The Experts below are selected from a list of 1863 Experts worldwide ranked by ideXlab platform
L.m.h. Ulander - One of the best experts on this subject based on the ideXlab platform.
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Detection of storm-damaged forested areas using airborne CARABAS-II VHF SAR image data
IEEE Transactions on Geoscience and Remote Sensing, 2002Co-Authors: J.e.s. Fransson, F. Walter, A. Gustavsson, K. Blennow, L.m.h. UlanderAbstract:Strong winds cause severe damage worldwide to forested land every year. The devastating storms that struck large parts of Europe in late 1999 destroyed the equivalent of several years of normal forest harvesting, amounting to very large economical sums. Therefore, rapid mapping of damaged areas is of major importance for assessment of short-term actions as well as for long-term reforestation purposes. In this paper, the use of airborne CARABAS-II very high frequency (VHF) (20-90 MHz) synthetic aperture radar (SAR) imagery for high spatial resolution mapping of wind-thrown forests has been investigated and evaluated. The investigation was performed at a test site located in southern Sweden and dominated by Norway spruce forests. A regression model estimating radar Backscattering Amplitude prior to the storm was developed. The estimated Amplitudes were compared to measured Amplitudes after the storm. The results clearly show that the Backscattering Amplitude, at a given stem volume, is considerably higher for wind-thrown forests than for unaffected forests. Furthermore, the Backscattering from fully harvested storm-damaged areas was, as expected, significantly lower than from unaffected stands. These findings imply that VHF SAR imagery has potential for mapping wind-thrown forests. However, to prevent ambiguities in increased Backscattering caused by normal stem volume growth or wind-fellings, multitemporal change detection techniques using VHF SAR images acquired prior to and after wind-fellings would be preferable.
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Mapping of wind-thrown forests using CARABAS-II VHF SAR image data
IGARSS 2001. Scanning the Present and Resolving the Future. Proceedings. IEEE 2001 International Geoscience and Remote Sensing Symposium (Cat. No.01CH, 2001Co-Authors: J.e.s. Fransson, L.m.h. Ulander, A. Gustavsson, F. WalterAbstract:Heavy storms are causing severe damage worldwide to forested land every year. The devastating storms that struck central Europe in late 1999 destroyed the equivalent of several years of normal forest harvesting, amounting to very large economical sums. Therefore, rapid mapping of damaged areas is of major importance for assessment of short-term actions as well as for long-term reforestation purposes. In this paper, the use of airborne CARABAS-II VHF (20-90 MHz) SAR imagery for high spatial resolution mapping of wind-thrown forests has been investigated and evaluated. The investigation was performed at a test site located in southern Sweden, dominated by Norway spruce forests. A regression model predicting forest stem volume from radar Backscattering Amplitude was used to retrieve stem volume for storm-damaged areas. Finally, the predicted volumes were compared with subjectively inventoried stem volumes. Unexpectedly, the results indicate that the Backscattering Amplitude is considerably higher for wind-thrown forests in comparison with Backscattering from unaffected forests. Nevertheless, this finding implies that VHF SAR imagery has potential for mapping wind-thrown forests, preferably using change detection techniques of images acquired prior to and after storm-fellings.
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Estimation of forest parameters using CARABAS-II VHF SAR data
IEEE Transactions on Geoscience and Remote Sensing, 2000Co-Authors: J.e.s. Fransson, F. Walter, L.m.h. UlanderAbstract:The use of airborne CARABASII VHF (20-90 MHz) SAR data for retrieval of forest parameters has been investigated. The investigation was performed at a test site located in the southwest of Sweden consisting mainly of Norway spruce forests. Regression models predicting forest parameters from radar Backscattering Amplitude were developed and evaluated. The results showed a linear relationship between Backscattering Amplitude and forest stem volume, stem diameter, and tree height. The analysis also showed that the radar signal is strongly affected by ground slope conditions. The root mean square errors from the regression analysis, restricted to forest stands on near-horizontal ground, were found to be 66 m/sup 3/ ha/sup -1/, 3.2 cm, and 2.3 m for stem volume, stem diameter, and tree height respectively. No saturation of the backscattered signal was observed up to the maximum stem volume of 625 m/sup 3/ ha/sup -1/, corresponding to a biomass of 375 tons ha/sup -1/. The results imply that VHF SAR data have significant potential for operational use in forestry.
J.e.s. Fransson - One of the best experts on this subject based on the ideXlab platform.
