Metodologías de mapeo de ruido submarino en aguas someras

Resumo

A growing awareness of environmental concerns is attracting increasing attention to the problem of underwater noise pollution and its effects. Several studies have demonstrated that anthropogenic ambient noise has a serious adverse impact on the health of marine biosystems and their fauna. In this scenario, governments and public administrations have started to take action; for instance, the European Parliament has defined a framework for community action in marine environmental policy through Directive 2008/56/EC and further documents, in which measuring underwater noise levels along European coasts and creating noise maps were identified as preliminary tasks necessary to establish the extent of the problem and to define further corrective actions. At the same time, it is recommend the use of propagation models to strengthen the analyses by "addressing the bias introduced by the variability of the spatial distribution of human pressure, and by the natural variability of the environment" as well as to extend the results to larger areas due to the impracticality of making measurements at all points. Present work carries out a study of the methodologies for the creation of underwater noise maps in shallow waters, proposing a practical solution for the evaluation of the specific environment of the ría de Vigo (42º 14.5’N, 8º 43.4’W). The selected environment stands out for being an area of great density and variety of traffic, with the port of Vigo as a world reference. It's a shallow water area (<45m) with more complex propagation characteristics (multipath, influence of bathymetry, influence of the bottom, etc.) and less historically investigated than deep waters. However, the solutions presented are easily exportable to deep water environments where the mechanisms of sound propagation are simplified. That is why the methodologies used during this project, despite being adjusted to a specific environment, can be considered generic in terms of validity and execution possibilities. Firstly, we will study the underwater noise measurement techniques proposing both methods for measuring sound pressure level and propagation losses. The measurement techniques are built upon the deep water normative, in spite of the lack of shallow water one. Propagation losses measurements have been made using a calibrated underwater source emitting tones in 1/3 octave frequency bands to a line of measuring points. These measurement techniques will be used to study the main noise sources, the vessels. Series of recording campaigns have been made in order to get more information of the different sources implied. All these measurements have been collected –and also all the information of the environmental conditions, source characteristics, measurement setup, etc.– to create an online database called ShipsEar, with open access to the research community. The usefulness of ShipsEar is illustrated through a simple experiment of vessel detection and vessel classification by size, with and overall classification rate over 75% and a 100% detection rate. On the other hand, we will study the modeling techniques used for the estimation of the propagation losses and the vessels source levels. The models selection will be adjusted trough measurements in two phases: we will first adjust the propagation model using propagation losses measurement to then jointly adjust the optimized propagation model and the source model with monitoring measurements at different points of the ría. A complete methodology based on this modeling and measurements techniques will be developed, aided by the construction of an independent AIS station and a control application –ShipsEar Mapping– to create, present and storage underwater noise maps. Finally, the proposed application is developed and detailed. ShipsEar Mapping allows the generation of underwater noise maps, detects areas where underwater fauna is affected and evaluates possible solutions. The tool reflects the recommendations of European regulations –as well as other examples of application that can serve as feedback to studies by biologists and all kinds of marine researchers– and gives the first estimate of underwater noise in the Vigo estuary following Marine Framework Strategy Directive indicators for the evaluation of continuous low frequency sound, related to maritime traffic.