Validation of a crosstalk correction algorithm for ASTER/SWIR

The mechanism of crosstalk phenomena in the shortwave infrared (SWIR) subsystem of the Advanced Spaceborne Thermal Emission and Reflection Radiometer, which has six bands in the wavelength region of 1.6-2.43 /spl mu/m, is investigated. It is found that light incident to band 4 is reflected at the detector and the filter boundary, and then transported to other bands by multiple reflections in the focal plane area. A crosstalk correction algorithm is developed to improve the spectral separation performance of SWIR. Parameters of the crosstalk model, i.e., the amount of stray light and its area of influence, are determined by image analysis. By careful investigation of SWIR images around peninsulas, lakes, and islands, the crosstalk model is validated. Therefore, the correction algorithm is implemented in the preprocessing of higher level data products.     

基于小波变换与像元对目标的短波红外图像增强算法

弱光夜视是短波红外成像的重要应用领域之一。针对短波红外弱光图像对比度低,增强后噪声也被放大的特点,提出了一种基于小波变换与像元对目标的短波红外图像增强算法。首先通过小波变换获得不同频率成分的子带图像;然后对低频子带图像进行基于像元对目标的灰度变换处理,对高频子带图像进行可变阈值降噪处理;最后通过小波反变换将处理后的子带重构得到增强结果。将该算法与基于直方图的增强算法,全局优化线性窗口色调映射算法和自然保持增强算法进行比较,采用图像的信息熵和基于Michelson法则的对比度增强度量作为客观评价指标,结果表明本文算法更为有效地提高了短波红外弱光图像的对比度,抑制了噪声的增强,提升了图像的视觉效果。     

ASTER geometric performance

The Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) system acquires multispectral images ranging from the visible to thermal infrared region. The ASTER system consists of three subsystems: visible and near-infrared (VNIR), short-wave infrared (SWIR) and thermal infrared (TIR) radiometers. The VNIR subsystem has a backward-viewing telescope as well as a nadir one. To deliver data products of high quality from the viewpoint of geolocation and band-to-band registration performance, a fundamental program, called Level-1 data processing, has been developed for images obtained using four telescopes with a cross-track pointing function. In this work, the methodology of the geometric validation is first described. Next, the image quality of ASTER data products is evaluated in view of the geometric performance over a period of four years. The band-to-band registration accuracy in the subsystem is better than 0.1 pixels and that between subsystems is better than 0.2 pixels. This means that the geometric database is determined accurately and the image matching method based on a cross-correlation function is effective in the operational usage.     

宽视场推扫式成像光谱仪杂散光校正方法研究

为了满足海洋水色宽覆盖与高灵敏度探测的遥感需求,正在研制一台宽视场推扫式成像光谱仪原理样机,针对该仪器存在的杂散光现象展开了研究。由于推扫式成像光谱仪穿轨和沿轨方向上视场存在巨大差异,这导致穿轨方向上的杂散光远大于沿轨方向,并明显地表现在图像中。为了避免杂散光影响海洋水色的定量化反演,建立了杂散光模型,并以此为基础提出了杂散光校正的方法,同时给出了校正效果的定量化表征。结果表明,该方法可以利用实验数据有效地消除成像光谱仪视场内杂散光的影响。     

杂光对三线阵相机光学系统成像的影响

针对高成像质量三线阵测绘相机杂光导致相机成像质量下降的问题,文章根据光学系统的设计结果,对相机的杂光系数进行分析与计算,提出合理的杂光抑制措施;利用ZEMAX软件和LightTools软件,分析了杂光对三线阵立体测绘相机成像的影响,通过模拟计算得到杂光系数小于5%的理论结果;实验检测了相机实际杂光系数,得到最大杂光系数小于6%的实测结果,模拟了杂光影响下的光学系统图像,证明了杂光抑制措施的有效性和杂光影响下成像分析的合理性。     

基于多光源模型的夜晚雾天图像去雾算法

依据夜间多光源导致强光处能见度低的现象,在传统大气散射模型中定义发光因子项,构建了一个专门针对夜晚雾天图像的去雾模型,在此基础上提出了一种夜晚雾天图像去雾算法.该算法将原输入图像分解为新雾天图像层和发光图像层,然后对此分解得到的新雾天图像层进行色偏纠正和引导滤波操作以得到最终的去雾结果.与暗原色原理方法、快速中值滤波方法、图像颜色迁移方法、夜晚成像模型方法等已有方法的对比实验证实了本文算法的有效性.该算法可应用于汽车防碰撞系统、道路监控系统,以及其他识别系统.     

