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Geoscience and Remote Sensing, IEEE Transactions on

Issue 12 • Date Dec. 2001

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Displaying Results 1 - 19 of 19
  • List of reviewers

    Page(s): 2563 - 2565
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    Freely Available from IEEE
  • Magnetoquasistatic response of conducting and permeable prolate spheroid under axial excitation

    Page(s): 2689 - 2701
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    An analytical solution is presented for the problem of magnetic diffusion into and scattering from a permeable, highly but not perfectly conducting prolate spheroid under axial excitation, expressed in terms of an infinite matrix equation. The spheroid is assumed to be embedded in a homogeneous nonconducting medium as appropriate for low-frequency, high-contrast scattering governed by magnetoquasistatics. The solution is based on separation of variables and matching boundary conditions where the prolate spheroidal wavefunctions with complex wavenumber parameter are expanded in terms of spherical harmonics. For small skin depths, an approximate solution is developed that avoids any reference to the spheroidal wavefunctions. The problem of long spheroids and long circular cylinders is solved by using an infinite cylinder approximation. In some cases, our ability to evaluate the spheroidal wavefunctions breaks down at intermediate frequencies. To deal with this, a general broadband rational function approximation technique is developed and demonstrated. We treat special cases and provide numerical reference data for the induced magnetic dipole moment or, equivalently, the magnetic polarizability factor. View full abstract»

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  • Author index

    Page(s): 2729 - 2739
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    Freely Available from IEEE
  • Subject index

    Page(s): 2739 - 2765
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  • Comparison of SAR-derived wind speed with model predictions and ocean buoy measurements

    Page(s): 2587 - 2600
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    As part of the Alaska synthetic aperture radar (SAR) Demonstration Project in 1999 and 2000, wide-swath RADARSAT SAR imagery has been acquired on a regular basis in the Gulf of Alaska and the Bering Sea. During 1998 and 1999, similar data were acquired off the East Coast of the United States as part of the StormWatch Project. The radar cross section measurements from these images were combined with wind direction estimates from the Navy Operational Global Atmospheric Prediction System model to produce high-resolution maps of the surface wind speed. For this study, 2862 SAR image frames were collected and examined. Averaged wind estimates from this data base have been systematically compared with corresponding wind speed estimates from buoy measurements and model predictions, and very good agreement has been found. The standard deviation between the buoy wind speed and the SAR estimates is 1.76 m/s. Details of the SAR wind extraction procedure are discussed, along with implications of the comparisons on the C-band polarization ratio View full abstract»

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  • A joint multicontext and multiscale approach to Bayesian image segmentation

    Page(s): 2680 - 2688
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    In this paper, a joint multicontext and multiscale (JMCMS) approach to Bayesian image segmentation is proposed. In addition to the multiscale framework, the JMCMS applies multiple context models to jointly use their distinct advantages, and we use a heuristic multistage, problem-solving technique to estimate sequential maximum a posteriori of the JMCMS. The segmentation results on both synthetic mosaics and remotely sensed images show that the proposed JMCMS improves the classification accuracy, and in particular, boundary localization and detection over the methods using a single context at comparable computational complexity View full abstract»

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  • Seasonal and short-term variability of multifrequency, polarimetric radar backscatter of Alpine terrain from SIR-C/X-SAR and AIRSAR data

    Page(s): 2634 - 2648
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    Signatures of glaciated and ice free areas were analyzed from polarimetric SAR data at C-, L-, and P-band and single polarization X-band data. The data base includes an AIRSAR scene from June 25, 1991, and SIR-C/X-SAR images from April and October 1994 (SRL-1 and SRL-2), acquired over the high Alpine test site Ötztal in Austria. The environmental conditions were different at the time of the three experiments. Ground measurements, meteorological observations, and backscattering modeling are the basis for interpreting the backscattering signatures. Seasonal differences are due mainly to the presence or absence of snow and due to changes of its properties. Short term variations of snow conditions can be monitored at C- and X-band. For unglaciated areas, the surface roughness has a dominant influence on backscattering in all seasons. The dependence of the mean backscattering and correlation coefficients on the incidence angle was analyzed. Spectral and depolarization ratios and the magnitude of the HHVV correlation coefficient were selected as components of the multidimensional feature vector for studying the target separability. Good separability was found between the accumulation and ablation areas on the glaciers, whereas on ice-free areas, the dominance of surface roughness limits the discrimination of different surface types. Short-term variations of backscattering have significant impact for the classification of accumulation and ablation areas on glaciers, as verified by comparisons with field data View full abstract»

