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Since oxygen is involved in most of the biological and chemical processes in aquatic environments, it is the single most important parameter needed to be measured. Oxygen can also be used as a tracer in oceanographic studies.
For environmental reasons it is critical to monitor oxygen in areas where the supply of oxygen is limited compared to demand e.g.:

• In shallow coastal areas with significant algae blooms.
• In fjords or other areas with limited exchange of water.
• Around fish farms.
• In areas interesting for dumping of mine or dredging waste.

The Aanderaa Oxygen Optodes are based on the ability of selected substances to act as dynamic fluorescence quenchers.
The fluorescent indicator is a special platinum porphyrin complex embedded in a gas permeable foil that is exposed to the surrounding water. A black optical isolation coating protects the complex from sunlight and fluorescent particles in the water.
This sensing foil is attached to a sapphire window providing optical access for the measuring system from inside a watertight titanium housing.
The foil is excited by modulated blue light, and the phase of a returned red light is measured (see illustration overleaf). By linearizing and temperature compensating, with an incorporated temperature sensor, the absolute O2 concentration can be determined.