分孔径中波红外多光谱成像光学系统的设计

为了同时获得目标的红外图像信息和光谱信息,设计了一种分孔径中波红外分波段成像光学系统。该系统可将位于成像器前方不同波段的目标红外场景通过分孔径方式成像到红外制冷型探测器的4个区域上。该系统通过内部分孔径的办法,在不同通道内放置滤光片的方式,实现在一个探测器上对3.5μm～4.1μm、4.4μm～5μm、3.5μm～5μm、4.4μm不同波段的目标同时成像。该系统F数为1.93,单通道的焦距为60mm,MTF接近衍射极限,同时实现了在-40℃～+60℃的无热化需求,可以满足应用和指标需求。

分孔径紫外多波段成像光学系统设计

为获得火焰燃烧过程中的黑体辐射与特征自由基发出的紫外辐射信息,实现对火焰温度与燃料成分的定量分析,本文设计了分孔径紫外多波段成像系统。该系统由前置分孔径光路与后置合像光路两部分组成,选择熔融石英和氟化钙为透镜材料。通过在各个分孔径光路内放置滤光片的方式,将目标在240~280 nm、308 nm、300~360 nm、390 nm 4个不同波段的紫外辐射同时成像到紫外探测器的4个区域上。该系统的F数为2.85,视场角为10°,总长为277.2 mm。分孔径光路的入瞳直径为10 mm,单通道焦距为43.88 mm,调制传递函数(MTF)接近衍射极限。合像光路边缘物面的MTF值在45 lp/mm处达到0.45。将两者组合优化后,总系统在45 lp/mm处各通道的MTF值均在0.5以上。对系统的各项公差进行了蒙特卡罗分析,结果表明有20%以上的良品率,该系统适合于科研加工装配,具有实用价值。

ENLARGING SAR PATCH-MAPPING AREA BY ANTENNA BEAM SCAN

The approach for enlargement of SAR patch mapping area by antenna beam scan is investigated, which serves for moderate fine-resolution mapping of medium-sized terrain patches. The scanning angular velocity and the scanning angular scope are determined respectively. The angular velocity of the scanning antenna is controlled to scan over just one azimuth 3 dB beam width in the time interval during which the radar platform moves over one synthetic aperture length determined from the desired cross-range resolution, radar wavelength, nominal slant range, and squint angle. The scanning angular scope is mainly determined by the azimuth width of the terrain patch, nominal slant range, squint angle, platform velocity, and azimuth beam width. Finally, the related experimental results of an airborne SAR are presented. The linear range-Doppler algorithm is employed in image formation after motion compensation is conducted to remove the effect of transnational motion of the radar platform relative to the map center.

Case study on the extraction of land cover information from the SAR image of a coal mining area

In this study,analyses are conducted on the information features of a construction site,a cornfield and subsidence seeper land in a coal mining area with a synthetic aperture radar (SAR) image of medium resolution. Based on features of land cover of the coal mining area,on texture feature extraction and a selection method of a gray-level co-occurrence matrix (GLCM) of the SAR image,we propose in this study that the optimum window size for computing the GLCM is an appropriate sized window that can effectively distinguish different types of land cover. Next,a band combination was carried out over the text feature images and the band-filtered SAR image to secure a new multi-band image. After the transformation of the new image with principal component analysis,a classification is conducted selectively on three principal component bands with the most information. Finally,through training and experimenting with the samples,a better three-layered BP neural network was established to classify the SAR image. The results show that,assisted by texture information,the neural network classification improved the accuracy of SAR image classification by 14.6%,compared with a classification by maximum likelihood estimation without texture information.

THE FAST FIXED-POINT ALGORITHM FOR SPECKLE REDUCTION OF POLARIMETRIC SAR IMAGE

In this letter, a simple and efficient method of image speckle reduction for polari- metric SAR is put forward. It is based on the fast fixed-point ICA (Independent Component Analysis) algorithm of orthogonal and symmetric matrix. Simulation experiment is carried out to separate speckle noise from the polarimetric SAR images, and it indicates that this algorithm has high convergency speed and stability, the image speckle noise is reduced effectively and the speckle index is low, and the image quality is improved obviously.

Study of SAR imaging with COMPASS signal

A concept of space-surface bistatic synthetic aperture radar (SS-BSAR) passive imaging system is proposed,which is parasitic on the signal of COMPASS Navigation Satellite System (CNSS).The feasibility is demonstrated by analyzing the signal ambiguity function and the range resolution as well as the system topology.Due to the multiple peaks of signal in the auto-correlation function,a new correlation is used to remove the side-peaks.A double-channel receiver is employed to receive the direct satellite signal and the ground reflected signal.The direct signal is a reference signal in range compression,and may also be used for transmitter-receiver signal synchronization.The reflected signal is raw data collected for imaging.Then,a modified range-Doppler imaging algorithm is derived based on the system geometric models and BSAR imaging principle.The proposed algorithm is verified via signal simulation.The work in this paper is of great value to the further use of COMPASS signal,as well as other global navigation satellite signals in passive imaging.

A multiphase texture segmentation method based on local intensity distribution and Potts model

Because texture images cannot be directly processed by the gray level information of individual pixel,we propose a new texture descriptor which reflects the intensity distribution of the patch centered at each pixel.Then the general multiphase image segmentation model of Potts model is extended for texture segmentation by adding the region information of the texture descriptor.A fast numerical scheme based on the split Bregman method is designed to speed up the computational process.The algorithm is efficient,and both the texture descriptor and the characteristic functions can be implemented easily.Experiments using synthetic texture images,real natural scene images and synthetic aperture radar images are presented to give qualitative comparisons between our method and other state-of-the-art techniques.The results show that our method can accurately segment object regions and is competitive compared with other methods especially in segmenting natural images.