Merged Sea-Ice Drift Vectors

Description

Product		Gridded merged sea-ice drift vectors (PSI-Drift)
Credits		Ifremer/CERSAT
Sources		SeaWinds onboard QuikSCAT [series L2A] SSM/I onboard DMSP F13, F14 [series MSFC SSM/I Brightness Temperature]
Level		4
Spatial coverage		north pole (central Arctic)
Spatial resolution		62.5 km
Media
Format		NetCDF
Abstract This product provides users with a continuous winter time series of drift vectors over Arctic. These drift vectors are provided on a polar stereographic grid every 62.5 km, over 3-days or 6-days overlapping time periods. It is a merging of the respective sea-ice drift vectors retrieved separately using respectively QuikSCAT (from winter 1999-2000) and SSM/I (in horizontal and vertical polarization, from winter 1991-92) observations. The estimation of sea-ice drift for each one relies on a basic correlation technique applied to the field of the second spatial derivative (Laplacian) of 12.5km resolution composite maps separated by a few days (backscatter maps for QuikSCAT and brightness temperature for SSM/I) The QuikSCAT backscatter maps (PSI-QuikSCAT product by CERSAT), from which were retrived the QuikSCAT drift vectors, were computed from the SeaWinds scatterometer observations contained in Level 2A product by JPL/PO.DAAC. The SSM/I drift maps were computed from the brightness temperature maps distributed by NSIDC, Colorado. The individual drift maps computed from QuikSCAT and SSM/I are also available on our site. We are grateful to the JPL/PO.DAAC which distributes the SeaWinds/QuikSCAT Level 2A data, and the NSIDC for the SSM/I brightness temperature maps.

Temporal Coverage

Satellite	Temporal Resolution	Temporal Coverage
	3 and 6 daily, monthly during winter (Oct-Apr)	since 1991-12-03

Data distribution

This product is distributed free of charge to the international oceanographic community. The data are stored as netCDF files. All fields, as netCDF zipped files, are available on CERSAT anonymous ftp site at IFREMER, in the directory ftp://ftp.ifremer.fr/ifremer/cersat/products/gridded/psi-drift/data/arctic/merged-quikscat-ssmi/. The dataset is regularly updated with the latest fields (arctic winter only). It is archived as follows :

                                                 psi-drift
                                                     |
                                     ---------------------------------
                                     |             |                 |
                                   data       documentation      quicklooks
                                     |                               |
                              --------------	            ----------------	 
                              |            |	            |              |	 
                           arctic       antarctic	 arctic         antarctic
                              |
                 -------------------                  (same sub-tree as data folder)
                 |                 |
        merged-quikscat-ssmi  intermediate
                 |                 |
                 |        -------------------
                 |        |        |        |
                 |     quikscat   ssmi-h   ssmi-v
                 |
                 ------------------------------
                 |                            |
              3-daily  	                    6-daily  	 
          (motion vectors	        (motion vectors
           over 3-days)  	         over 6-days)  
                 |                            |
        --------------------                 ...
        |                  |            (same sub-tree as
      ascii	        netcdf	         3-daily vectors)
(list of vectors   (list of vectors
in ascii format)   in netcdf format)
        |                  |
  -------------	     -------------	
  |     |     |	     |     |     |	
1999  2000   ...   1999  2000   ...

The sea-ice drift vectors are computed over 3 days and 6 days respectively. They are first computed independantly for each sensor (quikscat, ssmi in horizontal and vertical polarization mode), stored in the 'intermediate' folder, and then merged into a single product ('merged-quikscat-ssmi' folder).

The data are stored in two different formats :

ascii format :

Each file contains the list of all retrieved vectors. Columns corresponds to the following parameters : vector index, latitude of start point, longitude of start point, latitude of end point, longitude of end point, quality flag

netCDF format :

Each vector (given by its zonal and meridional components, and its quality flag) is mapped over the NSIDC grid. The grid is stored in a netCDf file (see below).

quicklooks :

Each sea-ice drift map can be browsed as a PNG file in the quicklooks folder.

Tools

View

All fields can be viewed as quicklook pictures, using the browser available for each of the following datasets :

• Merged drift maps

Documentations