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Antennas and Propagation Society International Symposium

作者： D. Chatterjee R.G. Plumb Radar Systems and Remote Sensing Laboratory Department of Electrical Engineering and Computer Science University of Kansas Lawrence KS USA

The E/sub /spl theta// patterns in the /spl theta/=90/spl deg/ plane of an array of /spl lambda//2 electric dipoles in presence of a circular cylinder are studied using the NEC-basic scattering code (NECBSC2). The results indicate that acceptable antenna patterns can be obtained by symmetrically weighting the amplitude excitation of dipoles with respect to the center element. The numerical technique for obtaining these patterns, and the effects of creeping waves in the azimuth (/spl theta/=90/spl deg/) plane, are discussed.

关键词： Radio networks Geometry Azimuth Adaptive arrays Radar scattering Dipole antennas Performance analysis Radar remote sensing remote sensing Laboratories

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A method of moments model for VHF propagation

A method of moments model for VHF propagation

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Antennas and Propagation Society International Symposium

作者： J.T. Johnson R.T. Shin J. Eidson L. Tsang J.A. Kong Department of Electrical Engineering and Computer Science Massachusetts Institute of Technology Cambridge MA USA Lincoln Laboratory MIT Lexington MA USA Electromagnetics and Remote Sensing Laboratory University of Washington Seattle WA USA

Site specific VHF propagation models remain a subject of continuing interest. A number of approximate methods exist and have been applied successfully in specific cases, but the limitations of the approximations of these models remain unclear. A numerically exact model based on the banded matrix iterative approach (BMIA) to the method of moments is presented which enables the solution of practical propagation problems. Although this model remains computationally complex, use of the iterative method along with parallel computing techniques enables large scale propagation problems to be solved within reasonable amounts of computational time. A typical VHF propagation problem involves predicting the power measured by a receiver as a function of altitude at a given distance away from a like polarised transmitter and above an inhomogeneous terrain profile.

关键词： Moment methods Iterative methods Concurrent computing Numerical models Computational modeling Parallel processing Large-scale systems Power measurement Polarization Transmitters

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Phase correction for coherent noise reduction in short-range radar measurements

Phase correction for coherent noise reduction in short-range...

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IEEE International Symposium on Geoscience and remote sensing (IGARSS)

作者： S.G. Beaven S.P. Gogineni P. Kanagaratnam Development Test & Evaluation Division Naval Command Control and Ocean Surveillance Center San Diego CA USA Radar Systems and Remote Sensing Laboratory Department of Electrical and Computer Engineering University of Kansas Lawrence KS USA

Short-range scatterometer systems are used to obtain radar backscatter signatures for understanding the interaction between electromagnetic energy and geophysical media in a number of remote sensing applications. Unlike long-range and intermediate-range radar systems, the sensitivity of short-range radars is not limited by thermal noise, but rather by reflections and leakage signals from the antenna and RF section. These leakage signals and their sidelobes are the primary sources of unwanted signals (coherent noise) in short-range FM radar systems. The authors have employed coherent noise reduction techniques to reduce the effects of these unwanted signal sources. Reduction of these coherent noise sources is critical to obtaining accurate backscatter measurements from geophysical targets. Recent advances include the use of phase correction to overcome limitations due to drift of local oscillators and effects of temperature changes on the system. The authors present results from the standard and phase-corrected coherent noise reduction techniques. These techniques increased the dynamic range of field and laboratory measurements of radar backscatter from sea ice and allows the authors to use data from past experiments that had previously been discarded due to low signal-to-noise ratio.

