearly and completely with reference to the accompanying drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, rather than all embodiments, and all other embodiments obtained by a person skilled in the art based on the embodiments of the present invention belong to the protection scope of the present invention without creative efforts.
The invention relates to a spectrometer optical system based on space measurement, which has higher radiation measurement accuracy and spectral measurement stability in an ultraviolet/visible wave band and is used for measuring solar radiation reflected and scattered by the earth atmosphere or the surface. By using differential absorption spectrum algorithm for scattered light measured from the nadir, the global/regional trace gas components such as NO can be inverted from narrower characteristic absorption lines2、SO2、O3And the distribution and change information of the aerosol can be extracted from the broadband scattering characteristic line. And the spatial distribution information of the atmospheric trace gas is inverted by analyzing the spectral characteristics of the received scattered radiation.
The differential absorption spectrometer based on the geosynchronous orbit adopts a south-north direction area array staring detection mode, an east-west direction sweep mirror is used for scanning detection, an area array detector on an image plane of the spectrometer provides required south-north direction spatial resolution and south-north direction coverage along rows, required spectral resolution is provided along CCD columns, and east-west direction coverage spatial resolution is realized by east-west scanning of the sweep mirror on the earth circular surface.
A differential absorption spectrometer based on geosynchronous orbit is an optical remote sensing instrument integrating images and spectra, and can provide continuous spectral images of a scene by combining a front telescopic imaging system and an Offner spectral imaging system by using an incident slit. The hyperspectral detection is carried out aiming at the ultraviolet/visible wave band (300-. In the dispersion type hyperspectral imager, a slit is matched with a telescopic system to obtain determined ground space resolution on one hand, and is matched with a spectrometer system and an area array detector to obtain determined spectral resolution on the other hand.
The technical scheme of the differential absorption spectrometer optical system based on the geosynchronous orbit comprehensively considers the application requirements, comprehensively balances the aspects of resources which can be provided by the satellite, technical capacity and the like, optimizes the optical structure and determines the instrument parameters.
In order to design a spaceflight light-weight high-resolution imaging spectrometer, a front telescopic imaging system and an Offner spectral imaging system based on a convex grating are preferably selected. The detection target strip along the slit direction is imaged on the slit through the front telescopic system, and then is split by the convex grating light splitting system to form a spectral image which is received by the detector. And acquiring an imaging data cube of the target by continuously sweeping the space in the horizontal direction, and performing space analysis and component identification on the target.
The convex grating light splitting system is a core part of the load and directly determines the spectral characteristics of the imaging spectrometer. Because the ultraviolet band signal is weak, for a high-resolution imaging spectrometer and a spectral instrument for detecting weak spectral signals, a higher signal-to-noise ratio is important, and the main way of improving the signal-to-noise ratio is to increase the luminous flux of the spectrometer and reduce the noise. The Offner spectroscopy system has the characteristics of large relative aperture, small inherent aberration, high imaging quality and high system etendue.
In order to match the pupil of the Offner spectral imaging system, the front telescope system must have an image-side telecentric structure and the resolution of the system is high over a wide wavelength band. The spatial resolution of the imaging spectrometer is determined by the front-end optical system, different front-end optical systems are selected according to different application purposes, and the measured waveband is mainly an ultraviolet waveband and is limited by ultraviolet glass materials, so that the reflective structure is preferably considered. The reflective telescope is suitable for wide spectrum, but is difficult to realize large field of view, wherein relatively large field of view and aperture are obtained by adding a motion sweep mechanism.
The differential absorption spectrometer optical system based on the geosynchronous orbit consists of a scanning mirror system, a front telescopic imaging system and an Offner spectral imaging system. The reflected light of the target object passes through the sweep pendulum mirror and is focused to the entrance slit of the spectrometer by the front telescope imaging system, and the band image formed by the target object emits light which is subjected to spectral dispersion in the direction vertical to the band after passing through the Offner spectral imaging system and is converged and imaged on the photosensitive surface of the detector. The row direction of the photosensitive surface is parallel to the slit, called the space dimension, and an image of a spectral band of the ground object is arranged on each horizontal photosensitive surface element; the direction of the columns of photosensitive surfaces perpendicular to the slits is the dispersion direction, called the spectral dimension, and each column of photosensitive surfaces is a spatially sampled field of view (pixel) spectral dispersion image of the terrain strip. The optical signal is photoelectrically converted by the detector, amplified, DC restored and filtered by the signal processing circuit, and converted into digital signal by the AD converter.
