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Signal Recovery and Synthesis, SRS 2001

作者： Cain, Stephen C. Hayat, Majeed M. Engineering Department Purdue University 2101 E. Coliseum Blvd. Fort WayneIN46805-1499 United States Electro-Optics Program Electrical and Computer Engineering Department University of Dayton DaytonOH45469-0245 United States

A new model describing the temporal transitions of atmospheric tilt is described and utilized in a Bayesian tilt-estimation algorithm. Using this model, images are synthesized from short-exposure data demonstrating th... 详细信息

ISBN: (纸本)1557526907

关键词： Image enhancement

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Theory of impact ionization in thin multiplication layers

Theory of impact ionization in thin multiplication layers

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IEEE Photonics Conference (IPC)

作者： M.M. Hayat Oh-Hyun Kwon M.A. Saleh Department of Electrical and Computer Engineering University of New Mexico Albuquerque NM USA Electro-optics Program University of Dayton Dayton OH USA

We use a model for the ionization coefficients to calculate the frequency response characteristics and the avalanche breakdown voltage in thin layers. Notably, calculations based on the dead-space theory for the APD time response reveal that in addition to a reduction in the excess noise factor, thin layers benefit from reduced spectral fluctuations in the buildup-time limited photocurrent.

关键词： Impact ionization Space exploration Fluctuations Predictive models Noise reduction Gain measurement Frequency response Time factors Photoconductivity Bandwidth

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Effects of uncorrelated and correlated noise on image information content

Effects of uncorrelated and correlated noise on image inform...

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IEEE International Symposium on Geoscience and Remote Sensing (IGARSS)

作者： R.M. Narayanan S.K. Ponnappan S.E. Reichenbach Department of Electrical Engineering and Center of Electro-Optics 209NWalter Scott Engineering Center University of Nebraska Lincolnshire NE USA Department of Computer Science and Engineering University of Nebraska Lincolnshire NE USA

The information content in remote sensing imagery depends upon various factors such as spatial and radiometric resolutions, radiometric contrast between different target types, and also the final application for which the imagery has been acquired. Our approach to quantifying image information content is based upon classification accuracy. As noise is added to the image, the classification accuracy reduces, thereby resulting in loss of "information". The relationship between the information content and the noise variance can be described by a negative exponential model. The model is seen to be applicable for relating the information content to noise variance for Landsat TM as well as multi-look and single-look SIR-C imagery. We observe that the relationship is independent of the type of noise (Gaussian, Rayleigh, or gamma). However, the rate of information loss increases with the correlation distance in the case of spatially correlated noise. The rate of information loss also increases with the number of classes chosen for classifying the scene. The model is useful in deducing allowable signal-to-noise ratios for different sensor systems.

关键词： Remote sensing Radiometry Spatial resolution Image resolution Noise reduction Satellites Gaussian noise Layout Signal to noise ratio Sensor systems

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Achievement of essentially full spatial coherence in a high-average-power soft-x-ray laser

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Physical Review A 2001年第3期63卷 033802-033802页

作者： Y. Liu M. Seminario F. G. Tomasel C. Chang J. J. Rocca D. T. Attwood Applied Science and Technology Graduate Program University of California Berkeley California 94720 Center for X-ray Optics Lawrence Berkeley National Laboratory Berkeley California 94720 Department of Electrical and Computer Engineering Colorado State University Fort Collins Colorado 80523 Department of Electrical Engineering and Computer Science University of California Berkeley California 94720

We report an observation of essentially full spatial coherence in a high average power soft-x-ray laser. Rapid coherence buildup due to strong refractive antiguiding in a long plasma column is experimentally demonstrated. This allows the generation of fully coherent, milliwatt-level average power soft-x-ray radiation by a tabletop device. The peak brightness of this laser reaches 2×1025photonss−1mm−2mrad−2 within 0.01% spectral bandwidth, making it one of the brightest soft-x-ray sources available.

关键词： .full spatial high average coherence buildup plasma column degree of spatial

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Prediction of excess noise factor and frequency response for thin avalanche photodiodes

Prediction of excess noise factor and frequency response for...

