The UAF SALMON Project operates four High Frequency (HF) Radar sites in Alaska. During the summers of 2005 and 2006, two switchable radars (13/25 MHZ) were located on the Arctic Ocean near Prudhoe Bay on the Beaufort Sea. Once freeze-up came to the shores of the Beaufort Sea in October 2006, those sites were moved to Cook Inlet until November 2007. The project also runs two 13 MHz sites in Prince William Sound off and on, which are currently decommissioned for the 2007/2008 winter. These surface current mappers (SCMs) are instruments manufactured by CODAR Ocean Sensors in Mountain View, California.

A single HF Radar site consists of two antennae, a transmit antenna and a receive antenna, separated by about 30 meters. A single site measures radial currents by transmitting a radio signal at a specific frequency out over the surface of the ocean. The radio waves scatter off of the waves on the surface of the ocean, and are then recorded by the receive antenna. These backscattered radio waves are used to compute currents moving toward or away from the site. Two sites in close proximity to one another complement each other in such a way that total surface currents over their region of overlap are computed.

A challenge specific to Alaska is operating SCMs in remote locations miles away from power and telecommunication lines. Over the course of two years our engineering team has developed the SALMON Project Electric Supply System or SPEPS for short. This system supplies continous power through a 24 volt DC battery bank to all the instruments necessary to maintain current mapping operations as well as deliver the products to users in near real time. We have chosen to use "green" alternative energy sources for the majority of our operations, but in case of failure, there is a propane powered generator that can provide backup charging capability to the battery bank.

Each HF Radar site creates a map of the coverage area with the radials currents displayed as vector arrows coming towards or away fromo the antennas. The magnitude of the current velocity is indicated by the length and the color of the arrow. Every hour, both HF Radar sites will send their radial maps to the central site, located at the University of Alaska Fairbanks. Here, the radial vectors are combined to create the a total vector map that accurately displays the surface currents in 2-D.

There are over 80 CODAR systems in operation around the world and the web is a great place to learn more about these instruments. Here are some of our favorite sites to begin your search.

CODAR Ocean Sensors, Inc.:
The company that is manufacturing these instruments. They have a great bibliography tracking the development of HF radar technology.

C.O.O.L CODAR Homepage:
A scientific site operated by The Rutgers University Coastal Ocean Observation Lab. This site displays real-time as well as archived CODAR data in the form of vector displays overlaid on top of maps of the coverage area. They also merge satellite-derived sea surface temperature images with surface current maps and provide these images online as well. This site contains an excellent tutorial covering the principles of surface current measurement through HF Radar.

MBARI CODAR:
This site contains animations of recently measured CODAR vectors over Monterey Bay, California.

NPS Rad Lab:
This site is operated by the Naval Postgraduate School's Rad Lab. It contains many images and animations of CODAR derived surface current vectors.

OSU CODAR Page:
Oregon State University's CODAR page contains real-time displays of currents off of Newport, Oregon.