双目立体视觉动态角度测量方法

为实现对大幅度动态摆角及运动过程中物体空间姿态角的在线测量,提出一种基于双目立体视觉技术的动态角度测量方法。通过标定好的双目系统实时跟踪采集被测物体的特征点图像,重建特征点的空间三维坐标,进而计算出待测物的动态摆角或空间姿态角。实验结果表明:该系统在测量摆角时示值误差为±0.02°,测量空间姿态角时示值误差为±0.12°,同时具有非接触的优点,适用于动态摆角的在线测量及运动物体的空间姿态跟踪。     

五自由度运动误差测量系统关键技术研究

设计了一种基于激光准直原理的运动平台激光五自由度运动误差测量系统,该系统基于双平行光束的准直原理对水平直线度、垂直直线度、偏摆角、俯仰角和滚转角误差进行同步测量.进行了系统直线度、偏摆角和俯仰角误差测量核心器件参数的自标定,针对双光束难以调平影响滚转角误差测量准确度的问题,利用水平仪对滚转角误差进行补偿修正.对整套系统...     

变温目标毫米波被动探测辐射特性分析

毫米波系统有着较微波、红外、光学系统不同特性的优点.目前,毫米波被动探测技术在反装甲导弹和末敏弹的制导中起着重要作用.针对目标动能等因素,通常目标温度变化,本文研究变温目标毫米波被动探测辐射特性,并通过实验分析了辐射能量与介电常数及物理温度的辐射关系特性,以及与探测角度关系的分析,并给出了目标毫米波被动探测隐身特性的基本要素与变温目标辐射特性的理论分析.     

基于热流固耦合的液膜密封动态追随性分析

为研究热流固耦合下液膜密封动态追随特性,基于小扰动法及热动力润滑理论,考虑非补偿环轴向振动、角向偏摆,建立补偿环三自由度运动方程,对比并分析纯流场和热流固耦合模型下力学元件参数、操作工况参数、结构参数对动态追随性的影响。结果表明：在热流固耦合模型下求解的液膜密封扰动量略小于纯流场模型下求解的扰动量;增加激励振幅,弹簧刚度和O型圈阻尼均会导致扰动增大,动态追随性变差;减小转速、增加介质压力会导致动态特性系数增加,有利于提高动态追随性;减少槽数会提高动态追随性,且在槽数给定时,槽深17μm,槽坝比0.8,螺旋角22°的结构参数设定会得到更好的动态追随性。     

地球表面热红外辐射的方向效应

利用装有红外辐射计的测角系统研究了自然地表面的红外辐射的方向特征, 检测了几种典型自然地表面的地面温度的角度关系. 地面亮度温度的测量值随观测天顶角、方位角和太阳位置而改变. 草地上的测量反映了植被覆盖典型的方向特征;在粗糙土壤地面上, 当太阳辐射方向与观测方向十分接近时, 观测到了"热斑效应";在人造土坡上, 测量到较大的亮度温度的角度变化;而在平静水面的观测中, 当水面未处于辐射热平衡状态时, 在观测天顶角小于 60°时, 没有观测到发射辐射的角度效应. 这些结果表明: 地面红外辐射方向特征引起的亮度温度的差异与地形及太阳辐射在地表面上的反射方向效应有关. 这些方向变化的特性可导致卫星遥感地面温度反演的偏差.     

380~780 nm总光谱辐射通量量值导出及不确定度评定

叙述了光源380~780 nm总光谱辐射通量量值导出的基本原理。该量值基于测量灯的总光通量及用变角辐射计测量灯的光谱辐射强度相对分布,溯源至总光通量国家基准和高温黑体光谱辐射照度国家基准。总光谱辐射通量量值导出的不确定度主要影响因素包括总光通量、光谱辐射标准灯、光谱辐射计自身特性、变角辐射计(机械部分)和测量系统重复性,扩展不确定度U=3.3%~1.6%, k=2。     