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Detection of storm-damaged forested areas using airborne CARABAS-II VHF SAR image data
IEEE Transactions on Geoscience and Remote Sensing, 2002Co-Authors: J.e.s. Fransson, F. Walter, A. Gustavsson, K. Blennow, L.m.h. UlanderAbstract:Strong winds cause severe damage worldwide to forested land every year. The devastating storms that struck large parts of Europe in late 1999 destroyed the equivalent of several years of normal forest harvesting, amounting to very large economical sums. Therefore, rapid mapping of damaged areas is of major importance for assessment of short-term actions as well as for long-term reforestation purposes. In this paper, the use of airborne CARABAS-II very high frequency (VHF) (20-90 MHz) synthetic aperture radar (SAR) imagery for high spatial resolution mapping of wind-thrown forests has been investigated and evaluated. The investigation was performed at a test site located in southern Sweden and dominated by Norway spruce forests. A regression model estimating radar Backscattering Amplitude prior to the storm was developed. The estimated Amplitudes were compared to measured Amplitudes after the storm. The results clearly show that the Backscattering Amplitude, at a given stem volume, is considerably higher for wind-thrown forests than for unaffected forests. Furthermore, the Backscattering from fully harvested storm-damaged areas was, as expected, significantly lower than from unaffected stands. These findings imply that VHF SAR imagery has potential for mapping wind-thrown forests. However, to prevent ambiguities in increased Backscattering caused by normal stem volume growth or wind-fellings, multitemporal change detection techniques using VHF SAR images acquired prior to and after wind-fellings would be preferable.
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Mapping of wind-thrown forests using CARABAS-II VHF SAR image data
IGARSS 2001. Scanning the Present and Resolving the Future. Proceedings. IEEE 2001 International Geoscience and Remote Sensing Symposium (Cat. No.01CH, 2001Co-Authors: J.e.s. Fransson, L.m.h. Ulander, A. Gustavsson, F. WalterAbstract:Heavy storms are causing severe damage worldwide to forested land every year. The devastating storms that struck central Europe in late 1999 destroyed the equivalent of several years of normal forest harvesting, amounting to very large economical sums. Therefore, rapid mapping of damaged areas is of major importance for assessment of short-term actions as well as for long-term reforestation purposes. In this paper, the use of airborne CARABAS-II VHF (20-90 MHz) SAR imagery for high spatial resolution mapping of wind-thrown forests has been investigated and evaluated. The investigation was performed at a test site located in southern Sweden, dominated by Norway spruce forests. A regression model predicting forest stem volume from radar Backscattering Amplitude was used to retrieve stem volume for storm-damaged areas. Finally, the predicted volumes were compared with subjectively inventoried stem volumes. Unexpectedly, the results indicate that the Backscattering Amplitude is considerably higher for wind-thrown forests in comparison with Backscattering from unaffected forests. Nevertheless, this finding implies that VHF SAR imagery has potential for mapping wind-thrown forests, preferably using change detection techniques of images acquired prior to and after storm-fellings.
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Estimation of forest parameters using CARABAS-II VHF SAR data
IEEE Transactions on Geoscience and Remote Sensing, 2000Co-Authors: J.e.s. Fransson, F. Walter, L.m.h. UlanderAbstract:The use of airborne CARABASII VHF (20-90 MHz) SAR data for retrieval of forest parameters has been investigated. The investigation was performed at a test site located in the southwest of Sweden consisting mainly of Norway spruce forests. Regression models predicting forest parameters from radar Backscattering Amplitude were developed and evaluated. The results showed a linear relationship between Backscattering Amplitude and forest stem volume, stem diameter, and tree height. The analysis also showed that the radar signal is strongly affected by ground slope conditions. The root mean square errors from the regression analysis, restricted to forest stands on near-horizontal ground, were found to be 66 m/sup 3/ ha/sup -1/, 3.2 cm, and 2.3 m for stem volume, stem diameter, and tree height respectively. No saturation of the backscattered signal was observed up to the maximum stem volume of 625 m/sup 3/ ha/sup -1/, corresponding to a biomass of 375 tons ha/sup -1/. The results imply that VHF SAR data have significant potential for operational use in forestry.
Vincent Fabbro - One of the best experts on this subject based on the ideXlab platform.
