Foreword to the Special Issue on Subsurface Sensing Using Ground-Penetrating Radar (GPR)

The 17 papers in this special issue focus on subsurface sensing using ground-penetrating radar (GPR). These papers describe new approaches to subsurface sensing, including developments in electromagnetic wave propagation imaging/inversion of GPR data and antenna/radar technologies. Associated applications range from glaciology to pavement evaluation to landmine detection.     

Exact and approximate filtering in signal detection: An example (Corresp.)

The innovations approach in communication theory solves the signal detection problem in terms of a related nonlinear filter. Simulation data is presented which shows that, at least for one example, using the appropriate linear filter instead results in a very small loss of detection power even though the variance of the linear filter is considerably greater than that of the nonlinear one. The results also illuminate the role of "predictable processes" in communication theory.     

Segmentation of retinal blood vessels by combining the detection of centerlines and morphological reconstruction

This paper presents an automated method for the segmentation of the vascular network in retinal images. The algorithm starts with the extraction of vessel centerlines, which are used as guidelines for the subsequent vessel filling phase. For this purpose, the outputs of four directional differential operators are processed in order to select connected sets of candidate points to be further classified as centerline pixels using vessel derived features. The final segmentation is obtained using an iterative region growing method that integrates the contents of several binary images resulting from vessel width dependent morphological filters. Our approach was tested on two publicly available databases and its results are compared with recently published methods. The results demonstrate that our algorithm outperforms other solutions and approximates the average accuracy of a human observer without a significant degradation of sensitivity and specificity.     

Design and test of the ground-based L-band Radiometer for Estimating Water In Soils (LEWIS)

In the framework of the preparation of the Soil Moisture and Ocean Salinity (SMOS) mission, several field experiments are required so as to address specific modeling issues. The goal is to improve current models and to test retrieval algorithms. However, adequate ground instrumentation is scarce and not readily available "off the shelf". In this context, a high-accuracy L-band radiometer was required for a specific long-term campaign for the preparation of the SMOS mission. For this purpose, a dual-polarized radiometer was designed and built to check algorithms for surface soil moisture retrieval from multiangular dual-polarized brightness temperatures. This radiometer has been tested in the field for 20 months and is operational since end of January 2003. The aim of this paper is to give details of the system architecture, calibration procedures, together with the performances obtained and some preliminary results.     

Detection of urban structures in SAR images by robust fuzzyclustering algorithms: the example of street tracking

The authors present a fuzzy approach to the analysis of airborne synthetic aperture radar (SAR) images of urban environments. In particular, they want to show how to implement structure extraction algorithms based on fuzzy clustering unsupervised approaches. To this aim, the idea is to segment first the sensed data and recognize very basic urban classes (vegetation, roads, and built areas). Then, from these classes, we extract structures and infrastructures of interest. The initial clustering step is obtained by means of fuzzy logic concepts and the successive analyses are able to exploit the corresponding fuzzy partition. As a possible complete procedure for urban SAR images, they focus on the street tracking and extraction problem. Three road extraction algorithms available in literature (namely, the connectivity weighted Hough transform (CWHT), the rotation Hough transform, and the shortest path extraction) have been modified to be consistent with the previously computed fuzzy clustering results. Their different capabilities are applied for the characterization of streets with different width and shape. The whole approach is validated by the analysis of AIRSAR images of Los Angeles, CA     

On the role of measurement configuration in contactless GPR data processing by means of linear inverse scattering

This paper deals with a linear two-dimensional inverse scattering problem within a half space geometry with data gathered far away from the interface, which is relevant in ground penetrating radar contactless data processing. In particular, the role of the measurement configuration is discussed with regard to the information retrievable from multifrequency data.     

ColorED: Color edge and segment detection by Edge Drawing (ED)

We extend our recent edge and segment detector, Edge Drawing (GrayED), to detect edge segments in color images. Edge Drawing for color images, named ColorED, takes in a color image, and outputs a set of edge segments, each a contiguous, 1-pixel wide chain of pixels. Detected edge segments are then passed through an ‘a contrario’ validation step due to the Helmholtz principle to eliminate perceptually invalid detections. We quantitatively evaluate ColorED with different colorspaces and vector gradient operators within the precision-recall framework of the widely-used Berkeley Segmentation Dataset and Benchmark (BSDS300), and compare its results with those of GrayED and a color version of the Canny edge detector named ColorCanny. We conclude that color edge detection is in general superior to grayscale edge detection, and that ColorED with edge segment validation (ColorEDV) greatly outperforms GrayED, ColorED, and ColorCanny, producing an F-score of 0.6593 with DiZenzo and 0.6747 with the Compass operator while taking an average time of 31.5 ms for BSDS300.     

