机动飞行条件下前斜SAR分辨率分析

在机动飞行的前斜合成孔径雷达(SAR)系统中,成像的几何构型随时间显著变化,传统的分辨率分析方法不适用于这种情况.为了描述该系统下的分辨率特性,提出了一种基于分辨椭圆的计算不同几何构型下的前斜SAR分辨率的方法,通过评估分辨椭圆面积找到目标识别最优位置.仿真结果表明,该方法适用于不同飞行参数和几何构型条件下的机动飞行的前斜SAR分辨率分析.     

微量浓度二元混合气体的超声检测研究

理论推导了使用参比法的超声检测二元混合气体的微量气体浓度的计算公式.基于超声传播在不同浓度的混合气体中具有微小时差的特性,设计了微量气体浓度检测系统.利用该系统对空气中六氟化硫(SF6)气体浓度进行了实验验证,验证结果与理论计算吻合,对空气中的六氟化硫来讲,检测的分辨率优于30×10-6(V/V).     

新型双光子引发剂光聚合行为及微器件制备

针对800 nm的激发光源设计合成了3种具有D-π-D分子构型的新型二苯乙烯衍生物(分别命名为BPSBP,BESBP和BCSBP)作为双光子引发剂.利用飞秒激光研究了该系列双光子引发剂的双光子光聚合行为,着重讨论双光子引发剂浓度对聚合阈值和双光子引发剂浓度、聚合能量及曝光时间对聚合分辨率的影响.综合影响聚合分辨率、系统加工效率和微器件表面质量的因素,以浓度为32μmol/g的BPSBP作为双光子引发剂的聚合体系,在9×105mJ/cm2的聚合能量下制作出了亚微米级的三维周期微结构等微器件,并用电镜(SEM)进行了表征.     

数码相机导购专题

参考价格CCD。CMOS分辨率最大有效分辨率感光度焦距对焦自动对焦精确度白平衡快门速度(秒)光圈曝光模式曝光补偿闪光灯测光方式卡口口径连拍(帧,,。秒)遥控自拍延时(秒)视频输出存储媒介压缩格式液晶显示屏液晶屏像素外部连接口电池,’充电器电池质量(克)尺寸(w×H×D)mtTI美能     

高光谱数据光谱分辨率对矿物识别的影响分析

本文针对光谱分辨率对矿物识别的影响进行了实验,在JPL-1光谱库中选择了6种含不同离子团的矿物光谱曲线,利用ENVI4.2对其进行重采样,模拟不同光谱分辨率条件下得到的光谱曲线.分别运用图示和SAM法进行定性和定量的分析,并将重采样的物质特征光谱在不同的光谱范围内与原光谱进行比较,通过分析各种矿物不同光谱分辨率条件下的光谱特征,得到的模拟实验结论,可以为用于地质调查的成像光谱仪在光谱分辨率的确定和优化等方面提供理论基础和技术支持.     

DOAS技术中光学密度计算方法对测量结果的影响

差分光学吸收光谱技术(DOAS)中,通过不同高通滤波方法获得差分光学密度,与经过相同数字滤波处理的实验室的标准参考谱作最小二乘拟合,反演出各种气体的浓度.通过几种平滑滤波和多项式滤波对相同测量信号进行光谱分析,比较其反演浓度的精度、残差的标准方差和峰峰值.结果表明,3点500次平滑滤波重复两次的高通滤波方法各项指标都优于其它方法,能有效地提高测量精确度和降低检测下限.     

下采样对复眼图像超分辨率重构效果的影响

针对复眼超分辨率重构系统中,当以不同成像分辨率(对应不同的下采样因子)的器件拍摄同一场景时,重构效果相对于各自低分辨率图像改善程度不同的问题,研究了下采样程度与复眼超分辨率重构效果之间的关系。通过仿真实验获取不同下采样因子下低分辨率图像的重构结果,从信息熵、信噪比和峰值信噪比对重构前后图像质量进行评价,并采用Romchi Ruling分辨率靶板对仿真结果进行实验验证。实验结果表明:以3至4为下采样因子对512×512的lena图像采样时,信噪比提高7.29db,重构效果改善明显;以相对下采样因子2.2对50mm×50mm的Romchi Ruling分辨率靶板采样时,分辨率提高3个等级。其研究结果可用于指导复眼成像系统研制过程中对成像器件的选型。     

本刊对来稿中统计学符号书写要求

利用甲烷气体在倍频2ν3带较强吸收线R(4)支的波长为1 650.96 nm,基于气体红外特征光谱吸收原理,设计了一套多点实时监测甲烷气体浓度的光纤传感器网络,并建立了谐波检测的数学模型.该系统以1 650 nm波段的分布反馈式半导体激光器(DFB LD)作为光源,采用锁定放大器SR830对微弱电信号进行处理.实验表明,系统中单个传感器的分辨率可达200×10-6,长时间的精确度和稳定性均可满足实际要求,单个传感器的响应时间小于2 s.通过理论分析得出系统中各传感器可放置于离地面20 km以上的矿井中,且系统可在多场合进行多点的实时监测.     

