For hyperspectral images, most traditional semisupervised classification algorithms ignore spatial information. An effective hyperspectral spatial–spectral semisupervised classification algorithm based on teaching–learning-based optimization (S3C-TLBO) is proposed. In the algorithm, two aspects were used to expand the training labeled set: first, the spatial neighborhood samples of the existing labeled samples with high confidence were labeled to expand the labeled training samples. Second, the margin sampling (MS) combined with improved TLBO was exploited to quickly select the unlabeled samples near the classification hyperplanes from the unlabeled sample set. In addition, spatial neighborhood information was incorporated into kernel function to train a spatial–spectral support vector machine, which was used to determine the category of the test sample comprehensively. The image noise points were removed by smoothing the classification result with neighborhood information. Two sets of experiments on two hyperspectral datasets showed that the proposed algorithm can produce greater classification accuracy and reduce noise points by organically using the combinative spatial information. In particular, the S3C-TLBO can produce better classification result in few labeled samples, which is a major difficulty in hyperspectral image classification.
:A new effective combined design method for low obscuration ratio (OR) three-mirror imaging system is proposed, which involves the correction of varied aberrations, such as spherical aberration, coma, astigmatism, etc., as well as the control of the OR introduced by the secondary mirror’s (SM) baffle effect at the optical design stage. The initial theoretical works include the derivation of the all-spherical system’s 3th-order aberration equations and the calculation of the baffles’ edge coordinates using paraxial ray-tracing. Next,the aberration equations are solved with the boundary conditions of suppressing stray lights to determine the focal powers and first-order parameters of each mirror. And then the system’s initial configuration is obtained as the starting point. During the optimization, conic aspheric surfaces are employed to correct aberrations with the consideration of decreasing the manufacture cost and fabrication difficulties. Meanwhile, the relationship between the SM’s baffle size and the baffles’ edge coordinates based on real ray-tracing is built to minimize the obscuration. Finally, a three- aspheric-mirror system with low OR and high imaging performance is achieved. An infrared-middle-wave system design of % OR is shown and the design result shows that the system’s limited spatial frequency is 33lp/mm and the MTFs of each field-of-view approach the diffraction limits. The stray-light analysis results utilizing FRED software verify the stray light suppression effectiveness of the baffles design of the proposed method.
The area array CMOS devices are usually used on the staring imaging space remote sensors on which the wide field angle. Only an RC system cannot match the requirement. So at present, the RC system coupled with a group of relay lens which is always used in the long focal length and wide field angle system can extend the field angle because the aberration of off axis of the RC system can be corrected by the relay lens. In order to reach the high precision alignment of the system, the computer aided alignment technology and the high precision spatial location reconfiguration technology will be introduced. Comparing with the group of relay lens and the secondary mirror both adjusted, this method fixed the group of relay lens. It made the secondary mirror be the only variable. The number of the variable of the alignment was reduced. The efficiency of the alignment was also improved and the period was shortened. The result was that the MTF of all the nine field angles was better than 0.315, which the design result was 0.345. The factor of the alignment was 91 percent.
Based on the theory of radiation energy transfer in the infrared optical system, two methods for stray radiation analysis caused by interior thermal radiation in infrared optical system are proposed, one of which is important sampling method technique using forward ray trace, another of which is integral computation method using reverse ray trace. The two methods are discussed in detail. A concrete infrared optical system is provided. Light-tools is used to simulate the passage of radiation from the mirrors and mounts. Absolute values of internal irradiance on the detector are received. The results shows that the main part of the energy on the detector is due to the critical objects which were consistent with critical objects obtained by reverse ray trace, where mirror self-emission contribution is about 87.5% of the total energy. Corresponding to the results, the irradiance on the detector calculated by the two methods are in good agreement. So the validity and rationality of the two methods are proved.
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