卫星姿态抖动对LASlS成像质量的影响

由于卫星姿态抖动(俯仰、侧滚和偏航)使得LASIS(大孔径静态干涉成像光谱仪)干涉图产生了非正常的像素偏移量，相邻干涉图之间的非正常偏移量在0．1像素量级或更小，但累积偏移量最多可达上百个像素，必须对干涉图进行校正处理。研究结论为设计正确有效的LASIS图像校正算法提供了参考依据，同时也为卫星平台设计提供了参考。     

大孔径静态干涉成像光谱仪图像校正技术

设计了一种基于相位相关与归一化积相关的联合图像校正算法。该算法针对卫星姿态变化对LASIS(大孔径静态干涉成像光谱仪)图像造成的畸变,根据傅里叶变换的旋转平移特性,实现图像序列旋转失真的高精度校正,校正精度达到0.01;同时,基于归一化积相关方法实现图像序列平移失真的校正。针对LASIS数据量大的特点提出了改进的快速自适应模板选取法,使算法的运算复杂度按4n递减。仿真结果表明,该算法能快速有效地校正LASIS图像。     

空间外差光谱仪的干涉图校正

空间外差光谱技术(SHS)作为一种新型超光谱分辨率的光谱分析技术近年来得到了快速发展和广泛应用。根据SHS的基本结构和原理,本文对SHS应用系统中能对干涉图产生影响的各种干扰和畸变进行了分析,并针对这些干扰提出了一种SHS干涉图校正方案。实验结果表明,该方案不仅可以对干涉图进行有效校正,而且复原光谱能够良好地反映输入光谱信息,提高SHS的反演精度。     

随机相移误差的Lissajous标定与校正

将Lissajous标定技术应用到相移干涉测量的相移算法(PSA)中,提出一种基于Lissajous标定技术的随机相移误差校正算法。该算法不需要计算各帧干涉图之间的实际相移量,直接用Lissajous标定和椭圆拟合的方法计算相移算法的相位提取误差(包括离焦、偏倚、相移量偏差)然后进行校正。数值模拟结果表明:该算法不需要迭代运算就能从大于3帧的带有随机相移误差的干涉图中有效恢复出正确的相位信息,运算时间少,计算精度高并且适合于所有的相移算法。实验结果表明:基于Lissajous标定技术的随机相移误差校正算法与现有的迭代随机相移算法(AIA)精度相当,但计算速度得到明显提升。     

高精度FTIR数据处理方法研究

为了实现对红外光谱的准确测量,对切趾、相位校正、波数校正等方法进行研究,建立了高精度的傅里叶红外光谱仪数据处理系统.在比较各种窗函数的优缺点的情况下选用四阶布莱克曼窗函数对干涉图进行切趾,根据红外光干涉图相位误差特点采用卷积法对单边干涉图进行相位校正,深入研究波数校正方法,采用能量重心法进行波数校正.实验结果表明,傅里...     

量块比较仪读数视觉自动化改造

本文主要针对光学量块比较仪自动化改造的现状,提出了利用计算机分析所采集的干涉图,根据所有像素信息,直接提取0级干涉暗纹的位置,并对单色光干涉的多条等厚干涉纹的光强分布进行计算机数值处理,自动进行定标的技术。     

基于机器视觉与等倾干涉术的平面度测量装置

为实现平晶平面度的快速测量,运用机器视觉技术对等倾干涉仪进行改造.计算机对CCD采集的干涉图进行实时处理,再利用所有像素样本点(约4000个)的最小二乘法同时拟合出多条干涉环直径并计算标准干涉环直径Do.对平晶表面不同的检定点,测量软件均能根据其实测Do值计算平面度.改造后的干涉仪不但显著提高了工作效率,且大大降低了劳动强度.     