单光纤光栅对温度与应变的同步测量

提出了一种采用单光纤布拉格光栅(FBG)进行温度与应变同步测量的新颖设计。一根FBG被分成等长的两部分,用环氧胶水涂敷在其中一部分的表面,再套上金属套管,此时可以看成具有不同的布拉格波长的2个FBG,利用它们之间不同的杨氏模量和热膨胀系数,应变和温度能够同步测量。实验结果表明,在2700με和75℃的测量范围内,可以达到约6.1με和1.0℃的应变和温度精确度,误差主要来源于光谱仪分辨率的限制和FBG其中一部分的胶水涂抹不够均匀,通过使用高分辨率的解调仪和提高胶水涂抹工艺可得到更高的测量精确度。     

大气痕量气体浓度反演中的谱对准偏差研究

在大气痕量气体浓度反演中,对测量光谱和计算得到的参考光谱做最小二乘拟合是常用的方法之一。但在获取光谱过程中,由于仪器光栅位置的不准确、温度等环境因素的变化、以及二者光谱分辨率的不同,均会导致在现场工作的监测设备所测得的光谱与计算的参考光谱之间存在谱对准偏差,即存在光谱在波长上的漂移、拉伸或压缩。这种不对准会给浓度反演带来很大的影响,介绍了在反演过程中校正谱对准偏差的算法,计算了不同光谱分辨率下由谱漂移造成的浓度反演误差。     

显微成像系统分辨率问题讨论（特邀）

空间分辨率是光学显微成像系统的核心指标,根据光学衍射理论,成像系统的空间分辨率由照明光波长与显微物镜的数值孔径共同决定。而在实际成像过程中,根据不同判据得出的显微成像系统分辨率略有差异,需要根据光源的相干性和被观测目标的结构等特征选择合适的判据来准确计算成像系统分辨率。通过理论分析和数值模拟,给出了不同情况下成像分辨率的计算方法,并对比了在相干光源和非相干光源照明下,对双缝目标和双点目标成像时成像分辨率的差异。     

Comparison of backscattered signal statistics as derived fromindoor scatterometric and SAR experiments

A comparison between indoor scatterometric and SAR measurements of distributed targets is presented. In particular, the backscattered signal statistics (in amplitude and phase) obtained in these two types of measurements are compared for different surface parameters (roughness and correlation length) and varying spatial resolutions in the SAR images. Experimental data have been taken in the European Microwave Signature Laboratory (EMSL) at JRC, an indoor facility which is able to measure extended targets both in scatterometric and linear SAR mode under the same conditions. The results confirm that, with spatial resolutions in the SAR image smaller than two autocorrelation lengths (ACL), the statistics of the backscattered signal depends significantly on the resolution cell size. For larger resolution cells, the experimental data are consistent with the Rayleigh model. This experimental finding substantially confirms the results based on numerical simulations, previously presented in the literature     

Multiresolution Gauss-Markov random field models for texturesegmentation

This paper presents multiresolution models for Gauss-Markov random fields (GMRFs) with applications to texture segmentation. Coarser resolution sample fields are obtained by subsampling the sample field at fine resolution. Although the Markov property is lost under such resolution transformation, coarse resolution non-Markov random fields can be effectively approximated by Markov fields. We present two techniques to estimate the GMRF parameters at coarser resolutions from the fine resolution parameters, one by minimizing the Kullback-Leibler distance and another based on local conditional distribution invariance. We also allude to the fact that different GMRF parameters at the fine resolution can result in the same probability measure after subsampling and present the results for first- and second-order cases. We apply this multiresolution model to texture segmentation. Different texture regions in an image are modeled by GMRFs and the associated parameters are assumed to be known. Parameters at lower resolutions are estimated from the fine resolution parameters. The coarsest resolution data is first segmented and the segmentation results are propagated upward to the finer resolution. We use the iterated conditional mode (ICM) minimization at all resolutions. Our experiments with synthetic, Brodatz texture, and real satellite images show that the multiresolution technique results in a better segmentation and requires lesser computation than the single resolution algorithm.     