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IEEE Photonics Conference (IPC)

作者： M.M. Hayat M.A. Saleh Ohhyun Kwon B.E.A. Saleh M.C. Teich Dept. of Electr. & Comput. Eng. Dayton Univ. OH USA Department of Electrical and Computer Engineering Boston University Boston MA USA Electro-Optics Program and the Department of Electrical and Computer Engineering University of Dayton Dayton OH USA

Summary form only given. Recent experimental measurements from InP and InAlAs avalanche photodiodes (APDs) with thin multiplication regions, collected by J.C. Campbell and collaborators at the University of Texas at Austin, show that, for a fixed gain the excess noise factor is significantly lower than that predicted by the conventional McIntyre theory. The observed dependence of the noise on the multiplication-region width cannot be explained using the conventional theory in which the excess noise factor is a function only of the mean gain and the ionization coefficient ratio. In the dead-space-multiplication theory (DSMT), a carrier must travel a certain distance, called the dead space, before gaining sufficient energy for impact ionisation to occur. Because this dead space regularizes the ionisation locations, the randomness of the avalanching mechanism is reduced. For thin multiplication-region APDs, this effect is proportionally higher and thus the noise is lower. We applied the DSMT to the experimental results for GaAs and AlGaAs and more recently for InP and InAlAs APDs. We were able to fit the ionization coefficients associated with devices of various thicknesses, as a function of the electric field, within the confines of a single exponential model.

关键词： Frequency response Avalanche photodiodes Ionization Indium phosphide Gallium arsenide Bandwidth electronic mail Indium compounds Signal to noise ratio Space exploration

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FDTD speedups obtained in distributed computing on a Linux workstation cluster

FDTD speedups obtained in distributed computing on a Linux w...

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Antennas and Propagation Society International Symposium

作者： G.A. Schiavone I. Codreanu R. Palaniappan P. Wahid Institute for Simulation and Training (IST) University of Central Florida USA Center for Research in Electro-optics and Lasers (CREOL) University of Central Florida USA Department of Electrical and Computer Engineering University of Central Florida USA

The project investigated various aspects of parallel FDTD implementation on a workstation cluster. The computation grid was divided among nodes. For a fixed size problem, as the number of processor increases, the speedup saturates. This happens because each processor spends less time computing but essentially the same time communicating with its neighbors. To take advantage of the parallel algorithm, the problem size must be sufficiently large compared with the number of processors. For very large problems, we can efficiently employ a large number of processors to obtain a linear speedup. In this work, the message passing interface (MPI) parallel implementation was integrated with POSIX threads using the pthreads library. This was required because each node in the cluster was equipped with two processors. On each node, each process contained two threads that executed in parallel. As expected, for sufficiently large problems the speedup was increased by almost a factor of two when using threads.

关键词： Finite difference methods Time domain analysis Distributed computing Linux Yarn Workstations Grid computing Parallel algorithms Message passing Libraries

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Dependence of image information content on gray-scale resolution

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Geocarto International 2000年第4期15卷 17-30页

作者： Narayanan, Ram M. Sankaravadivelu, T.S. Reichenbach, Stephen E. Department of Electrical Engineering Center for Electro-Optics University of Nebraska Lincoln NE 68588-0511 United States Department of Computer Science & Engineering University of Nebraska Lincoln NE 68588-0511 United States Department of Computer Science & Engineering University of Nebraska Lincoln NE 68588-0511 United States

Remote sensing images acquired in various spectral bands are used to estimate certain geophysical parameters or detect the presence or extent of geophysical phenomena. In a majority of cases, the raw image acquired by the sensor is processed using various operations such as filtering, compression, enhancement, etc. In performing these operations, the analyst is attempting to maximise the information content in the image to fulfill the end objective. The information content in a remote sensing image for a specific application is greatly dependent on the gray-scale resolution of the image. One of the measures to quantify information content is classification accuracy. In such applications, the loss in information content as a result of degraded gray-scale resolution may not be significant. This is because, although the value of a pixel may change as a result of the decrease in the resolution, the same pixel may, in most cases, be correctly classified. Our research reveals that the loss in information is exponential with respect to the number of gray levels. The model is seen to be applicable for Landsat TM and SIR-C images. Using our mathematical model for the information content of images as a function of gray-scale resolution, one can specify an “optimal” gray-scale resolution for an image. © 2000 Taylor & Francis Group, LLC.