关键词： Noise reduction Radar antennas Radar remote sensing Backscatter Radar measurements Geophysical measurements Sea measurements Radar applications Radar scattering Electromagnetic scattering

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ELECTROMAGNETIC IMAGING OF UNDERGROUND TARGETS USING CONSTRAINED OPTIMIZATION

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IEEE TRANSACTIONS ON GEOSCIENCE AND remote sensing 1995年第3期33卷 551-561页

作者： CHATURVEDI, P PLUMB, RG Department of Electrical Engineering and Computer Science Radar Systems and Remote Sensing Laboratory University of Kansas Lawrence KS USA

Several high-frequency electromagnetic techniques have been used in recent years to detect and identify buried objects. Post-processing of the collected data is performed in many of these techniques to obtain high-quality images of buried targets, Accurate reconstructions of the target's constitutive parameters can be obtained by casting the imaging problem in terms of an inverse electromagnetic scattering problem, A number of techniques have been put forth recently to invert the electromagnetic data to obtain such images, In this paper, we use a frequency-domain Born iterative method to reconstruct images of shallow targets, The Born iterative technique requires successive solutions to a forward scattering problem followed by an inverse scattering problem at each iteration step, We use a finite-difference time domain (FDTD) algorithm to solve the forward scattering problem and constrained optimization for the inverse problem. Two-dimensional simulated data for several canonical objects buried in the ground are obtained using the FDTD technique, The same FDTD code is also used in calculating the Green's function required for solving the constrained optimization problem, Lossy, inhomogeneous ground models are used in several simulations to illustrate the use of this technique for practical situations, The inversion process can be used to reconstruct images for many realistic dielectric contrasts for which a linear Born approximation fails. Moreover, it is also shown that a small number of measurements results in accurate reconstructions with this technique, Use of multiple frequencies is also investigated.

关键词： image reconstruction Finite difference methods Time domain analysis Electromagnetic scattering Buried object detection Inverse problems Constraint optimization Casting Iterative methods Iterative algorithms

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Texture segmentation using hierarchical wavelet decomposition

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PATTERN RECOGNITION 1995年第12期28卷 1819-1824页

作者： Salari, E Ling, Z Computer Vision and Image Processing Laboratory Department of Electrical Engineering University of Toledo Toledo OH 43606 U.S.A.

This paper presents a texture segmentation algorithm based on a hierarchical wavelet decomposition. Using Daubechies' four-tap filter, an original image is decomposed into three detail images and one approximate image. The decomposition can be recursively applied to the approximate image to generate a lower resolution of the pyramid. The segmentation starts at the lowest resolution using the K-means clustering scheme and textural features obtained from various sub-bands. The result of segmentation is propagated through the pyramid to a higher resolution with continuously improving the segmentation. The lower resolution levels help to build the contour of the segmented texture, while higher levels refine the process, and correct possible errors.

关键词： Texture segmentation Wavelet transform Clustering algorithm Multiresolution segmentation

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FDTD MODELING OF SCATTERERS IN STRATIFIED MEDIA

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IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION 1995年第10期43卷 1164-1168页

作者： DEMAREST, K PLUMB, R HUANG, ZB Radar Systems and Remote Sensing Laboratory Department of Electrical Engineering and Computer Science University of Kansas Lawrence KS USA

The FDTD technique is well suited for calculating the fields scattered by buried objects when the sources are close enough to the air/ground interface so that they can be incorporated into the solution space, Difficulties arise, however, when the sources are far from the interface since the total fields in the solution space are not all outgoing waves, Using well-known formulas for the fields transmitted and reflected by stratified media, this paper discusses a method whereby the fields scattered by a buried object can be easily calculated by the FDTD technique when the incident field is a plane wave.

关键词： electromagnetic fields electromagnetic wave reflection electromagnetic wave scattering electromagnetic wave transmission finite difference time-domain analysis EM fields EM scattering FDTD modeling air/ground interface buried objects incident field plane Electromagnetic wave reflection Scattering electromagnetic wave transmission Platanus hybrida Solution space Electromagnetic wave scattering plane Planing Buried object detection Finite difference time domain method Electromagnetic fields Fields

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Simultaneous 35, 95, and 225 GHz fully polarimetric measurements of fallen snow

Simultaneous 35, 95, and 225 GHz fully polarimetric measurem...

