Vibrometry and Sound Reproduction of Acoustic Sources on Moving Platforms Using Millimeter Wave Pulse-Doppler Radar

Abstract

This paper presents millimeter wave (MMW) pulse-Doppler radar for the remote sensing of acoustic vibration for targets in motion. A key advance in this work is the development of precision motion compensation for MMW vibrometry, making it possible for a monostatic radar to extract and reproduce small-scale vibrations on platforms undergoing large-scale motion. The motion compensation methodology uses a hierarchical approach combining direct and indirect estimation for the time dependent variation of target motion parameters across coherent samples in radar fast time and slow time. Additionally, the wide bandwidth commonly available at MMW allows vibrations to be selectively detected and disambiguated in range across the length of moving targets. Stretch processing compresses the received radar bandwidth by more than 10x, so that Hilbert sampling can be used to acquire quadrature samples using a single analog-to-digital converter. The resulting complex baseband response directly reproduces the target's acoustic signature. To demonstrate the technique, a 94 GHz pulsed linear frequency modulated (LFM) radar accurately reproduces the pitch of audio waveforms generated by a speaker in the rear of an accelerating automobile at an outdoor test range. These results should have major consequences for the development of MMW vibrometry as a remote sensing technique.