A Methodology for Characterizing Underwater Radiated Noise from Submerged Electric Vehicles in a Coastal Environment: An AUV Test Case

Submerged electric vehicles (SEVs), including autonomous underwater vehicles (AUVs), remotely operated vehicles, and diver propulsion systems, may radiate distinct tonal, harmonic, and modulated acoustic components associated with electric propulsion drives and motor-control electronics. Characterizing these signatures is relevant to passive detection and engineering diagnostics, but remains challenging in coastal environments because ambient noise, shallow-water propagation, and aspect-dependent radiation can obscure vehicle-related features. Existing underwater radiated noise (URN) standards, developed primarily for surface vessels, do not address the spectral, operational, and geometric complexity of SEV measurements. This paper presents an eight-step methodology for SEV URN characterization, covering measurement design, cavitation assessment, frequency-band selection, ambient-noise characterization, spectral and time-frequency analysis, subsystem-oriented interpretation, propagation-corrected source-related estimation, and angular and operational analysis. The novelty lies in integrating calibrated pass-by acoustics with synchronized vehicle metadata, ambient-noise context, and subsystem-oriented analysis to resolve tonal and modulated features that broadband methods cannot capture. The methodology is demonstrated using an A18D AUV measured in coastal water. Drive-related tonal groups were observed near 5.56, 11.1, and 22.2 kHz, with harmonic structure up to 105 kHz. Source-related tonal PSD estimates ranged from 77 to 120 dB re 1 uPa^2/Hz at 1 m