January 1968 | NTIA Technical Memo ERL TM ITS 136

Backscatter studies and 3 -D ray tracing final report

L. H. Tveten; R. D. Hunsucker; W. J. Surtees; Leslie A. Berry

Abstract: Feasibility of using backscatter to assess the accuracy of simultaneous direction-of-arrival measurements indicates poorer direction-of-arrival readings when backscatter shows travelling ionospheric disturbances. (Applies to simple mode paths.) The technique shows promise. No consistent relation between signatures of ionospheric irregularities as seen with vertical sounders, backscatter, and direction-of-arrival measurement, although there is usually some association. Mills T cross­correlation of a narrow azimuth beam and a narrow elevation beam to produce a pencil beam pattern shows promise. Using elevation angles of several incoming modes, backscatter elevation angles as a function of delay time, and transmission curves, the ground range of a source can be estimated with the rather surprisingly low error of about 4%. Sidescatter is usually present (generally unnoticed in presence of direct propagation modes) whenever direct ionospheric paths are open from both the trans­mitting and receiving locations to an area of the earth's surface. Angular spread in azimuth, ·multipath delay, and the scatter spectrum characteristic of sidescatter usually serv~ to distinguish it from direct propagation modes. 3-D ray-tracing program tested for model ionospheres generated from true-height analyses of ionograms and comparing these ray deviations from the great circle path with those measured. Program is accurate and reliable.

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