Enhancing underwater image via color correction and Bi-interval contrast enhancement

Underwater captured images often suffer from color cast and low visibility due to light is scattered and absorbed while it traveling in water. In this paper, we proposed a novel method of color correction and Bi-interval contrast enhancement to improve the quality of underwater images. Firstly, a simple and effective color correction method based on sub-interval linear transformation is employed to address color distortion. Then, a Gaussian low-pass filter is applied to the L channel to decompose the low- and high-frequency components. Finally, the low- and high-frequency components are enhanced by Bi-interval histogram based on optimal equalization threshold strategy and S-shaped function to enhancement image contrast and highlight image details. Inspired by the multi-scale fusion, we employed a simple linear fusion to integrate the enhanced high- and low-frequency components. Comparison with state-of-the-art methods show that the proposed method outputs high-quality underwater images with qualitative and quantitative evaluation well.     

多角度偏振成像仪杂散光仿真分析

杂散光仿真分析是保证多角度偏振成像仪获取高精度偏振辐射数据的关键手段之一。根据仪器光学系统的自身特点,分析了杂散光的主要来源。针对采用点源透过率法难以适用于大视场光学系统杂散光分析的问题,介绍了基于黑斑法原理进行杂散光仿真分析的方法。借助杂散光分析软件LightTools,建立仪器的三维几何模型及光学属性,采用选定视场点反向光线追迹的方法仿真分析得到光机系统的视场外和视场内杂散光系数。分析结果表明,杂散光主要来源于成像视场范围内,且中心视场受到的杂散光影响最大,杂散光系数为3.27%,达到了设计指标要求。此外,采用近轴光线和实际光线正向追迹,模拟得到局部杂光和全局杂光的能量分布,为后期的图像杂散光校正研究提供了理论依据与指导。     

复杂光学系统鬼像分析的单向链表实现算法

光学系统的杂散光极易在系统内形成多个鬼像，严重影响光束质量和传输特性。主要研究了复杂光学系统中折射面的多次反射和衍射面的多级衍射而形成的杂散光及其数学模型与计算方法，提出了一种采用单向链表数据结构进行鬼像分析的更加简洁、高效的实现算法。编制了专门的杂散光分析软件，实例计算表明，采用该软件可以快速地分析含衍射元件的复杂光学系统的杂散光，全面描述鬼像在像面的位置和能量分布，分析结果对在光学系统设计阶段排除鬼像的潜在危害具有重要参考价值。     

基于最优背景估计的星敏感器抗杂散光星点提取方法

研究了杂散光干扰下星敏感器星点提取问题。在杂散光干扰下,星点提取的效果会变差,这会使解算的姿态不准确和不可靠。为了抵抗杂散光干扰,提出了一种基于最优背景估计的抗杂散光星点提取方法。首先,分析了杂散光在星敏感器中的成像特点,构建了杂散光的具有闭合解的曲面模型;然后,设计了基于最优曲面的杂散光背景估计方法和星点提取方法;最后,采用仿真的杂散光图像和星敏感器采集的杂散光图像验证了算法的性能。实验结果表明:该方法得到的星点检测率、误检率和质心定位精度均优于现有基于背景和形态学的方法,该方法对杂散光有较好的抑制能力。     

Inflight straylight analysis for ASTER thermal infrared bands

The Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) instrument was launched into Earth orbit on the Terra platform in late 1999. ASTER produces images of the Earth in 14 spectral bands including five bands in the thermal infrared (TIR) part of the electromagnetic spectrum (8-12 /spl mu/m). On one occasion ASTER was used to image the Moon as part of the long-term calibration strategy for instruments on the Terra platform. Analysis of the imagery revealed that the TIR band had noticeable straylight effects (ghosting), and an algorithm was developed to correct for these effects. The algorithm was applied to ASTER/TIR images acquired over a vicarious calibration (VC) site at Cold Springs Reservoir (CSR), NV. Data from CSR had been evaluated in three previous VC experiments and showed large unexplained differences between the ASTER image radiance and vicarious predicted radiance not observed in other larger, more laterally homogenous sites. After straylight correction the vicarious and image radiances were in good agreement. A further comparison with nearly simultaneous airborne TIR data acquired with the MODIS/ASTER (MASTER) sensor indicated that the ASTER straylight corrected data also agreed with the airborne data. Finally, the algorithm was applied to artificially created models. The results indicated that a radiance change caused by straylight reached 6% to 8% of a radiance contrast for a smaller square target than 10/spl times/10 pixels or a narrower line target than five pixels. Straylight in ASTER/TIR imagery may not be very large for most targets, but may become an error factor for high-radiance-contrast targets.     

Design and preflight performance of ASTER instrument protoflightmodel

The Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) is an advanced multispectral imager with high spatial, spectral, and radiometric resolution, built to fly on the EOS-AM1 spacecraft along with four other instruments, which will be launched in 1998. The ASTER instrument covers a wide spectral region, from visible to thermal infrared with 14 spectral bands. To meet the wide spectral coverage, optical sensing units of ASTER are separated into three subsystems: visible and near-infrared (VNIR) subsystem, shortwave infrared (SWIR) subsystem, and thermal infrared (TIR) subsystem. ASTER also has an along-track stereoscopic viewing capability using one of the near-infrared bands. To acquire the stereo data, the VNIR subsystem has two telescopes, one for nadir and another for backward viewing. Several new technologies are adopted as design challenges to realize high performance. Excellent observational performances are obtained by a pushbroom VNIR radiometer with a high spatial resolution of 15 m, a pushbroom SWIR radiometer with high spectral resolution, and a whiskbroom-type TIR radiometer with high spatial, spectral, and radiometric resolutions. The preflight performance is evaluated through a protoflight model (PFM)     

利用消杂散光的偏振光技术提高光学读出红外成像检测灵敏度

在基于刀口滤波技术的光学读出的非制冷红外成像技术中,光学元件的反射会在CCD靶面引入杂光光斑,使得检测到的光强信号中FPA的像所占比例降低,因此降低了光学检测灵敏度。采用偏振光学读出系统,即在光路中添加偏振片、四分之一波片,利用对透过光和反射光的偏振方向有选择的偏振分光棱镜代替原有分光棱镜,用偏振光原理消除光路中光学元件的反射杂散光,使FPA像在CCD靶面接收到的光强中所占比例大幅度增加,进而提高光学检测灵敏度。偏振光路检测实验结果显示,检测灵敏度比非偏光实验提高了约47%,与理论分析值一致。     

基于细节信息提取的全色与多光谱图像融合方法

全色（Panchromatic, Pan）图像与多光谱（Multi-spectral, MS）图像融合的目的是生成具有高空间分辨率的多光谱图像。为了进一步提升融合图像的质量，提出一种基于细节信息提取的融合方法。首先，使用滚动引导滤波器与差值运算分别获取Pan与MS的高频分量。其次，采用自适应强度-色度-饱和度（Adaptive Intensity-Hue-Saturation，AIHS）变换处理MS的高频分量与经像素显著性检测后Pan的高频分量，生成对应的强度分量（Intensity，I），再将Pan与I作差值运算获取细节图像。接着，采用引导滤波器计算Pan与MS的高频分量的差值，得到残差图像。最后，利用最速下降法将细节图像与残差图像注入到原始的MS图像中获得最终融合结果。实验结果表明，本文所提算法得到的融合图像能够取得较好的主观视觉效果，且客观定量评价指标较优。     

基于像素偏振片阵列的实时水下目标成像技术

借助偏振成像可以增强水下目标的探测效果。传统的偏振成像方法需要光学检偏器的机械转动来实现,这限制了其在水下的实时探测性能。采用基于像素偏振片阵列图像传感器开发的相机设计了一种水下实时成像系统。系统通过阵列上排布的四向微偏振片一次性捕获四向偏振图像,从而全局估算背景杂散光的偏振角和偏振度。然后利用偏振信息反解得到杂散光光强,最后借助水下成像物理模型得到去散射后的目标增强图像。实验结果表明,将像素偏振片阵列图像传感器应用到水下成像能够有效增强水下图像的对比度,且成像处理过程实时快速,进一步提高了水下目标的探测效率。     

吸收涂层法抑制龙虾眼透镜杂散光

龙虾眼光学的灵感来自于生物界中龙虾眼睛独特的结构形式。龙虾眼透镜的像点是十字形分布,由焦臂、焦点组成,在光波段应用存在明显的背景杂光,严重制约了其应用。通过对龙虾眼透镜的聚焦过程进行分析,提出了使用吸收涂层法对龙虾眼透镜杂散光进行抑制,综合运用末端涂层法和贯穿涂层法消除十字焦臂及背景光从而抑制杂散光。通过使用杂光分析软件进行建模对比分析表明,在不降低中心焦点照度的前提下,使用吸收涂层可以显著抑制龙虾眼透镜的杂光。背景杂光水平降低约一个数量级,而十字焦臂弥散减小并且强度下降约40%。从而可以明显提高信噪比与图像的对比度。     

基于机器视觉的导光板缺陷检测方法研究

导光板在无尘车间制造过程中,因现场环境以及 生产治具的影响,不可避免的出现各种各样的缺 陷,造成产品质量的严重下降。针对这种问题,根据导光板的光学特性、缺陷形成原理及特 征,本文提出 一种基于机器视觉的导光板缺陷检测的方法。首先,根据导光板的导光点分布特性,提出了 基于密度的自 动分区算法;其次,针对不同分区,分别设计一个高斯双方向导数滤波器对导光板图像进行 卷积操作,并 利用在两个大小不一的均值滤波基础上做差,以去除正常导光点的干扰,获得缺陷增强图像 ;进而,利用 二值化阈值操作提取疑似缺陷连通区域,并在分析其区域特征基础上确认是否为缺陷,再加 以分类;最 后,在工业现场采集的导光板图像基础上,进行了大量的实验。实验结果表明,针对亮点、 压伤和线刮伤 缺陷具有较高的检测精度,基本可以满足工业检测要求。     

一种基于小波变换的雷达图像边缘提取方法

图像最基本的特征是边缘,边缘特征提取是多传感器信息融合与景象匹配中的重要内容.合成孔径雷达图像通常带有较强的相干斑噪声,用传统的边缘检测算法效果很不理想.本文针对合成孔径雷达自身的特点,利用小波变换的特性,提出一种将小波变换的多尺度分析与模糊加权中值滤波相结合的边缘特征提取方法.实验证明方法有效,边缘定位准确,并对噪声有抑制作用,将提取结果用于匹配,定位精度达到1个象素.     

Radiometric performance evaluation of ASTER VNIR, SWIR, and TIR

Radiometric performance of the Advanced Spectrometer for Thermal Emission and Reflection Radiometer (ASTER) is characterized by using acquired imagery data. Noise-equivalent reflectance and temperature, sensitivity (gain), bias (offset), and modulation transfer function (MTF) are determined for the visible and near-infrared (VNIR), the shortwave infrared (SWIR), and the thermal infrared (TIR) radiometers that constitute ASTER. The responsivity evaluated from onboard calibration (OBC) and from instrumented scenes show similar trends for the VNIR: the OBC data yield 2.7% to 5.5% a year for the VNIR. The SWIR response changed less than 2% in the 3.5 years following launch. The zero-radiance offsets of most VNIR and SWIR bands have increased about 1/2 digital number per year. The in-orbit noise levels, calculated by the standard deviation of dark (VNIR and SWIR) or ocean (TIR) scenes, show that all bands are within specification. The MTF at Nyquist and 1/2 Nyquist frequencies was determined for all bands using the Moon (VNIR and SWIR) or terrestrial scenes with lines of sharp thermal contrast. In-orbit performance along-track and cross-track is better than prelaunch for the VNIR and SWIR bands in nearly all cases; the TIR effectively meets specification in-orbit.     

改善全彩LED显示屏对比度的选择性滤光片设计方法

环境杂散光会显著降低LED显示屏的对比度,本文提出在全彩屏前增加一个干涉滤光片的方法,选择性地透过RGB三色光,杂散光却被反射,从而提高显示屏的对比度。文章提出了RGB发射峰的数学模型和滤光片设计的评价函数,给出了详尽的设计方法、步骤和一个例子的设计结果。