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Skidaway Institute, in cooperation with the University of South Carolina,
has installed two shore-based HF-radars along the Georgia, South Carolina
coastline to measure surface currents and waves across the continental shelf.
The radars were installed with SEACOOS funding (through ONR) and
Georgia Research Alliance funding, and have been operational since April 2006.
These HF-radars are long-range WERA installations manufactured by
Helzel MessTechnik of Germany. Our long-range system operates at a frequency of
8.3 MHz, and has a daytime range of 220 km, reaching across the broad shelf and
over the shoreward flank of the Gulf Stream.
Each installation measures near
surface currents (upper ~one-meter depth) along radials towards or away from the
installation. Where coverage from two installations overlap and their
respective radials are sufficiently non-parallel, vector velocities can be
constructed from the radial velocities.
Shown below is the array of receiving antennae deployed on the coast of St
Catherine's.
photo by Trent Moore
Click here for the most recent snapshot of the surface currents.
Percent data return for vector velocities over the entire record to date
is quite good. A strong day-night contrast exists (see here),
with low coverage between the hours of 8 to 11:30AM local time, when background AM, FM and HAM
radio activity noise peaks.
Temporal resolution is 30 minutes while horizontal resolution is 3 km along radials,
with 2o azimuthal resolution (equivalent to 3.5 km at 100 km). A wealth of
detail is apparent in the surface current snapshot and zoomed image shown
here. The grid spacing is 3 km. Along the transect indicated in this
figure, grid spacing is 3 km. Along the transect indicated in this
figure,
2006 mean speed is shown here. Gulf Stream structure is evident: seaward of shelf
averages (near 0.2 m/s), speed rapidly increases across the Gulf Stream's shoreward flank
beginning at 120 km, reaches the Gulf Stream jet axis (the position of maximum velocity)
at about 155 km, and falls off more slowly across the seaward flank to the east
of the axis.
There is a known difficulty with the data from the Pritchard's Island
installation at ranges of about 80 and 160km. An example of the problem is shown
here. This results from electronic noise at appoximately 60Hz in the records
from one of the receive antennae. We are working to resolve this problem, and
will be reprocessing archived data to eliminate the input from this antenna,
which will allow us to correct the velocity estimates at these ranges.
Contact Dr. Dana K. Savidge with questions or comments.
Dr. Savidge and Skidaway Institute are grateful to St. Catherine's Island
Foundation and Staff for their permission and assistance
in deploying this valuable oceanographic tool.
More information:
Manufacturers of HF-radar systems
- Helzel
Archival Data
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