基于深度学习的GPR时频域联合电磁反演方法

对探地雷达(ground penetrating radar, GPR)数据进行电磁反演可以获得探测区域中目标的几何参数和电磁参数. 本文针对GPR时域数据与频域数据在图像域的特征差异,首先设计了基于深度学习的GPR维度变换自编码器提取GPR回波数据的时域特征,并对GPR时频域特征进行一致化处理;然后设计了基于时频融合数据的电磁反演处理框架GPR-EInet,并分别使用2000和200个GPR B-Scan数据对GPR-EInet进行训练和测试. 仿真实验结果表明,GPR-EInet可以在SNR=?10 dB、目标介电常数与背景介电常数的相对偏差为50%的情况下实现单/双目标的电磁反演,介电常数反演结果与真实值的结构相似性指数（structure similarity index measure, SSIM）达到了0.995 64. 分别运用GPR-EInet、ünet与PINet对仿真数据进行电磁反演,结果表明: GPR-EInet的抗噪性能要优于PINet与ünet. 对实测的GPR数据也开展了电磁反演实验,获得了探测区域的目标参数信息. 与单独的时域或频域数据反演相比,时频融合数据提升了GPR-EInet的电磁反演精度与噪声抑制能力.     

Standing-wave EO phase modulator using nonperiodic domain inversionfor large modulation index

A deep microwave EO phase modulator using a standing-wave electrode structure together with nonperiodic domain inversion is presented. The calculation and experimental results show that the maximum modulation index obtained by this modulator is 30% higher than the best result obtained for a travelling-wave EO phase modulator with periodic domain inversion     

准相位匹配LN倍频波导铁电畴反转光栅的研究

从准相位匹配理论出发,对铁电畴反转区域长度和畴界位置的偏差造成偏离理想准相位匹配的情况进行了理论分析和研究,得出这些偏差直接影响二次谐波输出功率。     

基于X波段雷达图像反演近岸水深技术研究

在浅水区域,局部的海底地形影响着表面波的传播,基于这种传播变化可反演出局部的水深。首先通过输入非等值水深模拟出浅水区域的非均匀波浪场时间序列图像,继而根据X波段雷达的成像机理,模拟出了时间序列的雷达图像。利用局部反演算法对模拟数据进行处理反演出局部的水深值,并与输入的水深值进行对比,结果吻合较好,对进一步利用实际的雷达图像反演非均匀场的水深具有重要的指导意义。     

Electrooptic wafer beam deflector in LiTaO/sub 3/

A novel electrooptic beam deflector is reported based on ferroelectric domain inversion extending through the thickness of a Z-cut LiTaO/sub 3/ wafer. The selective domain inversion is achieved by electric-field poling assisted by proton exchange, rather than proton exchange followed by rapid thermal annealing. The deflection sensitivity of the device was measured to be 5.0 mrad/KV. This is 93% of the theoretical value for this geometry, and a significant improvement over the value of 80% of theoretical previously reported for a waveguide deflector. This improvement is attributed to the new domain inversion process. No degradation of deflection sensitivity is observed up to the frequency of 300 KHz, which is then limited by the response time of detectors.     

考虑量子效应的双栅MOSFET的阈电压解析建模

推导了双栅MOSFET器件在深度方向上薛定谔方程的解析解以求得电子密度和阈电压.该解析解考虑了任意深度情况下沟道中深度方向上电势的不均匀分布,结果与数值模拟吻合.给出了电子密度的隐式表达式和阈电压的显式表达式,它们都充分考虑了量子力学效应.模型显示,在亚阈值区或者弱反型区,电子密度随深度增加而增加;然而,在强反型区,它与深度无关,这与数值模拟的结果吻合.结果进一步显示,只考虑方形势阱的量子力学结果,略高估计了阈电压,且低估了电子密度.误差随着深度的增加或者栅氧厚度的减少而增加.     

自由空间中二维电磁目标的时域非线性反演

提出一种基于电磁等效原理的一组积分方程，应用变分方法和傅立叶变换理论，得到了时域散射场与目标电磁参数之间非线性关系的频域表示式，即反演自由空间中二维电磁目标的时域非线性迭代方法的反演方程。列举了一些典型的数值反演实例，对反演性能进行了多方面的考察，指出本法是一种具有良好反演性能的时域非线性反演方法。     

