SNR enhancement for composite application using multiple Doppler vibrometers based laser ultrasonic propagation imager

In recent years, the technology of using laser ultrasonic propagation imaging for damage visualization of composite structures were applied to real-world applications. Among many choices of sensor for the Ultrasonic Propagation Imager, the laser interferometry has several advantages: it is non-invasive, and portable, and with extraordinarily long-range measurement. However, the critical issue with interferometry sensing is its low signal-to-noise ratio (SNR), where the background noise can mask the damage-induced waves and making it impossible to identify the damages, especially in composite structures. In this paper, we propose a hardware-based SNR enhancement technique using multiple Laser Doppler Vibrometers (LDVs). The out-of-plane mode of ultrasonic signals are measured by multiple LDVs at a common sensing point and then averaged in real time. We showed that the SNR enhancement in experiments was consistent with the theoretical prediction, and also the test results showed a clear improvement for damage visualization of structures using Ultrasonic Wave Propagation Imaging and Ultrasonic Wavenumber Imaging algorithms.     

Relating geologic units and mobility system kinematics contributing to Curiosity wheel damage at Gale Crater,Mars

Curiosity landed on plains to the north of Mount Sharp in August 2012. By June 2016 the rover had traversed 12.9 km to the southwest, encountering extensive strata that were deposited in a fluvial-deltaic-lacustrine system. Initial drives across sharp sandstone outcrops initiated an unacceptably high rate of punctures and cracks in the thin aluminum wheel skin structures. Initial damage was found to be related to the drive control mode of the six wheel drive actuators and the kinematics of the rocker-bogie suspension. Wheels leading a suspension pivot were forced onto sharp, immobile surfaces by the other wheels as they maintained their commanded angular velocities. Wheel damage mechanisms such as geometry-induced stress concentration cracking and low-cycle fatigue were then exacerbated. A geomorphic map was generated to assist in planning traverses that would minimize further wheel damage. A steady increase in punctures and cracks between landing and June 2016 was due in part because of drives across the sharp sandstone outcrops that could not be avoided. Wheel lifetime estimates show that with careful path planning the wheels will be operational for an additional ten kilometers or more, allowing the rover to reach key strata exposed on the slopes of Mount Sharp.     

利用LBH辐射图像数据反演大气O/N2方法

利用极光Lyman-Birge-Hopfield (LBH) 辐射图像数据可用来研究太阳风磁场与地球磁场耦合、亚暴与磁暴等过程,综合LBH辐射图像数据和O原子135.6nm辐射数据可反演电离层氧原子与氮气分子O/N2比值分布,进而研究高层大气组分信息及电离层分布变化,对科学研究和空间天气预报具有重要意义. 本文给出了LBH辐射传输机理和我国自主研制的搭载在风云三号D星（FY-3D）上的广角极光成像仪（Wide-field Auroral Imager, WAI）在轨获得的LBH 140-180nm波段极光辐射图像数据. 结合大气紫外辐射积分代码（Atmospheric Ultraviolet Radiance Integrated Code, AURIC）计算O135.6nm辐射数据、LBH辐射光谱以及MSISE00大气模型计算的O、N2数据,给出了利用WAI观测的LBH辐射图像数据反演大气O/N2比值理论计算方法,该方法将为利用我国自主观测LBH辐射数据和O135.6nm辐射数据开展空间信息反演研究打下基础.     

永磁微型磁共振成像仪的梯度线圈与图像质量

通过理论分析结合计算机仿真试验剖析了磁共振成像(MRI)中梯度场线性对图像质量影响的原理,在梯度场线性有缺陷的情况下,用实例和计算机模拟直观的展示了重建图像和模拟结果. 结合研发实践发现,在永磁微小口径、低场强用于鼠类等小动物成像情况下,对梯度场线性度的要求远高于文献中提出的指标. 依靠软件改进,图像没有本质的提高,尝试补偿技术耗时费力效果也不理想. 说明了对永磁微小口径成像仪研发线性度更好的梯度线圈是提高图像质量的关键技术之一. 揭示了在理想条件下普适的理论原理,在不同的实践条件下有不同的趋近理想条件要求. 将具有独立知识产权的高线性梯度线圈安装在自行研制的仪器上得到了较好的图像.     

