Research On Key Technologies Of Optomechanical System For Space-based Imaging Spectrometer Via Curved Prism Dispersion

This dissertation,with the support of the aerospace pre-research project,carried out the research on the key technologies of optomechanical system for space-based imaging spectrometer via curved prism dispersion,to satisfy the urgent requirements of high luminous flux,large field of view,low spectral distortion,high signal-to-noise ratio,excellent environmental adaptability and highly integrated hyperspectral imagers.Two engineering prototypes of visible(VIS)and short-wave infrared(SWIR)hyperspectral imagers have been developed using above key technologies,which is of great significance to promote the development of high resolution and hyperspectral earth detection technology and the application in optical remote sensing.The principle,classification and application of spectral imaging were firstly discussed in detail,state of art in spaceborne hyperspectral loads and support technology of curved prisms were fully investigated and summarized,to comb the development trend of spaceborne hyperspectral imaging technology.The current requirement was to design and develop the imaging spectrometer with high signal-to-noise ratio,high resolution and large width.However,the difficulty was how to improve the luminous flux of the system and then to balance the contradiction with high spatial resolution and high spectral resolution.It can be achieved to use the spaceborne spectral imaging technology based on curved prism,which had significant research significance and practical application value.Thus,the key technologies of optomechanical system were studied,including:1.Research on spectral imaging technology via curved prismA high-performance coded SWIR spectral imaging system,based on the imaging principle and aberration theory of curved prism,was designed by using Offner relay imaging configuration.The imaging system was with object field of view 92 mm ×19.8mm,and the spectral smile,color distortion and field distortion were lower than0.2 pixels,0.1 pixels and 0.2 pixels,respectively.The system exhibited excellent imaging performance with the average spectral resolution of 10 nm ranging from0.9-2.5μm,and the MTF was higher than 0.55@16.67 lp/mm.On this basis,the tolerance analysis of the system was completed,and a high-precision machining process was proposed to meet the high requirements of surface inclination tolerance of curved prisms.2.Micro-stress,rigid-flexible,dual mode coupling support technology for curved prismsA micro-stress,rigid-flexible,dual-mode coupling support technology for spaceborne curved prisms was proposed,which could realize micro-stress clamping and high stability support of rectangular curved prisms,rectangular plane reflectors and curved prisms.And the root mean square value(RMS)of surface shape errors of each rectangular mirror group was better than(1/40)λ within the temperature range and mechanical conditions required by the satellite environment conditions.The minimum first-order natural frequency of each rectangular mirror assembly was 172.5Hz,and the maximum magnification of acceleration response in random mechanical vibration was 5.64.Hence,the rectangular mirror assemblies achieved excellent environmental adaptability.Consequently,we summarized the design optimization process of rigid-flexible,dual-mode coupling support structure for rectangular mirror body of any type,material and size.3.Integrated structure design technology of imaging spectrometer via curved prism dispersionThe integrated structure design of the SWIR imaging spectrometer was completed,adopting the common substrate,with 6 rectangular mirrors adopting rigid-flexible,dual-mode coupling support structure.The overall dimension of the system is 760×481 × 380 mm and the weight was 48 kg.The analysis of mechanical characteristics showed the maximum displacement deformation of the system under coupling conditions was 0.012 mm,and the maximum RMS acceleration magnification in sinusoidal vibration was 1.33,without obvious amplification.During random vibration analysis,the maximum response stress of structural parts was 47.3Mpa,and the maximum response stress of optical parts was 1.10 Mpa.The system has successfully passed the random vibration test.The test results show that the first-order natural frequency of the system was 182.5Hz,and the maximum magnification of the acceleration response was 3.34.4.Integration and test verification of spectral imaging system based on curved prismsAn integration method,based on spherical autocollimation,for off-axis imaging spectrometer via curved prism dispersion was proposed.The integration of SWIR imaging spectrometer was completed using point source microscope(PSM)and coordinate measuring instrument(CMM).Moreover,the tests showed the MTF of the system could reach 0.415@16.67 lp/mm in edge field of view.And then the system could realize low distortion image in a large field of view with the spectral smile and spectral keystone lowering than 0.2 pixels and 0.1 pixels,respectively.The SWIR imaging spectrometer based on the above technologies has obtained a good hyperspectral data cube in the push-broom test.The technologies have been used in the development of VIS imaging spectrometer,which provides the technical support for the development of spaceborne hyperspectral imager.