Tidal time-scale variations of sound propagation in the Hudson River Estuary

Abstract

The nowcast and forecast of sound propagation in an urban estuary is important for the development of acoustic surveillance systems. Sound propagation in an estuary is highly affected by the temporal and spatial variability of salinity and temperature due to tides, freshwater inflows, winds, etc. Estuarine processes are analyzed here focusing on the formation and breakdown of the salinity and temperature stratification and their influence on sound attenuation. Transmission loss (TL) variability was determined first using real‐time data collected in the Hudson River near Hoboken, New Jersey. For TL forecasting, 24‐h forecasts of salinity and temperature distributions from a high‐resolution New York harbor observing and prediction system (NYHOPS) developed at Stevens were used (www.stevens.edu/maritimeforecast/). These forecasts provided the basis for calculating sound speed profiles. A parabolic equation based acoustic model was implemented to simulate the acoustic field structure. Real‐time TL measurements were made by transmitting sweep frequency signals (1–100 kHz) to a distance of 175 m. The observed tidal time‐scale TL variation of 10 dB was in good agreement with the model calculations. The results indicate that TL can be predicted within the context of the NYHOPS system. [Work supported by ONR Project No. N00014‐05‐1‐0632: Navy Force Protection Technology Assessment Project.]