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  • QuikSCAT geophysical model function for tropical cyclones and application to Hurricane Floyd

    Page(s): 2601 - 2612
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    The QuikSCAT radar measurements of several tropical cyclones in 1999 have been studied to develop the geophysical model function (GMF) of Ku-band radar σ0 values (normalized radar cross section) for extreme high wind conditions. To account for the effects of precipitation, the authors analyze the co-located rain rates from the Special Sensor Microwave/Imager (SSM/I) and propose the rain rate as a parameter of the GMF. The analysis indicates the deficiency of the NSCAT2 GMF developed for the NASA scatterometer, which overestimates the ocean σ0 for tropical cyclones and ignores the influence of rain. It is suggested that the QuikSCAT σ0 is sensitive to the wind speed of up to about 40-50 m s-1. The authors introduce modifications to the NSCAT2 GMF and apply the modified GMF to the QuikSCAT observations of Hurricane Floyd. The QuikSCAT wind estimates for Hurricane Floyd in 1999 was improved with the maximum wind speed reaching above 60 m s-1. The authors perform an error analysis by comparing the QuikSCAT winds with the analyses fields from the National Oceanic and Atmospheric Administration (NOAA) Hurricane Research Division (HRD). The reasonable agreement between the improved QuikSCAT winds and the HRD analyses supports the applications of scatterometer wind retrievals for hurricanes View full abstract»

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  • Linear GPR inversion for lossy soil and a planar air-soil interface

    Page(s): 2713 - 2721
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    A three-dimensional inversion scheme for fixed-offset ground penetrating radar (GPR) is derived that takes into account the loss in the soil and the planar air-soil interface. The forward model of this inversion scheme is based upon the first Born approximation and the dyadic Green function for a two-layer medium. The forward model is inverted using the Tikhonov-regularized pseudo-inverse operator. This involves two steps: filtering and backpropagation. The filtering is carried out by numerically solving Fredholm integral equations of the first kind and the backpropagation is performed using fast Fourier transforms. Numerical results are provided to illustrate the performance of the inversion scheme View full abstract»

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  • Effects of stand size on the accuracy of remote sensing-based forest inventory

    Page(s): 2613 - 2621
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    The comparison of results of different forest studies is extremely difficult due to differences in test sites and studied stand characteristics, validation procedures, parameters used as an evaluation criteria, selection of stands, and the number of predictors used to name but a few. All these account for a large variation of the obtained accuracy. Additionally, in most reports inadequate information is given to convert statistically results from one study to the other. Since very few studies, such as Hyyppä et al. (2000), exist where various remote sensing data sources and methods are verified in the same test site, much of the knowledge of the applicability of various data sources and methods for forest inventory has to be obtained by studies carried out in different tests sites. However, there is a single parameter, stand size, affecting strongly comparisons of forestry inventory results. The effect of stand size on the accuracy of remote sensing-based standwise forest inventory has not been reported extensively. The most dramatic changes occur at the level where stands are small. Not surprisingly, stand size has been successfully utilized as an auxiliary parameter in some studies. This paper describes how the accuracy of estimation is influenced by the stand size. Both spaceborne and airborne data are used in order to show that the effect is not just based on large pixel sizes or the effects of border pixels in spaceborne data. The accuracy of the following remote sensing data, SPOT Pan and XS, Landsat TM, ERS-1/2 SAR PRI and SLC, and airborne data from imaging spectrometer (AISA) is verified as a function of stand size in the range 1 to 20 ha. The paper presents curves that assist in converting results from one stand size to another and compares results of some studies in different test sites. Stand size seems to explain most of the variability of the results; however, for detailed comparison, more carefully described results are needed. Recommendations to design future forest studies are given in order to help the statistical conversion of results from one study to another View full abstract»

