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Geoscience and Remote Sensing, IEEE Transactions on

Issue 1 • Date Jan 1994

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Displaying Results 1 - 25 of 26
  • An optimum interpolation method applied to the resampling of NOAA AVHRR data

    Publication Year: 1994 , Page(s): 131 - 151
    Cited by:  Papers (8)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1832 KB)  

    Two main problems must be solved in the geometric processing of satellite data: geometric registration and resampling. When the data must be geometrically registered over a reference map, and particularly when the output pixel size is not the same as the original pixel size, the quality of the resampling can determine the quality of the output, not only in the visual appearance of the image, but also in the numerically interpolated values when used in multitemporal or multisensor studies. The “optimum” interpolation algorithm for AVHRR data is defined over a 6×6 window in order to: consider overlapping effects among adjacent pixels. The response for each new pixel R(x, y) is determined as a linear combination of the response R i(xiyi) of the surrounding pixels in the window (i=1,36). The weighting coefficients μi are calculated from the ground projection of the effective spatial response function for each AVHRR pixel, taking into account the particular viewing angle and geometry of the pixels on the ground. This method is intended to give an optimal interpolation of AVHRR scenes along all the scanline, in order to compensate for off-nadir radiometric alterations associated to the varying spatial resolution and the blurring introduced by the pixel overlaps. The optimum method, as mathematically defined, is highly expensive in CPU time. Then, a big effort is necessary to implement the algorithms so that they could be operationally applied. Two approaches are considered: a general numerical method and a pseudo-analytical approximation. A Landsat TM image corresponding to the same date of the AVHRR image is used to test the quality of the radiometric interpolation procedure View full abstract»

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  • Snow mapping in alpine regions with synthetic aperture radar

    Publication Year: 1994 , Page(s): 152 - 158
    Cited by:  Papers (21)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (688 KB)  

    Active microwave sensors can discriminate snow from other surfaces in all weather conditions, and their spatial resolution is compatible with the topographic variation in alpine regions. Using data acquired with the NASA AIRSAR in the Otztal Alps in 1989 and 1991, the authors examine the usage of synthetic aperture radar (SAR) to map snow- and glacier-covered areas. By comparing polarimetric SAR data to images from the Landsat Thematic Mapper obtained under clear conditions one week after the SAR flight, the authors found that SAR data at 5.3 GHz (C-band) can discriminate between areas covered by snow from those that are ice-free. However, they are less suited to discrimination of glacier ice from snow and rock. The overall pixel-by-pixel accuracies-74% from VV polarization alone with topographic information, 76% from polarimetric SAR without any topographic information, and 79% from polarimetric SAR with topographic information-are high enough to justify the use of SAR as the data source in areas that are too cloud-covered to obtain data from the Thematic Mapper. This is especially true for snow discrimination, where accuracies exceed 80%, because mapping of a transient snow cover during a cloudy melt season is often difficult with an optical sensor. The AIRSAR survey was carried out in summer during a heavy rainstorm, when the snow surfaces were unusually rough. Even better results for snow discrimination can be expected for mapping in the spring, when snow is usually smoother View full abstract»

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  • Polarimetric radar studies of atmospheric ice particles

    Publication Year: 1994 , Page(s): 1 - 10
    Cited by:  Papers (12)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (848 KB)  

    Single scattering properties of ice crystals are described at microwave frequencies using discrete dipole approximations and Rayleigh scattering techniques. For a given shape, the average bulk densities of ice crystals can be estimated using the ratio of the copolarized radar signal in a linear (horizontal, vertical) polarization basis. Reflectivity depends on the ice content (g×m-3), and also on both size distribution parameters and average bulk density of the scatterers. Differential propagation phase is primarily a function of shape, ice water content, and is independent of size distribution parameters. Thus, by using a combination of polarimetric radar measurements, average ice content, bulk density, and shape of distributed scatterers call be inferred. These techniques become quite complex in the case of a winter storm where scatterers can exist with varying shape and bulk densities. Polarimetric radar properties of such complex distributed scatterers are modeled. Physical variations in the relation among ice water content, reflectivity, and differential propagation phase are considered with respect to change in the shape of size distribution, bulk density,,and average shape of the scatterers. Also, simultaneous polarimetric radar observations and in situ aircraft measurements are shown to demonstrate practical applicability of the techniques View full abstract»