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Effects of source traffic shaping on MPEG video transmission over next generation IP networks 8

Effects of source traffic shaping on MPEG video transmission...

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8th International Conference on computer Communications and Networks, ICCCN 1999

作者： Alam, Mohammad F. Atiquzzaman, Mohammed Karim, Mohammad A. Electro-Optics Program University of Dayton DaytonOH45469-0245 United States Department of Electrical and Computer Engineering University of Dayton DaytonOH45469-0226 United States Department of Electrical and Computer Engineering University of Tennessee KnoxvilleTN37996-2100 United States

ISBN: (纸本)0780357949

The Internet engineering Task Force (IETF) has defined the integrated services model for supporting real-time services. Guaranteed service is one of these services with firm delay and bandwidth guarantees. Before setting up a guaranteed service flow, traffic parameters of the source have to be specified in terms of token bucket traffic descriptors. The source must conform to these descriptors by shaping its traffic. In this paper, we study the effects of a token bucket traffic shaper at the source on the transmission characteristics of Motion Picture Experts Group (MPEG) video streams over the guaranteed service. For different types of MPEG video sequences, the effects of the shaper parameters on the transmission performance are studied. We develop an analytical model of the traffic shaper, and also carry out numerical simulation of the transmission performance to verify the analytical model. Our study also provides a technique to analyze stored MPEG video sequences to determine the token bucket traffic descriptors that have to be specified during flow set up. © 1999 IEEE.

关键词： Analytical models

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Efficient MPEG video traffic shaping for the next generation Internet

Efficient MPEG video traffic shaping for the next generation...

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IEEE Conference and Exhibition on Global Telecommunications (GLOBECOM)

作者： M.F. Alam M. Atiquzzaman M.A. Karim Electro-optics Program University of Dayton Dayton OH USA Department of Electrical and Computer Engineering University of Dayton Dayton OH USA Department of Electrical and Computer Engineering University of Tennessee Knoxville TN USA

The Internet engineering Task Force (IETF) has defined the Guaranteed Service (GS) with firm delay and bandwidth guarantees in the Integrated Services model for supporting real-time services. Before setting up a GS flow, the traffic parameter of the source have to be specified in terms of a number of token bucket traffic descriptors. The source must conform to these descriptors by shaping its traffic. In this paper we study a novel traffic shaper for efficient transmission of MPEG video streams over GS. We develop an analytical model of the traffic shaper, and also carry out numerical simulation of the transmission performance to verify the analytical model. Our study also provides a methodology to determine the token bucket traffic descriptors that have to be specified during flow set up.

关键词： Traffic control Communication system traffic control Telecommunication traffic Web and internet services Delay effects Streaming media Analytical models IP networks Transport protocols Bandwidth

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Information content characterization in remote sensing imagery based on classification accuracy

Information content characterization in remote sensing image...

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IEEE International Symposium on Geoscience and Remote Sensing (IGARSS)

作者： R.M. Narayanan M.K. Desetty S.E. Reichenbach Department of Electrical Engineering and Center for Electro-optics University of Nebraska Lincolnshire NE USA Department of Computer Science and Engineering University of Nebraska Lincolnshire NE USA

The information content in remote sensing imagery depends upon various factors. Various textural measures are used to characterize the image information content. Our approach to quantifying image information content is based upon classification accuracy. We have developed a negative-exponential model that relates information content to spatial resolution, which is seen to be applicable to real images acquired by Landsat TM optical as well as SIR-C SAR sensors. An interesting conclusion that emerges is that although the TM image has higher information content than the SIR-C image at lower pixel sizes, the opposite is true at higher pixel sizes. The transition occurs at a pixel size of about 720 meters. This tells us that for applications that require higher resolutions (or smaller pixel sizes), the TM sensor is more useful for terrain classification. On the contrary, for applications involving lower resolutions (or larger pixel sizes), the SIR-C sensor has an advantage. Thus, the model is useful in comparing different sensor types for different applications.

关键词： Remote sensing Spatial resolution Pixel Optical sensors Image sensors Image resolution Image edge detection Spaceborne radar computer science Satellites

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