According to the embodiment of the invention, the differential absorption spectrometer optical system based on the geosynchronous orbit comprises a scanning mirror system, a front telescopic imaging system and an Offner spectral imaging system, as shown in FIGS. 1 and 2; the scanning mirror system comprises a window 1 and a sweeping and swinging mirror 2; information light is detected based on a geosynchronous orbit, and enters a front telescopic imaging system after being scanned through a window 1 and a swing mirror 2. The front telescopic imaging system specifically comprises: a primary mirror 3, an aperture stop 4, a secondary mirror 5 and a third mirror 6. In the front telescope imaging system, the detection light emitted by the sweep pendulum mirror 2 is reflected to the primary mirror 3, enters the secondary mirror 5 through the aperture diaphragm 4, is reflected to the third reflector 6, and is finally focused to the entrance slit 7, and a (300- & ltSUB- & gt 500- & gt) nm spectrum detection channel is formed. The Offner spectral imaging system specifically comprises an incident slit 7, an optical filter 8, a depolarizer 9, a plane turning mirror 10, a first concave reflecting mirror 11, a convex grating 12, a second concave reflecting mirror 13 and an area array detector 14. Light with a target object of (300-500) nm waveband is focused to an entrance slit 7 from a front telescopic imaging system, is filtered by an optical filter 8, is subjected to depolarization by a depolarizer 9, is reflected to a first concave reflector 11 by a plane turning mirror 10, is reflected to a convex grating 12 to form dispersion light splitting, is reflected by a second concave reflector 13, and is finally focused to an area array detector 14.
According to one embodiment of the invention, the primary mirror 3, the secondary mirror 5 and the third reflector 6 of the front telescopic imaging system respectively determine the secondary aspheric coefficients thereof as follows through design optimization: primary mirror 3k (inclusive) is-3, secondary mirror 5k (inclusive) is 0.46, and third mirror 6k (inclusive) is 0.22. Entrance slit 7 size: 12 mm. times.40 μm. The area array detector 14 has a pixel size of 13 × 13 μm, a detection area of 13.3 × 13.3mm, and a pixel size of 1024 × 1024 pixels.
The invention adopts an imaging spectrometer based on an area array detector as a scattered light signal collecting unit, and one dimension of the area array detector is a spectral dimension and covers a spectral band of (300-; the other dimension is a space dimension, covers a bar-shaped area with a certain width (here, the north-south direction of the earth), and acquires area information through once sweeping. The load obtains high-resolution spectral information from ultraviolet to visible wave bands, atmospheric spectral measurement is realized by utilizing a differential absorption spectrum algorithm through respective fingerprint absorption of the polluted gas to be measured in the later period, and meanwhile, a scanning mirror system finishes information acquisition work of the earth in the east-west direction area through scanning, and finally measurement of the atmospheric trace gas in the whole area is realized.
The differential absorption spectrometer optical system based on the geosynchronous orbit mainly comprises a scanning mirror system, a front telescope imaging system and a rear Offner spectral imaging system, the three systems can be separated, are respectively designed, manufactured and adjusted, and then are combined and adjusted, and meanwhile, the optical aberration of the front telescope imaging system can be compensated by the rear Offner spectral imaging system during design. When the whole optical system is adjusted, optical optimal imaging, focusing and inclination compensation of the subsystem and the integrated system are satisfied. Initial structures are respectively obtained through the preliminary design of a telescopic imaging system and a beam splitting system at the front end of the convex grating imaging spectrometer. In order to improve the imaging quality of the imaging spectrometer, the latter two initial structures are integrally designed, a front-end telescopic imaging system and a rear-end spectral splitting system are combined to be used as an integral system to optimize an optical system, and in the optimization process, the aberration of the two systems is reasonably distributed, so that the imaging quality of the integral system is finally improved.
In order to match the pupil of the Offner spectral imaging system, the front telescope imaging optical system must have an image space telecentric structure, the resolution of the system in a wide wavelength band is high, and the system must have a large relative aperture in order to meet the requirement of the signal-to-noise ratio. The front telescope imaging system is a key part for realizing high spatial resolution of a differential absorption spectrometer and aims to meet the technical requirements of a certain field angle, high resolution, no polarization effect and the like. The front-end introduction optical system from ultraviolet to visible light wave band adopts a reflection system as the most feasible and economical scheme.
