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Geoscience and Remote Sensing, IEEE Transactions on

Issue 3 • Date May 1991

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Displaying Results 1 - 15 of 15
  • Estimation of ocean wave spectra using two-antenna SAR systems

    Page(s): 463 - 465
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (328 KB)  

    Data from synthetic aperture radar, (SAR) systems can be used to estimate ocean wave directional spectra, but the method is limited by nonlinearities associated with the velocity bunching mechanism and the azimuth falloff effect, which reduces the range of azimuth wavelengths that can be observed. A theoretical analysis which suggests that the use of two or more receive antennas, spaced in the along-track direction, may reduce these limitations is presented. Specifically, the band of usable azimuth wavenumbers is shifted by an amount proportional to the antenna spacing, so that a broader range of wavenumbers can be covered by combining the spectrum obtained from the two-antenna signals with the conventional image spectrum View full abstract»

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  • Doppler frequency estimation and the Cramer-Rao bound

    Page(s): 385 - 390
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    Addresses the problem of Doppler frequency estimation in the presence of speckle and receiver noise. An ultimate accuracy bound for Doppler frequency estimation is derived from the Cramer-Rao inequality. It is shown that estimates based on the correlation of the signal power spectra with an arbitrary weighting function are approximately Gaussian-distributed. Their variance is derived in terms of the weighting function. It is shown that a special case of a correlation-based estimator is a maximum-likelihood estimator that reaches the Cramer-Rao bound. These general results are applied to the problem of Doppler centroid estimation from SAR (synthetic aperture radar) data View full abstract»

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  • The Danish SAR system: design and initial tests

    Page(s): 417 - 426
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    In January 1986, the design of a high-resolution airborne C -band synthetic aperture radar (SAR) started at the Electromagnetics Institute of the Technical University of Denmark. The initial system test flights took place in November and December 1989. The authors describe the design of the system, its implementation, and its performance. They show how digital technology has been utilized to realize a very flexible radar with variable resolution, swath-width, and imaging geometry. The motion-compensation algorithms implemented to obtain the high resolution and the special features built into the system to ensure proper internal calibration are outlined. The data processing system, developed for image generation and quality assurance, is sketched, with special emphasis on the flexibility of the system View full abstract»

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  • Polarimetric radar measurements of a forested area near Mt. Shasta

    Page(s): 444 - 450
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    The authors present the results of an experiment using the NASA/JPL DC-8 AIRSAR (aircraft synthetic-aperture radar) over a coniferous forest near Mt. Shasta (California) in 1989. Calibration devices were deployed in clearings and under the forest canopy and passes at 20°, 40°, and 55° incidence angles were made with the AIRSAR. A total of eight images at differing incidence angles have been processed and calibrated. The multipolarization multifrequency data were examined, and it was found that the C-band cross section averaged over like and cross polarizations is the best parameter for distinguishing between two stands with differing forest biomass. The average cross section at P- and L-bands is useful only for smaller incidence angles. Parameters describing the polarization behavior of the scattering were primarily useful in identifying the dominant scattering mechanisms for forest backscatter View full abstract»

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  • Multibeam radar altimetry: spaceborne feasibility

    Page(s): 465 - 469
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    An analysis of the inherent height and spatial resolution of an off-nadir radar altimeter is presented. For the general case, mean-square height uncertainty is shown to be proportional to the cross-track beamwidth divided by the along-track beamwidth. Thus, the cross-track beamwidth should be minimized and the along-track beamwidth maximized, subject to resolution and other constraints. A pure multibeam system with a 50-km beam offset, an altitude of 800 km, a 13.5-GHz frequency, and a 4.5-m-diameter antenna is found to yield a height random error of less than 5 cm. For the same conditions, errors decrease with increasing frequency: however, rain attenuation becomes a factor View full abstract»

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  • Estimating splash pine biomass using radar backscatter

    Page(s): 427 - 431
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    L-band HV multiple-incidence-angle aircraft synthetic aperture radar (SAR) data were analyzed in relation to average stand biomass, basal area, and tree height for 55 slash pine plantations located in northern Florida. This information was used to develop a system of equations to predict average stand biomass as a function of L-band (24.5-cm) radar backscatter. The system of equations developed in this study using three-stage least-squares and combinatorial screening accounted for 97% of the variability observed in average stand biomass per hectare. When applied to an independent data set, the biomass equations had an average bias of less than 1% with a standard error of approximately 3% View full abstract»

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  • Terrain influences in SAR backscatter and attempts to their correction

    Page(s): 451 - 462
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    Synthetic aperture radar (SAR) images reveal radiometric image distortions that are caused by terrain undulations. The authors present the results of a study extracting and investigating the various components of these terrain influences. An imaging model, is set up for the geometric rectification of the SAR image and for a reconstruction of the imaging geometry. A prerequisite for the setup of this model is the use of a digital elevation model. Eight different geometric parameters are derived and investigated for their influence on grey-value variations in the geocoded SAR image. Image grey-value variations of three major land-use classes-forest, agricultural land, and urban/suburban areas-are examined. Empirical models of the SAR-backscatter variations are used to describe the relations between image grey values and various geometric parameters View full abstract»

