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  • 1980-1984  (4)
  • 1
    Publication Date: 2011-08-18
    Description: The utility of radar scatterometers for discrimination and characterization of natural vegetation was investigated. Backscatter measurements were acquired with airborne multi-frequency, multi-polarization, multi-angle radar scatterometers over a test site in a southern temperate forest. Separability between ground cover classes was studied using a two-class separability measure. Very good separability is achieved between most classes. Longer wavelength is useful in separating trees from non-tree classes, while shorter wavelength and cross polarization are helpful for discrimination among tree classes. Using the maximum likelihood classifier, 50% overall classification accuracy is achieved using a single, short-wavelength scatterometer channel. Addition of multiple incidence angles and another radar band improves classification accuracy by 20% and 50%, respectively, over the single channel accuracy. Incorporation of a third radar band seems redundant for vegetation classification. Vertical transmit polarization is critically important for all classes.
    Keywords: EARTH RESOURCES AND REMOTE SENSING
    Type: ESA IGARSS 84. Remote Sensing: From Res. towards Operational Use, Vol. 1; p 149-154
    Format: text
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  • 2
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    In:  Other Sources
    Publication Date: 2019-06-27
    Description: Riometer records and the electric field records obtained during the same period at two different locations are compared in order to investigate the effect of cosmic radio wave backscatter by E region plasma waves on the cosmic radio wave power reaching riometers. The data on the relation between absorption events of small magnitude (a few tenths of a decibel to about 1 dB) and intense ionospheric electric fields are in agreement with the idea that a number of absorption events measured by riometers result from radiation backscatter into space by E region plasma waves of the Farley-Buneman type.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research; 85; Apr. 1
    Format: text
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  • 3
    Publication Date: 2019-07-13
    Description: Nonlinearities within a synthetic aperture radar (SAR) present significant obstacles to the calibration of the output imagery. The problem of calibrating a SAR is considerably more involved than that of calibrating a real aperture radar (RAR) or scatterometer, since the SAR relies heavily on the principle of superposition, which fails in nonlinear systems. It is shown in this paper that non-linearities can distort SAR imagery to such an extent that two areas of equal backscatter on the ground can be imaged to have significantly different intensities in the image.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: International Geoscience and Remote Sensing Symposium; Jun 08, 1981 - Jun 10, 1981; Washington, DC
    Format: text
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  • 4
    Publication Date: 2019-06-28
    Description: Backscattering measurements were acquired with airborne scatterometers over a site in Cass County, North Dakota on four days in the 1981 crop growing season. Data were acquired at three frequencies (L-, C- and Ku-bands), two polarizations (like and cross) and ten incidence angles (5 degrees to 50 degrees in 5 degree steps). Crop separability is studied in an hierarchical fashion. A two-class separability measure is defined, which compares within-class to between-class variability, to determine crop separability. The scatterometer channels with the best potential for crop separability are determined, based on this separability measure. Higher frequencies are more useful for discriminating small grains, while lower frequencies tend to separate non-small grains better. Some crops are more separable when row direction is taken into account. The effect of pixel purity is to increase the separability between all crops while not changing the order of useful scatterometer channels. Crude estimates of separability errors are calculated based on these analyses. These results are useful in selecting the parameters of active microwave systems in agricultural remote sensing.
    Keywords: EARTH RESOURCES AND REMOTE SENSING
    Type: E83-10403 , NASA-CR-171673 , SR-L3-04428 , NSC-18885 , NAS 1.26:171673 , LEMSCO-19422
    Format: application/pdf
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