Prince William Sound Field Experiment

why care about surface currents?

We can use currents to understand the ecosystem of the Sound as well as the set and drift of vessels in the tanker traffic corridor leading to the Port of Valdez. Currents also help us predict trajectories of drifting debris, icebergs and oil spills.

surface currents
in the sound

high frequency radar in prince william sound

Go to AOOS HF Radar and Surface Current data


High Frequency Radar for Surface Current Measurements

Principal Investigator:
Mark Johnson, university of alaska fairbanks

The mean tidal range in the Sound is large -- about 3 meters -- so all mariners should consider the currents created by tidal ebb and flood.

When winds and waves are also factors, current velocity can magnify waves to dangerous heights.

high-frequency radar stationAbout HF Radar

An array of instruments in the Sound measures the direction and speed of surface currents in the central basin and transmits this information to the Internet.

High-Frequency (HF) radar is one tool that can be used to measure surface current velocities. HF radar is a combination of a powerful radio wave transmitter and receiver that use the Doppler shift to determine the speed of surface currents.

In 2004, two HF radar stations were set up at Knowles Bay and Shelter Bay to transmit and receive radio waves that travel as far as 60 km across the Sound in all directions. As each radio wave reflected off the ocean and returned to the receiver, changes in the waves’ Doppler frequency shift was determined and then used to estimate the surface currents. The two sites combined to determine surface horizontal velocity.

HF Radar Reveals a New Phenomenon

In mid-summer of 2004 the stations began to reveal something that had never been directly measured before: a counter-clockwise flow into Hinchinbrook Entrance and out into the head of Montague Strait. This cyclonic circulation pattern is likely a result of a combination of things: inflow of dilute Alaska Coastal Current water through Hinchinbrook Entrance, inflow of freshwater from the Sound’s surrounding coast, and the basin-like bathymetry of the central Sound.

What’s Next for HF Radar

Our goal is to provide an uninterrupted data flow from July 15th through August 5th, 2009.

We have contracted the Auklet from July 6-16 to carry four UAF investigators to the Knowles and Shelter Bay sites. We will arrive on site and clear brush and transport all gear to the beach and install a biodiesel generator at each site. We expect to begin powering up both sites by the 13th or so and configure the radar and test the satellite telecommunications. Our goal is to be operational by 15 July to give three days to test data transmission and give Yi Chao at JPL time to “spin-up” his model and work out any issues with initialization.

On July 16th the Auklet will return us to Cordova and two of the UAF team will depart. Hank S. and Mark J. will stay in Cordova at the Orca Adventure Lodge and will have available the Whisky Shackle on a daily basis to run out to either of the two sites. It may be useful to share contract costs for the Whisky Shackle with others so that this boat is available to chase drifters or AUVs or gliders. We will monitor the data flow from Cordova, and plan to have webcams at both sites to help identify problems and facilitate repair remotely.

The two biodiesel generators are designed to run for six hours and charge a battery bank that will power the HF radar for 18 hours. Timing is such that the biodiesel generators will turn on each morning so we can monitor them from Cordova. If either generator fails, we will run out to the site the fix the problem.

On August 5th, we again have the Auklet chartered and will begin decommissioning both sites and remove as much gear as possible.