Crater Lake Drifter Test - Preliminary Data Report

Test dates: 11-13 August 1997

Oregon State University personnel: Jack Barth, Mike Kosro, Stephen Pierce, and Andy Dale

National Park Service Crater Lake Research Team: Scott Girdner, Jeff Milder, and Ashley Gibson

Objectives: Test new Wide Area Differential GPS (WADGPS) surface drifters and examine Crater Lake circulation.

We have implemented WADGPS on a surface drifter. WADGPS is a technique to improve GPS positioning accuracy from +/-100 m to +/- 20 m or better. See Wilson et al. (1996) for technical details. This Crater Lake work was the "full field test" mentioned in the Wilson et al. paper, planned for August 1996 but delayed until August 1997.

Figure 1. One drifter tracked over 18 hours with a fix every 5 min. Note improvements in positions and speed estimates using WADGPS.

Figure 2. Drifter location and speed vs. time for all four drifters over repeated deployments. Maximum speed observed is ~30 cm/s, surprisingly large.

Figure 3. Drifter tracks in eastern half of Crater Lake. Triangles mark deployment locations; marks every half-hour give indication of speed. Note counter-clockwise circulation in eastern basin.

Figure 4. Drifter tracks color-coded by speed. Strong southward flow in mid-lake and intermittently strong "ram" current on eastern side.

Photos showing drifters, their use and deployment on the Park Service research boat (Neuston).

Future plans: Plot up wind records (we have these in hand) and interpret drifter motions in terms of simple closed-basin, wind-forced circulation models.