基于PolInSAR的植被区高精度数字表面模型反演方法

针对传统方法无法估计电磁波在植被中的穿透深度导致植被数字表面模型(DSM)反演误差较大的问题,该文提出一种高精度DSM估计方法。该方法首先通过极化干涉相干最优中最大化相位差法分离得到电磁波在植被中高、低散射相位中心的干涉相位。然后提出一种归一化高、低散射相位中心高度随消光系数变化的模型,基于该模型搜索得到电磁波在植被中的最浅穿透深度。最后利用干涉处理方法得到高散射相位中心的高程,将最浅穿透深度补偿到该高程中,从而提升植被区DSM估计精度。利用PolSARpro软件在不同植被种类和不同植被高度下进行仿真试验以及机载全极化数据进行实测数据试验,试验结果表明该方法能有效提高植被区DSM反演精度。     

激光雷达和毫米波雷达的卷云微物理特性的联合反演方法

联合激光雷达和毫米波雷达对卷云观测可以得到更全面的卷云特性信息,是卷云观测的一种发展趋势。使用美国大气辐射观测(Atmospheric Radiation Measurement,ARM)计划中卷云观测数据,将激光雷达和毫米波雷达反演的云边界信息相结合,得到更为准确的卷云边界信息。提出卷云微物理特性的激光雷达和毫米波雷达联合反演算法,该联合反演算法能在激光雷达不能穿透或毫米波不能识别卷云的情况下,反演出整个卷云的冰水含量、光学厚度。使用联合反演算法对一次卷云过程进行反演,其中激光不能穿透的区域冰水路径含量反演精度提高24%,毫米波雷达无法识别的区域冰水路径含量反演精度提高48%。在正确反演冰水含量的基础上,利用冰水含量、粒径分布与光学厚度的关系得到卷云过程的光学厚度,克服了由于卷云对激光雷达强衰减导致的光学厚度观测的困难。     

Hg_(1-x)Cd_xTe反型层子能带结构的实验研究

本文在4.2K下测定了液相外延HgCdTe MIS结构样品的电容谱,磁阻振荡以及迴旋共振效应,并从实验测量结果,采用物理参数拟合法,确定了该样品在电量子限条件下反型层电子子能带结构,包括基态子能带能量E_o、费密能级E_F,子能带电子有效质量m~*(E_F)、m~*(E_o)、反型层平均厚度Z_i、耗尽层厚度Z_d,以及它们随子能带电子浓度N_s的变化。     

Phased array imaging of moving targets with randomized beamsteering and area spotlighting

This paper presents a system model and inversion for imaging moving targets using phased arrays. The system model provides a mathematical framework to represent the motion of a moving target in the beam-steering domain which is identified as the slow-time domain. The inversion provides a reconstruction of the moving targets in the spatial and velocity domains. It is shown that a randomized beam steering strategy in the slow-time domain can improve the resolution in the velocity domain. The imaging problem is also formulated for a phased array system that spotlights a target area with its transmitted beam to improve the target to clutter power ratio, and obtains beam-steered data in the receive mode for high-resolution imaging. We cite a diagnostic medical ultrasound problem due to the practical difficulties and challenges that are associated with it.     

On Bayesian scatterometer wind inversion

In a quest for a generic unbiased scatterometer wind inversion method, the different inversion procedures currently in use are revisited in this paper. A careful examination of both the errors in the wind and in the measurement domain, combined with the nonlinear shape of the geophysical model function (GMF), leads to a generic and novel Bayesian wind retrieval approach in the measurement domain. In this approach the shape of the GMF solution manifold in measurement space is more important than the specified noise. This shape is related to the system wind direction sensitivity, and when this sensitivity is uniform, realistic and precise wind direction distributions are retrieved, even when measurements lie far from the GMF manifold. A simplified measurement space transformation that produces such uniform sensitivity for the European Remote Sensing Satellite (ERS) scatterometer is presented and shown to have reduced wind direction bias compared to the more traditional (measurement-noise normalized) inversion for ERS. Moreover, the simplified wind inversion reveals a similar performance to the current operational ERS wind inversion, but is potentially more generally applicable. The simplified method is then applied to SeaWinds but is ineffective. In this case the instrument geometry results in a low sensitivity to wind direction at a few specific directions. As a consequence, certain wind direction solutions remain favored in the SeaWinds inversion.     

