How Does the COOLroom Work?
- CODAR Lets Us Check Out the Ocean Without Ever Leaving the Shore

If you have ever dropped something in the ocean, you have probably seen how the ocean tends to carry it away from you and you've watched it bob up and down in waves. The movement you've seen is caused by the influence of the ocean's surface currents and waves on the dropped object.

Wind and surface currents affect all objects on the surface of the ocean. The direction of surface current movement is the result of the interaction of many forces, including salinity and density currents, land and sea breezes, tides, gravity and global rotation. For that reason, locating an object floating in the ocean can become a complex problem. It requires gathering and processing several pieces of data.

In the COOLroom, oceanographers determine surface currents and wave heights and frequency using information gathered by a radar system called Coastal Ocean Dynamics Application Radar, sometimes called Coastal RADAR, or CODAR for short. The computers in the COOLroom interpret the data and then re-present them as real-time maps of the ocean using arrows to indicate currents. At certain beaches off New Jersey, they are also able to provide real-time charts displaying wave height and speed.

How does CODAR work?
The Rutgers CODAR network is comprised of two systems:
- A long-range system using low frequency, that measures the surface currents over an extended area larger than the size of New Jersey.
- A standard system that measures the sea surface current between the towns of Brant Beach and Brigantine, New Jersey. This system can only take measurements of a small area of the ocean but has the advantage of producing high-resolution data and the system can be easily moved to study other coastline currents in the future.

The flow of a particular parcel of water in the ocean is called a current, and in order to map them, we measure the ocean for its speed and direction or velocity. 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. The standard system can also determine the height and frequency of the waves near the shore.

However, each antenna site can only determine how fast the water is moving toward or away from that antenna. But the water might actually be moving away and to the right or left at the same time or, in other words, at an angle. 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. Then the computers combine the readings to come up with the net direction of the ocean.

Once the speed and direction of an object are determined, it’s possible to predict where the object might be headed in the near future. By using vectors, each distance and time may be estimated or calculated with significant precision.

With the use of long-range CODAR, scientists now can take measurements of surface water as far as 100 miles offshore. In the future, buoys will be added even further offshore, increasing the range significantly.

To learn how to read a CODAR Surface Velocity Map go to the Control Room and click on the CODAR lever.

Check out the COOLroom to find out: today's ocean surface currents and the sea surface conditions off Tuckerton. The COOLroom also archives CODAR data if you want to research a past date.

So, who uses this stuff?
People other than oceanographers find these surface velocity maps useful. The Coast Guard's Sea and Rescue uses them to track disabled and lost ships for survivors. The food that fish feed on tends to get trapped where two areas of water meet in a convergence zone and, therefore, fishermen find those areas on the velocity map where currents are pushing the water together. It is easier to steer a boat with the current rather than against it, so boaters and sailors use these images to track surface currents.

And, of course, surfers use them to figure out which beach has the biggest waves.

Doppler Shift Theory
Doppler Shift explains the change in frequency of a signal when it is bounced off a moving object. For example, a train whistle sounds differently depending upon whether it is moving toward you or away from you and how fast it is going.

One way to explain this is by imagining yourself throwing tennis balls at a stationary object. The distance and time it takes for each ball to leave your hand, strike the object, and then return would be the same for each tennis ball. Thus, if you throw a ball every two seconds, the balls should return to you in two second intervals.

Now imagine that the object is moving toward you. The first ball leaves your hand, strikes the object, and returns. By the time the second ball makes contact with the object, the object has moved closer. Thus the return trip for the second ball is shorter than the trip for the first ball. As a result, if the starting intervals are two seconds between tennis balls, the return interval will be less than two seconds.

This shift in time interval is called Doppler Shift. If the return is less than the release interval, the target object must be moving toward you. Conversely, if the return interval is greater than the release interval, the object must be moving away.

CODAR works the same way. If two different CODAR stations record how long it takes for their signal to bounce off a target and return to the station, scientists can tell whether the target is moving toward, or away from the station. All the stations then combine their data (the component data), and determine the actual resulting motion of the object.



Listen to Josh Kohut describe how CODAR uses radio waves to "listen" for which way the ocean is moving.