Surface drifters are sophisticated microprocessor-controlled oceanographic data collection instruments. A drifter consists of a surface float which is tethered to a drogue that holds the drifter almost motionless relative to a horizontal area, known as a layer, relatively near the ocean's surface that the researcher desires to observe. The device works much like tossing a chip in a river to render the current more observable. The surface float houses a microprocessor that controls the collection and transmission of data from sensors, the transmitter that sends information to a satellite, a power supply, and antenna. Drifters can operate unattended for periods up to two years.
Our surface drifters provide oceanographers and meteorologists valuable
information that can be obtained only by an instrument that is at a
specific location in the ocean. For example, surface drifters provide
accurate sea surface temperature for satellites observing sea surface
temperature (SST). SST from drifters is disseminated through World
Meteorological Organization environmental databases and used to calibrate
satellite SST maps and to update areas which are obscured by clouds.
WHAT IS THE CLEARSAT 2.0™ CONTROLLER?
The key to the versatility of Clearwater's oceanographic instruments is the ClearSat 2.0™. This advanced microprocessor-based device allows the various instruments on board any of Clearwater's drifters to communicate with each other via the NMEA 1-second message. This allows dynamic configuration of transducers and data conditioning; for instance, using the ClearSat 2.0™, a GPS system could direct a seawater surface temperature transducer to take a measurement. Service Argos has certified the ClearSat 2.0™ as an Argos PTT, and a version is available with a serial interface for transmitting data via the Argos system from a host controller.
The American-French Argos system is a satellite-based system with worldwide coverage. Equipping a drifter with an Argos reciever allows equipment location and transmission of data collected by the drifter. Clearwater's ClearSat 2.0 microprocessor-based controller has been certified by Service Argos as an Argos platform transmitter terminal, and can collect instrument readings and send them via the Argos signal. This data can be accessed worldwide.
Argos can locate items to within 150-1000 meters. While Argos is not as accurate as GPS, its power consumption is quite low and the components are small, making it a perfect choice for oceanographic instrumentation.
Service Argos can be reached at http://www.argosinc.com/
The Global Positioning System (GPS) is a network of satellites originally deployed by the US military to allow instantaneous and accurate location of equipment. Commercial systems have access to the signals from these satellites, allowing location readings accurate to within several meters. GPS recievers can communicate with other equipment on the drifter using the NMEA one-second commercial message, activating particular sensors at particular locations.
Clearwater uses Rockwell's Jupiter system in all GPS-equipped drifters and buoys. Time to first fix is usually less than three minutes, and subsequent fixes can be obtained within thirty seconds from the initial request.