合成孔径声纳干涉相位图噪声抑制方法分析

讨论了合成孔径声纳的干涉相位图降噪问题。利用加性噪声模型,分析了四种降噪算法:像素平均法、非线性条件邻域均值法、模糊中值法和向量滤波法。通过仿真数据生成的干涉相位图进行降噪分析得到结论:通过像素平均法和条件邻域均值法降噪后不能准确地生成高度图,不推荐在实际中使用。而模糊中值法和向量滤波法通过降噪可以准确地生成高度图。通过相位图残留点数和高度图方差对比发现,向量滤波法性能最优,是一种快速有效的噪声抑制方法。     

利用白光扫描干涉测量表面微观形貌

由于激光显微干涉只能测量表面微观形貌的相对高度值,不能进行绝对测量,本文提出了白光显微干涉测量方法,研制了测量仪器,并对CCD像素格值和PZT进行了标定.该仪器以白光干涉理论为基础,利用空间频域算法计算白光干涉图零级条纹中心位置,根据零级条纹中心移动量来得到被测工件表面微观形貌.对被测工件表面进行了测试,试验结果表明:...     

干涉图条纹数据的快速自动采集

干涉图条纹的数据采集是干涉图数据处理的前提和基础，提出了一种有效的从数字化干涉图中由计算机自动采集干涉条纹数据的算法，该算法的主要特点是首先用尺度验证技术对灰值干涉图进行干涉条纹细化，然后利用细化后的二值干涉图对干涉条纹进行条纹跟踪和数据采集。     

Fast line-shape correction procedure for imaging Fourier-transform spectrometers

An instrument line-shape correction method adapted to imaging Fourier-transform spectrometers is demonstrated. The method calibrates all pixels on the same spectral grid and permits a direct comparison of the spectral features between pixels such as emission or absorption lines. Computation speed is gained by using matrix line-shape integration formalism rather than properly inverting the line shape of each pixel. A monochromatic source is used to characterize the spectral shift of each pixel, and a line-shape correction scheme is then applied on measured interferograms. This work is motivated by the emergence of affordable infrared CCD cameras that are currently being integrated in imaging Fourier-transform spectrometers.     

Modeling, calibration, and correction of nonlinear illumination-dependent fixed pattern noise in logarithmic CMOS image sensors

At present, most CMOS image sensors use an array of pixels with a linear response. However, pixels with a logarithmic response are also possible and are capable of imaging high dynamic range scenes without saturating. Unfortunately, logarithmic image sensors suffer from fixed pattern noise (FPN). Work reported in the literature generally assumes the FPN is independent of illumination. This paper develops a nonlinear model y=a+bln(c+x)+/spl epsi/ of a pixel for the digital response y to an illuminance x and shows that the FPN arises from a variation of the offset a, gain b, and bias c from pixel to pixel. Equations are derived to estimate these parameters by calibrating images of uniform stimuli, taken with varying illuminances. Experiments with a Fuga 15d image sensor, demonstrating parameter calibration and FPN correction, show that the nonlinear model outperforms previous models that assume either only offset or offset and gain variation.     

Spatial mismatch calibration using circular carrier technique in the simultaneous phase shifting interferometry

In most simultaneous phase shifting interferometry (SPSI) systems, a group of phase shifting interferograms are captured simultaneously at the different physical locations to retrieve the phase. The data of different interferograms should be spatially matched correctly, which is hard to realize by existing methods or this spatial mismatch will lead to phase retrieving error. In this paper, a spatial mismatch calibration method is proposed, where the circular carrier is introduced in the interferograms of the SPSI system, and the modulating phases of any two interferograms can be retrieved by the demodulation technique of circular carrier interferogram. The slope of the difference between these two phases is proportional to the mismatch value, so this error can be extracted and the experiment setup calibrated. The main error sources of the proposed method are analyzed with the conclusion that its match precision can be achieved up to 0.5 pixel. In addition, the simulated interferograms and actual interferograms captured in a SPSI system are processed to validate our proposed method.     