二维工作台角度误差实时补偿研究

为减小二维工作台在运动过程中俯仰角、偏摆角对其定位、测量及加工精度的影响,提出一种实时补偿二维工作台角度误差的方法。将激光测量系统作为角度反馈装置,基于压电陶瓷致动器和柔性铰链设计出的六自由度微动工作台作为补偿机构,通过软件控制微动台中压电陶瓷的输入电压,达到补偿工作台角度误差的目的。实验结果表明:二维工作台在50 mm的运动范围内,角度误差实时补偿后,向X方向运动的角度基本可以控制在±3″内,向Y方向运动的角度基本可以控制在±2″内。该方法能够实现对二维工作台角度误差的实时补偿,对提高工作台的定位精度有参考价值。     

环境温度对星敏感器测量精度的影响

环境温度对星敏感器测量精度有一定影响.运用光机结合方法,研究环境温度对星敏感器测量精度的影响.在计算典型星敏感器光学系统热效应引起的结构参数变化的基础上,分析了星敏感器星点定位误差.计算结果表明:在视场角0°附近,环境温度变化对星点定位精度影响较小;通过材料匹配,减小系统温度焦移系数,可以减小环境温度变化引起的星点定位误差.热补偿设计后,在环境温度-20～60℃范围内,星敏感器最大测量误差仅为0.02″,约为原系统的1/7.     

磁头面内运动的测量与抑制

为了进一步提高读写头的定位精度,实验研究了磁头稳定飞行时的面内运动.在将主轴系统与磁头加载机构分离开后,利用激光多普勒测振仪测量磁头面内运动和盘片偏摆大小,通过幅值谱对测量信号进行频谱分析,讨论了面内运动与盘片偏摆的相关性.结果表明,磁头面内运动主要是由盘片偏摆引起的,其运动幅值与盘片偏摆的幅度呈正相关,当偏摆幅值从6.9624μm减小到3.3330μm时,偏离磁道方向的运动振幅从140.6nm降低到59.1nm.通过抑制盘片的偏摆幅度可以有效地抑制磁头偏离磁道方向的运动幅值,有助于提高磁头定位的精确度.     

导引头性能检测装置设计

为实现在室内对多款导引头的目标识别、跟踪、光轴一致性、激光回波接收性能的检测,提出多目标识别方法、基于相对运动的跟踪方法和多光谱光轴一致性的检测方法,并设计一套由目标模拟器和两轴运动转台组成的检测装置。目标模拟器采用反射望远系统,可以提供不同灰度值的可见光目标、不同能级的红外目标以检测导引头的目标识别性能;转台带动导引头运动,检测导引头的跟踪性能;目标模拟器的准直系统提供光轴基准,检测导引头的多光谱光轴一致性;目标模拟器发出不同能级和角度的模拟回波激光,来检测激光回波接收性能。实际检测结果表明,可以实现对3～5个目标的识别,跟踪精度优于0.001 rad,光轴一致性检测精度达到15″,可接收视场角±1°,能级1 nW～10μW的激光回波信号。满足在室内对导引头性能检测的要求。     

Far-infrared sensor for cirrus (FIRSC): an aircraft-based Fourier-transform spectrometer to measure cloud radiance

We describe an aircraft-based Fourier-transform spectrometer (FTS) designed to measure the Earth outgoing radiance spectrum in the far-infrared-submillimeter spectral range. The instrument features include a rapid-scan FTS to obtain high spatial resolution from a moving aircraft platform, a sensitive two-channel detector, and a CCD camera for recording the nadir cloud scene with each scan record. Such measurements demonstrate the sensitivity of Earth radiance to high clouds and provide spectral data for improving techniques for remote sensing and retrieval of atmospheric and cloud properties.     