基于光谱相似性进行水深探测的研究

基于水深遥感反演方程与水面接收光谱随水深变化的特点,实验研究了水深光谱相似性与水深间的关系。结果表明,不同水深一阶微分光谱相似l性与水鎏值近似满足指数挛化规律。利用拟合公式进行误差分析,测量水深与实际值最大误差为16％,反演效果良好。     

MPL反演南京北郊气溶胶光学厚度准确度的研究

微脉冲激光雷达是探测气溶胶的有效工具。为了验证探测的准确度,对一台微脉冲激光雷达观测数据采用Fernald算法进行反演,得到了南京北郊上空的气溶胶光学厚度,并将反演结果同太阳光度计观测数据、喇曼-瑞利-米雷达观测数据和中分辨率成像光谱仪的标准气溶胶产品进行了比较。结果表明,它们之间具有一定相关性。微脉冲激光雷达是反演气溶胶光学厚度的有效手段,可以用于其它观测手段的地面验证。     

无深度反转的集成成像一次拍摄方法

针对传统集成成像显示技术存在深度反转,需要进行二次成像的问题,提出一种无深度反转的集成成像一次拍摄方法。该方法采用离轴平行式集成成像拍摄结构对三维(3D)场景进行拍摄,通过设计合理的拍摄参数,重排图像元,生成无梯形畸变的图像阵列(EIA),直接用于集成成像显示,解决了传统集成成像的深度反转问题,避免了复杂且繁琐的图像校正和二次成像过程,可快速生成具有正确深度信息的EIA。该方法所获取的EIA在集成成像3D显示实验中重建的3D图像具有正确的深度和逼真清晰的立体显示效果,验证了本文方法的正确性。     

Retrieval of snow parameters by iterative inversion of a neuralnetwork

The inversion of snow parameters from passive microwave remote sensing measurements is performed, using an iterative inversion of a neural network (NN) trained with a dense-media multiple-scattering model. Inversion of four parameters is performed based on five brightness temperatures. The four parameters are mean grain size of ice particles in snow, snow density, snow temperature, and snow depth. Iterative inversion of a data-driven forward NN model is justified on a theoretical and methodological basis. An error analysis is performed, comparing iterative inversion of a forward model with the use of an explicit inverse for the retrieval of independent snow parameters from their corresponding measurements. The NN iterative inversion algorithm is further illustrated by reconstructing a synthetic terrain of snow parameters from their corresponding measurements, inverting all four parameters simultaneously. The reconstructed parameter contours are in good agreement with the original synthetic parameter contours     

基于探地雷达的机场场道脱空层检测及厚度估计

机场道面的脱空状况对机场场道的质量检测、定期维护具有十分重要的意义。探地雷达在机场道面脱空检测中有着非常好的效果。本文研究了基于探地雷达的机场场道道面脱空层的检测及其厚度估计问题。首先,将时频分析方法——S变换引入到机场道面脱空薄层的检测中,利用脱空薄层反射回波所对应的S 变换波形的底部失真特性检测脱空薄层,这是基于S变换检测机场场道脱空薄层的首次尝试。同时利用改进的电磁波在道面下多层介质中的传输模型及系统辩识方法,成功提取了与脱空薄层上下界面所对应的时域脉冲对,基于谱反演优化算法实现脱空薄层的厚度估计。仿真结果证明了本文方法的有效性,且脱空薄层厚度估计误差控制在5%以内。      

一种结构感知损失的域适应深度估计方法

针对域适应深度估计方法中域图像间结构差异较大问题,文中提出一种结构感知损失的域适应深度估计方法。该方法通过预训练的卷积神经网络对图像进行特征提取,在特征上进行结构相似性度量,减小了域图像之间的差异性,提高了转换模块的稳定性。该方法使用合成图像深度对和真实图像训练,不需要真实图像的深度标签和物理几何信息。在KITTI数据集上进行实验,深度准确率达到了96.6%,证明该方法可有效提高深度准确率。     

基于矩阵重构的功率倒置算法研究

功率倒置算法适用于全球定位导航系统等期望信号弱而干扰较强的场合。针对弱干扰源时,功率倒置算法阵列方向图在干扰方向零陷深度不够,干扰抑制效果不理想的问题,本文在分析功率倒置算法实质的基础上,提出基于矩阵重构的改进算法,对弱干扰取得了满意的抑制效果。     

Modeling of a nonpinchoff depletion mode MOSFET

A depletion-mode MOSFET is typically formed with a thin channel of opposite conductivity type to the substrate. When a large gate voltage is applied to deplete this channel, an inversion layer is induced. As strong inversion occurs, the depletion layer depth reaches a maximum and cannot be further increased. If this depth is less than the thickness of the channel, the channel cannot be pinched off unless a reverse bias is applied to the substrate. Such a depletion-mode MOSFET is modeled as a MOSFET connected in parallel with a JFET which shares a portion of the channel. The MOSFET has zero background bias so long as the JFET is not pinched off. When the substrate bias V/SUB SS/ is larger than V/SUB p/ to pinch off the JFET, the MOSFET channel depth is reduced, equivalent to applying a background bias to the MOSFET. This background bias V/SUB B/ is shown to be a square root function of V/SUB SS/ and V/SUB p/.