Approccio semi-empirico alla valutazione del mascheramento acustico da rumore navale per la Balaenoptera physalus
Author(s)
Puppini, Alessandro
Date Issued
February 10, 2011
Type
Doctoral Thesis
Abstract
Acoustic masking from anthropogenic noise is increasingly considered as a potential threat to
marine mammals, especially for those specializing in low frequencies, such as the Fin whale
(Balaenoptera physalus). One of the sources of anthropogenic noise that affects large areas is
shipping noise, which has grown considerably of the past decades. In the Mediterranean Sea
shipping routes also affect protected areas for cetaceans such as the Pelagos Sanctuary for
marine mammals, where the concentration of fin whales is higher than elsewhere in the
Mediterranean. This paper presents a method for the quantification of the acoustic risk from
vessel traffic applied to fin whales, integrating empirical measures and simulation modeling and
applying the results to the Pelagos Sanctuary. The semi-empirical approach can resolve both the
passive sonar equation and the active one, providing both an estimate of the naval Source Levels
and of the SNR (Signal to Noise Ratio) to measure areas affected by masking in 2D space (depth
vs. Range). The simulation encompassed two different habitats with each one coastal and one
pelagic site in order to obtain a complete picture of the acoustic propagation model obtained with
RAMSGeo (Range-dependent Acoustic Modeling). The latter considers several functions
allowing one to integrate the two solutions obtained with the sonar equations. Within the coastal
site we measured five ships (ro-ro pax) which are representative of shipping wihin the Pelagos
Sanctuary by adopting an innovative system that integrates a calibration tone (@2100 Hz) within
the measuring system, thus facilitating the achievement of absolute measures (in dB re 1 μPa).
Measures of shipping noise are added to ambient noise measurements to provide evidence of the
possible various acoustic scenarios. The levels and frequencies adopted for the classification of
the sounds of Fin whales are taken in part from the literature. The results show that in two
simulated environments there are acoustic "thresholds" necessary for effective propagation of
sound: 60 dB in coastal environment, and 40 dB in the pelagic environment. The values of SNR
show that ro-ro pax noise is always masking fin whales sounds, while within the ambient noiseonly
scenario of propagation, masking areas are very limited, thus allowing fin whales to
communicate in excess of 220km. The method presented is suited to be applied to different
species, different habitats and environments to estimate the potential impact of acoustic masking
for non-impulsive acoustic sources.
Additional information
Dottorato di ricerca in Ecologia e gestione delle risorse biologiche
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