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Two-Dimensional Spectra of Radar Returns From Sea: 2. Analysis of the Group Line From Experimental Data
Journal of Geophysical Research. Oceans, 2019Co-Authors: Florestan Platzer, Marc Saillard, Vincent FabbroAbstract:Wavenumber-frequency spectra are obtained by performing a two-dimensional Fourier transform of range-time normalized radar cross-section (NRCS) or Doppler velocity maps. In such diagrams, some energy is present at low space-time frequencies, resulting from the nonlinear behavior of the measured quantity related to the sea surface geometry. This feature is called the group line, since for a narrow-band wave packet the energy is concentrated along a straight line with group velocity as slope. Which physical nonlinear process generates the group line remains an open question. Breaking waves have been proposed as the most probable contributor. However, numerical simulations from weakly nonlinear surfaces without breaking events and experiments performed at low winds also provide such feature. In a companion paper, a theoretical and numerical analysis has permitted to predict the energy distribution of the group line depending on the kind of nonlinearity. It provides some means to characterize a group line in a rigorous way. In this paper, it is used to analyze the group lines derived from the experimental MARLENE data. The group lines computed from the Backscattering Amplitude behave as the one of the square of sea surface slopes. The analysis of the Doppler velocities provides similar results, which significantly differ from what is expected if breaking waves are the main contributors and do break at velocities reported in the literature. Our results suggest that the group line mainly reflects the asymptotic behavior of the scattering Amplitude at grazing incidence, of which the leading nonlinear term is proportional to the square of surface slope.
F. Walter - One of the best experts on this subject based on the ideXlab platform.
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Detection of storm-damaged forested areas using airborne CARABAS-II VHF SAR image data
IEEE Transactions on Geoscience and Remote Sensing, 2002Co-Authors: J.e.s. Fransson, F. Walter, A. Gustavsson, K. Blennow, L.m.h. UlanderAbstract:Strong winds cause severe damage worldwide to forested land every year. The devastating storms that struck large parts of Europe in late 1999 destroyed the equivalent of several years of normal forest harvesting, amounting to very large economical sums. Therefore, rapid mapping of damaged areas is of major importance for assessment of short-term actions as well as for long-term reforestation purposes. In this paper, the use of airborne CARABAS-II very high frequency (VHF) (20-90 MHz) synthetic aperture radar (SAR) imagery for high spatial resolution mapping of wind-thrown forests has been investigated and evaluated. The investigation was performed at a test site located in southern Sweden and dominated by Norway spruce forests. A regression model estimating radar Backscattering Amplitude prior to the storm was developed. The estimated Amplitudes were compared to measured Amplitudes after the storm. The results clearly show that the Backscattering Amplitude, at a given stem volume, is considerably higher for wind-thrown forests than for unaffected forests. Furthermore, the Backscattering from fully harvested storm-damaged areas was, as expected, significantly lower than from unaffected stands. These findings imply that VHF SAR imagery has potential for mapping wind-thrown forests. However, to prevent ambiguities in increased Backscattering caused by normal stem volume growth or wind-fellings, multitemporal change detection techniques using VHF SAR images acquired prior to and after wind-fellings would be preferable.
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Mapping of wind-thrown forests using CARABAS-II VHF SAR image data
IGARSS 2001. Scanning the Present and Resolving the Future. Proceedings. IEEE 2001 International Geoscience and Remote Sensing Symposium (Cat. No.01CH, 2001Co-Authors: J.e.s. Fransson, L.m.h. Ulander, A. Gustavsson, F. WalterAbstract:Heavy storms are causing severe damage worldwide to forested land every year. The devastating storms that struck central Europe in late 1999 destroyed the equivalent of several years of normal forest harvesting, amounting to very large economical sums. Therefore, rapid mapping of damaged areas is of major importance for assessment of short-term actions as well as for long-term reforestation purposes. In this paper, the use of airborne CARABAS-II VHF (20-90 MHz) SAR imagery for high spatial resolution mapping of wind-thrown forests has been investigated and evaluated. The investigation was performed at a test site located in southern Sweden, dominated by Norway spruce forests. A regression model predicting forest stem volume from radar Backscattering Amplitude was used to retrieve stem volume for storm-damaged areas. Finally, the predicted volumes were compared with subjectively inventoried stem volumes. Unexpectedly, the results indicate that the Backscattering Amplitude is considerably higher for wind-thrown forests in comparison with Backscattering from unaffected forests. Nevertheless, this finding implies that VHF SAR imagery has potential for mapping wind-thrown forests, preferably using change detection techniques of images acquired prior to and after storm-fellings.
