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shuttle imaging radar - physical controls on signal penetration and subsurface scattering in the eastern saharaInterpretation of Shuttle Imaging Radar-A (SIR-A) images by McCauley et al. (1982) dramatically changed previous concepts of the role that fluvial processes have played over the past 10,000 to 30 million years in shaping this now extremely flat, featureless, and hyperarid landscape. In the present paper, the near-surface stratigraphy, the electrical properties of materials, and the types of radar interfaces found to be responsible for different classes of SIR-A tonal response are summarized. The dominant factors related to efficient microwave signal penetration into the sediment blanket include (1) favorable distribution of particle sizes, (2) extremely low moisture content and (3) reduced geometric scattering at the SIR-A frequency (1.3 GHz). The depth of signal penetration that results in a recorded backscatter, here called 'radar imaging depth', was documented in the field to be a maximum of 1.5 m, or 0.25 of the calculated 'skin depth', for the sediment blanket. Radar imaging depth is estimated to be between 2 and 3 m for active sand dune materials. Diverse permittivity interfaces and volume scatterers within the shallow subsurface are responsible for most of the observed backscatter not directly attributable to grazing outcrops. Calcium carbonate nodules and rhizoliths concentrated in sandy alluvium of Pleistocene age south of Safsaf oasis in south Egypt provide effective contrast in premittivity and thus act as volume scatterers that enhance SIR-A portrayal of younger inset stream channels.
Document ID
19860059435
Document Type
Reprint (Version printed in journal)
Authors
Schaber, G. G.
(Geological Survey Flagstaff, AZ, United States)
Mccauley, J. F.
(Geological Survey Flagstaff, AZ, United States)
Breed, C. S.
(USGS Flagstaff, AZ, United States)
Olhoeft, G. R.
(USGS Denver, CO, United States)
Date Acquired
August 12, 2013
Publication Date
July 1, 1986
Publication Information
Publication: IEEE Transactions on Geoscience and Remote Sensing
Volume: GE-24
ISSN: 0196-2892
Subject Category
EARTH RESOURCES AND REMOTE SENSING
Funding Number(s)
CONTRACT_GRANT: NASA ORDER W-15788
CONTRACT_GRANT: NASA ORDER W-08760
Distribution Limits
Public
Copyright
Other