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Geoscience and Remote Sensing, IEEE Transactions on

Issue 5  Part 1 • Date May 2007

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Displaying Results 1 - 25 of 27
  • [Front cover]

    Publication Year: 2007 , Page(s): C1
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  • IEEE Transactions on Geoscience and Remote Sensing publication information

    Publication Year: 2007 , Page(s): C2
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  • Table of contents

    Publication Year: 2007 , Page(s): 1097 - 1098
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  • Random Noise Radar/Sodar With Ultrawideband Waveforms

    Publication Year: 2007 , Page(s): 1099 - 1114
    Cited by:  Papers (8)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1642 KB) |  | HTML iconHTML  

    Random noise waveforms with ultrawide bandwidth improve the range resolution and reduces the probability of intercept in radar/sodar. As a result of the nonperiodic waveform, the range ambiguity is removed as well. By transmitting a sine signal that is phase or frequency modulated by random noise, autocorrelation functions with improved side lobe suppression in range can be formed. There are great similarities in the signal-processing algorithms applied in noise radar and sodar. The much slower propagation velocity of sound compared to light reduces the signal bandwidth but increases the time of measurement, however. In both sodar and radar, the range resolution is determined by the wavelength band occupied by the transmitted waveform, while the velocity resolution is controlled by the ratio of wavelength and time of measurement. The slower sound velocity also enhances the range/Doppler ambiguity problem in sodar when periodic waveforms are applied. This ambiguity could be suppressed if nonperiodic waveforms are introduced, such as random noise. In this paper, fundamental similarities and differences on system level between sodar and radar are first discussed, and signal-processing algorithms applied in random noise radar/sodar are reviewed. In particular, the noise floor of the ambiguity function and its relationship to spectrum width and time of measurement are analyzed, including improved side lobe suppression using mismatched filtering. The signal-processing algorithms were tested on raw data from sodar measurements on moving targets, buildings, vegetation, and water surfaces. An adaptive filter algorithm for suppression of the increased noise floor from dominant reflectors was derived and successfully applied to both sodar and stepped frequency radar data View full abstract»

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  • Analysis of the Effects of Faraday Rotation on Spaceborne Polarimetric SAR Observations at \hbox {P} -Band

    Publication Year: 2007 , Page(s): 1115 - 1122
    Cited by:  Papers (13)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (463 KB) |  | HTML iconHTML  

    Spaceborne microwave observation of subcanopy and subsurface requires the polarimetric synthetic aperture radar (SAR) technology at lower microwave frequencies, such as P-band. However, SAR observation at P-band is remarkably influenced by the Faraday rotation (FR) effect through the ionosphere. An example in this paper illustrates why the measured polarimetric data with FR at P-band cannot be directly applied to terrain surface classification. We further present that the parameters u, nu, H, alpha, A for terrain surface classification derived from the polarimetric data without FR, which are recovered from the data with FR, can be applied to the surface classification, there is a plusmnpi/2 ambiguity error unresolved. Based on gradual change of the FR degree along a geographical location, a method to eliminate the plusmnpi/2 ambiguity error is designed. Thus, the polarimetric scattering vector and Mueller matrix without FR and plusmnpi/2 ambiguity can be fully inverted from the measured polarimetric data with FR View full abstract»

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  • SAR Imaging Degradation by Ionospheric Irregularities Based on TFTPCF Analysis

    Publication Year: 2007 , Page(s): 1123 - 1130
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (260 KB) |  | HTML iconHTML  

    The effects of ionospheric irregularities on spaceborne synthetic aperture radar (SAR) signal propagation with double path and multilook angle are studied in a model in which a two-frequency and two-position coherence function (TFTPCF) has been adopted for analysis. The TFTPCF is derived from the phase-screen principle. The ambiguity function based on TFTPCF has been used to analyze the effects of ionospheric turbulence on range resolution and cross resolution. The results show that, in some cases, the effects from the irregularities on SAR imaging can be very serious View full abstract»