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  • One-dimensional signal processing techniques for airborne laser bathymetry

    Publication Year: 1994 , Page(s): 35 - 46
    Cited by:  Papers (9)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (916 KB)  

    The application of one-dimensional signal processing techniques for the preprocessing of waveforms obtained in airborne laser bathymetry is investigated. Specifically, a special type of smoothing digital filter is used to remove noise in the waveforms while preserving the information content up to a desired degree. An algorithm, which incorporates a lowpass digital differentiator is then used to detect the bottom reflection. The optimal cutoff frequency of the differentiator is determined on the basis of the spectral content of the bottom reflection. After preprocessing, a waveform-decomposition technique recently described by the authors is used to separate the surface and bottom reflections for sea-depth estimation. In order to evaluate the effectiveness of the techniques developed, sea-depth estimates obtained are compared to corresponding estimates obtained by a local surveying company, and a high degree of agreement is observed between the two sets of results. When the resolution between the surface and bottom returns is low, the proposed techniques together with waveform decomposition offer a significant improvement in the sea-depth estimates View full abstract»

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  • Foliage transmission measurements using a ground-based ultrawide band (300-1300 MHz) SAR system

    Publication Year: 1994 , Page(s): 118 - 130
    Cited by:  Papers (8)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1188 KB)  

    The attenuation of a forest clearly impacts the ability of airborne SAR systems to image objects within the forest. The level of this attenuation is a function of tree characteristics over the frequency band used in the radar. To experimentally measure the transmission properties of foliage, a bistatic (line-of-site) wide-band system has been built by the Environmental Research Institute of Michigan (ERIM), sponsored by the Air Force's Wright Laboratory, Avionics directorate. This system is polarimetric and can operate coherently over the band from 300 to 1300 MHz. The variation in foliage transmission over the frequency band is important because an imaging radar typically operates coherently over a bandwidth. The system can scan foliage in angle to determine spatial variations in the foliage attenuation. This angular variation in foliage attenuation is quite important because imaging radars typically synthesize an aperture by scanning over a range of angles. The ERIM Wide-Band System is ground-based, with one antenna attached to a carriage which can move 10 m horizontally along an elevated rigid track and the other antenna attached to a fixed tripod. Measurements with the system were conducted during July 1991 at the University of Michigan Biological Field Station in Pellston, MI. The measurements of the mean attenuation as a function of depression angle (15-45°) and frequency (300-1300 MHz) of four different forest types are presented. In addition to mean attenuation, the variance in attenuation and the autocorrelation of the attenuation (in angle) are presented. These results imply that the variation of the foliage properties over the bandwidth and scan geometry (or angular variation) will degrade the ability of a radar to focus a foliage obscured object View full abstract»

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  • Resolution of a phase ambiguity in a calibration procedure for polarimetric radar systems

    Publication Year: 1994 , Page(s): 213 - 216
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (340 KB)  

    A cross-pol/co-pol phase ambiguity in a previously published calibration procedure for polarimetric radar systems is discussed. The original procedure is modified to resolve the ambiguity while still retaining insensitivity to calibration target orientation. The modified form is then generalized and applied to an ultrawideband radar system for which the ambiguity in the original procedure is particularly evident View full abstract»

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  • Sea surface velocities from visible and infrared multispectral atmospheric mapping sensor (MAMS) imagery

    Publication Year: 1994 , Page(s): 220 - 223
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (352 KB)  

    High resolution (100 m), sequential multispectral atmospheric mapping sensor (MAMS) images were used to calculate sea surface velocities from the advection of visible and thermal surface features using maximum cross correlation (MCC) and subjective techniques. The visible gradient image velocities agreed well with the subjective motion, while the infrared channel performed best without computing gradients View full abstract»

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  • Unified full wave solutions to interpret Apollo lunar surface data

    Publication Year: 1994 , Page(s): 72 - 77
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (440 KB)  

