| Hyperspectral imaging spectrometer is widely used in aviation, aerospace and other observation systems because it could acquire both of the spectral and image information. Normally, reflectance spectrum of ground vegetation mainly concentrates in the visible/near-infrared wave band(400 nm to 1000 nm), and on this band imaging spectrometer performs with high signal-to-noise ratio of image under strong solar radiation energy. Therefore, along with the development of aerospace equipments such as small satellites and unmanned aerial vehicles, visible/near-infrared imaging spectrometer especially real-time imaging spectrometer is widely used to monitor plant growth, identify plant type, and distinguish military camouflage. The technology of real-time imaging spectrometer is relatively mature abroad, and there are so many excellent products. However, domestic products are still in its infancy. This is because some key technologies are hard to break. Considering the basis of the existing technical conditions, this paper mainly deals with the front telescope objective system and the spectral imaging system.Front telescopic objective is the eye of the whole system which is used to collect the energy and spatial information of the target. The performance of front telescopic objective affects color image quality of the target and spectral resolution of the system, and so its optimization design is the key of the whole optical system design. In this paper we introduce the calculation method of the symmetrical double gauss lens firstly, and then make the symmetrical structure asymmetric and deformation, and object telecentric control in order to achieve small F number, small distortion and high image quality.Spectral imaging system, including collimation system, beam splitting system and collection system, is of transmission light path design to reduce stray light. We choose prisms as beam splitting system because of its high energy utilization ratio and little stray light on the wide wave band. In order to realize bandwidth match, and collect correct spectral data and image, beam splitting system should be with linear dispersion, little smile and little keystone. It possesses important actual value to solve the problems of nonlinear dispersion, smile and keystone in prismatic imaging spectrometer. By theoretical calculation,the central wavelength coaxial condition of triplet prisms is given, which provides important theoretical basis in the design of coaxial optical system and the calculation of parameters. Method to calculate initial structure of triplet prisms and five-element symmetric prisms is proposed, and method to realize linear dispersion is given. Smile and keystone produced by prisms are calculated by ray tracing, and then they are eliminated by prisms structure design. In order to ensure the final spectral imaging quality, collection system is object telecentric and collimation system is of inverse of the collection system. It should be also considered to match them with front telescope objective system and grayscale camera. The system’s performance depends strongly on alignment of the whole instrument. The wavelength calibration platform is designed, the key position is analyzed and the wavelength calibration of whole field is completed. Finally, some imaging experiments of different types of fruits, different growth of vegetables, and true or false plants are completed. The results show that the instrument could be used in the detection of fruits and vegetables on-line, and in the discrimination of military camouflage.The characteristics of the instrument are are as follows. The spatial resolution is 0.15 mrad, the average spectral resolution is better than 12 nm, the dispersion linearity design is achieved, and the smile and keystone are less than half of the pixel size. The system has the advantages such as small in instrument size, easy for processing and alignment, good in working stability. |
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