Bubble Cloud Acoustic Spectrography in the James River Estuary
Abstract
The James River Estuary hosts a salt wedge during its tidal cycle that is typical in estuarine environments but is atypical in its V-shape. Linear frequency-modulated acoustic signals in the 5005000 Hz range were transmitted during the advance and retreat of the salt wedge during the James River Estuary acoustics field experiment from April 1825, 2019. Using simple instrumentation, correlations were made between the acoustical characteristics and observational parameters such as current profiles and geological descriptors and features. Data analyzed included acoustic data from underwater hydrophones positioned at three depths through the water column, echosounder data collected across the front, low-angle radar images of the surface, and modeled salinity. Received signal data shows lower energy level when the front occupies the acoustic transect and higher, mixed signal levels as the front moves away from the acoustic transect. A decrease in signal level of about 8 dB within 1.25 hours was recorded due to attenuation from scattering and absorption by bubble clouds and fish, sound refraction, ducting, bottom scatter and flow noise. Understanding of these transmission and propagation loss patterns can aid in the acoustic interpretation of data collected in constrained or denied environments and facilitate a future predictive capability in autonomous underwater vehicle (AUV) sonar systems.
Document Details
- Document Type
- Technical Report
- Publication Date
- Jun 01, 2020
- Accession Number
- AD1114739
Entities
People
- Jessica A. Rogers
Organizations
- Naval Postgraduate School