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  • Comparisons Between SAR Backscattering Coefficient and Results of a Thermodynamic Snow/Ice Model for the Baltic Sea Land-Fast Sea Ice

    Publication Year: 2007 , Page(s): 1131 - 1141
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (937 KB) |  | HTML iconHTML  

    We have compared the time series of C-band HH-polarization backscattering coefficients (sigmadeg) of the Baltic Sea land-fast level ice with results from a 1-D high-resolution thermodynamic snow/ice model (HIGHTSI). The sigmadeg time series were obtained from ENVISAT synthetic aperture radar (SAR) images. The study period was from the middle of the winter to the early melt season, February 3-April 7, 2004. Due to the large incidence angle range of the SAR images, the sigmadeg values were divided into three subseries. In general, the HIGHTSI results greatly helped to interpret the sigmadeg behavior with changing ice and weather conditions. The modeled snow-surface temperature, cases of snow melting, and evolution of snow and ice thickness were related to the changes in sigmadeg. Equally useful information could not be obtained solely on the basis of large-scale atmospheric models. Realistic forcing data for HIGHTSI were available in the form of coastal-weather observations and model results of the European Centre of Medium-Range Weather Forecasts (ECMWF). The latter make it possible to apply HIGHTSI in the interpretation of SAR data from all ice-covered seas. There were some cases where detailed ground truth, combined with theoretical sigmadeg modeling, would have been needed for interpretation of the sigmadeg trends. A very interesting observation was the large variation of level ice sigmadeg with changing weather conditions, which complicates automatic classification of the SAR images, and thus, the algorithms must be tuned for different ice conditions. The HIGHTSI model could act as an indicator of various ice conditions for algorithm development View full abstract»

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  • Submillimeter Accuracy of InSAR Time Series: Experimental Validation

    Publication Year: 2007 , Page(s): 1142 - 1153
    Cited by:  Papers (34)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (596 KB) |  | HTML iconHTML  

    This paper presents the results of a blind experiment that is performed using two pairs of dihedral reflectors. The aim of the experiment was to demonstrate that interferometric synthetic aperture radar (InSAR) measurements can indeed allow a displacement time series estimation with submillimeter accuracy (both in horizontal and vertical directions), provided that the data are properly processed and the impact of in situ as well as atmospheric effects is minimized. One pair of dihedral reflectors was moved a few millimeters between SAR acquisitions, in the vertical and east-west (EW) directions, and the ground truth was compared with the InSAR data. The experiment was designed to allow a multiplatform and multigeometry analysis, i.e., each reflector was carefully pointed in order to be visible in both Envisat and Radarsat acquisitions. Moreover, two pairs of reflectors were used to allow the combination of data gathered along ascending and descending orbits. The standard deviation of the error is 0.75 mm in the vertical direction and 0.58 mm in the horizontal (EW) direction. GPS data were also collected during this experiment in order to cross-check the SAR results View full abstract»

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  • Data Fusion for Reconstruction of a DTM, Under a Woodland Canopy, From Airborne L-band InSAR

    Publication Year: 2007 , Page(s): 1154 - 1163
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (859 KB) |  | HTML iconHTML  

    This paper investigates the utility of different parameters from polarimetric interferometric synthetic aperture radar (InSAR) data for the identification of ground pixels in a woodland area to enable accurate digital terrain model (DTM) generation from the InSAR height of the selected ground hit pixels. The parameters assessed include radar backscatter, interferometric coherence, surface scattering proportion (based on Freeman-Durden decomposition), and standard deviation of the interferometric height. The method is applied to Monks Wood, a small seminatural deciduous woodland in Cambridgeshire, U.K., using airborne E-SAR data collected in June 2000. The 1428 variations of SAR-derived terrain models are validated with theodolite data and a light detection and ranging-derived DTM. The results show that increasing the amount of data used in the DTM creation does not necessarily increase the accuracy of the final DTM. The most accurate method, for the whole wood, was a fixed-window minimum-filtering algorithm, followed by a mean filter. However, for a spatial subset of the area using the upsi3 backscattering coefficient to identify ground pixels outperforms the minimum filtering method. The findings suggest that backscatter information may often be undervalued in estimating terrain height under forest canopies View full abstract»