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  • Two-dimensional coherent noise suppression in seismic data using eigendecomposition

    Page(s): 379 - 384
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    A method for the suppression of coherent noise in seismic data based on the eigendecomposition of a data covariance matrix is demonstrated. Based on the Karhunen-Loeve transform, the proposed procedure is useful against noise energy exhibiting both two-dimensional space and time coherencies or coherent two-dimensional patterns which are not necessarily linear and therefore cannot generally be velocity-filtered. This method trains on a region containing the undesired coherent noise; the dominant eigenvectors determined from the covariance matrix of that noise are used to reconstruct the noise in the region of interest. Subtracting the reconstruction from the original data leaves a residual in which the coherent noise has been suppressed. In the example considered, this method effectively suppresses the noise in a record of marine seismic data containing backscattered source energy View full abstract»

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  • The derivative ratio algorithm: avoiding atmospheric effects in remote sensing

    Page(s): 350 - 357
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    The author describes the development of the derivative ratio algorithm based on derivatives of a simple radiative transfer equation. The limiting conditions of the algorithm are derived and demonstrated using examples of reflectance spectra of turbid water and an ash leaf. For these example targets, the algorithm indicates that some spectral features do survive the trip through the atmosphere and are recognizable using ratios of the spectral derivatives. The most detectable spectral features tended to be those that spanned bandwidths substantially larger than the minimum bandwidth tested (10 nm) View full abstract»

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  • Radiowave propagation in a coal seam with inhomogeneous rock walls

    Page(s): 469 - 472
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    An idealized slab model of a horizontal coal seam is adopted. The structure is laterally uniform, but the media within and outside the slab are allowed to be inhomogeneous in the vertical direction. A general mode equation is obtained, and simplifications are made to facilitate computation of the propagation constant of the dominant mode. Using an exponential variation of the rock conductivity, it is shown that the frequency dependence of the attenuation rate is strongest for a conductivity increasing with distance into the rock media View full abstract»

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  • Synergic inversion technique for active and passive microwave remote sensing of the ocean

    Page(s): 391 - 406
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    A unified approach for combining active and passive microwave measurements for remote sensing applications is described. A synergic inversion technique has been developed and applied to the retrieval of geophysical parameters of the ocean surface and of the atmosphere. It is based on the combination of radiometric and radar measurements at the electromagnetic and cell level and not only on the correction of radar measurements by radiometric measurements, or conversely. Such a combination is performed through a common quantity: the bistatic scattering coefficient of the observed surface. This is used in a direct model to simulate combined measurements from active and passive sensors. It requires a rather complete and accurate calculation of the scattering of microwaves by the rough sea surface View full abstract»

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  • Transform methods for seismic data compression

    Page(s): 407 - 416
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    The authors consider the development and evaluation of transform coding algorithms for the storage of seismic signals. Transform coding algorithms are developed using the discrete Fourier transform (DFT), the discrete cosine transform (DCT), the Walsh-Hadamard transform (WHT), and the Karhunen-Loeve transform (KLT). These are evaluated and compared to a linear predictive coding algorithm for data rates ranging from 150 to 550 bit/s. The results reveal that sinusoidal transforms are well-suited for robust, low-rate seismic signal representation. In particular, it is shown that a DCT coding scheme reproduces faithfully the seismic waveform at approximately one-third of the original rate View full abstract»

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  • A model for the imaging of urban areas by synthetic aperture radar

    Page(s): 432 - 443
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    A numerical model developed to simulate synthetic aperture radar images of urban targets is described. The model is based on ray tracing and is designed to simulate the effects of strong specular scatterers such as corner cubes as well as the diffuse scatter from the rough surfaces of buildings. The model uses a vectorial approach to the electromagnetic fields and so is able to simulate the polarization dependence of the images. An example of the model is given, and the validation and future development of the model are discussed View full abstract»

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  • Head-banging: robust smoothing in the plane

    Page(s): 369 - 378
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    The head-banging technique is a median-based smoother intended for use on nongridded spatial data. The smoother is designed to remove small-scale local variations within a data set while preserving regional trends. Several synthetic and field data sets are used to test the performance of the technique. Head-banging is shown to be particularly adept at preserving edge structures and is thus applicable in the field of structural geology, where data often contain edges due to faults or other steep formations View full abstract»

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  • Enhanced autoregressive moving average spectral estimation applied to the measurement of Doppler spectral width

    Page(s): 358 - 368
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    The measurement of clear-air turbulence with a Doppler radar is investigated. An autoregressive moving average (ARMA) model is proposed to improve the Doppler spectral width estimates. An iterative algorithm that has its origin in system identification is used for the estimation of the ARMA parameters. By taking advantage of a priori knowledge of the correlation matrix, which arises in the derivation of the governing equations of the ARMA parameters, the ARMA spectral estimate can be improved. This improvement is shown in terms of bias and variance of the spectral width estimate 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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Meet Our Editors

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