Abstract:

297 near-surface CODE-type ocean drifters (drogued at a depth of one meter) tracked in real-time using SPOT GPS units, were launched in the northern Gulf of Mexico near DeSoto Canyon in July 2012 as part of the CARTHE Grand Lagrangian Deployment (GLAD) experiment. Most of these drifters were launched in nested triplets (separated by roughly 100 m, resp. 500 m, at launch) in an attempt to measure multi-scale near surface dispersion. No temperature or salinity sensors were attached to these drifters. Positions are interpolated to uniform 5 minute intervals starting on whole hours over the period July 20 through October 22, 2012. Velocities are computed using the spline coefficients. 12 of the drifters were prematurely abducted and subsequently re-released. Their trajectories have been split into two segments, with different drifter numbers assigned to each. A companion dataset is included, from 10 surface drifters consisting of GPS-equipped and weighted otter boxes, whose trajectories were processed the same way. These were released alongside some of the CODE-style drifters. This dataset was created by the Consortium for Advanced Research on Transport of Hydrocarbon in the Environment (CARTHE). This research was made possible by a grant from BP/The Gulf of Mexico Research Initiative.

Suggested Citation:

Tamay Özgökmen. 2016. Grand Lagrangian Deployment (GLAD) CODE-style and flat drifter trajectories (5-min interpolation, no filtering), northern Gulf of Mexico near DeSoto Canyon, July-October 2012. Distributed by: GRIIDC, Harte Research Institute, Texas A&M University–Corpus Christi. doi:10.7266/N7416V0M

Publications:

Huntley, H. S., Lipphardt, B. L., & Kirwan, A. D. (2019). Anisotropy and Inhomogeneity in Drifter Dispersion. Journal of Geophysical Research: Oceans, 124(12), 8667–8682. doi:10.1029/2019jc015179

Purpose:

CODE-style drifters were launched nearly simultaneously in nested triangles (100 m and 500 m separations) to measure near-surface relative dispersion over scales ranging from 100 m to 100 km. In addition, ten flat surface drifters were launched alongside some of the CODE-style drifters to investigate the role of drifter design in capturing ocean currents.

Data Parameters and Units:

Column 1: drifter ID string (like CARTHE_XXX, XXX=3 digit integer) Column 2: date (yyyy-mm-dd) Column 3: time (HH:MM:SS.SS) Column 4: latitude (decimal degrees) Column 5: longitude (decimal degrees) Column 6: estimated position error (meters) Column 7: u (east-west) velocity (m/sec) Column 8: v (north-south) velocity (m/sec) Column 9: estimated velocity error (m/sec)

Methods:

Drifter positions were reported in real-time roughly every five minutes via the Globalstar satellite network. Positions reported by the SPOT handheld GPS units inside each drifter were nominally accurate to within seven meters. Occasionally, position errors much larger than this nominal value are found. These may be due to errors in GPS baselines (due to poor satellite reception), data dropout, and, in some cases, drifters that were picked up by small boats. Each drifter record ends when the drifter was known to be picked up by a boat, when the signal was lost for more than 24 hours, or when the drifter traveled more than 80 km in a 12 hours period (implying a mean speed of 1.85 m/sec over 12 hours). For each record, positions that imply an instantaneous drifter speed greater than 3 m/sec were deleted. Also, positions that imply the drifter track rotated through more than 360 compass degrees within three hours were deleted. Next, outliers were identified as positions that were more than 100 meters away from estimated positions at the same times interpolated from a set of both past and future positions. These outliers were deleted. All valid positions were then interpolated to uniform, five-minute time intervals using spline interpolation. The spline coefficients were used to compute estimates of u (east-west) and v (north-south) velocities. Crude estimates of position error are also provided for each position in the final records. The error was set to 10 meters (a nominal value) for positions recorded at times for which there were no gaps in the five-minute raw data records over the previous hour. The error was increased according to the ratio of the average sample time interval for the previous 12 raw data positions to the nominal sample interval of 5 minutes, multiplied by the 10 meter nominal error value. Velocity errors were computed by dividing the sum of two consecutive position errors by the corresponding time interval.

Instruments:

CODE II drifter body with SPOT Satellite GPS Messenger and Otter Boxes with weights and SPOT Satellite GPS Messenger

Individual Files: