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HIGH-FREQUENCY BACKSCATTER FROM TERRAIN WITH BUILDINGS
STANFORD UNIV CA STANFORD ELECTRONICS LABS
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It is becoming more apparent that a fair proportion of high-frequency backscatter from level portions of the earths surface results from upright targets such as trees and buildings. Using the standing-wave method, at 26 MHz, trees have been investigated at angles of incidence with respect to the horizontal up to 22.5 degrees. It was found that a tree may provide significant scatter. The present undertaking was to measure--by the same technique-- backscatter from cement walls of different sizes and conditions at 26MHz. Using a balloon-borne transmitting antenna and telemetering probe, cross sections for both horizontal and vertical polarization were obtained for angles of incidence between 2.5 degrees and 22.5 degrees. Magnitudes of cross sections were much greater for vertical polarization at lower angles of incidence. For angles of incidence other than broadside, but with the radiation perpendicular to the intersection of the wall and the ground, the wall-ground combination behaved as a corner reflector the experimental results for larger walls showed agreement with the corresponding theory. Subsequent extrapolation of the theory suggests that buildings may have cross sections much higher than trees.
APPROVED FOR PUBLIC RELEASE