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  • Detection of buried targets using a new enhanced very early time electromagnetic (VETEM) prototype system

    Page(s): 2702 - 2712
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    In this paper, numerical simulations of a new enhanced very early time electromagnetic (VETEM) prototype system are presented, where a horizontal transmitting loop and two horizontal receiving loops are used to detect buried targets, in which three loops share the same axis and the transmitter is located at the center of receivers. In the new VETEM system, the difference of signals from two receivers is taken to eliminate strong direct-signals from the transmitter and background clutter and furthermore to obtain a better SNR for buried targets. Because strong coupling exists between the transmitter and receivers, accurate analysis of the three-loop antenna system is required, for which a loop-tree basis function method has been utilized to overcome the low-frequency breakdown problem. In the analysis of scattering problem from buried targets, a conjugate gradient (CG) method with fast Fourier transform (FFT) is applied to solve the electric field integral equation. However, the convergence of such CG-FFT algorithm is extremely slow at very low frequencies. In order to increase the convergence rate, a frequency-hopping approach has been used. Finally, the primary, coupling, reflected, and scattered magnetic fields are evaluated at receiving loops to calculate the output electric current. Numerous simulation results are given to interpret the new VETEM system. Comparing with other single-transmitter-receiver systems, the new VETEM has better SNR and ability to reduce the clutter View full abstract»

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  • An adaptive classifier design for high-dimensional data analysis with a limited training data set

    Page(s): 2664 - 2679
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    Proposes a self-learning and self-improving adaptive classifier to mitigate the problem of small training sample size that can severely affect the recognition accuracy of classifiers when the dimensionality of the multispectral data is high. This proposed adaptive classifier utilizes classified samples (referred to as semilabeled samples) in addition to original training samples iteratively. In order to control the influence of semilabeled samples, the proposed method gives full weight to the training samples and reduced weight to semilabeled samples. The authors show that by using additional semilabeled samples that are available without extra cost, the additional class label information may be extracted and utilized to enhance statistics estimation and hence improve the classifier performance, and therefore the Hughes phenomenon (peak phenomenon) may be mitigated. Experimental results show this proposed adaptive classifier can improve the classification accuracy as well as representation of estimated statistics significantly View full abstract»

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  • Microwave emission from dry snow: a comparison of experimental and model results

    Page(s): 2649 - 2656
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    Field measurements of microwave emission from snow-covered soil were carried out in 1996, 1997, and 1999 on the Italian Alps using a three-frequency dual polarized microwave system. At the same time, nivological time measurements were carried out using standard methods and an electromagnetic contact probe. Collected data confirmed the possibility of separating wet from dry snow and of estimating the water equivalent of dry snow. Simulations performed by means of a model based on the dense medium radiative theory (DMRT) were able to reproduce experimental data very well View full abstract»

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  • Effect of spatial resolution on classification errors of pure and mixed pixels in remote sensing

    Page(s): 2657 - 2663
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    It is observed in remote sensing that a finer spatial resolution does not necessarily improve the classification performance. These observations have been understood by using the conceptual explanation that "boundary effect" and "within-class variability" work against one another. Though easily understood, this conceptual explanation cannot be readily used for a quantitative investigation. The authors design a simulation scheme to evaluate systematically the impacts of various parameters on the classification accuracy. The authors employ a model for the class spectral covariance of pure pixels and a linear mixing model for the spectral responses of mixed pixels. Based on these models, the authors derive the statistical characteristics for mixed pixels and assess the corresponding classification errors. As the ratio of ground sampling distance to field size decreases, the classification error associated with pure pixels tends to increase, whereas the classification error associated with mixed pixels tends to decrease from the smaller area of mixed pixels. The simulation results show that the overall classification error first decreases with decreasing ratio of ground sampling distance to field width, reaches a minimum value, and then may increase with further decreasing ratio. The study on the classification error may help the development of classification schemes for high spatial resolution imagery View full abstract»