基于超光谱成像探测系统的线阵CCD的调制传递函数特性研究

超光谱成像是一种场景图谱合一的技术,在战场侦察中得到了迅速应用,其成像质量的评价问题受到越来越多人的关注。根据调制传递函数对比度定义,建立了超光谱成像探测系统的线阵CCD调制传递函数的数理模型,对输入信号与线阵CCD的空间相对位置对调制传递函数的影响进行了计算和分析。结果表明,在Nyquist分频处,相对位置对调制传递函数的影响较大,且随频率的增大而增大;在其他频率处,相对位置对调制传递函数的影响与偏离百分比|ζ|有关,|ζ|＜0.1%的频域,偏离百分比|ζ|越小,相对位置对调制传递函数的影响越大;|ζ|＞0.1%的频域,相对位置对调制传递函数的影响几乎可以忽略不计。所得结论对超光谱成像系统的调制传递函数测量系统设计具有一定的指导意义。     

基于精确光谱响应匹配的星载成像光谱仪交叉辐射定标

星载遥感器在轨运行中受到外太空环境以及遥感器自身特性衰变的影响,辐射特性会发生变化。为确保星载遥感数据能真实地反映被观测地物目标特征及其变化规律,需要定期对星载遥感器进行在轨辐射定标。环境小卫星超光谱成像仪(HJ1A/HSI)由于缺乏配套的星上定标系统,基于场地定标的方法难以满足高频次定标的需求。以EO-1/Hyperion为参考遥感器,以HJ1A/HSI为待定标遥感器,通过反卷积方法对两成像光谱仪光谱通道之间进行精确光谱响应匹配,消除波段设置的差异性,显著降低了HSI定标系数的不确定度。基于本定标方法得到的HSI 115个波段的绝对定标系数中,Band 1至Band 60之间的定标系数的不确定度稳定在5%～8%,除760 nm附近的氧气吸收波段与940 nm附近的水汽吸收波段外,其余波段的定标系数的不确定度为7%～18%,随着波长的增加,不确定度增大。与传统波段匹配方法相比,提高了约50%的精度,该定标精度基本可以满足遥感数据定量化应用的需求。该方法解决了在轨星载成像光谱仪光谱通道设置差异大、交叉定标精度低,难以实用的问题,为星载成像光谱仪高频率更新辐射定标数据提供了一种有效方法。     

A low cost uncooled focal plane array test system

The commercial test equipments from Pulse Instruments, Lumitron and Electro Optical Industries Inc. are very expensive. So, we proposed a new method of very low cost test system for testing the non-uniformity and signal/noise (S/N) and other characteristics of the uncooled focal plane array (UFPA). It uses complex programmable logic device to generate the necessary pulse for the UFPA and the low noise low dropout micropower regulator to obtain the low noise bias. A proportional-integral-differential controlled thermal electrical cooler based on micro-processor unit stabilizes the UFPA. The National Instruments 6111E Data Acquisition Card is used to convert the analog output of UFPA into digital signal into computer. Its 12-bits conversion capability provides sufficient accuracy for evaluating the S/N ratio and non-uniformity of 128×128 pixels UFPA. Labview is used to analyze the signal. The instrument is fast and convenient to adapt the system to other types of UFPA. Further discussion is presented to determine factors that affect the accuracy of the tester.     

Super-Resolution Tension PAINT Imaging with a Molecular Beacon

DNA-PAINT enabled super-resolution imaging through the transient binding of fluorescently-labelled single-stranded DNA (ssDNA) imagers to target ssDNA. However, its performance is constrained by imager background fluorescence, resulting in relatively long image acquisition and potential artifacts. We designed a molecular beacon (MB) as the PAINT imager. Unbound MB in solution reduces the background fluorescence due to its natively quenched state. They are fluorogenic upon binding to target DNA to create individual fluorescence events. We demonstrate that MB-PAINT provides localization precision similar to traditional linear imager DNA-PAINT. We also show that MB-PAINT is ideally suited for fast super-resolution imaging of molecular tension probes in living cells, eliminating the potential of artifacts from free-diffusing imagers in traditional DNA-PAINT at the cell-substrate interface.     

成像光谱仪星上定标技术

成像光谱仪是同时获取地物图像和光谱信息的新一代光学遥感仪器。星上定标是成像光谱仪光谱图像数据定量化应用的基础。本文阐述了成像光谱仪星上定标的原理,按照星上定标采用的参考标准对星上定标技术进行了分类,详细介绍了星上辐射定标和光谱定标技术,并展望了成像光谱仪未来发展趋势。绝对辐射定标已经成为成像光谱仪星上定标的基本要求,太阳将逐步代替星上标准灯成为绝对辐射标准。基于不同参考标准的定标方法的综合应用将使星上定标精度和可靠性大大提高。随着定标精度的进一步提高,地面光谱定标装置将逐步空间化,基于探测器的星上辐射定标系统也将逐步得到应用。