Type of Document	Dissertation
Author	Myers, Theodore J.
Author's Email Address	ted@casper.ee.vt.edu
URN	etd-81897-1428
Title	Determination of Bragg Scatter in an Aircraft Generated Wake Vortex System for Radar Detection
Degree	PhD
Department	Electrical Engineering
Advisory Committee	Advisor Name Title Scales, Wayne A. Committee Chair Brown, Gary S. Committee Member Davis, Willam A. Committee Member de Wolf, David A. Committee Member Devenport, William J. Committee Member Ragab, Saad A. Committee Member
Keywords	wake vortex bragg radar radar cross section doppler radar
Date of Defense	1997-08-28
Availability	unrestricted
Abstract Remote detection and tracking of wingtip generated wake vortices is important for hazard avoidance especially near airports. Aircraft that fly through these hazardous vortices experience sudden induced roll. Experiments have demonstrated that there is sufficient radar cross section for remote detection at frequencies ranging from VHF to C band (100 MHz to 5 GHz). The mechanism that yields this radar cross section is Bragg scattering from the index of refraction variations due to the atmospheric water vapor and potential temperature fields being mixed by the wake vortex system. Refractive index variations of the size that correspond to half the operating radar wavelength produce the observed radar return. Previous analysis has postulated turbulence within the wake vortex to be the generator of the index of refraction variations. In this work, a new mechanism is identified that does not assume turbulence within the wake vortex system. This "laminar flow mechanism" causes refractive index structuring that stretches into successively smaller spirals over time as the wake vortex system swirls and descends through the stratified atmosphere. The results are quantitatively consistent with experimental data. Results indicate that this new mechanism has a sharply peaked doppler spectrum which is encouraging for coherent detection by doppler radar.
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