To satisfy a space patrol telescope system with high angular resolution, large space area and high stray light suppression, the stray light environmental characteristics at low earth orbit are summarized. In accordance with the parameters, which diameter is 1.5m, focal length is 20m, field of view is 1.1°×1°, and the optical and mechanical structure joint-design stray light suppression is compared and analyzed for on-axis cross type, off-axis back end type and off-axis sideway type. A method of optical and mechanical structure joint-design stray light suppression is proposed to reduce the stray light suppressing angle to enhance the efficiency of the observation time and sky patrol efficiency in orbit. The detailed stray light suppression design and optimization of off-axis sideway type is given. The simulation and analysis of total optical and mechanical periodic line is presented, and the major stray ray path is simulated and analyzed.Compared with the other two types, the off-axis sideway type presents the best performance of image quality and stray light suppression. The modulation transfer functions (MTF) approach the diffraction limit at all fields. When the evadable angle out of the field is 40°, the PST is less than 10-11 and the system can approach to the stray light suppression limitation.
The precisely extraction of construction areas in remote sensing images can play an important role in territorial planning, land use management, urban environments and disaster reduction. In this article, we propose a method for extracting construction areas using Gaofen-1 panchromatic remote sensing images by adopting the improved Pantex[1] (a procedure for the calculation of texture-derived built-up presence index) and unsupervised classification. First of all, texture cooccurrence measures of 10 different directions and displacements are calculated. In this step, we improve the built-up presence index that we use the windows size of 21*21 to calculate the GLCM contrast measure instead of 9*9 according to the spatial resolution of Gaofen-1 panchromatic image. Then we use the intersection operator “MIN” to combine the 10 different anisotropic GLCM contrast measure to generate the final built-up presence index result. At last, we use the unsupervised classification method to classify the Pantex result into two classes and the one with larger cluster center is the construction area class. Confusion matrix of Beijing-Tianjin-Hebei region experiment shows that this method can effectively and accurately extract the construction areas in Gaofen-1 panchromatic images with the overall accuracy of more than 92%.
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