Data of different satellite sensors are combined to obtain a global data set of the sea ice drift, separately for the northern and southern hemisphere, gridded onto a Lambert-Azimuthal Equal Area Grid with 25 km grid resolution.
Because of the limited availability of the satellite data used, the data set is based on a spatially and temporally varying amount of input data. For the Antarctic, data provided by the Scanning Multichannel Microwave Radiometer (SMMR), the Special Sensor Microwave/Imager (SSM/I) and Imager+Sounder (SSMIS), and the Advanced Very High Resolution Radiometer (AVHRR) are used. For the Arctic, in addition to the above-mentioned data, data of the Advanced Multichannel Scanning Radiometer (AMSR-E), buoy observations of the International Arctic Buoy Program (IABP), and ice motion derived from NCEP/NCAR surface wind vectors are used.
These are the periods over which the different input data are used:
- AVHRR: 1981-07-24 to 2000-12-31
- SMMR - SSM/I - SSM/IS: 1978-10-21 to 2018-012-31
- AMSR-E: 2002-06-19 to 2011-08-08 (only northern hemisphere)
- IABP buoys: 1979-01-18 to 2018-12-31 (only northern hemisphere)
- NCEP/NCAR: 1979-11-01 to 2018-12-31 (only northern hemisphere)
The documentation on the respective NSIDC web page informs about the methods used. Compared to version 03 the following changes have been applied to version 04 (the one offered here now):
- All data are provided in netCDF file format (also the input data)
- Merging of drift vectors into the gridded product is not solely based on distance weighing of the 15 closest (to the grid-cell center) drift vectors but weighing is done for the 15 drift vectors with the highest accuracy primarily with distance information being secondary.
- SSM/I input data filtering is enhanced.
- Each buoy provides one daily sea-ice motion instead of twice (0 UTC and 12 UTC) daily.
- No monthly and annual means are offered anymore by NSIDC.
The figure on top of this page shows to sample maps of the mean annual sea ice drift in the Arctic and Antarctic for the year 1992 from product version 03).
ICDC enhanced / modified the data set as follows:
- Translation of the error variable into 3 variables for easier usage
- Computation of the drift velocity
- Computation of the u- and v-component following classical convention (u: positive West to East, v: positive South to North)
- Computation of monthly means (> 10 days with valid daily drift data required)
This is version 4.1 of the NSIDC sea-ice motion data set downloaded on April 26, 2019.
Last update of data set at ICDC: May 16, 2019