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While satellite observations provide a global perspective, in-situ underwater sensors provide a continuous 3D presence in the local water column. Two-way interactions are established between an integrated sensor web system and predictive models.

Observing systems comprise a collection of sensor and non-sensor marine environment measurements and their transmission from regional and national platforms. U.S. IOOS observing subsystem data collectors transmit their data from the sensor (hardware or human) to data providers such as ocean data assembly centers (DACs) and ocean data archive centers.

Sensors measuring a host of interdisciplinary variables from moorings and other platforms can be configured to provide a continuous early warning  system to global change in the ocean, changing ocean conditions (e.g., optical properties), and ocean pollution.

Underwater sensor nodes find applications in oceanographic data collection, pollution monitoring, offshore exploration, disaster prevention, assisted navigation and tactical surveillance applications. Moreover, unmanned or autonomous underwater vehicles, equipped with sensors, will enable the exploration of natural undersea resources and gathering of scientific data in collaborative monitoring missions. Underwater acoustic networking is the enabling technology for these applications. Underwater networks consist of a variable number of sensors and vehicles that are deployed to perform collaborative monitoring tasks over a given area.

Acoustic Sensors

Underwater acoustic communications are mainly influenced by path loss, noise, multi-path, Doppler spread, and high and variable propagation delay. All these factors determine the temporal and spatial variability of the acoustic channel, and make the available bandwidth of the Under- Water Acoustic channel (UW-A) limited and dramatically dependent on both range and frequency.

Underwater acoustic communication links can be classified according to their range as very long, long, medium, short, and very short links Acoustic links are also roughly classified as vertical and horizontal, according to the direction of the sound ray with respect to the ocean bottom.

Optical Sensors

An optical sensor is a device that converts light rays into electronic signals. They measure the physical quantity of light and translates it into a form read by the instrument. Usually, the optical sensor is part of a larger system integrating a measuring device, a source of light and the sensor itself. This is generally connected to an electrical trigger, which reacts to a change in the signal within the light sensor.

One of the features of an optical sensor is its ability to measure the changes from one or more light beams. This change is most often based around alterations to the intensity of the light. When a phase change occurs, the light sensor acts as a photoelectric trigger, either increasing or decreasing the electrical output, depending on the type of sensor.

Future Developments

The field of ocean sensors and systems is constantly evolving. Scientists and engineers are making strides in improved bio-fouling protection, autonomous water sampling systems, optical and acoustic systems, airborne variable sensors, and two-way, low-cost, low-power telecommunications.