Release notes for version 1.01 of the hourly Global Drifter Program (GDP) dataset.
-The methods of interpolation of drifter trajectories positioned from Argos system ("Argos-tracked") and positioned by the Global Positioning Sytem ("GPS-tracked") are the same as for version 1.00, and are described in Elipot et al. (2016), "A global surface drifter data set at hourly resolution", doi:10.1002/2016JC011716.
-This 1.01 update of the dataset adds newer data to the previous version, one year of quality-controlled data up to 30 June 2016 for Argos-tracked drifters, and more than one year of GPS-tracked data up to 1 October 2016. In addition, we have added older data by considering all GPS-tracked drifters since the beginning of the GDP (previously since 1 January 2005). We have also added all Argos-tracked drifter data since the beginning of the GDP (previously since 1 January 2005) when the average of the uneven sampling intervals per trajectory is less than or equal to 3 hours.
-In the previous version (1.00) of the dataset, some drifters were erroneously categorized as being either Argos-tracked or GPS-tracked. This has been corrected in this version 1.01. In addition, when drifters were tracked by both systems, only the GPS trajectory is now contained in the dataset. Previously, there were repeats when merging the Argos and GPS files.
-The position and velocity estimates from GPS-tracked data are now provided with formal 95% confidence intervals from the weighted least squares solutions of the estimation, assuming an observational error of 22 m for GPS positions. We diagnosed this observational error from the overall distribution of the GPS data received at the Data Assembly Center of the GDP. In order to obtain acceptable confidence intervals, the LOWESS processing of the GPS positions has been implemented to make sure that at least 3 data points are used for each estimation. This differs from version 1.00 of the dataset for which only 2 data points were sometimes used.
-The 1.01 dataset now totals over 117.4 million estimates of position and velocity with confidence intervals from 12,287 Argos-tracked drifter trajectories, and over 5.6 million estimates of position and velocity with confidence intervals from 985 GPS-tracked drifter trajectories.
-Simplified versions of the Matlab codes used to generate this dataset are available through the GitHub repository https://github.com/selipot/hourly-drifters
Questions should be addressed to either Rick.Lumpkin@noaa.gov, Renellys.Perez@noaa.gov, or Shane Elipot at selipot@rsmas.miami.edu