The demand for spatial infrared remote sensors with high spatial resolution and wide imaging swatch becomes more and more urgent. Optical system is an important constraint on the performance of spatial infrared remote sensors. In this paper, a novel off-axis catadioptric optical system configuration with intermediate image is proposed. The imaging principle and the initial configuration solution method are analyzed. And an off-axis catadioptric freeform optical system is designed with the spectrum of 7.8-10.2μm, the aperture of 435 mm, the focal length of 1038 mm, and the field of view (FOV) of 9×1.1°. The modulation transfer function (MTF) value is better than 0.316@25lp/mm. The maximum relative distortion is -0.27%. And this optical system has good image-side telecentricity and image illumination consistency. The results show that the spatial infrared off-axis catadioptric freeform optical system has good imaging quality and engineering feasibility.
High performance infrared lens used in aerospace optical remote sensing systems have great benefit in resource exploration, pollution monitoring etc. However the high technical threshold of manufacture, the production and launch cost due to the heavy infrared optical materials, and the long period of alignment have restricted its use especially for civil and commercial aerospace. Here we present a realization of aerospace infrared lens for mass production. An unique opto-mechanical structure design has been implemented in order to meet the requirements of the mass production of space infrared lens. Some high effective, low cost processing technology are used both for optical and mechanical parts. The produced lenses have the biggest diameter of 300mm and the best RMS of λ/50(λ=632.8nm). A smart alignment based on an online device with lens alignment and image quality measurement reduces the period from 30 days to 7 days. With the well assembled infrared lens, the space camera has a system wavefront of 0.1λRMS (λ=3.39μm) and the MTF of 0.38(@25lp/mm).
According to the need of high resolution and VIS/IR composite image, the task requirements and the necessity of spectrum selection were given. based on the analysis of the imaging mode, the design route of VIS/IR composite imaging using off-axis linear field of optical system is determined. According to the aberration auto-balance optimization of optical design software, the two channel aberrations were initially balanced. The aspheric surfaces were introduced to correct residual aberration, and the compact requirement of the composite optical system is realized. An example of the design was given, The technical indicators: The VIS channel optical system focal length is 7800mm,F number is 11.73,field of view is 2.2°×0.2°,the operating wave band is 400~900nm, the modulation transfer function of the pan-spectral is above 0.30 all over the field of view at the Nyquist frequency of 71.4lp/mm, the modulation transfer function of the multi-spectral is above 0.80 all over the field of view at the Nyquist frequency of 18lp/mm. The IR channel optical system focal length is 2500mm,F number is 3.76,field of view is 3°×0.2°,the operating wave band is 3~5μm, the modulation transfer function of the system is above 0.32 all over the field of view at the Nyquist frequency of 33lp/mm. The system can achieved the resolution 0.45m/3m at 500km orbital altitude.
A kind of flexible device is used for stress unloading of a certain type of space remote sensor. It is necessary to establish a static model of unloading device for on orbit stress analysis. According to the load characteristics of unloading device on orbit, the reaction of unloading device to remote sensor is decomposed into elastic force and frictional force, and a static model of unloading device including three elastic elements and three friction elements is established. The nonlinear curves of load with displacement of each element in the static model are obtained based on experiment and simulation. The unloading device is simulated by the elastic element, and the static analysis of the remote sensor with nonlinear stiffness is realized through the iteration of linear analysis. The engineering example shows that the rigid displacement of the remote sensor mirror is smaller when the unloading device stiffness is nonlinear, compared with the linear stiffness. It is more accurate to use the static model to judge whether the mirror is misalignment.
As to the need of low distortion MWIR optical system with high resolution and large width, the initial structure of the coaxial two-mirror and the relay optical system were calculated based on the aberration theory and Gauss’s optical imaging formula. According to the aberration auto-balance optimization of optical design software, the aspheric surface is introduced to correct residual aberration, and the compact requirement of infrared optical system was realized. Focal length 2000mm, F number 3, field of view 3°×0.5°, the operating wave band 3~5μm and 100% cold shied efficiency reached. High imaging quality was realized. The modulation transfer function of the system exceed 0.34 all over the field of view at the Nyquist frequency of 33lp/mm, and the relative distortion below 0.1%.The results of the design revealed the target depth that can be realized by the coaxial two-mirror system and relay optical system. The system can achieved a resolution 3.75m and a width of 26km.
In order to meet the high positioning requirement of space camera for image acquisition,the camera boresight and the ground should be ensured into a fixed angle.At the same time, CCD integal direction and TDI imagery heading must be maintained the same.This paper presents an boresight testing and calculating approach based on the space coordinate transformation.The measuring principle of the theodolite is given,and then the measuring coordinate system is established. The space angle is transformed into space coordinates,data processing is then performed.The measurement method of the boresight is given. The formula to calculate the boresight and the linear array direction is also deduced.The experimental results show that the measurement accuracy of the boresight and the linear array direction is 4″.The testing method is reasonable and feasible,and the algorithm is simple and effective.The method can be used to most of the spce camera.
Both light-field and polarization information contain lots of clues about scenes, and they can be widely used in variety of computer vision tasks. However, existing imaging systems cannot simultaneously capture the light-field and polarization information. In this paper, we present a low-cost and high-performance miniaturized polarimetric light-field camera, which is based on the six heterogeneous sensors array. The main challenge for the proposed strategy is to align the multi-view images with different polarization characteristics, especially for regions with high degree of polarization -- in which the intensity correlations are commonly weak. To solve this problem, we propose to use Convolutional Neural Network (CNN) based stereo matching method for aligning the heterogeneously polarized images accurately. After stereo matching, both the light field and the Stokes vectors of scene are estimated, and the polarimetry conventions, e.g., the polarization angle, the linear polarization degree and the circular polarization degree, are given. We implement the prototype of the multisensor polarization light-field camera and perform extensive experiments on it. The polarimetric light-field camera achieves six live streaming on time and the heterogeneous processor of NVIDIA Jetson TX2 is exploited for image processing. Benefiting from the multi-sensor parallel polarization imaging and efficient parallel processing, the proposed system achieves promising performance on time resolution, signal-to-noise ratio. Besides, we develop the object recognition applications to show the superiorities of proposed system.
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