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Geoscience and Remote Sensing, IEEE Transactions on

Issue 3 • Date May 1990

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Displaying Results 1 - 13 of 13
  • A new correction to the Born approximation

    Publication Year: 1990 , Page(s): 394 - 399
    Cited by:  Papers (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (620 KB)  

    A correction to the Born approximation for the apparent conductivity (induced voltage) in a layered medium is derived. The correction involves a single constant a and is nonlinear in conductivity. An algorithm for choosing a for induction logging applications is derived. The correction is shown to be significantly more accurate than the uncorrected Born approximation at high conductivity contrasts between adjacent beds. The correction does not significantly increase the computation time or complexity of the Born approximation. Thus, it has application to the related inverse problem where the speed of computation of the forward problem is important. In typical cases studied, the correction is shown to reduce the root mean square (RMS) error of the Born approximation to no more than 5% in regions where the Born approximation without correction has a RMS error of up to 30%.<> View full abstract»

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  • Synthetic aperture radar calibration using reference reflectors

    Publication Year: 1990 , Page(s): 374 - 383
    Cited by:  Papers (67)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (916 KB)  

    A simple expression for the terrain backscatter coefficient is derived in terms of the integrated power of an adjacent known radar reflector in a synthetic aperture radar (SAR) image. It is shown that this technique for SAR image calibration is independent of the radar system focus or partial coherence and thereby possesses an important advantage over the usual technique, which relies on an estimate of the peak of the reflector impulse response. Results from airborne SAR overflights of corner reflectors and active radar calibrators are used to demonstrate the validity and consistency of the method and to show that the method is robust under defocus caused by an incorrect FM rate or inadequate motion compensation of data collected during turbulence. It is also shown that the fading errors associated with the integral method are comparable to or slightly worse than those associated with the peak estimation method. However, this small disadvantage is outweighed by the fact that the integral method is independent of actual resolution View full abstract»

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  • Calibration of polarimetric radar images using only image parameters and trihedral corner reflector responses

    Publication Year: 1990 , Page(s): 337 - 348
    Cited by:  Papers (160)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1080 KB)  

    A technique that uses the radar return from natural targets and at least one trihedral corner reflector to calibrate compressed polarimetric radar data is described. Calibration for relative amplitude, relative phase, absolute amplitude, and system crosstalk is addressed. The crosstalk calibration method is based on the theoretical result that for natural targets with azimuthal symmetry the copolarized and crosspolarized components of the scattering matrix are uncorrelated, and the method does not require any external calibration targets to be deployed before imaging. Because compressed data are used, one is forced to model the transmitting and receiving systems as reciprocal. Even though the inferred transmit and receive matrices are not each simply related to the physical transmitter and receiver, the true Stokes matrix for each pixel in an image can be accurately determined by this approach. The method is illustrated by estimating the crosstalk parameters of the NASA/JPL aircraft for different types of terrain and for two frequencies. For the C-band system, the crosstalk is less than -20 dB for all ranges in the images. The crosstalk of the L-band system is a function of range, however, and may be as poor as -10 dB in the near range, leading to a noticeable distortion of the polarization signatures View full abstract»

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  • Microwave dielectric properties of dry rocks

    Publication Year: 1990 , Page(s): 325 - 336
    Cited by:  Papers (12)
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    The use of a combination of several measurement techniques to investigate the dielectric properties of 80 rock samples in the microwave region is discussed. The real part of the relative dielectric constant ε' was measured in 0.1-GHz steps from 0.5 to 18 GHz, and the imaginary part ε" was measured at five frequencies extending between 1.6 and 16 GHz. In addition to the dielectric measurements, the bulk density was measured for all the samples and the bulk chemical composition was determined for 56 of the samples. This study shows that ε' is frequency-independent over the range of 0.5-18 GHz for all rock samples, and that the bulk density ρb accounts for about 50% of the observed variance of ε'. For silicate rocks, as much as 78% of the observed variance of ε' may be explained by the combination of density and the fractional contents of various oxides determined by X-ray fluorescence when the silicates are subgrouped by genesis. In contrast, the loss factor ε" decrease with increasing frequency for most rock samples. It was not possible to establish statistically significant relationships between ε" and the measured density of the rock samples. However, in the case of silicate rocks, 60% of the variance in ε" generally can be explained by the bulk chemical composition when the silicates are subgrouped by genesis View full abstract»

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  • Enhancement of high spectral resolution remote-sensing data by a noise-adjusted principal components transform

    Publication Year: 1990 , Page(s): 295 - 304
    Cited by:  Papers (86)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1600 KB)  

    High-spectral-resolution remote-sensing data are first transformed so that the noise covariance matrix becomes the identity matrix. Then the principal components transform is applied. This transform is equivalent to the maximum noise fraction transform and is optimal in the sense that it maximizes the signal-to-noise ratio (SNR) in each successive transform component, just as the principal component transform maximizes the data variance in successive components. Application of this transform requires knowledge or an estimate of the noise covariance matrix of the data. The effectiveness of this transform for noise removal is demonstrated in both the spatial and spectral domains. Results that demonstrate the enhancement of geological mapping and detection of alteration mineralogy in data from the Pilbara region of Western Australia, including mapping of the occurrence of pyrophyllite over an extended area, are presented View full abstract»

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  • Microwave coherent propagation in cylindrical-shaped forest components: interpretation of attenuation observations

    Publication Year: 1990 , Page(s): 315 - 324
    Cited by:  Papers (13)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (780 KB)  

