HomeEducationCurrents

# Age of Exploration

## Currents Tutorial

----

Since the age of exploration, mariners have  needed to know the speed and direction (velocity) of ocean currents to  steer their ships within harbors and along trade and exploration  routes. A mariner needs to be able to measure the velocity of currents  by observing distance, time, and direction.

The simplest method of determining the velocity of a current involves an  observer, a floating object or drifter, and a timing device. The observer stands on an anchored ship with a timer. He or she then places  the drifter (such as a piece of wood) into the water and measures the  amount of time the drifter takes to move along the length of the ship.  He or she then stops the timer after the object has traveled some  distance, and measures that distance, noting the direction in which the  object moved.

The  observer then divides the distance the object traveled by the time it  took the object to travel that distance, which equals the speed of the  current. By combining the speed of the object with the direction in  which it moved, the observer can then determine the current’s velocity.  Ocean currents typically are measured in knots.

Although  they still follow the same essential concept to measure ocean currents,  mariners today use more accurate and sophisticated instruments. Today,  drifters are often elaborate buoys equipped with multiple oceanographic  instruments. Some are equipped with global positioning system  technology and satellite communications to relay their position in the  ocean back to observers on land. Other drifters submerge for long  periods of time to measure the ocean currents at depth. The drifter  occasionally rises to the surface to send a signal that relays its  position.

----

----

All drifter  measurements are termed “Lagrangian measurements,” named after  mathematician Joseph Louis Lagrange (1736-1813), who first described  the path followed by fluids. But current velocities can be measured  another way as well—using “Eulerian measurements.” Named after Swiss  mathematician Leonhard Euler (1707-1783), Eulerian measurements involve  describing fluid flow by measuring the speed and direction of the fluid  at one point only. In this method, an instrument is anchored in the  ocean at a given location, and the water movement is measured as it  flows past the instrument.

Measuring  currents by Eulerian methods is becoming increasingly more common. One  reason is that it is easier to retrieve these expensive but stationary  instruments than it is to locate floating drifters.

### Currents Lessons

              - Welcome
              - Tidal Currents 1
              - Tidal Currents 2
              Coastal Currents
              - Waves
              - Longshore Currents
              - Rip Currents
              - Upwelling
              Surface Ocean Currents
              - The Coriolis Effect
              - Surface Ocean Currents
              - Boundary Currents
              - The Ekman Spiral
              The Global Conveyor Belt
              - Thermohaline Circulation
              - The Global Conveyor Belt
              - Effects of Climate Change
              How Are Currents Measured?
              - Age of Exploration
              - What is a "knot"?
              - Shallow Water Drifter
              - Deep Ocean Drifter
              - Current Profiler
              - Shore-based Current Meters
              - How Currents Affect Our Lives?
              - References
              - Roadmap to Resources
              - Subject Review

###### **Search** Education

###### Get **Social**

Contact Us

            - Provide Feedback 
            -  Contact Us 
            -  Report an error 

##### Science. Service.Stewardship.

###### 						About NOS 					

            - About Us
            - NOS Program Offices
            - Media Inquiries
            - Website Acknowledgements

###### 						Resources 					

            - Site Index
            - Disclaimer
            - Freedom of Information Act
            - Accessibility

###### 						More Resources 					

            - Information Quality
            - Privacy Policy
            - NOS For Employees
            - USA.gov

          -  National Ocean Service
          -  National Oceanic and Atmospheric Administration
          -  Department of Commerce

##### 						Social 					

            - 
            - 
            - 
            - 
            -