Spectral calibration requirement for Earth-looking imaging spectrometers in the solar-reflected spectrum

Earth-looking imaging spectrometers operating in the solar-reflected spectrum measure spectra of the total upwelling radiance for each spatial element in an image. These measurements are used to derive physical parameters of the Earth's surface and atmosphere from the energy, molecular absorption, and constituent scattering characteristics expressed in each spectrum. To achieve these quantitative objectives, the measured spectra must be spectrally, radiometrically, and spatially calibrated. The ubiquitous presence of numerous, strong, narrow atmosphere and solar absorptions in the upwelling spectral radiance in conjunction with the narrow spectral channels of imaging spectrometers forms the basis for a general spectral calibration requirement. In order to determine the requirement for spectral calibration accuracy, a sensitivity analysis has been completed for imaging spectrometers with contiguously sampled spectral channel response functions of 5, 10, and 20 nm full width at half-maximum from 400 to 2500 nm. This sensitivity analysis shows that spectral calibration errors of 10% and 5% cause significant, spectrally distinct errors in the measured radiance throughout the solar-reflected spectrum. These errors result from the sensitivity of the measured radiance to the exact convolution of the narrow channels of imaging spectrometers with the upwelling spectral radiance that contains narrow atmosphere and solar absorptions. These errors are systematic and add directly to the radiometric calibration uncertainty for every spectrum in the image. This analysis establishes that a spectral calibration accuracy approaching 1% of the full width at half-maximum throughput of the spectral response function for both spectral channel position and shape is necessary to suppress these errors in the measured radiance spectrum.     

Effect of deposition angle on fiber axis tilt in sputtered aluminum nitride and pure metal films

We show that the fiber axis orientation in sputtered aluminum nitride (AlN) responds strongly to deposition angle as compared with pure metal films. Fiber axis tilt was measured in films deposited at angles from 0° to 68° from the substrate normal. For pure metal films of Al and Ag, the strong (111) texture has a fiber axis tilt of < 10° from the substrate normal. For pure Nb films, the strong (110) texture also has a tilt of < 10°. In contrast, for films of the compound AlN, the distinct c-axis texture responds strongly to the deposition direction, with the fiber axis tilt almost following the deposition angle.     

Estimation of the total uncertainty of sky-radiance measurements in field experimental conditions: implications for the aerosol single-scattering albedo

We compare the spectral sky radiance measured by three ground-based optical radiometers during the second Aerosol Characterization Experiment (ACE-2) to estimate the total uncertainty of the radiance in field experimental conditions. The propagation of this uncertainty on the column-integrated aerosol single-scattering albedo omega0 at 868 nm is investigated. The radiance measurements are affected by a systematic gain uncertainty of less than 2% in the visible spectral region and within 6% in the near-IR region. Correcting the measured radiance by a systematic uncertainty reduces the dispersion of the omega0 from 0.07 to 0.03. Besides, the total relative uncertainty of the radiance measurements in field experimental conditions is within 4% at any wavelength. The corresponding uncertainty delta omega0 is 4% for an aerosol optical thickness of 0.2.     

Surface temperature correction for active infrared reflectance measurements of natural materials

Land surface temperature algorithms for the moderate resolution imaging spectroradiometer satellite instrument will require the spectral bidirectional reflectance distribution function (BRDF) of natural surfaces in the thermal infrared. We designed the spectral infrared bidirectional reflectance and emissivity instrument to provide such measurements by the use of a Fourier transform infrared spectrometer. A problem we encountered is the unavoidable surface heating caused by the source irradiance. For our system, the effects of the heating can cause a 30% error in the measured BRDF The error caused by heating is corrected by temporally curve fitting the radiance signal. This curve-fitting technique isolates the radiance caused by reflected irradiance. With this correction, other factors dominate the BRDF error. It is now ~5% and can be improved further. The method is illustrated with measurements of soil BRDF.     

Temperature and nonlinearity corrections for a photodiode array spectrometer used in the field

Temperature and nonlinearity effects are two important factors that limit the use of photodiode array spectrometers. Usually the spectrometer is calibrated at a known temperature against a reference source of a particular spectral radiance, and then it is used at different temperatures to measure sources of different spectral radiances. These factors are expected to be problematic for nontemperature-stabilized instruments used for in-the-field experiments, where the radiant power of the site changes continuously with the sun tilt. This paper describes the effect of ambient temperature on a nontemperature-stabilized linear photodiode array spectrometer over the temperature range from 5?°C to 40?°C. The nonlinearity effects on both signal amplification and different levels of radiant power have also been studied and are presented in this paper.     