    Bistatic radar experiments carried out by Tyler and Howard during the Apollo 14, 15, and 16 missions provide a very useful dataset with which to compare theoretical models and experimental data. Vesecky et al. (1988) report that their model for near grazing angles compares favorably to experimental data. However, for angles of incidence around 80°, all the analytical models considered by Vesecky et al. predict values for the quasi-specular cross sections that are about half the corresponding values taken from the Apollo 16 data. In this work, questions raised by this discrepancy between the reported analytical and experimental results are addressed. The unified full wave solutions are shown to be in good agreement with the bistatic radar data taken during Apollo 14 and 16 missions. Using the full wave approach, the quasi-specular contributions to the scattered field from the large scale surface roughness as well as the diffuse Bragg-like scattering from the small scale surface roughness are accounted for in a unified self-consistent manner. Since the full wave computer codes for the scattering cross sections contain ground truth data only, it is shown how it can be readily used to predict the rough surface parameters, based on the measured data View full abstract»

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  • Robotic aided dense medium target fabrication

    Publication Year: 1994 , Page(s): 217 - 219
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (292 KB)  

    A method for fabricating dense medium targets with known distributions and scatterer locations has been developed. The technique involves the use of a robot for accurate scatterer positioning. Performing measurements on these targets will give a better understanding of dense medium scattering mechanisms View full abstract»

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  • Application of EOF's to multispectral imagery: data compression and noise detection for AVIRIS

    Publication Year: 1994 , Page(s): 25 - 34
    Cited by:  Papers (8)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (924 KB)  

    Investigates the first stage of a two stage approach to data compression for multispectral imagery. The first stage is to compress the data spectrally using empirical orthogonal functions (EOFs). In the second stage, each EOF image is further compressed using standard techniques, such as transform encoding. The characteristics of EOFs make them ideal for spectral compression. The EOFs form the orthogonal basis in the data space which provides the most economical data representation. Furthermore, and perhaps of more interest, EOFs are effective noise filters. In the authors experiments with the 224 channel AVIRIS data, lossy compression ratios of order 50:1 are attained by the EOF representation under the condition that the residual rms error be smaller than the independently measured instrument noise View full abstract»

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  • Observations of variations in ERS-1 SAR image intensity associated with forest fires in Alaska

    Publication Year: 1994 , Page(s): 206 - 210
    Cited by:  Papers (11)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (456 KB)  

    Investigations have shown that fires in boreal forests result in characteristic responses which are recorded on ERS-1 SAR imagery. Using one of the many fire signatures observed on ERS-1 SAR imagery, the analysis of the data revealed there is >10 dB in variation in image intensity within the burned areas on the SAR images. Possible explanations for this variation include increases in soil moisture, increased surface roughness exposed to the incoming microwave radiation, and damage to the vegetation canopy by the fire View full abstract»

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  • A unified algorithm for phase and cross-talk calibration of polarimetric data-theory and observations

    Publication Year: 1994 , Page(s): 89 - 99
    Cited by:  Papers (61)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (908 KB)  

    A unified approach to phase and cross-talk calibration of polarimetric data which can be applied to calibrating scattering matrix data or to extraction of the descriptors of distributed targets is described. It relies on the scene being dominated by targets with uncorrelated like and cross-polarized backscattering coefficients, but provides cross-talk calibration of targets for which this is not true. The algorithm needs unsymmetrized data, but uses only quantities derived from the covariance matrix of large areas. It makes no assumptions about system reciprocity, permits ready interpretation of the terms in the calibration procedure, allows comparison of the relative magnitude of the system-induced mixing of terms in the observed covariance matrix, is noniterative, and produces indicators which allow testing of whether it meets its own underlying assumptions. The linear distortion model is shown to lead to an inconsistent system of equations; this inconsistency can be removed by introducing an extra parameter which has properties expected of system noise. The modulus of the copolarized correlation coefficient, which is important in polarimetric classification and as a phase descriptor, is shown to be invariant under all effects embodied in the linear distortion model. Calibration of the scattering matrix data is based on a minimum least squares principle. This suggests that current methods of symmetrization are not optimal. The same analysis shows that estimates of parameters needed to form an equivalent reciprocal system are also nonoptimal. The method is more general than the well-known van Zyl algorithm for cross-talk removal, and permits an analysis of the conditions under which the van Zyl algorithm will yield valid results. Correction of phase distortion induced by channel imbalance Is treated as an optional extra step relying on a known HH-VV phase difference in some region of the image. Results from the algorithm are discussed using scattering matrix data from the 1989 MAESTRO campaign View full abstract»