As shown in fig. 2, the Offner spectral imaging system of the present invention includes an entrance slit 7, a filter 8, a depolarizer 9, a plane turning mirror 10, a first concave mirror 11, a convex grating 12, a second concave mirror 13, and an area array detector 14. After entering from the entrance slit 7, the light beam passes through the optical filter 8, the depolarizer 9 and the plane turning mirror 10, and then enters the first concave reflector 11 after being collimated by a detection target (300 + 500) nm with a certain divergence angle, and is reflected to the convex grating 12, so that the light beam diffracted from the first concave reflector is returned to the second concave reflector 13 and then focused on the area array detector 14. The front telescopic imaging focuses the strip image of the slit 7 to be imaged on the area array detector 14 above the entrance slit. The convex grating 12 in the present invention is a key core device of the Offner imaging spectrometer. The Offner imaging spectrometer based on the convex grating has better resolution in both space and spectral directions, and is widely used in low-dispersion and large-field-of-view image spectrometers. The convex grating is designed according to the channel characteristics, such as fringe density, and the like, so as to obtain higher optical efficiency of the optical system and achieve higher diffraction efficiency as far as possible. Typically the-1 order of diffraction is used for imaging. When the number of the stripes of the grating is increased, the diffraction light with longer wavelength is blocked by the convex grating after being reflected for the second time by the concave reflecting mirror, so that the dispersion of the grating cannot be overlarge. According to the embodiment of the invention, preferably, the design scribing line of the convex grating is 400lines/mm, the incident angle is 15.7 degrees, the blaze angle is 4.2 degrees +/-0.1 degrees, and the diffraction efficiency is more than or equal to 45 percent.
As shown in fig. 3, the front telescope imaging system of the present invention focuses on the entrance slit of the rear Offner spectrometer, passes through the entrance slit 7, the optical filter 8, the depolarizer 9 in sequence, and reflects in the rear optical path through the plane turning mirror 10. The optical filter mainly plays a role in inhibiting out-of-band stray light, a depolarizer completes the depolarization function of the system, and the plane turning mirror realizes the light path turning and is suitable for the space reasonable layout of the whole satellite platform.
As shown in FIGS. 4(a), (b), and (c), the root mean square values obtained by taking representative wavelengths 300nm, 400nm, 500nm in the detection band (300-500nm), wherein (a) is the wavelength 300nm, are shown as the wavelength point charts of the system; (b) a wavelength of 400 nm; (c) a wavelength of 500 nm; in the figure, the root mean square value RMS is within 1 pixel (13 mu m), and the detection requirement of the system spatial resolution can be met.
As shown in FIG. 5(a), (b), (c) are graphs of MTF (Diffraction MTF) of each wavelength of the system, the MTF of the Offner imaging spectrometer is at 300nm, 400nm, 500nm, and (a) is at 300 nm; (b) a wavelength of 400 nm; (c) a wavelength of 500 nm; in the figure, the direction T represents the spectral dimension direction, the direction S represents the spatial dimension direction, and according to the size of a CCD pixel (13 mu m), the light intensity resolution contrast ratio under a certain spatial frequency (38.5L/mm) can be calculated. The MTF value is more than or equal to 0.68, which proves that the system has good imaging quality and meets the use requirement. In the figure, the abscissa is the Spatial Frequency in cycles per mm and the ordinate is the modulation optical transfer function OTF value (Module of the OTF).
The invention utilizes the introduction of geosynchronous orbit detection light information by adopting a sweep pendulum mirror, and detection is carried out by combining an Offner spectral imaging system through front telescopic imaging. The integral optical system has higher spatial resolution and spectral resolution. The Offner spectral imaging performance is excellent, the spatial resolution is greatly improved, the requirements of high spectral resolution and spatial resolution of (300-.
Although illustrative embodiments of the present invention have been described above to facilitate the understanding of the present invention by those skilled in the art, it should be understood that the present invention is not limited to the scope of the embodiments, but various changes may be apparent to those skilled in the art, and it is intended that all inventive concepts utilizing the inventive concepts set forth herein be protected without departing from the spirit and scope of the present invention as defined and limited by the appended claims.
The invention has not been described in detail and is part of the common general knowledge of a person skilled in the art.