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Estimation of forest parameters using CARABAS-II VHF SAR data
IEEE Transactions on Geoscience and Remote Sensing, 2000Co-Authors: J.e.s. Fransson, F. Walter, L.m.h. UlanderAbstract:The use of airborne CARABASII VHF (20-90 MHz) SAR data for retrieval of forest parameters has been investigated. The investigation was performed at a test site located in the southwest of Sweden consisting mainly of Norway spruce forests. Regression models predicting forest parameters from radar Backscattering Amplitude were developed and evaluated. The results showed a linear relationship between Backscattering Amplitude and forest stem volume, stem diameter, and tree height. The analysis also showed that the radar signal is strongly affected by ground slope conditions. The root mean square errors from the regression analysis, restricted to forest stands on near-horizontal ground, were found to be 66 m/sup 3/ ha/sup -1/, 3.2 cm, and 2.3 m for stem volume, stem diameter, and tree height respectively. No saturation of the backscattered signal was observed up to the maximum stem volume of 625 m/sup 3/ ha/sup -1/, corresponding to a biomass of 375 tons ha/sup -1/. The results imply that VHF SAR data have significant potential for operational use in forestry.
Andrey V. Chubukov - One of the best experts on this subject based on the ideXlab platform.
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Test of the low-energy model for one-dimensional interacting Fermi systems
Physical Review B, 2008Co-Authors: Andrey V. Chubukov, Dmitrii L. Maslov, Fabian H. L. EsslerAbstract:Bosonization predicts that the specific heat $C(T)$ of a one-dimensional interacting Fermi system is a sum of the specific heats of free collective charge and spin excitations, plus the term with the running Backscattering Amplitude which flows to zero logarithmically with decreasing $T$. We verify whether this result is reproduced in the $g$-ology model. Of specific interest are the anomalous terms in $C(T)$ that depend on the bare Backscattering Amplitude. We show that these terms can be incorporated into a renormalized spin velocity. We do this by proving the equivalence of the results for $C(T)$ obtained within the $g$-ology model and by bosonization with velocities obtained by the numerical solution of the Bethe-ansatz equations for the Hubbard model.
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Specific heat of a one-dimensional interacting Fermi system: Role of anomalies
Physical Review B, 2008Co-Authors: Andrey V. Chubukov, Dmitrii L. Maslov, Ronojoy SahaAbstract:We re-visit the issue of the temperature dependence of the specific heat C(T) for interacting fermions in 1D. The charge component C_c(T) scales linearly with T, but the spin component C_s (T) displays a more complex behavior with T as it depends on the Backscattering Amplitude, g_1, which scales down under RG transformation and eventually behaves as g_1 (T) \sim 1/\log T. We show, however, by direct perturbative calculations that C_s(T) is strictly linear in T to order g^2_1 as it contains the renormalized Backscattering Amplitude not on the scale of T, but at the cutoff scale set by the momentum dependence of the interaction around 2k_F. The running Amplitude g_1 (T) appears only at third order and gives rise to an extra T/\log^3 T term in C_s (T). This agrees with the results obtained by a variety of bosonization techniques. We also show how to obtain the same expansion in g_1 within the sine-Gordon model.
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Cooper channel and the singularities in the thermodynamics of a Fermi liquid
Physical Review B, 2007Co-Authors: Andrey V. Chubukov, Dmitrii L. MaslovAbstract:We analyze how the logarithmic renormalizations in the Cooper channel affect the nonanalytic temperature dependence of the specific heat coefficient $\ensuremath{\gamma}(T)\ensuremath{-}\ensuremath{\gamma}(0)=A(T)T$ in a two-dimensional Fermi liquid. We show that $A(T)$ is expressed exactly in terms of the fully renormalized Backscattering Amplitude, which includes the renormalization in the Cooper channel. In contrast to the one-dimensional case, both charge and spin components of the Backscattering Amplitudes are subject to this renormalization. We show that the logarithmic renormalization of the charge Amplitude vanishes for a flat Fermi surface when the system becomes effectively one dimensional.
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thermodynamics of a fermi liquid beyond the low energy limit
Physical Review Letters, 2005Co-Authors: Andrey V. Chubukov, Dmitrii L. Maslov, Suhas Gangadharaiah, L I GlazmanAbstract:We consider the nonanalytic temperature dependences of the specific heat coefficient, C(T)/T, and spin susceptibility, chi(s)(T), of 2D interacting fermions beyond the weak-coupling limit. We demonstrate within the Luttinger-Ward formalism that the leading temperature dependences of C(T)/T and chi(s)(T) are linear in T, and are described by the Fermi liquid theory. We show that these temperature dependences are universally determined by the states near the Fermi level and, for a generic interaction, are expressed via the spin and charge components of the exact Backscattering Amplitude of quasiparticles. We compare our theory to recent experiments on monolayers of He3.