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  • Multitemporal passive microwave mapping in MACHYDRO'90

    Publication Year: 1994 , Page(s): 201 - 206
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (516 KB)  

    MACHYDR0'90 was an experiment conducted in Pennsylvania in 1990 to study the synergistic use of remote sensors in multitemporal hydrologic studies. As part of this mission the pushbroom microwave radiometer was flown and used to produce brightness temperature maps. Verification studies and vegetation algorithms for mixed land cover areas are described View full abstract»

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  • Analysis of the POLDER polarization measurements performed over cloud covers

    Publication Year: 1994 , Page(s): 78 - 88
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1016 KB)  

    The POLDER instrument is designed to provide wide field of view bidimensional images in polarized light. During campaigns of the airborne version of the instrument, images of homogeneous cloud fields were acquired in polarized bands centered at 450 and 850 nm. The polarization of these images is analyzed. The bidirectional polarization distribution function measured in the 850 nm band is shown to make evident the liquid phase of the cloud droplets, by the large characteristic polarization of the cloudbows detected in backward scattering directions. The sensitivity of this feature to cloud parameters is discussed. On the contrary, for observation directions at about 90°-100° from the Sun, the cloud polarization is negligible. In these directions, the polarized light observed in the 450 nm band is characteristic of the molecular scattering about the cloud, which allows the cloud top altitude to be derived. The feasibility of the method is analyzed and is tested on cloud pictures acquired at different altitudes above cloud fields View full abstract»

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  • Pulse compression with very low sidelobes in an airborne rain mapping radar

    Publication Year: 1994 , Page(s): 211 - 213
    Cited by:  Papers (17)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (252 KB)  

    Pulse compression allows a substantial reduction in the peak transmitted power of a radar and is attractive for spaceborne remote sensing applications. In the case of a downward looking rain measuring radar, however, the range sidelobes associated with surface return can mask return from rain and must be kept to a minimum. The authors describe the pulse compression system for the NASA/JPL Airborne Rain Mapping Radar. This system uses time-domain weighting of the transmitted pulse and is able to achieve a range sidelobe level of -55 dB or better in flight tests. This is significantly lower than other values reported in the open literature View full abstract»

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  • An iterative inversion algorithm with application to the polarimetric radar response of vegetation canopies

    Publication Year: 1994 , Page(s): 62 - 71
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (884 KB)  

    The retrieval of scene parameters from polarimetric radar data using an iterative inversion approach is considered. The theoretical development of a general, model-based iterative algorithm for inversion of polarimetric radar data is presented. Factors relevant to its implementation, such as sensor configuration, algorithm optimization and computational structure are discussed. The algorithm is applied to the specific problem of inverting the vector radiative transfer model for a simplified, representative vegetation canopy consisting of vertical trunks, leaves, and a rough ground surface. The results of this inversion are in excellent agreement with simulated data generated using the radiative transfer model. The convergence properties of the algorithm are evaluated, and it is found that successful convergence is achieved in about 90% to 95% of the cases tested for the implementation used in this work. An error analysis is presented which considers the effect of both systematic and measurement derived errors. Typical error bounds for the current application are approximately ±3%, allowing for ±0.5 dB accuracy in the measured radar data View full abstract»

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  • Adaptation of the MIMICS backscattering model to the agricultural context-wheat and canola at L and C bands

    Publication Year: 1994 , Page(s): 47 - 61
    Cited by:  Papers (21)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (976 KB)  

    Presents the results obtained from the MIMICS (Michigan Microwave Canopy Scattering) forest backscattering model which was modified to accommodate agricultural parameters. In the MIMICS model, the forest canopy is divided into three regions: the crown layer, the trunk region, and the underlying rough ground. The crop cover situation is simulated by a rough ground and a crown layer composed of scatterers with different forms, distributions, and dielectric constants. The authors omit trunks from the final agricultural representation because these components are of the same order as the wavelength, contrary to the model's implicit assumptions. The simulation results are compared to ground based scatterometer data of wheat and canola. The paper describes the simulation results for the two crops at L and C bands and the two like polarizations. An analysis of the different backscattering mechanisms is also given for each crop. Good simulation results were obtained at L and C bands for HH polarization for both these crops throughout the growing season. An error analysis indicates that the soil moisture can be predicted with a precision better than 0.03 g/cm3 for both crops, if all other model parameters are known. In addition, if the moisture is known, the height of the stems and the diameter of the leaves of the canola crop can be estimated with a precision better than ±5 cm and ±0.5 cm, respectively View full abstract»

