Low-Cost Underwater Sound Recorder for coastal applications.

Sound is the most widespread and pervasive kind of anthropogenic energy that human activities introduce into the marine environment. Sound energy input can be highly variable both in time and space, becoming an important part of the total ocean acoustic background. Moreover, the underwater sound plays an ecologically important role in marine ecosystems, being a critical sensory modality for many marine organisms that can be useful for both sensing the environment and communication. With the Marine Strategy Framework Directive (MSFD) (2008/56/EC, EU 2008), underwater noise has been recognized as pollution and included in the qualitative high-level descriptors to achieve good environmental status, GES.

During recent years, passive acoustic monitoring in the ocean has become a standard technique across the oceanographic community and is used to address biological, geological and meteorological issues. Due to the highly spatio-temporal variability of the ocean noise, a large number of the observing systems would be needed. Extended marine monitoring would require a reduction in the cost of platforms and instruments, without compromising data quality. Despite, a significant effort has been invested by the scientific community in the development of low-cost PAM recorders, much work still remains. Most of the problems are related to the pressure to which the devices are exposed, the battery pack limits, storage memory limits, and sensibility of the sound sensor once waterproofing and so on.

Here, we present a low-cost underwater sound recorder for coastal applications developed to be applied in both background noise monitoring and bioacoustic monitoring. This recorder consists of a high-performance USB-based microcontroller development system with an audio adapter that guarantees high audio quality. Additionally, test were conducted using both an ECM (Electret Condenser Microphone) and a MEMS microphone (Micro-Electro-Mechanical System) for a wide frequency range recordings to find the better solutions for good data quality. Compact and small in size, it can be easily installed on various oceanographic platforms for different types of sampling.

Here we present the first results of the laboratory and field tests, comparing our assembled device with a commercial recorder and a pre-calibrated hydrophone.