Ocean Acoustic Waveguide Remote Sensing (OAWRS) of marine ecosystems

Abstract

Ocean Acoustic Waveguide Remote Sensing (OAWRS) has recently been shown to be capable of instantaneously imaging and continuously monitoring fish populations over continental shelf-scale areas, covering thousands of km 2 . We show how OAWRS can be used in a variety of oceanic ecosystems to remotely assess populations and study the behavior of fish and other marine organisms, such as Antarctic krill, to help the study of marine ecology and the ecosystem-based approach to fisheries management.

Feasibility of Acoustic Remote Sensing of Large Herring Shoals and Seafloor by Baleen Whales

“…Similar analysis is performed for shallow shoals given measured constraints. The TLA term in Equation (4) can be written [23] for monostatic sensing as:…”

“…The expected magnitude square of the scattered field, |Φ F | 2 , received at location r from N omni-directional targets randomly distributed with uniform probability in a vertical layer of thickness H centered at z = z 0 within a resolution footprint A R (ρ C ) centered at horizontal location ρ C can be determined from [23,30]:…”

“…In Equation (4), Φ re f = 1 µPa is the reference acoustic pressure in water, SL is the whale call source level with mean and standard deviation [1,2] given in Table 1 consistent with circular complex Gaussian random fields fluctuations [26], TLA is the depth-averaged two-way transmission loss to individual targets integrated over one resolution footprint area [23] given in Equation (5), TS = 10 log 10 S r re f k 2 is the expected target strength of a single herring, S is the plane wave scatter function of a single herring, k is the acoustic wavenumber, r re f = 1 m is the reference length, n A,re f = 1 fish/m 2 is the reference areal fish population density, and n A = N/A R (ρ C ) is the expected areal density of the targets within a spatially varying resolution cell centered at horizontal location ρ C . When the instantaneous bandwidth BW of baleen whale vocalizations [1,2] is greater than the one-third octave bandwidth BW 1/3 given in Table 1, an adjusted whale call source level SL adj = SL + 10 log 10…”

“…Using a fish swimbladder resonance model [23,31], the expected target strength TS of a single herring in a uniform vertical layer of herring is determined from:…”

“…Detection of large herring shoals and the seafloor is then investigated using theoretical and numerical methods developed for analyzing Ocean Acoustic Waveguide Remote Sensing (OAWRS) of fish shoals [21][22][23][24][25] given these active sensing parameters. Sensing resolution in cross-range is determined by spatial array theory and in range by incoherent energy analysis [1,2,[21][22][23][24][25][26], since evidence suggests temporally coherent auditory processing is unlikely [27,28].…”