NOTE: this README file applies to files from 17 Feb 2012
(the first version) through 17 May 2012.  File formats
were altered after that; see README.TXT.

This directory contains updated estimates of drogue off dates
for drifters in the time period October 1992-November 2010,
sorted by severity (amount of drogue-off time misdiagnosed
as drogue-on prior to this reevaluation).

For more information, see:
Lumpkin, R., S. Grodsky, M.-H. Rio, L. Centurioni, J. Carton and
D. Lee, 2012: Removing spurious low-frequency variability in 
drifter velocities.  Geophys. Res. Letters, submitted April 2012.

Each file is named YYYY_MM_DD_drogueoff.dat according to its
creation date.  Older versions are kept in the folder "archive".

The first column gives the ID of the drifter.

The second column is the original drogue off date in the
drifter Data Assembly Center metadata file.
"9999-99-99" indicates that the drogue was still
attached as of 30 November 2010.  Subsequent updates of
the DAC metadata may have included a drogue off date.
"1978-12-31" indicates drogue status uncertain from beginning
of record.

The third column is the automatically detected drogue off
date generated by the methodology described in Lumpkin
et al. (2012).
If this date is earlier that the drogue off date in
the second column, we recommend using this date until
the data have been examined manually (fourth column).

The fourth column is the result of a manual reevaluation
of the data, concurrently using submergence/tether strain, 
anomalous downwind motion, and transmission frequency 
variation.  This process began after the first version
of the update (using the automatic procedure) was created.
"9999-99-99" indicates that the drifter has not yet been
reevaluated manually.  Any other value should be considered 
the best possible estimate of drogue-off date and will be 
included in a future update of the DAC metadata.

In all cases, a drogue off date of "1979-01-01" indicates
that the drogue status was uncertain from the beginning.