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  • Reversible image compression bounded by noise

    Publication Year: 1994 , Page(s): 19 - 24
    Cited by:  Papers (21)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (552 KB)  

    Reversible image compression rarely achieves compression ratios larger than about 3:1. An explanation of this limit is offered, which hinges upon the additive noise the sensor introduces into the image. Simple models of this noise allow lower bounds on the bit rate to be estimated from sensor noise parameters rather than from ensembles of typical images. The model predicts that an 8-b single-band image subject to noise with unit standard deviation can be compressed reversibly to no less than 2.0 b/pixel, equivalent to a maximum compression ratio of about 4:1. The model has been extended to multispectral imagery. The Airborne Visible and Infra Red Imaging Spectrometer (AVIRIS) is used as an example, as the noise in its 224 bands is well characterized. The model predicts a lower bound on the bit rate for the compressed data of about 5.5 b/pixel when a single codebook is used to encode all the bands. A separate codebook for each band (i.e., 224 codebooks) reduces this bound by 0.5 b/pixel to about 5.0 b/pixel, but 90% of this reduction is provided by only four codebooks. Empirical results corroborate these theoretical predictions View full abstract»

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  • Spatial and frequency averaging techniques for a polarimetric scatterometer system

    Publication Year: 1994 , Page(s): 187 - 196
    Cited by:  Papers (10)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (664 KB)  

    Radar scattering signals from distributed targets exhibit fading due to interference associated with coherent scattering from individual scatterers within the resolution volume. Uncertainty in radar measurements which arises as a result of fading is reduced by averaging independent samples. Independent samples are obtained by collecting the radar returns from nonoverlapping footprints (spatial averaging) and/or nonoverlapping frequencies (frequency agility techniques). An improved formulation of fading characteristics for the spatial averaging and frequency agility technique is derived by taking into account the rough surface scattering process. Kirchhoff's approximation is used to describe rough surface scattering. Expressions for fading decorrelation distance and decorrelation bandwidth are derived. Rough surface scattering measurements are performed between L and S bands. Measured frequency and spatial correlation coefficients show good agreement with theoretical results View full abstract»

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  • Microwave backscattering and emission model for grass canopies

    Publication Year: 1994 , Page(s): 177 - 186
    Cited by:  Papers (23)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (860 KB)  

    Microwave radar and radiometer measurements of grasslands indicate a substantial reduction in sensor sensitivity to soil moisture in the presence of a thatch layer. When this layer is wet it masks changes in the underlying soil, making the canopy appear warm in the case of passive sensors (radiometer) and decreasing backscatter in the active case (scatterometer). A model for a grass canopy with thatch is presented in order to explain this behavior and for comparison with observations. The canopy model consists of three layers: grass, thatch, and the underlying soil. The grass blades are modeled by elongated elliptical discs and the thatch is modeled as a collection of disk shaped water droplets (i.e., the dry matter is neglected). The ground is homogeneous and flat. The distorted Born approximation is used to compute the radar cross section of this three layer canopy and the emissivity is computed from the radar cross section using the Peake formulation for the passive problem. Results are computed at L-band (1.4 GHz) and C-band (4.75 GHz) using canopy parameters (i.e., plant geometry, soil moisture, plant moisture, etc.) representative of Konza Prairie grasslands. The results are compared to C-band scatterometer measurements and L-band radiometer measurements at these grasslands View full abstract»

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  • Experiments with wavelets for compression of SAR data

    Publication Year: 1994 , Page(s): 197 - 201
    Cited by:  Papers (23)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (472 KB)  

    Wavelet transform coding is shown to be an effective method for compression of both detected and complex synthetic aperture radar (SAR) imagery. Three different orthogonal wavelet transform filters are examined for use in SAR data compression; the performances of the filters are correlated with mathematical properties such as regularity and number of vanishing moments. Excellent quality reconstructions are obtained at data rates as low as 0.25 bpp for detected data and as low as 0.5 bits per element (or 2 bpp) for complex data View full abstract»

