Considerações às comunicações acústicas É cada vez mais comum a instalação de sistemas capazes de monitorizar o ambiente envolvente e o controlo de equipamentos subaquáticos junto à costa. Tipicamente estes sistemas são constituídos por sensores localizados no fundo do mar ou na água e são ligados à costa tanto por cabo como por via radio network através de bóias à superfície. Nem sempre é possível a colocação de bóias, ou de cabos devido às costas associadas, condições ambientais, ou actividades piscatórias. Em tais condições a melhor maneira de transferir informação é através da comunicação acústica.

Considerações às comunicações acústicas Tem como principais desvantagens : 1)O ambiente acústico em áreas costeiras, especialmente perto de marinas é muito poluído. Pode ser caracterizado por : -propagação em vários sentidos -condições de alteração rápida -alto nível de ruído -ausência de um caminho directo para o som entre dois modems 2)Possui baterias com duração limitada 3)Normalmente estas áreas são visitadas por mamíferos aquáticos, logo, são necessários cuidados para não ferir esses animais, com a contínua operação dessa rede subaquática de sensores

Sensores alternativos Argo System

Argo System Comprised of three subsystems: Hydraulics: control buoyancy adjustment via an inflatable external bladder, so the float can surface and dive. Microprocessors: deal with function control and scheduling. Data transmission system: controls communication with satellite. Approx. Weight: 25 Kg Max. operating depth: 2000m Crush depth: 2600m

Argo Floats Argo is an international collaboration that collects high-quality temperature and salinity profiles from the upper 2000m of the ice-free global ocean and currents from intermediate depths. The data come from battery-powered autonomous floats that spend most of their life drifting at depth where they are stabilised by being neutrally buoyant at the "parking depth" pressure by having a density equal to the ambient pressure and a compressibility that is less than that of sea water. At typically 10-day intervals, the floats pump fluid into an external bladder and rise to the surface over about 6 hours while measuring temperature and salinity. Satellites determine the position of the floats when they surface, and receive the data transmitted by the floats. The bladder then deflates and the float returns to its original density and sinks to drift until the cycle is repeated. Floats are designed to make about 150 such cycles. floats Argo Float Models The three float models in use are the PROVOR built by MARTEC in France in close collaboration with IFREMER, the APEX float produced by Webb Research Corporation, USA and the SOLO float designed and built by Scripps Institution of Oceanography, USA.PROVORAPEXSOLO Two temperature/salinity sensor suites are used - SBE, and FSI. The temperature data are accurate to a few millidegrees over the float lifetime.SBEFSI Argo Data Transmission As the float ascends a series of typically about 200 pressure, temperature, salinity measurements are made and stored on board the float. These are transmitted to satellites when the float reaches the surface.

Cable Architecture The Project Observatory Network Cable is based on CELTNET architectureCELTNET The cable is the best option for Long-term and continuous marine monitoring Subsea cabled observatories are the only means of continuously acquiring large amounts of different data in areas where satellites cannot see and are crucial for observing natural processes that are very episodic or that require long time series to detect The architecture is a robust, ring design, repeater driven backbone cable that services primary nodes through branching units and spur cables is proposed to provide a link from shore to the remote deep sea sites This option would reduce the risk of cost and time delays System Main Features The communication infrastructure of CELTNET will be based on optically amplified technology using Wavelength Division Multiplexing (WDM). The system wavelengths will be in the 1550nm wavelength window in order to use telecommunication industrial components (state of the art design). It will have the following key features:CELTNET – Repeaters (where needed) designed for WDM applications. – Equalization and dispersion management. – WDM Line Terminal Equipment supporting. – Global data rate = number of nodes X data rate for one node (namely 2.5Gb/s – original design). – High reliability submerged components – Forward Error Correction (FEC). – Network Management System (state of the art design).