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IEEE International Symposium on Geoscience and remote sensing (IGARSS)

作者： S.P. Lohmeier J.M. Baker J.B. Mead R.E. McIntosh Microwave Remote Sensing Laboratory Department of Electrical & Computer Engineering University of Massachusetts Amherst MA USA

During the winter of 1994, a three frequency polarimetric radar system operating at 35, 95, and 225 GHz was configured to take simultaneous measurements of the Mueller matrix and normalized radar cross section (NRCS). In addition to the radar measurements, in situ data characterized the snow pack and meteorological parameters. It was found that NRCS is inversely related to the amount of liquid water content in the snow pack up to the depth of penetration. Additionally, a supervised classification using the minimum distance classifier was used to classify the data into four snow type categories with a 97% accuracy.

关键词： Snow Radar antennas Radar polarimetry Radar cross section Radar remote sensing Frequency Radar measurements Temperature remote sensing Meteorology

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Dual polarization pulse pair technique for high unambiguous Doppler and range measurements of tornadoes with a 95 GHz radar

Dual polarization pulse pair technique for high unambiguous ...

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IEEE International Symposium on Geoscience and remote sensing (IGARSS)

作者： A.L. Pazmany J. Galloway R.E. McIntosh Microwave Remote Sensing Laboratory Department of Electrical & Computer Engineering University of Massachusetts Amherst MA USA

Since 1993 the University of Massachusetts (UMass) Microwave remote sensing laboratory and the University of Oklahoma (UO) department of Meteorology have collaborated to investigate tornadoes using the UMass 95 GHz polarimetric cloud radar. The project objective is to obtain high resolution horizontal cross section images of the reflectivity and velocity structure of a tornado and its vicinity in a supercell storm. To accurately measure the high wind speeds and gradients inside a tornado, a dual polarization pulse pair technique was implemented. This paper describes the technique and presents high resolution images of the hook echo and forward flank down draft of a supercell storm.

关键词： Polarization Tornadoes image resolution Storms Pulse measurements remote sensing Laboratories Meteorology Collaboration Clouds

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Investigation of the azimuthal response of off-nadir backscatter from the ocean surface

Investigation of the azimuthal response of off-nadir backsca...

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IEEE International Symposium on Geoscience and remote sensing (IGARSS)

作者： J. Carswell W. Donnelly R. McIntosh Microwave Remote Sensing Laboratory Department of Electrical & Computer Engineering University of Massachusetts Amherst MA USA

The University of Massachusetts participated in several field campaigns collecting C-band and Ku-band backscatter measurements of the ocean surface with a C-band and a Ku-band airborne scatterometer. These two instruments conically scanned the ocean surface providing the full backscatter response at 21/spl deg/, 31/spl deg/, 41.5 and 52/spl deg/ incidence. During the field campaigns winds ranging from less than 1 m/spl middot/s/sup -1/ to greater than 30 m/spl middot/s/sup -1/ were sampled. These observations will be presented and the full azimuthal response at both frequencies characterized with emphasis on the location of the minima.

关键词： Backscatter Oceans Sea surface Sea measurements Wind Radar measurements Instruments Frequency Microstrip antenna arrays remote sensing

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An efficient algorithm for DTMF decoding using the subband NDFT

An efficient algorithm for DTMF decoding using the subband N...

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IEEE International Symposium on Circuits and Systems (ISCAS)

作者： S. Bagchi S.K. Mitra Department of Electrical and Computer Engineering Signal and Image Processing Laboratory University of California Santa Barbara CA USA

An algorithm based on the subband nonuniform discrete Fourier transform (SB-NDFT) is proposed for decoding dual-tone multi-frequency (DTMF) signals. To decode a DTMF signal, its energy at the eight DTMF frequencies must be determined by evaluating samples of the NDFT at these frequencies. In the proposed SB-NDFT algorithm, these NDFT samples are computed by decomposing the input signal into two subbands. Since DTMF signals occupy the low-frequency part of the telephone bandwidth, the higher subband can be discarded for a fast, approximate computation. A performance comparison between algorithms based on the NDFT, SB-NDFT, DFT, and SB-DFT shows that the SB-NDFT requires the lowest number of computations to attain a specified level of performance.

关键词： Decoding Frequency Discrete Fourier transforms Signal processing image processing Laboratories Telephony Bandwidth Communication system signaling Telephone sets

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