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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