Satellite Tracked Drifting Buoys
The buoys are SVP drifters manufactured by Technocean
in Cape Coral, Florida. The drifters have a surface float with a GPS receiver
for positioning and telemetry electronics for communicating with the ARGOS
satellite. The drifter is linked by a cable to a drogue engineered to follow
the current. At regular intervals, the drifter communicates with the ARGOS satellite
and uploads hourly GPS positions and other data.
Buoy deployments have been done from the Cook Inlet Spill Prevention and Response,
Inc. (CISPRI) vessel Montana, and by Dr. Carl Schoch and Dr. Scott
Pegau, oceanographers with the Kachemak Bay Research Reserve, in Homer, Alaska.
We wish to thank CISPRI's Buzz Rome and Steve Russell for their help with the
buoys, and Doug Lentsch for making this collaboration possible. Our long-term
results depend on this kind of support to deploy the drifters. We are interested
in hearing from other Cook Inlet stakeholders who may wish to help with this
project.
Data Processing
The internal GPS records the position at the top of each hour. New data, plus
older data still stored in the GPS buffer, are sent to the ARGOS satellite,
downloaded to an ARGOS receive station, and then emailed to UAF on a daily basis.
The ARGOS satellite also acquires the position of the buoy at irregular intervals.
However, the GPS data are far more accurate in space (a few meters) compared
to the ARGOS position fixes (tens of meters). In our data processing, we have
ignored the ARGOS position fixes in most cases and used only the GPS position
fixes.
The data come from ARGOS in hexadecimal and are re-processed at the Institute
of Marine Science by Mark Johnson. Hex data are converted to decimal data to
provide the time, position (latitude and longitude), battery voltage, and a
"drogue sensor" which indicates whether the drogue is still intact.
Redundant data are deleted, and the hourly positions are used to compute the
east-west, north-south, and overall speeds. Obvious errors are removed. Acceleration
is then calculated and obvious errors are again removed. Following this process,
the hourly positions are plotted on a map, along with other relevant information.
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