So how does all that CODAR stuff work?

CODAR stands for Coastal Ocean Dynamics Applications Radar, or in short, Coastal RADAR.

What is CODAR?

CODAR is a High Frequency (HF) radar system that remotely measures ocean surface currents. The system allows one to get a complete map of ocean currents (left) without stepping foot aboard a boat or deploying an expensive array of current meters. Each map has a range of about 50 kilometers (about 30 miles) from the coast with a measurement every 1.5 kilometers ( 0.9 miles). The Rutgers University CODAR system, deployed along the New Jersey coast, is the only operational HF-Radar system of its kind in the entire eastern United States. It consists of two remote sites, located in Brant Beach and Brigantine New Jersey, and a central site in Tuckerton, New Jersey.

How does it all work?

Each remote site contains two antennas and a small 6'x 8' shed. One antenna (left) transmits a radio wave out across the ocean surface. The power of this transmitted signal is only 40 watts. Therefore this antenna behaves like a household lamp with a 40 watt light bulb. Unlike radio stations that only transmit a signal, CODAR uses the second antenna (far left) to listen for and measure the transmitted signal. So that the part of the transmitted signal that is reflected back toward the site by the ocean waves can be recorded and processed. It is this returned signal that is used to measure the moving ocean surface.

The shed (right) contains a weatherproof box (lower right) that houses all of the equipment necessary for transmitting, receiving and processing the radio signal. Within this box (from top to bottom) there is a Macintosh computer, responsible for processing the incoming signal, a transmitter and a receiver.

How can we get ocean currents from the beach?

CODAR uses the theories of the Doppler Shift to determine the surface current from the backscattered radio wave. The Doppler shift explains the change in frequency of a signal scattered off a moving object. For example, a train whistle or ambulance siren sounds different depending on the speed and direction of the vehicle. Doppler theory can be used to determine if a scattering object is moving toward or away from an observer as well as the speed at which it is moving. These theories also apply to the ocean surface.

By measuring the return signal, the CODAR system can determine the speed of the ocean waves that scattered the signal. From this wave speed a surface current can be calculated. One limitation to Doppler theory is that it only explains the velocity of the train in the direction of the observer.

Consequently, a remote site can only measure how fast the water is moving toward or away from the antennas (left). The net movement of the water (shown in red) can only be determined using information collected from each of the two sites (shown in green and yellow), as illustrated in the figure to the left.

CODAR Applications

  Safe and efficient navigation and marine operations

• Efficient oil and hazardous material spill trajectory prediction and clean up
• Monitoring, predicting and mitigating coastal hazards
• Military operations
• Education
• Scientific research
• Search and rescue

The Future of CODAR along the New Jersey Coast

The future of the CODAR system along the New Jersey coast involves plans to increase the present area of coverage. To accomplish this, several adaptations will be made to the present system. The first will add two additional transmit antennas offshore. In addition to extending the coverage in both the along-shore and cross-shore directions, this improved system will be able to measure surface currents right to the beach (left). By measuring these currents, one can begin to examine storm effects on beach erosion as well as complicated inlet dynamics influencing commercial traffic.

The second adaptation changes the frequency of the transmitted radio wave so that the signal will travel further offshore resulting in a much larger coverage area. The figure to the right illustrates the present configuration in yellow. Using three of these new long-range systems, the coverage area will be extended to include those areas shaded in red, blue and green. Also shown in the illustration is the location of three recent ship sinkings off the New Jersey coast. One can easily see that with the larger coverage area perhaps current maps could have been used by the Coast Guard to more efficiently aid those in distress.

For more information please see the CODAR Ocean Systems website.