A bayesian approach to classification of multiresolution remote sensing data

Several earth observation satellites acquire image bands with different spatial resolutions, e.g., a panchromatic band with high resolution and spectral bands with lower resolution. Likewise, we often face the problem of different resolutions when performing joint analysis of images acquired by different satellites. This work presents models and methods for classification of multiresolution images. The approach is based on the concept of a reference resolution, corresponding to the highest resolution in the dataset. Prior knowledge about the spatial characteristics of the classes is specified through a Markov random field model at the reference resolution. Data at coarser scales are modeled as mixed pixels by relating the observations to the classes at the reference resolution. A Bayesian framework for classification based on this multiscale model is proposed. The classification is realized by an iterative conditional modes (ICM) algorithm. The parameter estimation can be based both on a training set and on pixels with unknown class. A computationally efficient scheme based on a combination of the ICM and the expectation-maximization algorithm is proposed. Results obtained on simulated and real satellite images are presented.     

Performance dependency of retinal image quality assessment algorithms on image resolution: analyses and solutions

Retinal image quality assessment (RIQA) is the first step performed in retinal image processing systems necessary to assure that the processed images are suitable for analysis and medical diagnosis. RIQA algorithms created for controlled environments can result in degraded performance for cross-dataset experiments in which the train and test images have different resolutions. The effect of image resolution on the performance of four different RIQA algorithms, chosen to include generic, segmentation, and transform-based quality features, is studied using datasets of various resolutions. Analyses showed that for cross-dataset classifications, the performance of some RIQA algorithms was reduced by up to 50% in cases where the train and test dataset image resolutions were significantly different. A statistical analysis was conducted to study how the retinal image quality features are affected by image resolution which resulted in their categorization into resolution-dependent and resolution-independent features. Feature scaling was then introduced to overcome the transform-based RIQA algorithm’s cross-dataset performance degradation resulting in a 100% performance enhancement. Based on this study, the investigation and enhancement of the cross-dataset performance of RIQA algorithms are recommended as a standard part of their design in order to assure their performance reliability in processing images of various resolutions.     

线性相关距离扩展目标检测性能分析

随着雷达距离分辨率的不断提高,目标回波信号由占据一个距离单元的点目标会分裂为占据多个相邻距离单元的距离扩展目标,目标在不同距离单元之间的相关性是不应该被忽略的。本文研究了目标的空间相关性对距离扩展目标的自适应匹配滤波(AMF)检测器检测性能的影响。研究结果表明,如果背景的协方差矩阵结构Rc和目标的模式矩阵H可以写成对角阵的形式,那么对距离扩展目标的检测可以看作是在目标所占据的各个距离单元内分别独立完成,最后进行累加;距离扩展目标所占的单元数目L对信噪比有着重要的影响,对L的不准确估计会使输出信噪比降低;距离扩展目标占据的距离单元完全相关情况下,距离扩展目标的检测就退化为点目标检测。      

估算红外成像作用空间分辨率的新方法

提出了一种新的基于特征熵的估算红外成像作用空间分辨率的方法，研究红外目标在各分辨等级（发现、识别、确认）所需的红外成像空间分辨率。首先，通过下采样获取各分辨率等级下的目标图像；其次，提取目标的特征（纹理、形状和全局统计特征），并对目标的特征空间进行归一化，得到其特征直方图；然后通过计算其特征熵，度量目标的信息量；最后根据设定的阈值，给出红外目标在不同的识别等级下所需的最低成像分辨率结论，并以计算机仿真红外目标为例进行验证。实验结果表明:文中结论与识别结果较好吻合，能够为红外识别系统的优化设计和分析提供参考依据。     

Improved speech recognition through videotelephony: experimentswith the hard of hearing

Three experiments were carried out to assess the potential effectiveness of videotelephony as an adjunctive aid to speech reception by the hard of hearing. The experimental procedure consisted of audio-only and audio-visual presentation of standard prerecorded sentences to hard-of-hearing subjects who subsequently had to repeat as many words as possible. The percentage of correctly reported syllables was taken as the speech reception score. Several independent variables related to picture quality parameters. The temporal resolution (frame rate) and the spatial resolution of the video image were the most important of these. The spatial resolutions were QCIF (180×144 pixels) and 1CIF (360×288 pixels), and for both these resolutions the image was processed through a 64-kb/s codec     

Adaptive scale fixing for multiscale texture segmentation.

This paper addresses two challenging issues in unsupervised multiscale texture segmentation: determining adequate spatial and feature resolutions for different regions of the image, and utilizing information across different scales/resolutions. The center of a homogeneous texture is analyzed using coarse spatial resolution, and its border is detected using fine spatial resolution so as to locate the boundary accurately. The extraction of texture features is achieved via a multiresolution pyramid. The feature values are integrated across scales/resolutions adaptively. The number of textures is determined automatically using the variance ratio criterion. Experimental results on synthetic and real images demonstrate the improvement in performance of the proposed multiscale scheme over single scale approaches.