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  • 1
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    A Thermal Wave Approach for Heat Transfer in a Nonuniform Soil (2000)
    Wiley
    Details
    Publication Date: 2000-07-01
    Print ISSN: 0361-5995
    Electronic ISSN: 1435-0661
    Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Published by Wiley
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    PAPER CURRENT
  • 2
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    A microwave polarimetric scattering model for forest canopies based on vector radiative transfer theory (1995)
    Elsevier
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    Publication Date: 1995-07-01
    Print ISSN: 0034-4257
    Electronic ISSN: 1879-0704
    Topics: Architecture, Civil Engineering, Surveying , Geography
    Published by Elsevier
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    PAPER CURRENT
  • 3
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    Effect of tree structure on X-band microwave signature of conifers (1993)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: Experimental studies are performed on some coniferous trees (Austrian pine, Nordmann spruce, and Norway spruce) to investigate the relation between the tree architecture and radar signal at X-band. For a single tree, the RCS is measured as a function of the scatterer location at 90 deg incidence. It is found that the main scatterers are the leafy branches and the difference between sigma(vv) and sigma(hh) is significant at the upper portion of the tree. At the lower portion of the tree, sigma(vv) and sigma(hh) have almost the same level. For a group of trees the angular trends of sigma(vv) and sigma(hh) are measured. It is found that the levels of sigma(vv) and sigma(hh) are of the same order, but their angular trends vary from one tree species to the other depending on the tree species structure. The interpretation of these experimental results is carried out with the help of a theoretical model which accounts for the structure of the tree. According to this theoretical study, the major scattering trend is due to the leaves, while the perturbation to the angular trend and the level difference between sigma(vv) and sigma(hh) are due to the branch orientation distributions (i.e., the tree architecture).
    Keywords: EARTH RESOURCES AND REMOTE SENSING
    Type: IEEE Transactions on Geoscience and Remote Sensing (ISSN 0196-2892); 31; 3; p. 655-667.
    Format: text
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  • 4
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    Relating ground truth collection to model sensitivity (1993)
    In:  Other Sources
    Details
    Publication Date: 2019-01-25
    Description: The importance of collecting high quality ground truth before a SAR mission over a forested area is two fold. First, the ground truth is used in the analysis and interpretation of the measured backscattering properties; second, it helps to justify the use of a scattering model to fit the measurements. Unfortunately, ground truth is often collected based on visual assessment of what is perceived to be important without regard to the mission itself. Sites are selected based on brief surveys of large areas, and the ground truth is collected by a process of selecting and grouping different scatterers. After the fact, it may turn out that some of the relevant parameters are missing. A three-layer canopy model based on the radiative transfer equations is used to determine, before hand, the relevant parameters to be collected. Detailed analysis of the contribution to scattering and attenuation of various forest components is carried out. The goal is to identify the forest parameters which most influence the backscattering as a function of frequency (P-, L-, and C-bands) and incident angle. The influence on backscattering and attenuation of branch diameters, lengths, angular distribution, and permittivity; trunk diameters, lengths, and permittivity; and needle sizes, their angular distribution, and permittivity are studied in order to maximize the efficiency of the ground truth collection efforts. Preliminary results indicate that while a scatterer may not contribute to the total backscattering, its contribution to attenuation may be significant depending on the frequency.
    Keywords: COMMUNICATIONS AND RADAR
    Type: JPL, Progress In Electromagnetics Research Symposium (PIERS); p 161
    Format: text
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  • 5
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    A microwave scattering model for layered vegetation (1992)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A microwave scattering model was developed for layered vegetation based on an iterative solution of the radiative transfer equation up to the second order to account for multiple scattering within the canopy and between the ground and the canopy. The model is designed to operate over a wide frequency range for both deciduous and coniferous forest and to account for the branch size distribution, leaf orientation distribution, and branch orientation distribution for each size. The canopy is modeled as a two-layered medium above a rough interface. The upper layer is the crown containing leaves, stems, and branches. The lower layer is the trunk region modeled as randomly positioned cylinders with a preferred orientation distribution above an irregular soil surface. Comparisons of this model with measurements from deciduous and coniferous forests show good agreements at several frequencies for both like and cross polarizations. Major features of the model needed to realize the agreement include allowance for: (1) branch size distribution, (2) second-order effects, and (3) tree component models valid over a wide range of frequencies.
    Keywords: EARTH RESOURCES AND REMOTE SENSING
    Type: Universities Space Research Association, Goddard Visiting Scientist Program for the Space and Earth Sciences Directorate; 18 p
    Format: application/pdf
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  • 6
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    Electromagnetic wave scattering from some vegetation samples (1988)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: For an incident plane wave, the field inside a thin scatterer (disk and needle) is estimated by the generalized Rayleigh-Gans (GRG) approximation. This leads to a scattering amplitude tensor equal to that obtained via the Rayleigh approximation (dipole term) with a modifying function. For a finite-length cylinder the inner field is estimated by the corresponding field for the same cylinder of infinite lenght. The effects of different approaches in estimating the field inside the scatterer on the backscattering cross section are illustrated numerically for a circular disk, a needle, and a finite-length cylinder as a function of the wave number and the incidence angle. Finally, the modeling predictions are compared with measurements.
    Keywords: EARTH RESOURCES AND REMOTE SENSING
    Type: IEEE Transactions on Geoscience and Remote Sensing (ISSN 0196-2892); 26; 799-808
    Format: text
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    NASA TECHNICAL REPORTS
  • 7
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    Electromagnetic wave scattering from a forest or vegetation canopy - Ongoing research at the University of Texas at Arlington (1993)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: The Wave Scattering Research Center at the University of Texas at Arlington has developed a scattering model for forest or vegetation, based on the theory of electromagnetic-wave scattering in random media. The model generalizes the assumptions imposed by earlier models, and compares well with measurements from several forest canopies. This paper gives a description of the model. It also indicates how the model elements are integrated to obtain the scattering characteristics of different forest canopies. The scattering characteristics may be displayed in the form of polarimetric signatures, represented by like- and cross-polarized scattering coefficients, for an elliptically-polarized wave, or in the form of signal-distribution curves. Results illustrating both types of scattering characteristics are given.
    Keywords: EARTH RESOURCES AND REMOTE SENSING
    Type: IEEE Antennas and Propagation Magazine (ISSN 1045-9243); 35; 2; p. 18-26.
    Format: text
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  • 8
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    Leaf-shape effects in electromagnetic wave scattering from vegetation (1989)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: A vegetation medium is modeled as a half-space of randomly distributed and oriented leaves of arbitrary shape. In accordance with the first-order radiative transfer theory, the backscattering coefficient for such a half-space is expressed in terms of the scattering amplitudes. For disc- or needle-shaped leaves, the generalized Rayleigh-Gans approximation is used to calculate the scattering amplitudes. This approach is valid for leaf dimensions up to the size of the incident wavelength. To examine the leaf-shape effect, elliptic discs are used to model deciduous leaves, and needles are used to model coniferous leaves. The differences between the scattering characteristics of leaves of different shapes are illustrated numerically for various orientations, frequencies, and incidence angles. It is found that the scattering characteristics of elliptic disc-shaped leaves are sensitive to the three angles of orientation and disc ellipticity. In general, both like and cross polarizations may be needed to differentiate the difference in scattering due to the shapes of the leaves.
    Keywords: EARTH RESOURCES AND REMOTE SENSING
    Type: IEEE Transactions on Geoscience and Remote Sensing (ISSN 0196-2892); 27; 687-697
    Format: text
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