Surface Drifters Data Types and Products

Surface Drifters data are transferred on a six-month basis from AOML, Miami, to MEDS, Ottawa, for archiving and distribution to the scientific community. The types of data received by MEDS from AOML are:

1) "B" files (Raw data files). These files contain data received from Service ARGOS with engineering units changed to physical units. Multiple sensor readings are condensed to one value for each satellite pass; no other processing is done. The fields contained in these files are:

S1-S3 hold extra sensor data, depending on the kind of buoy, i.e. sea level pressure for barometer drifters, salinity, temperature and conductivity for salinity drifters, etc. If it is a standard drifter, S1-S3 are columns of o's. These files are kept by MEDS as is for future reference if required.

2) "P" files (Position files). These files come from editing the raw files and separating out the position-related fields. Values that violate acceleration criteria are edited from these series [Hansen and Poulain, 1996]. The fields contained in these files are:

3) "S" files (Sensor files); These files come from editing the raw files and separating out the SST-related fields. The fields are edited according to Hansen and Poulain [1996]. The fields contained in these files are:

4) "K" files (Interpolated files). These files contain data interpolated to uniform six-hour intervals using an optimum interpolation procedure called Kriging [Hansen and Poulain, 1996]. The fields contained in these files are:

5) "Directory file". The directory file contains detailed information about each drifter. The fields contained in these files are:

MEDS merges the "P" and "S" files together by matching the observation date/time from the "S" file to the position date/time from the "P" file; the merged output files are archived by observation date and time and are available to the users; the data from these files can be retrieved by area, time frame or buoy Id.

To compare AOML data to MEDS data, the buoy id/number is assigned differently.  When recycling buoy numbers, AOML's convention is to add a 2 digit qualifier to the original generic buoy number to indicate the year the buoy stopped reporting.. AOML adds the qualifier as a prefix while MEDS reverses this and adds the qualifier as a suffix for easier use within its processing system. For example AOML buoy id 9712345 is represented in MEDS as 1234597.

The Krigged data file constitutes the output product of the CLIVAR Surface drifters programme. The entire data set submitted by AOML is archived by MEDS. This file contains all associated information, such as drogue type, deployment date, date drogue lost, etc.  The data from this file can be retrieved by area and time frame.  The output format is in MEDS "Ocean" format although GF-3 format and CSV file format are also available. A full description of both formats is available from MEDS upon request. The histogram shown below illustrates the statistics on volume of data transmitted to MEDS by AOML to the present.

A Metafile put together by the Global Drifter Center (Scripps) is also available from MEDS. This file contains detailed engineering descriptions and calibration information for each Surface Drifter contained in the raw data and Krigged data archives. The Metafile has been created with FileMaker Pro 2.1 and can be sent by FTP upon request in full or for selected experiments or ARGOS numbers. The file size is 2.6Mb. The user must have the commercial application FileMaker Pro to run this application. A limited version (CSV file) can be sent by MEDS upon request.

Reference:

Hansen, D.V. and P.-Marie Poulain, 1996, Quality control and interpolation of WOCE/TOGA drifter data, J. Atmos. Oceanic Tech., 13, p.900-909.