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Measuring Currents - Deep Ocean Drifter

To monitor ocean currents and ocean water characteristics far beneath the ocean surface, scientists use devices called profiling floats. While Davis drifters remain at the ocean surface during their deployment, profiling floats are programmed to sink to a particular depth and remain there for a specific period of time. At that depth, which scientists call a "parking depth", the profiling float drifts with the prevailing current. After the pre-programmed time period, the profiling float begins to rises to the ocean surface. As the profiling float ascends, it can be programmed to take a series measurements from the surrounding water, which may include the water's temperature, salinity, and pressure. When the profiling float reaches the surface, it transmits its data to an orbiting satellite to determine the profiling float's position, and begin to receive the profiling floats data. The satellite also receives information about the path the float has taken while it was drifting. When all of the float's data has been transmitted, the float sinks again to drift and the cycle is repeated. Floats are designed to make about 150 such cycles. Some floats, such as the one depicted in the image below, can sink and drift up to 2,000 meters (approximately 6,500 feet) beneath the surface of the ocean.

Relationship between vertical and horizontal components for tides

Source: NOAA's Ocean Service

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