Degree of linear polarization in spectral radiances from water-viewing infrared radiometers

Infrared radiances from water become partially polarized at oblique viewing angles through both emission and reflection. I describe computer simulations that show how the state of polarization for water varies with environmental conditions over a wavelength range of 3-15 mum with 0.05-mum resolution. Polarization at wavelengths longer than approximately 4 mum generally is negative (p, or vertical) and increases with incidence angle up to approximately 75 degrees , beyond which the horizontally polarized reflected atmospheric radiance begins to dominate the surface emission. The highest p polarization (~4-10%) is found in the atmospheric window regions of approximately 4-5 and 8-14 mum. In the 3-5-mum spectral band, especially between 3 and 4 mum, reflected atmospheric radiance usually is greater than surface emission, resulting in a net s polarization (horizontal). The results of these simulations agree well with broadband measurements of the degree of polarization for a water surface viewed at nadir angles of 0-75 degrees .     

Spectrometer slit-power-coupling calculations for natural and laser guide-star adaptive optics

We use numerical calculations to examine the relation between adaptive optics (AO) turbulence compensation and power coupled through a spectrometer slit for both laser and natural guide-star AO systems. The AO system and observing parameters used are relevant to the Gemini-North 8-m telescope. For this study, we separate residual tilt from residual higher-order aberrations to isolate their relative effects under a variety of operating conditions. Our results demonstrate that slit-coupled intensity is not uniquely determined by system Strehl alone; we show that this is due to the differing effects of higher-order and tilt aberrations on the shape of the compensated point-spread function. For the Gemini spectrometer and AO system, the wider point-spread function halo associated with an added residual higher-order aberration reduces slit-coupled intensity more rapidly than a broad point-spread function core induced by residual tilt.     

Passive remote sensing of pollutant clouds by Fourier-transform infrared spectrometry: signal-to-noise ratio as a function of spectral resolution

In a passive infrared remote sensing measurement, the spectral radiance difference caused by the presence of a pollutant cloud is proportional to the difference between the temperature of the cloud and the brightness temperature of the background (first-order approximation). In many cases, this difference is of the order of a few kelvins. Thus the measured signals are small, and the signal-to-noise ratio (SNR) is one of the most important quantities to be optimized in passive remote sensing. A model for the SNR resulting from passive remote sensing measurements with a Fourier-transform infrared spectrometer is presented. Analytical expressions for the SNR of a single Lorentzian line for the limiting cases of high and low spectral resolutions are derived. For constant measurement time the SNR increases with decreasing spectral resolution, i.e., low spectral resolutions yield the highest SNRs. For a single scan of the interferometer, a spectral resolution that maximizes the SNR exists. The calculated SNRs are in good agreement with the measured SNRs.     

Incorporating higher-order modal measurements in tilt estimation: natural and laser guide star applications

Tilt compensation performance is generally suboptimal when phase measurements from natural or laser guide stars are used as the conjugate phase in an adaptive optics system. Optimal compensation is obtained when the conjugate-phase coefficients are estimated from beacon measurements, given knowledge of the correlation between the on-axis object phase and the beacon measurements. We apply optimal compensation theory to tilt correction for the case of an off-axis beacon. Because off-axis higher-order modes are correlated with the on-axis tilt components, a performance gain can be realized when the tilt estimator includes higher-order modal measurements. For natural guide star compensation, it is shown that equivalent tilt compensation can be achieved at beacon offsets that are three times larger when higher-order modes through Zernike 15 are used in the tilt estimator. For a laser guide star, although tilt information cannot be measured directly because of beam reciprocity, off-axis higher-order modal measurements can be used to estimate tilt components, leading to a maximum Strehl ratio of approximately 0.3 for the relative aperture diameter D/r(0) = 4 and the relative turbulence outer scale L(0)/D = 10.