(Organic) Switching phenomenon in lateral structures: Tuning by gate voltage

We have fabricated devices based on copper phthalocyanine (CuPc) that exhibited electrical bistability and switching phenomenon. Apart from sandwiched structures, coplanar (lateral) electrodes or field-effect transistor structures have also been characterized. The observation of switching and memory phenomenon in lateral structures with Au/Au electrode combination primarily rules out (1) migration of metal ions into the organic materials, (2) metal filament formation through a redox-driven process, and (3) electroreduction of the molecules as possible mechanisms of electrical bistability in CuPc. The existence two conducting state and bistability have been explained in terms of trapping and detrapping of carriers in the molecular layer. Furthermore, the lateral structures show possibilities to tune switching processes through the bias of the base (gate) electrode.     

First-principles of wurtzite ZnO (0001) and (0001) surface structures

The surface structures ofwurtzite ZnO(0001) and(0001) surfaces are investigated by using a first-principles calculation of plane wave ultra-soft pseudo-potential technology based on density functional theory(DFT).The calculated results reveal that the surface energy of ZnO-Zn is bigger than that of ZnO-O,and the ZnO-Zn surface is more unstable and active.These two surfaces are apt to relax inward,but the contractions of the ZnO-Zn surface are smaller than the ZnO-O surface.Due to the dispersed Zn4s state...     

A data correction method in radio-occultation experiments using regional atmospheric models by the example of Arctic

A method for correction of the data obtained in atmospheric studies using radio-occultation experiments is proposed. The method is based on obtaining the a priori data from regional atmospheric models, estimating the distortions inherent in radio-occultation experiments, and constructing the correction algorithms. As a result, the accuracy of reconstruction of the refractive index in real atmosphere is improved in the range of heights from 2 km to 12 km. By the example of the Arctic region, a technique for testing the suggested correction methods with the use of independent sonde measurements of atmospheric profiles is developed. Using the data obtained from the CHAMP satellite in the years 2001–2004, the suggested correction methods are tested and the statistical analysis of their efficiency is carried out. The validity limits of the suggested method are determined for different geographic conditions.     

Heteroepitaxy of HgCdTe(112) infrared detector structures on Si(112) substrates by molecular-beam epitaxy

High-quality, single-crystal epitaxial films of CdTe(112)B and HgCdTe(112)B have been grown directly on Si(112) substrates without the need for GaAs interfacial layers. The CdTe and HgCdTe films have been characterized with optical microscopy, x-ray diffraction, wet chemical defect etching, and secondary ion mass spectrometry. HgCdTe/Si infrared detectors have also been fabricated and tested. The CdTe(112)B films are highly specular, twin-free, and have x-ray rocking curves as narrow as 72 arc-sec and near-surface etch pit density (EPD) of 2 × 10⁶ cm⁻² for 8 μm thick films. HgCdTe(112)B films deposited on Si substrates have x-ray rocking curve FWHM as low as 76 arc-sec and EPD of 3-22 × 10⁶ cm⁻². These MBE-grown epitaxial structures have been used to fabricate the first high-performance HgCdTe IR detectors grown directly on Si without use of an intermediate GaAs buffer layer. HgCdTe/Si infrared detectors have been fabricated with 40% quantum efficiency and R₀A = 1.64 × 10⁴ Ωm₂ (0 FOV) for devices with 7.8 μm cutoff wavelength at 78Kto demonstrate the capability of MBE for growth of large-area HgCdTe arrays on Si.     

