Sonar signal analysis: Biological consequences of out-of-band acoustic signals from active sonar systems

Abstract

Within the aquatic environment acoustic monitoring systems are widely used to monitor and assesses anthropogenic noise sources and potential impacts on many aquatic species. Passive acoustic studies are, however, often limited to acoustic observation of changes in the species vocalization. Changes in vocalizations such as vocal calls or use of echolocation signals can be interpreted as both presence/absence, i.e., the animals have moved away or a change in acoustic behaviours, for example, not vocalizing as before. Active sonar systems can offer an attractive alternative in behavioural response studies potentially providing high-resolution spatial and temporal tracking of non-vocalizing or currently “quite” species. The main frequency of the sonar signal chosen to be outside the hearing range of the species of interests. The potential, however, exists for signal generation away from the design frequency of the sonar based on both the transducer/electronics as well as the pulsed nature of the signal. These signals might be perceived by the species of interest and therefore alter the behavioural response under study. Typical active sonar signals are analysed and compared to known hearing and integration periods for a range of species and the potential biological consequences of this out-of-band energy evaluated.