The flow of a particular parcel of water in the ocean is called a current, and in order to map currents, the speed and direction of the surface water is measured.

To measure the movement of water at the surface of the ocean (surface currents), COOLroom scientists use a system called CODAR. CODAR stands for "Coastal Ocean Dynamics Applications Radar" or Coastal Radar for short. The CODAR system is a series of antennae, like the one shown here.

The Rutgers CODAR network is comprised of two antennae systems:

- A long-range antenna system using low frequency, that measures the surface currents over an extended area larger than the size of New Jersey.

- A standard antenna system that at the moment is set up to measure the sea surface current between the towns of Brant Beach and Brigantine, New Jersey. This system can only take measurements of coastal waters, but has the advantage of producing high-resolution data and can be easily moved to study other coastline currents in the future.

The antennae are placed at six sites along the New Jersey coastline. The CODAR systems take these measurements by bouncing radio waves off the surface of the ocean. Each CODAR site has two antennas: the first transmits a radio signal out across the ocean surface and the second listens for the reflected radio signal after it has bounced off the ocean's waves. By measuring the change in frequency of the radio signal that returns, the CODAR system determines how fast the water is moving toward or away from the antenna. This works on the principle of the Doppler Shift theory. The returned signals are used to create vectors, which are represented by arrows that show the speed and direction of the surface currents.

The water’s direction (motion) may be represented by a resultant vector--an arrow that represents the sum of all the forces acting on the object. Since a resultant vector is the sum of all forces acting on an object, a resultant vector can be broken down into the contributing forces by using algebra or geometry. For example, a person can walk one block to the north then turn and walk one block to the east. The “resultant” of this walk is the diagonal line that connects the starting point directly to the end point. The two separate walks, each one block long, are the contributing pathways called component vectors. Graphically, this walk would form a right triangle with components being the sides and the resultant being the hypotenuse.

Use the vector tool below to see how vectors measure speed and direction.

Move your mouse over the graph. You will notice the arrow changing size and direction, and the X, Y, angle and mag values change as it moves. Click to make a permanent vector. The angle represents the direction of the vector, while the magnitude represents the speed.

Each CODAR antenna can only determine how fast the water is moving toward or away from that one antenna. However, at a particular spot in the ocean, the water might be moving at an angle, or even perpendicular to, the CODAR signal, which is difficult to detect using one antenna. Therefore, in order to determine the ocean's actual direction, the COOLroom computers process measurements taken of the same spot of the ocean at the same time from two different antenna sites. By adding together the vectors measured from one spot in the ocean using more than one antenna, a resultant vector can be created. Resultant vectors give scientists a more accurate measurement of the net movement of the ocean surface. Use the resultant vector tool below to see how vectors are added together.

Now make another vector by clicking the "Add Vector" button. Move your mouse over the graph and click to make another vector. The purple arrow represents the second vector, and the red arrow represents the resultant vector. Notice how the resultant vector has a different magnitude and direction than the original two vectors.

By combining vectors from six CODAR towers, COOLroom scientists can create maps that show the real-time speed and direction of the surface currents of the ocean that lie within about 50 kilometers (about 30 miles) of our research station.

Here is the type of image we create with the CODAR data:

The arrows on the image are the resultant vectors calculated from the component vectors measured by two of the CODAR antennae (the two blue squares along the coastline). The direction of the vectors shows the direction of the surface water. The speed of the current can be calculated by comparing the color of the vector(s) to the color scale on the right side of the graph. The speed can also be determined by the size of the vector - the larger the vector (or arrow), the greater the speed.

Visit the COOLroom to find out how fisherman use CODAR to set their course and how CODAR measures waves.