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  • Spatial and Temporal Behavior of Microwave Backscatter Directional Modulation Over the Saharan Ergs

    Publication Year: 2007 , Page(s): 1164 - 1173
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (932 KB) |  | HTML iconHTML  

    Radar backscatter (sigmadeg) from ergs is modulated with view direction [incidence (thetas) and azimuth (phi) angles], where the modulation characteristics reflect the surface geometry. sigmadeg also varies spatially and reflects the spatial inhomogeneity of the sand surface. We use sigmadeg measurements at different thetas and phi angles from the NASA, European Remote Sensing satellite, and SeaWinds scatterometers to understand the relationship between wind and erg bedforms. A model incorporating the sigmadeg phi-modulation and spatial inhomogeneity is proposed. Surface slope variations are related to the sigmadeg spatial inhomogeneity. We compare the backscatter model results with numerically predicted wind direction data provided by the European Centre for Medium-Range Weather Forecasts (ECMWF) over the erg surfaces. We use the maxima of the phi-modulation at thetas=33deg to infer the orientation of the dominant slip-sides on the sand surface. These orientations are consistent with the ECMWF wind directions spatially and temporally View full abstract»

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  • A Hybrid Analytic-Numerical Algorithm of Scattering From an Object Above a Rough Surface

    Publication Year: 2007 , Page(s): 1174 - 1180
    Cited by:  Papers (15)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (310 KB) |  | HTML iconHTML  

    A hybrid algorithm, combining analytic Kirchhoff approximation (KA) and numerical method of moments (MoMs), is developed to solve the coupling electric-field integral equations (EFIEs) of scattering from a perfect electric conducting (PEC) object above a randomly rough PEC surface under TE-polarized plane-wave incidence. The MoM with the conjugate gradient approach is used to first solve the EFIE of the object. The surface fields on the rough surface are analytically expressed using the KA method, and large memory and computations for those fields are greatly reduced. An iterative approach of the surface fields induced on both object and rough surface is then utilized to take into account interactions between the object and underlying rough surface. Convergence of this hybrid algorithm is numerically validated. Making use of Monte Carlo realization, bistatic scattering from a 2-D PEC cylindrical object above a PEC rough surface is well simulated by this hybrid KA-MoM algorithm View full abstract»

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  • Statistical Properties of Low-Grazing Range-Resolved Sea Surface Backscatter Generated Through Two-Dimensional Direct Numerical Simulations

    Publication Year: 2007 , Page(s): 1181 - 1197
    Cited by:  Papers (17)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1046 KB) |  | HTML iconHTML  

    Statistical properties of the X-band sea clutter are studied using 2-D direct numerical simulations. Surfaces are modeled as realizations of a Gaussian random process with the Pierson-Moskowitz or Elfouhaily spectrum. The Creamer transform is further applied to account for the lowest-order surface nonlinearities. Backscattered field at a given frequency is found using the first-principles boundary integral equation (BIE) technique. Calculations are repeated at a number of frequencies, which allows synthesizing the surface response to a pulse as short as 2.2 ns (the corresponding spatial resolution is 0.33 m). Large-scale Monte Carlo trials are used to evaluate the correlation properties and to obtain the probability distributions for the vertically- and horizontally-polarized clutter. This paper concentrates on the incident angle of 85deg (5deg grazing), with a few results for moderate 60deg incidence also reported for comparison. The effects of variations in wind speed (sea state) and radar resolution on the clutter statistics are investigated. An L-band example (with proportionally longer pulse) helps explore the role of a different electromagnetic (e/m) wavelength. The simulation technique also allows for the isolation and examination of the impacts of certain e/m and hydrodynamic approximations, including the replacement of rigorous solution to the BIE by a simpler analytical scattering model. The amplitude statistics of the simulated backscatter are compared to the Weibull and K distributions that are often used to describe surface clutter View full abstract»