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  • Piecewise continuous models for resistivity soundings

    Page(s): 2725 - 2728
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    A robust method is presented for constructing layered Earth models from surface resistivity data. The algorithm automatically accommodates any number of discontinuities without the need to specify a priori its number or location in the vertical profile. It further includes automatic correction factors for the common segmentation of Schlumberger soundings due to static shift effects View full abstract»

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  • PIn. I. An operational nonlinear physical inversion algorithm for precipitable and cloud liquid water estimate in nonraining conditions over sea

    Page(s): 2566 - 2574
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    For pt.II see ibid., vol.39, no.12, p.2575-86 (2001). An operational nonlinear physical inversion (PIn) algorithm for precipitable and cloud liquid water estimate is described. It is suited for a generic conical scanning satellite microwave radiometer acquisition over sea in nonraining conditions. The algorithm does not need any calibration phase and is independent of the availability of in situ data, being consistent in different geographical and climatological situations. Adopted formulation is addressed to provide observational data to help in validating water vapor and cloud fields produced by a numerical weather prediction model. Furthermore, such a technique can be utilized for the purpose of global reanalysis, improving estimates of primary fields of the hydrological cycle. A sensitivity study of the forward model and a comparison between output brightness temperatures and those from a robust numerical code are also reported. The discrepancies that result are considered acceptable with respect to instrumental constraints and computation time View full abstract»

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  • PIn. II. Comparative evaluation of SSM/I and TMI precipitable water estimate for the Mediterranean Sea

    Page(s): 2575 - 2586
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    For pt.I see ibid., vol.39, no.12, p.2566-74 (2001). To estimate integrated precipitable water vapor along with liquid water path and water vapor effective profile (i.e. standard atmospheric profile approximation), utilizing the Special Sensor Microwave/Imager (SSM/I) and Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI) radiometers, an operative procedure was developed and assessed. This procedure is based on a fast nonlinear physical inversion algorithm (PIn) developed by the authors. A large data set of near-coincident TMI and SSM/I data acquisitions were collected and used to supply the procedure. Retrieved parameters were compared against retrievals achieved with well-accepted statistical algorithms, and consistency between TMI and SSM/I retrievals was confirmed. As far as TMI and SSM/I precipitable water retrieving consistency is concerned, this research revealed a linear relationship up to 20 kg/m2 and a general overestimate of TMI retrieving, for higher values. A new algorithm for obtaining integrated precipitable water from TMI brightness temperatures was introduced and the goodness of its accuracy was reported. The procedure proved to be reliable and portable and its integrated precipitable water vapor retrieving was assessed to be as accurate as the best radiometric retrieving algorithms, reported in literature. For SSM/I data, developed-procedure liquid water path estimates seemed to be in good agreement with statistical retrievals. Eventually the procedure provided effective water vapor vertical profiles which belong to a deterministic distribution area characterized by an upper and lower limit; it was confirmed that SSM/I and TMI vertical profile distribution areas mainly overlap even if they are characterized by different sensitivities to profile parameters View full abstract»

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  • Acoustic seafloor sediment classification using self-organizing feature maps

    Page(s): 2722 - 2725
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    A self-organizing feature map (SOFM), a kind of artificial neural network (ANN) architecture, is used in this work for continental shelf seafloor sediment classification. Echo data are acquired using an echosounding system from three types of seafloor sediment areas. Excellent classification (~100%) for an ideal output neuron grid size of 15×1 is obtained for a moving average of 35 input snapshots View full abstract»

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  • Forestry parameter retrieval from texture in CARABAS VHF-band SAR images

    Page(s): 2622 - 2633
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    Methods for retrieval of the stem volume, dominant tree height, and dominant tree diameter values using CARABAS images are presented. Both intensity and its texture can be used, but texture detects sparse, low stem volume forests overlooked by the intensity. The texture parameters used are the zero and first-order constants of the log-log regression of the standard deviation of the intensity and the distance over which it is determined. The accuracy of the stem volume estimates is of the order of the ground truth. The dominant diameter and height values are less accurate View full abstract»

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Aims & Scope

 

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