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Use of the envelope detection method to detect micro-Doppler

Georgia Tech Research Institute (GTRI) was tasked by the U.S. Department of Transportation (USDOT), Federal Highway Administration (FHWA), to test the Safety Warning System® (SWS) for application as an in-vehicle communications system. In addition to the communications function, the system has a 24 GHz homodyne Doppler radar function that provides the system’s micro-controller with traffic counts and speed information on passing vehicles. One task was to use the homodyne radar to see if the resonant frequency of an 18 wheel tractor trailer could be determined while the truck was at a distance from the radar (Greneker, et al.). This led to a study of additional methods to detect low frequency resonance effects excited by the interaction between the highway and the suspension system of a tractor trailer when the body induced Doppler signal is many orders of magnitude larger than the resonance frequency of interest. This paper describes a method that the authors call the “envelope detection” method. This micro-Doppler extraction technique has proven useful to extract small vibration and resonance induced signals in the presence of a large Doppler signal from the radar energy reflected from the radiator, hood and cab of the tractor trailer used in testing.