Claims (8)
1. A differential absorption spectrometer optical system based on geosynchronous orbit observation is characterized in that:
the optical system comprises a scanning mirror system, a front telescopic imaging system and an Offner spectral imaging system;
the scanning mirror system comprises a window (1) and a swinging mirror (2); detecting information of a celestial object and a bottom target object based on a geosynchronous orbit, introducing spectral information of the terrestrial object with the wavelength of 300nm-500nm into a front telescopic imaging system through a window (1) and a sweep pendulum mirror (2);
the front telescopic imaging system comprises: a primary mirror (3), an aperture diaphragm (4), a secondary mirror (5) and a third reflector (6); in the front telescope imaging system, detection light emitted by a sweep pendulum mirror (2) is reflected to a main mirror (3), enters a secondary mirror (5) through an aperture diaphragm (4), is reflected to a third reflector (6), and is finally imaged to an entrance slit (7);
the Offner spectral imaging system is matched with a front telescopic imaging system detection spectrum band of 300-500nm to form an independent spectral detection channel, and specifically comprises an incident slit (7), a light filter (8), a depolarizer (9), a plane turning mirror (10), a first concave reflector (11), a convex grating (12), a second concave reflector (13) and an area array detector (14);
the front telescope imaging system focuses and images optical information of a spectrum detection waveband of 300-500nm to an entrance slit (7), target optical information sequentially passes through the entrance slit (7), an optical filter (8) and a depolarizer (9), then passes through a plane turning mirror (10) to realize optical path turning, enters a first concave reflector (11), is subjected to dispersion and light splitting through a convex grating (12), then passes through a second concave reflector (13), and finally is focused and imaged to an area array detector (14).
2. The optical system of the differential absorption spectrometer based on the geosynchronous orbit observation as claimed in claim 1, wherein:
the spectrum detection wave band of the optical system is 300nm-500nm, the positions of a first concave reflecting mirror (11), a convex grating (12) and a second concave reflecting mirror (13) are arranged in an Offner spectrum imaging system, so that the imaging of the optical system accords with a Roland circle, the first concave reflecting mirror (11) and the second concave reflecting mirror (13) are vertically and symmetrically distributed according to the convex grating (12), and the curvature radiuses of the first concave reflecting mirror (11) and the second concave reflecting mirror (13) are the same or within a preset threshold value.
3. The optical system of the differential absorption spectrometer based on the geosynchronous orbit observation as claimed in claim 1, wherein:
the front telescope imaging system is designed as an off-axis three-mirror telescope and comprises three aspheric reflectors; wherein the primary mirror (3), the secondary mirror (5) and the third reflector (6) are designed by quadric surfaces; the aperture diaphragm (4) is inclined in a preset way, so that no central blocking is realized; an aperture diaphragm (4) is arranged on the secondary mirror (5), the central view field is inclined, and the diaphragm (4) is not off-axis.
4. The optical system of the differential absorption spectrometer based on the geosynchronous orbit observation as claimed in claim 1, wherein: the sweep pendulum mirror (2) sweeps the east-west direction of the observation of the nadir, the optical information detected by the nadir is introduced into the front telescopic imaging system, and the concrete material of the sweep pendulum mirror (2) is silicon carbide or beryllium mirror.
5. The optical system of the differential absorption spectrometer based on the geosynchronous orbit observation as claimed in claim 1, wherein: the design of the front telescopic imaging system meets the following requirements: firstly, an image space telecentric structure is provided; and the numerical aperture of the imaging system is matched with the numerical aperture of a convex grating light splitting system of the rear-end Offner spectral imaging system.
6. The optical system of the differential absorption spectrometer based on the geosynchronous orbit observation as claimed in claim 1, wherein: the incident slit (7), the optical filter (8) and the depolarizer (9) are sequentially arranged on one component, the optical filter is coated with a band-pass optical filter film, the thickness of the depolarizer is controlled to be 1-2 mm, and spatial resolution detection is not influenced.
7. The optical system of the differential absorption spectrometer based on the geosynchronous orbit observation as claimed in claim 1, wherein: the first concave reflector, (11) and the second concave reflector (13) are made of ULE optical glass and are respectively plated with metal dielectric films, and the optical efficiency is improved.
8. The optical system of the differential absorption spectrometer based on the geosynchronous orbit observation as claimed in claim 1, wherein: the lens of the front telescopic imaging system is made of microcrystalline glass or ULE; the lens of the front telescope imaging system is selectively plated with a metal dielectric film, so that high optical efficiency reflection of ultraviolet and visible broadband is realized.
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| CN114486912A (en) * | 2022-01-17 | 2022-05-13 | 合肥知常光电科技有限公司 | Optical element defect detection device and method based on line spectral confocal technology |
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| CN115685535B (en) * | 2022-11-18 | 2023-10-24 | 中国科学院长春光学精密机械与物理研究所 | Dynamic scanning optical system based on optical quick-swing mirror |
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