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  • Band-Limited Exponential Correlation Function for Rough-Surface Scattering

    Publication Year: 2007 , Page(s): 1198 - 1206
    Cited by:  Papers (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (785 KB) |  | HTML iconHTML  

    A band-limited exponential correlation function is presented for use in studies of rough-surface scattering. This model of surface statistics is developed by multiplying the power spectral density of a standard exponential correlation function surface with a Gaussian rolloff at high frequencies in order to limit the high-frequency spectral content of the surface. A parameter is introduced to describe the Gaussian rolloff, and the corresponding correlation function is determined. The primary proposed use of the model is in assessing the contributions of surface high-frequency content in the scattering process, particularly in approximate theories of surface scattering. Methods for incorporating this surface description into standard approximate scattering theories are described, and sample backscattering results provided to illustrate use of the model View full abstract»

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  • Field-Supported Verification and Improvement of a Passive Microwave Surface Emission Model for Rough, Bare, and Wet Soil Surfaces by Incorporating Shadowing Effects

    Publication Year: 2007 , Page(s): 1207 - 1216
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (462 KB) |  | HTML iconHTML  

    To investigate the potential of passive microwave techniques for observing the atmosphere over land, it is important to understand the nature of emissions from the land surface. The heterogeneity of large-scale land surface emissions has been cited as a major impediment in conducting observations of the atmosphere over land. Many models, both theoretical and empirical, have been developed to explain the surface emission with varying degrees of success. In the past, most field-supported research in soil observations using microwave techniques has concentrated on lower frequencies (L-band). This paper reports on a study, supported by field data, that seeks to improve our understanding of surface emission at various frequencies using passive microwave radiometers. This provides a crucial link between remote sensing of the land surface and the atmosphere. We show that it is important to consider shadowing associated with rough wet surfaces. By incorporating shadowing effects, the advanced integral equation model (AIEM) shows remarkable agreement with observations at all frequencies and polarizations. Although the roughness parameters obtained during our experiment correspond to very rough conditions, by including shadowing effects the AIEM model is able to transition from the not so rough natural condition as observed from space to the very rough as obtained during field experiments View full abstract»

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  • Increasing the Existence of Very Shallow-Water LIDAR Measurements Using the Red-Channel Waveforms

    Publication Year: 2007 , Page(s): 1217 - 1223
    Cited by:  Papers (10)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (377 KB) |  | HTML iconHTML  

    Mapping shallow-water bathymetry with acoustic techniques is complicated and expensive. The environmental parameters in shallow-water (<2 m) areas become more variable and greatly impact the depth extraction from the survey measurements. Current airborne light detection and ranging (LIDAR) bathymetry surveying in shallow-water depths uses green-channel waveforms to measure the water depth. Unfortunately, due to difficulties in distinguishing between the surface and bottom return of the water column, the timing of the bottom return is often ambiguous. Furthermore, the water often becomes optically "dirty" due to turbulence at these shallow depths. Therefore, it is common to find coastal areas that lack any measured depths. This paper presents a novel approach for measuring water depths in these shallow coastal waters with airborne LIDAR. Observations of the red-channel waveforms show that the waveforms are divided into two groups, namely: (1) waveforms in deep waters (>2 m) whose shape is invariant with respect to the water depth and (2) waveforms in shallow-water depths that show a change in shape as a function of the depth in the water column. The data for this study are from the US Geological Survey LIDAR surveys of Lake Tahoe, CA, and Lake Michigan, using a SHOALS-400 LIDAR system View full abstract»

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  • Angular Dependence of {cal K} -Distributed Sonar Data

