Hourly Drifter Data
Hourly location, current velocity, and temperature collected from Global Drifter Program drifters world-wide
This dataset includes hourly sea surface temperature and current data collected by satellite-tracked surface drifting buoys ("drifters") of the NOAA Global Drifter Program. The Drifter Data Assembly Center (DAC) at NOAA’s Atlantic Oceanographic and Meteorological Laboratory (AOML) has applied quality control procedures and processing to edit these observational data and obtain estimates at regular hourly intervals. The data include positions (latitude and longitude), sea surface temperatures (total, diurnal, and non-diurnal components) and velocities (eastward, northward) with accompanying uncertainty estimates. Metadata include identification numbers, experiment number, start location and time, end location and time, drogue loss date, death code, manufacturer, and drifter type.
Two papers describe how these dataset were derived:
Elipot et al. 2016 (for position and velocity) and
Elipot et al. 2022 (for sea surface temperature).
Please see below the release notes and how to access and cite this dataset.
Figure caption: Adapted from Elipot et al. (2022): Top panel: Spatial distribution of total SST estimates of dataset version 2.00 expressed as a density per (50 km)2 in half- degree spatial bins. Bottom panel: temporal distributions of position and velocity, total SST (sm), and diurnal SST (sD) estimates in 10-day bins from 03-Oct-1987 13:00:00 to 30-Jun-2020 23:00:00.
Data Access
The hourly dataset version 2.00 is officially available from NOAA NCEI at https://doi.org/10.25921/x46c-3620. After accessing this page, click on the “Lineage” tab and on the link for “Output Datasets”, then “data”, then “0-data”, and finally on “gdp_v2.00.nc” to download through your web browser. Alternatively, click on this link to download the NetCDF file directly (size is about 12GB).
The dataset is distributed as a single NetCDF file containing contiguous ragged arrays, one for each data variable, as well as all metadata.
In order to get you started with this hourly dataset, you can head over to this Jupyter Notebook on GitHub that shows you a couple of simple examples on how to use these data.
Alternative ways of accessing this dataset or the previous versions are given below.
Citations
When using this dataset in your studies or publications, please use the following citation:
Elipot, Shane; Sykulski, Adam; Lumpkin, Rick; Centurioni, Luca; Pazos, Mayra (2022). Hourly location, current velocity, and temperature collected from Global Drifter Program drifters world-wide.[indicate subset used]. NOAA National Centers for Environmental Information. Dataset. https://doi.org/10.25921/x46c-3620. Accessed [date].
Additionally, we would be very grateful if you could cite the papers describing how the dataset were derived. If you use the dataset of position and velocity, please cite:
And if you use the dataset of sea surface temperature, please cite:
Release notes for version 2.00, September 2022:
- The hourly position and velocity dataset is now augmented by variables of sea surface temperature at hourly time steps: sea water temperature, non-diurnal sea water temperature, and diurnal sea water temperature, and their accompanying uncertainty estimates and quality flags. See Table 6 of Elipot et al. 2022.
- The position and velocity estimates are exactly the same as for version 1.04c (same number of drifters and same temporal range).
- The dataset is now officially distributed by the NOAA National Center for Environmental Information as a single NetCDF file containing contiguous ragged arrays, one for each data variable, as well as metadata.
Release notes for version 1.04:
- Version 1.04c: NetCDF files corrected to eliminate several errors including one-day offset, errors on GPS positions, and to clarify drogue metadata. Matlab files unchanged from 1.04(a).
- The interpolation methods for drifter trajectories tracked by the Argos system and by the Global Positioning Sytem are the same as for version 1.00, described in Elipot et al. (2016).
- An error was found in the calculation of GPS errors in version 1.01-1.02 which caused the errors to generally be overestimated. This was corrected for v1.03.
- The 1.04 update adds an additional 4 years and 9 months of quality-controlled data to v1.00, up to 4 April 2020. Starting in v1.02, we have added data before 1 September 2005 (the start date of v1.00) by considering all GPS-tracked drifters since the beginning of the GDP, and all Argos-tracked drifter data since the beginning of the GDP, when the average of the uneven sampling intervals per trajectory is less than or equal to 3 hours. As a consequence, the hourly dataset is a subset of the 6h dataset, which goes back to 1979.
- In v1.00, some drifters were erroneously categorized as being either Argos-tracked or GPS-tracked. This was corrected in v1.01. In addition, when drifters were tracked by both systems, only the GPS trajectory is contained in the dataset (starting v1.01). In v1.00, there were repeats when merging the Argos and GPS files.
- In verions 1.00 and 1.01, the WMLE (Argos) data were contained in a single, very large file. They have now been broken into smaller non-overlapping files, with file extensions "_blockN". Each file contains a unique set of drifters (no drifter is in multiple files). The only updated data for v1.03 is in block 7; blocks 1-6 contains drifters no longer alive as of v1.02, and will not be updated after v1.02.
- For version 1.04, the few Argos drifters that were alive as of v1.03 in block 7 were moved to a new block 8. Those that died before are retained in a smaller new block 7.
- The position and velocity estimates from GPS-tracked data are now provided (since v1.01) 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 v1.00 of the dataset for which only 2 data points were sometimes used.
- Simplified versions of the Matlab codes used to generate this dataset are available through a GitHub repository
Alternative ways of accessing dataset versions 2.00 and earlier:
The version 2.00 of the dataset can also be obtained as 17,324 individual NetCDF files, one per drifter, from the FTP server of the DAC using the following address in a FTP client ftp://ftp.aoml.noaa.gov/phod/pub/lumpkin/hourly/v2.00/ or use ftp over https at this link
Finally, to obtain a subset of the data based on various criteria (temporal, spatial, etc), you may go to the OSMC ERDDAP server and reference these instructions.
The previous versions (releases) of the dataset (from v1.00 to v1.04) are also available in various formats (Matlab and NetCDF) at ftp://ftp.aoml.noaa.gov/phod/pub/buoydata/hourly_product/.