    A theory of the coherent field propagation is presented to explain attenuation observations previously obtained at X-band through various forest components. On the basis of the Foldy-Lax approximation, a polarimetric loss factor model for a sparse medium is developed. This model accounts for both observation parameters and vegetation characteristics, including the scatterer orientation distributions. The model is valid for any scatterer shape, but for comparison purposes only the cylindrical shape is considered. The forest components, such as bare twigs and leafy coniferous branches are represented as dielectric, homogeneous, infinite-circular cylinders characterized by their dielectric properties, dimensions, number density, and orientation probability density functions. For the model-experiment comparison, the infinite-circular cylinder scattering function is incorporated into the model View full abstract»

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  • Magnetic dipole excitation of an insulated conductor of finite length

    Publication Year: 1990 , Page(s): 289 - 294
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (416 KB)  

    Excitation of currents on an insulated conductor of finite length and with arbitrary terminations is studied for a magnetic dipole source. For matched terminations, the results agree closely with previous results for an infinitely long conductor, but other terminations produce end reflections that cause standing waves. Specific calculations for a vertical magnetic dipole source are presented, because this source produces the appropriate horizontal electric field and could be used in a borehole-to-borehole configuration. Numerical results for the induced current and secondary magnetic field indicate that long conductors produce a strong anomaly over a broad frequency range for any type of termination View full abstract»

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  • A semiempirical model for interpreting microwave emission from semiarid land surfaces as seen from space

    Publication Year: 1990 , Page(s): 384 - 393
    Cited by:  Papers (67)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1756 KB)  

    A radiative transfer model for simulating microwave brightness temperatures over land surfaces is described. The model takes into account sensor viewing conditions (spacecraft altitude, viewing angle, frequency, polarization) and atmospheric parameters over a soil surface characterized by its moisture, roughness, and temperature and covered with a layer of vegetation characterized by its temperature, water content, single scattering albedo, structure and percent coverage. In order to reduce the influence of atmospheric and surface temperature effects, the brightness temperatures are expressed as polarization ratios that depend primarily on the soil moisture and roughness, canopy water content, and percentage of cover. The approach used is described, and the sensitivity of the polarization ratio to these parameters is investigated. Simulation of the temporal evolution of the microwave signal over semiarid areas in the African Sahel is presented and compared to actual satellite data from the SMMR instrument on Nimbus-7 View full abstract»

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  • Propagation along a two-wire line located at the air-Earth interface

    Publication Year: 1990 , Page(s): 400 - 402
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (184 KB)  

    A simple quasi-static expression for the propagation constant of a two-wire transmission line located at the air-Earth interface is derived. A numerical solution of the mode equation shows that the quasi-static approximation is valid when the wire separation is much less than a free-space wavelength. The quasi-static approximation can be used to determine the complex dielectric constant of the Earth from measurements of either the propagation constant or the characteristic impedance of the transmission line View full abstract»

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  • Model-based estimation of wind fields over the ocean from wind scatterometer measurements. I. Development of the wind field model

    Publication Year: 1990 , Page(s): 349 - 360
    Cited by:  Papers (10)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (928 KB)  

    For pt.II see ibid., vol.28, no.3, p.361-373 (1990). A parametric model for near-surface mesoscale wind fields suitable for use in a model-based approach to estimate the wind field over a large region of the scatterometer measurement swath from measurements of the radar backscatter of the ocean's surface is discussed. The assumptions made in developing the model are described, and the accuracy of the resulting model is evaluated. The model is based only on scatterometer data and is computationally tractable, consisting of a linear equation relating the near-surface wind field to a vector of model parameters which is estimated from the scatterometer measurements. Tradeoffs in the accuracy of the model and the number of unknown parameters are considered View full abstract»

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  • Image registration by recognition of corresponding structures

    Publication Year: 1990 , Page(s): 305 - 314
    Cited by:  Papers (25)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1372 KB)  

    A method for automatic image registration which is characterized by its insensitivity to scaling, rotation, and intensity changes is described. The method is based on similarity assessment of the structures in the images and on a check of their spatial arrangement. Pairs of structures that correspond to each other provide sets of control points to geometric mapping functions. An application of the method to remote-sensing image alignment with a reference map is presented View full abstract»

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  • Analysis of an electromagnetic induction detector for real-time location of buried objects

    Publication Year: 1990 , Page(s): 278 - 288
    Cited by:  Papers (25)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (792 KB)  

    Spatial response characteristics of an electromagnetic induction sensor as it passes over a metallic object are investigated using a simple analytical technique. In this low-frequency technique, one replaces a metallic object with equivalent electric and magnetic dipoles and then applies the principles of reciprocity to obtain the induced EMF in a sensor coil. Analysis is carried out for a sensor employing rectangular coils, and the object set is confined to a sphere and a prolate spheroid. The simple approach, which is illustrated with both numerical and experimental data, is found to be adequate to understand the effect on the response characteristics of parameters such as object depth, orientation, aspect ratio, and material properties View full abstract»

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  • Model-based estimation of wind fields over the ocean from wind scatterometer measurements. II. Model parameter estimation

    Publication Year: 1990 , Page(s): 361 - 373
    Cited by:  Papers (9)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1252 KB)  

    For pt.I see ibid., vol.28, no.3, p.349-360 (1990). The feasibility of a model-based approach to wind field estimation is discussed. In this approach the parametric model for near-surface mesoscale wind fields developed in pt.I is used. The parameters of the model are estimated from the wind scatterometer measurements; the wind field estimate is then computed from the estimated model parameters. Unlike the traditional pointwise approach, this approach takes advantage of the inherent correlation in the winds at different sample points to estimate the wind field more accurately and resolve directional ambiguity. The accuracies of wind field estimates obtained using the traditional pointwise estimation scheme and the model-based approach using simulated scatterometer measurements are compared 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