GOCD Data Category

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Frequently Asked Questions

What are moored ADCPs?
A moored ADCP measures vertical profiles of steady and time-dependent horizonal ocean currents repeatedly at a fixed station. The resulting collection of profiles is called a time series profile.
What is the timeSeriesProfile format?
A data variable may contain a collection of such timeSeriesProfile features, one feature per station. The instance dimension in the case of a timeSeriesProfile is also referred to as the station dimension. The instance variables, which have just this dimension, including latitude and longitude for example, are also referred to as station variables and are considered to contain information describing the stations.
What is an ocean glider?

An ocean glider is an autonomous underwater vehicle used to collect oceanographic data. Gliders may be equipped with a wide variety of sensors to monitor temperature, salinity, currents, and other ocean conditions.

Types of Ocean Gliders
  • Sea Glider (Developed by the University of Washington/iRobot Corp.)
  • Slocum Glider (Developed by Teledyne Webb Research)
  • Spray Glider (Developed by a team of scientists from Scripps Institution of Oceanography and Woods Hole Oceanographic Institution)
  • Wave Glider (Developed by Liquid Robotics)
What are the Glider-derived Currents?
Underwater gliders use an accurate hydrodynamic model to determine the path of the vehicle in still water based on its speed and direction. Using this model, depth-averaged currents are determined by comparing the predicted surfacing location of the vehicle with the actual surfacing position according to the GPS. Depth average currents estimates have an accuracy of 1 cm/s and are assumed to act over the whole profile uniformly.
What are the High Frequency Radar-derived Currents?

High frequency (HF) radar is used by ocean researchers to measure surface current velocity fields near the coast. Radar antennas (typically in pairs) are positioned on shore and can measure surface currents (the top 1-2 m of the water column) up to 200 km away with resolutions ranging from 500 m to 6 km depending on the radar frequency.

Although the precise amount of error for the observed surface currents,is difficult to quantify, HF Radar data is generally expected to be accurate to within 10 cm/s of current speed and 10 degrees of current direction. It is important to note, that the presented values are spatial and time averages - so that they may not be representative of the currents of a specific point within a grid cell (particularly near shore) or of an instant in time during the observed hourly period.

What are the Drifter-derived Currents?
Rather, they are indirect determinations of ocean surface currents based on the ship drift method. In this method, the difference between a ship's dead-reckoned position (determined from its previous position, speed, and heading) and actual position determined from a navigational fix is ascribed solely to the effect of surface currents.