Digital color image watermarking based on phase-shifting interferometry and neighboring pixel value subtraction algorithm in the discrete-cosine-transform domain

A novel single-channel color-image watermarking with digital-optics means based on phase-shifting interferometry (PSI) and a neighboring pixel value subtraction algorithm in the discrete-cosine-transform (DCT) domain is proposed. The converted two-dimensional indexed image matrix from an original color image is encrypted to four interferograms by a PSI and double random-phase encoding technique. Then the interferograms are embedded in one chosen channel of an enlarged color host image in the DCT domain. The hidden color image can be retrieved by DCT, the improved neighboring pixel value subtraction algorithm, an inverse encryption process, and color image format conversion. The feasibility of this method and its robustness against some types of distortion and attacks from the superposed image with different weighting factors are verified and analyzed by computer simulations. This approach can avoid the cross-talk noise due to direct information superposition, enhance the imperceptibility of hidden data, and improve the efficiency of data transmission.     

Correction of phase distortion in spatial heterodyne spectroscopy

The detailed analysis of measured interferograms generally requires phase correction. Phase-shift correction methods are commonly used and well documented for conventional Fourier-transform spectroscopy. However, measured interferograms can show additional phase errors, depending on the optical path difference and signal frequency, which we call phase distortion. In spatial heterodyne spectroscopy they can be caused, for instance, by optical defects or image distortions, making them a characteristic of the individual spectrometer. They can generally be corrected without significant loss of the signal-to-noise ratio. We present a technique to measure phase distortion by using a measured example interferogram. We also describe a technique to correct for phase distortion and test its performance by using a simulation with a near-UV solar spectrum. We find that for our measured example interferogram the phase distortion is small and nearly frequency independent. Furthermore, we show that the presented phase-correction technique is especially effective for apodized interferograms.     

Loopy MSC: a simple way to improve multiplicative scatter correction

Multiplicative scatter correction (MSC) is a widely used normalization technique. It aims to correct spectra in such a way that they are as close as possible to a reference spectrum, generally the mean of the data set, by changing the scale and the offset of the spectra. When there are other differences in the spectra than just a scale and an offset, the mean spectrum changes after MSC. As a result, another MSC, with the new mean spectrum as the reference, will result in an additional correction. This paper studies the effect of multiple applications of MSC.     

Direct image transmission through a multimode optical fiber

One-way transmission of a multipixel image through the multimode optical fiber based on the phase-conjugation principle is realized. Adistortion-compensating hologram for each pixel of an image to be transmitted is superposed on a photoplate. Each hologram is recorded with a reference beam of different beam incidence angle to provide proper wave-front correction for each pixel without any interference from other pixels. The reference beams are holographically generated from a photoplate in which small holographic lenslets are aligned in a matrix pattern. Images of up to 25 pixels are transmitted through the fiber experimentally.     

Interframe intensity correlation matrix for self-calibration in phase-shifting interferometry

A new method of estimating reference phase shifts in phase-shifting interferometry is proposed. The reference phase shifts are determined from a matrix that represents the interframe intensity correlation (IIC) of phase-shifted interferograms. The root-mean-square error of intensity measurement is automatically obtained from the smallest eigenvalue of the IIC matrix. The proposed method requires only four interferograms, unlike others, and can extract phase shifts reliably even from interferograms without well-defined fringes, such as speckle patterns. In typical conditions, reference phase shifts and wave-front phases can be determined with an accuracy of lambda/6310 and lambda/150, respectively. The validity of the method is tested by comparing it with other methods in experiments and simulations.     

Optical and electronic design of a calibrated multichannel electronic interferometer for quantitative flow visualization

Calibrated multichannel electronic interferometry is an electro-optic technique for performing phase shifting of transient phenomena. The design of an improved system for calibrated multichannel electronic interferometry is discussed. This includes a computational method for alignment of three phase-shifted interferograms and determination of the pixel correspondence. During calibration the phase, modulation, and bias of the optical system are determined. These data are stored electronically and used to compensate for errors associated with the path differences in the interferometer, the separation of the phase-shifted interferograms, and the measurement of the phase shift.