    Publication Year: 2007 , Page(s): 1224 - 1235
    Cited by:  Papers (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2043 KB) |  | HTML iconHTML  

    Backscattered signal statistics are widely used for target detection and seafloor characterization. The K-distribution shows interesting properties for describing experimental backscattered intensity statistics. In addition to the fact that its probability distribution function accurately fits actual sonar data, it advantageously provides a physical interpretation linked to the backscattering phenomenon. Sonar systems usually record backscattered signals from a wide angular range across the ship's track. In this context, previous studies have shown that backscatter statistics strongly depend on the incidence angle. In this paper, we propose an extension of previous works to model the angular evolution of the K-distribution shape parameter. This evolution is made clear and analyzed from experimental data recorded with two sonar systems: a 95-kHz multibeam echosounder and a 110-kHz sidescan sonar. Model fitting with data backscattered from six seafloor configurations shows the improvement provided by our extension as compared to two previous models View full abstract»

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  • Use of C-Band Ground Penetrating Radar to Determine Backscatter Sources Within Glaciers

    Publication Year: 2007 , Page(s): 1236 - 1246
    Cited by:  Papers (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1289 KB) |  | HTML iconHTML  

    The question of penetration of synthetic aperture radar (SAR) signals at C-band frequency into polar glaciers is addressed by comparing ground penetrating radar (GPR) and SAR backscatter signatures. Profiles of the Kongsvegen glacier, Svalbard, were obtained with a C-band GPR. The received signal is converted to the equivalent radar cross section using the standard radar equation, thus mapping the effective scattering sources within the glacier at this frequency. The depth of the observed scattering sources is greatest in the superimposed ice where layers are clearly seen to a depth of approximately 14 m. The very high scattering properties of the upper firn layers preclude layers deeper than approximately 6 m from being imaged. Integrating the radar cross sections over the depth gives a single backscatter value that we compare with the backscatter coefficient (scattering cross section per unit area) of the processed SAR data for the same profile. The comparison indicates that for coincidentally acquired GPR and SAR data, the radar cross section measured by the GPR does represent the features that contribute to the SAR signal View full abstract»

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  • Optimal Maneuvering of Seismic Sensors for Localization of Subsurface Targets

    Publication Year: 2007 , Page(s): 1247 - 1257
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (871 KB) |  | HTML iconHTML  

    We consider the problem of detecting and locating subsurface objects by using a maneuvering array that receives scattered seismic surface waves. We demonstrate an adaptive system that moves an array of receivers according to an optimal positioning algorithm that is based on the theory of optimal experiments. The goal is to minimize the number of distinct measurements (array movements) needed to localize objects such as buried landmines. The adaptive localization algorithm has been tested using data collected in a laboratory facility. The performance of the algorithm is exhibited for cases with one or two targets and in the presence of common types of clutter such as rocks in the soil. Results are also shown for a case where the propagation properties of the medium vary spatially. In these tests, the landmines were located using three or four array movements. It is envisioned that future systems could incorporate this new method into a portable mobile mine-location system View full abstract»

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  • Three-Dimensional Bayesian Inversion With Application to Subsurface Sensing

    Publication Year: 2007 , Page(s): 1258 - 1270
    Cited by:  Papers (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (925 KB) |  | HTML iconHTML  

    A Bayesian formalism is considered for inverting for the parameters of a heterogeneity profile based on measured scattering data. It is shown that the typical use of regularization (e.g., Thikonov) corresponds to a maximum a posteriori point approximation to the full-posterior density function on the heterogeneity parameters, given the observed data. In the Bayesian framework considered here, the full posterior is approximated as a multidimensional Gaussian distribution. The mean of this distribution may be used as a point estimate of the heterogeneity profile, with the covariance matrix providing associated "error bars" (a measure of confidence in the inversion). In addition to providing an approximation to the full posterior of the heterogeneity profile, this formalism addresses the proper weighting to apply for inversion regularization. Specifically, an important limitation of previous regularization procedures is the need to place a weight on the importance of the regularization relative to the importance of fitting the data to the underlying model. In the Bayesian analysis outlined here, we also assign such a weight, but now the weight is treated as a random variable, with a statistical prior. The measured data are then used to determine a posterior distribution on the parameter, based on the measured data. We present here the basic Bayesian inversion framework, with several example results presented for subsurface-sensing problems View full abstract»

