Incorporating Environmental Information into Underwater Acoustic Sensor Coverage Estimation in Estuaries

Abstract

Monitoring underwater environments is challenging. Terrestrial and aerial surveillance technology cannot be adopted directly since optical and electromagnetic waves have extremely high attenuation in water. Most existing underwater detection technologies rely upon sound waves as sound can travel a relatively long distance in water. However underwater sound propagation is highly susceptible to interference depending on the water conditions. Sharp gradients in salinity and temperature cause sound to refract and reflect. Thus the listening range, or coverage, of a sound detector is largely influenced by the underwater environment. This effect is particularly prominent in an estuary where fresh water mixes with sea water, and tidal action causes significant current changes. We study the behavior of estuary water conditions and attempt to characterize the acoustic sensor coverage in an estuary. We use environmental data extracted from the NYHOPS forecast model. Acoustic conditions in water are evaluated based on sound speed variation. Based on scans over a ten-month period, we characterize the impacts from major environmental factors on underwater sound propagation. We further calculate sound transmission loss for typical water conditions and analyze the variation of sensing range for underwater sound detectors.