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  • Synthetic aperture FM-CW radar applied to the detection of objects buried in snowpack

    Publication Year: 1994 , Page(s): 11 - 18
    Cited by:  Papers (9)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (672 KB)  

    Presents the principle of synthetic aperture frequency modulated continuous wave (FM-CW) radar and demonstrates the detection results of several objects buried in natural snowpack using the radar system. First, the synthetic aperture technique is explained with emphasis placed on showing that the Fourier transformed beat signal obtained by the FM-CW radar is equivalent to one kind of Fresnel hologram, which leads the authors to use the SAR technique. Then a radar system operative in the microwave L-band is explored to detect objects buried in natural snowpack. Several detection results are presented demonstrating the potential capability of high resolution imaging in the azimuth direction, comparing with real aperture images View full abstract»

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  • Optimum polarizations in the bistatic scattering from layered random media

    Publication Year: 1994 , Page(s): 169 - 176
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (560 KB)  

    Investigates the polarimetric bistatic scattering characteristics of layered random media. On applying the Born approximation, the authors have calculated the bistatic Mueller matrix of a half-space random medium. The power received by a receiving antenna is the quantity chosen to optimize. The variables of the problem are the polarizations of the transmitting and receiving antennas. For the case when the polarizations of the transmitting and receiving antennas are identical, the authors have calculated the optimum polarizations and they have found that the optimum polarizations include both linear and elliptical polarizations. The conditions for maximum and minimum received power are also obtained. In the backscattering case, they have considered the situation when the transmitting and receiving antennas have independent polarizations. For a two-layer problem, they have observed the influence of the thickness of the layer in the classification of the optimum polarizations View full abstract»

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  • Estimation of sea-surface winds using backscatter cross-section measurements from airborne research weather radar

    Publication Year: 1994 , Page(s): 110 - 117
    Cited by:  Papers (8)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (700 KB)  

    A technique is presented for estimation of sea-surface winds using backscatter cross-section measurements from an airborne research weather radar. The technique is based on an empirical relation developed for use with satellite-borne microwave scatterometers which derives sea-surface winds from radar backscatter cross-section measurements. Unlike a scatterometer, the airborne research weather radar is a Doppler radar designed to measure atmospheric storm structure and kinematics. Designed to scan the atmosphere, the radar also scans the ocean surface over a wide range of azimuths, with the incidence angle and polarization angle changing continuously during each scan. The new sea-surface wind estimation technique accounts for these variations in incidence angle and polarization and derives the atmospheric surface winds. The technique works well over the range of wind conditions over which the wind speed-backscatter cross-section relation holds, about 2-20 m/s. The problems likely to be encountered with this new technique are evaluated and it is concluded that most problems are those which are endemic to any microwave scatterometer wind estimation technique. The new technique will enable using the research weather radar to provide measurements which would otherwise require use of a dedicated scatterometer View full abstract»

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  • Statistical characteristics of simulated radar imagery from bare soil surfaces: effects of surface roughness and soil moisture variability

    Publication Year: 1994 , Page(s): 159 - 168
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (832 KB)  

    The potential of high-resolution radar imagery to estimate various hydrological parameters, such as soil moisture, has long been recognized. Image simulation is one approach to study the interrelationships between the radar response and the underlying ground parameters. In order to perform realistic simulations, the authors incorporated the effects of naturally occurring spatial variability and spatial correlations of those ground parameters that affect the radar response, primarily surface roughness and soil moisture. Surface roughness and soil moisture images were generated for a hypothetical 100×100 m bare soil surface area at 1 m resolution using valid probability distributions and correlation lengths. These values were then used to obtain copolarized radar scattering coefficients at 2 GHz (L band) and 10 GHz (X band) frequencies using appropriate backscatter models, which were then converted to a digital number within 0-255 gray scale in order to generate radar images. The effect of surface roughness variability causes variability in the radar image, which is more apparent under smooth soil conditions. On the other hand, the inherent spatial pattern in soil moisture tends to cause similar patterns in the radar image under rougher soil conditions. The maximum difference between contrast-enhanced mean values of the radar image digital number due to moisture variations occurs at surface roughness values in the 1.5-2.0 cm range View full abstract»

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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