Ecological Acoustic Recorder (EAR) Technology
The EAR is a digital, low power system that records ambient sounds at frequencies up to 30 kHz on a programmable schedule. The EAR can also respond to transient acoustic events that meet specific criteria, such as signals indicating a vessel passing nearby. There are two types of EAR devices: a deep water version that is rated to a depth of 500 m and a shallow water version for use at depths down to 36 m.
The deep water EAR is deployed simply by dropping it over the side of a vessel and recovered by activating an acoustic release that allows the recorder to float back to the surface. It can be deployed for up to six months. The shallow water EAR is deployed by divers and can be left in place for a year or longer, depending on the number of batteries used and the recording schedule. Acquisition of acoustic data by the EAR is not adversely affected by marine biofouling.
The EAR system consists of a Persistor-based microprocessor and an analog-to-digital converter that records sounds detected around the recorder and stores the recordings on an onboard disk. Recording sessions are started in one of three ways: on a software-regulated schedule, on a start trigger tuned to detect vessel-generated sound, and/or on a trigger tuned to sounds produced by cetaceans.
An important aspect of the passive acoustic technology work is the development of software used to analyze the data. Deployments of EAR devices over several months generate an amount of data far too great for manual analysis. Custom software algorithms are being refined to automate the processing and analysis of data.
The availability of field-tested EARs of low cost, high endurance (1+ years of deployment), and portability and the development of software tools to automate the analysis of data collected from passive acoustics systems have great utility for assessing and monitoring biological and human activity in the marine environment.