激光光谱合成技术研究进展与展望（特邀）

光谱合成技术利用色散元件或双色元件,使多路不同波长的激光在近场和远场同时实现空间重叠,合成至单一孔径输出的激光,是实现高功率、高光束质量激光输出的技术途径之一,受到了研究者的极大关注。特别在近十年来,随着光栅等合成元件性能的不断改善,高功率高光束质量的光谱合成激光输出在工业、国防等领域发挥了重要作用,有着广泛的应用前景。文中对半导体激光器和光纤激光器两种典型激光工作介质进行归类,梳理并回顾了光谱合成技术的发展历程,综述了当前高功率光谱合成技术的主流方案与国内外研究现状。此外,结合笔者所在课题组在光谱合成方面的研究工作,展示了光谱合成技术近年的发展态势,并展望了光谱合成技术的未来发展方向。     

结合MR数据设计方案提高TD-LTE室分故障排查效率方法的研究

本文结合现网室内分布系统各项关键指标对现有室分系统故障排查流程进行了分析,对利用MR数据排查室分故障的优缺点进行分析;分析了利用规划设计方案进行问题点定位方法的可能性,提出了调整后室内分布系统故障排查及分析流程;对调整后室内分布系统故障排查及分析流程进行了验证。     

Modeling of electromagnetic interference induced by electrostaticdischarge (ESD) inside resonant structures

This paper presents an accurate analysis of the effects produced by electrostatic discharge (ESD) inside a metallic enclosure, representing the metallic shield of an apparatus. The considered discharges are either directly generated inside the cavity or guided into the enclosure through a transmission line. The model, which makes use of a modal approach for the calculation of the electromagnetic (EM) field inside the cavity, evaluates the disturbance induced by the different kinds of ESDs on a victim line. The results both in the frequency and time domain have been validated by experimental measurements and highlight the effects of the resonant nature of the structure on the intensity and the duration of the disturbance     

仿生虾蛄眼偏振特性结构研究(简讯)

虾蛄眼具有强大的视觉系统,具有多光谱和偏振探测能力。以虾蛄眼微绒毛阵列结构为基础,进行仿生研究。针对偏振探测中的能量利用率以及空间分辨率的问题,仿生虾蛄眼微绒毛阵列结构,研究了孔阵列光子晶体结构,实现偏振滤波与光谱滤波的集成;根据虾蛄眼微绒毛具有光谱滤波及光信号吸收特性,以纳米线栅为仿生结构基础,实现偏振、光谱吸收特性的集成;依据虾蛄眼双向微绒毛阵列结构,以正交纳米线栅为仿生结构基础,实现单位像元的双向偏振吸收。     

两种苔蛾触角感器扫描电镜观察

应用扫描电子显微镜观察了美苔蛾Miltochrista miniata和之美苔蛾M.ziczac的触角,发现5种触角感器:毛形感器(3个亚型)、刺形感器、腔锥形感器(2个亚型)、栓锥形感器和B?hm氏鬃毛(2个亚型).触角感器数量最多的是毛形感器,其次为B?hm氏鬃毛,栓锥形感器的数量最少,其余两种感器数量居中;之美苔蛾的触角感器的总数多于美苔蛾;两种苔蛾雄性个体触角感器的总数均多于雌性个体触角感器的总数.本文对两种苔蛾触角各感器的形态、分布进行描述,对种间、种内差异进行讨论.     

Radiation hardness of wide-gap semiconductors (using the example of silicon carbide)

Results obtained in studying the effect of ionizing radiation on epitaxial layers and devices based on silicon carbide (SiC) are considered. It is shown that, in investigations of wide-gap semiconductors (WGS), account should be taken of how the rate of removal of mobile charge carriers—the standard parameter in determining the radiation hardness of a material—depends on temperature. The use of data obtained only at room temperature may lead to an incorrect assessment of the radiation hardness of WGS. A conclusion is made that the WGS properties combine, on the one hand, high radiation hardness of high-temperature devices based on these semiconductors and, on the other, the possibility of effective radiation-induced doping (e.g., for obtaining semi-insulating local regions in a material at room temperature).     

无载频脉冲探地雷达性能分析及其FD—TD法数值模拟计算

探测深度和分辩率是探地雷达的两项重要指标。本文分别对无载频脉冲探地雷达的探测深度和分辩率进行了分析，指出了影响雷达探测深度和分辩率的因素，并利用２。５维时时有限差分方法对雷达的探测性能进行了数值模拟计算，给出了地下单体目标和多体目标的回波信号电平图，并将部分计算结果与实验测试结果进行了对比，二者具有好的一致性。