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  • Electromagnetic Propagation of GPR Signals in Martian Subsurface Scenarios Including Material Losses and Scattering

    Publication Year: 2007 , Page(s): 1271 - 1281
    Cited by:  Papers (10)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (460 KB) |  | HTML iconHTML  

    A study on the electromagnetic propagation in various models of the Martian subsurface is performed with a relevance to ground penetrating radar (GPR) operating onboard rover missions. Measurements of the electromagnetic properties of Mars soil simulants are obtained; on this basis, the attenuation features of the GPR signals are estimated, including both electric and magnetic losses. The effect on propagation of inhomogeneities inside the soil is also taken into account by means of a specific model with randomly distributed scatterers. The GPR performance in terms of resolution and maximum penetration depth is evaluated in the considered scenarios for different operating frequencies, thus providing a basic information for the design of systems for future subsurface sounding investigations on Mars View full abstract»

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  • Integral Electric Current Method in 3-D Electromagnetic Modeling for Large Conductivity Contrast

    Publication Year: 2007 , Page(s): 1282 - 1290
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (696 KB) |  | HTML iconHTML  

    We introduce a new approach to 3-D electromagnetic (EM) modeling for models with large conductivity contrast. It is based on the equations for integral current within the cells of the discretization grid, instead of the electric field or electric current themselves, which are used in the conventional integral-equation method. We obtain these integral currents by integrating the current density over each cell. The integral currents can be found accurately for the bodies with any conductivity. As a result, the method can be applied, in principle, for the models with high-conductivity contrast. At the same time, knowing the integral currents inside the anomalous domain allows us to compute the EM field components in the receivers using the standard integral representations of the Maxwell's equations. We call this technique an integral-electric-current method. The method is carefully tested by comparison with an analytical solution for a model of a sphere with large conductivity embedded in the homogenous whole space View full abstract»

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  • Higher Order Inhomogeneous Impedance Boundary Conditions for Perfectly Conducting Objects

    Publication Year: 2007 , Page(s): 1291 - 1297
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (264 KB) |  | HTML iconHTML  

    A new, simple, and fast method for the solution of electromagnetic scattering problems for perfectly conducting objects of arbitrary shape is presented. The method is based on an equivalent representation of the conducting object in terms of a circular one having a higher order impedance boundary condition on its surface. As a first result, a new universal relation between the higher order surface impedances and the shape of the object is obtained. Then, by taking advantage of this relationship, the scattering problem related to a conducting object is recast as the solution of a matrix equation whose coefficients are determined from the higher order impedances. Numerical simulations show that the method yields to accurate results, and that, it is computationally effective View full abstract»

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  • Explore IEL IEEE's most comprehensive resource [advertisement]

    Publication Year: 2007 , Page(s): 1298
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  • IEEE Geoscience and Remote Sensing Society announces the creation of TGARS letters section

    Publication Year: 2007 , Page(s): 1299
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  • Special issue on meteorology, climate, ionosphere, geodesy, and reflections from the ocean surfaces: studies by radio occultation methods

    Publication Year: 2007 , Page(s): 1300
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    Freely Available from IEEE

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IEEE TRANSACTIONS ON GEOSCIENCE AND REMOTE SENSING (TGRS) is a monthly publication that focuses on the theory, concepts, and techniques of science and engineering as applied to sensing the land, oceans, atmosphere, and space; and the processing, interpretation, and dissemination of this information.

 

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Editor-in-Chief
Antonio J. Plaza
University of Extremadura