This is the sea ice concentration archive calculated with the ARTIST
Sea Ice (ASI) algorithm (see www.seaice.de) using AMSR-E (Advanced
Microwave Scanning Radiometer) data.

I. Path and Filenames

Each file is stored in a directory and under a name following these
conventions:

Example: /n6250/2004/apr/asi-n6250-20040420-v5_visual.png 

Explanation:
  n	Hemisphere n (North) or s (South)
  6250	Resolution of the grid in meters
  2004 	Year
  apr   	Month
  asi    	asi or asi180: 'asi' data is projected by using the arctic grids from NSID (www.nsidc.org),
          	'asi180' data uses the same grid as the  ASI SSM/I data on www.seaice.de
	   bootstrap or bootstrap180: the associated bootstrap data (just hdf, no png files)
  n6250    	hemisphere and grid resolution
  20040420 	Year, month and day in the format yyyymmdd
  v5	ASI version (defines the tie-points; older files does not have this flag)
  visual   	colortable used for visualization. Empty for hdf files.
  png      	file format: tif, hdf, png (see below). 


II. Data Set Structure

For every day and hemisphere there exist four files:
  1. Sea ice concentrations stored as GEOTIFF file (.tif) in byte format (0 to 255).
      The ice concentrations between 0% and 100%  are scaled to the values 0 to 200.
      So every value of the Geotiff byte data represents a range of 0.5% ice concentration.
      A value of 255 is used for false or missing data.
      The value 251 represents land.

     The same polar stereographic projection and map borders as for the NSIDC sea ice data (http://nsidc.org/data/docs/daac/nsidc0002_ssmi_seaice.gd.html) is used.
     The data is calculated by using exactly that projection but for the GEOTIFF format an other ellipsoid has to be used. Some programs like ENVI are not capable of using self defined ellipsoids like the Hughes ellipsoid used by the NSIDC. For this reason the standard WGS84 ellipsoid is used in the GEOTIFF format. This causes errors in the geolocation of up to 500 meter at the corners of the maps. For most applications this should be negligible.

     The colortable is adapted from the NIC colortable used for sea ice data (http://www.natice.noaa.gov):
		R (red)	G (green)	B (blue)
     0% to 9%		0	0	139
     10% to 19%	30	144	255
     20% to 29%	30	250	160
     30% to 39%	34	139	34
     40% t0 49%	0	250	0
     50% to 59%	125	250	0
     60% to 69%	173	255	47
     70% to 79%	250	250	0
     80% to 84%	250	125	0
     85% to 89%	250	0	0
     90% to 95%	186	85	211
     96% to 98%	148	0	211
     99% to 100%	120	0	90

     Land (251)	100	100	100

  2. Sea ice concentrations as floating point values (hdf format). 
     Missing or wrong data is marked as NaN (Not a Number) values
     using the IEEE standard.  The data is stored in the Hierarchical
     Data Format (HDF) using the multi-file Scientific Data Set model
     (short: HDF SDS file) and has the file extension '.hdf'.

     Software to read this data and a lot of additional information
     can be obtained from 'http://hdf.ncsa.uiuc.edu/'. HDF SDS is the
     standard data format for AMSR data and should be compatible with
     the single-file HDF SDS used by the NSIDC for the 'DMSP SSM/I
     Daily Polar Gridded Brightness Temperatures'.

  3. and 4. Visualization of the data as Portable Network Graphics
     (PNG). They have the file extension '.png'. This bitmap graphic
     format should be readable with every bitmap graphic program or
     web browser.
     Files with the extension '_nic.png' show the data using a false
     color colortable.
     Files with the extension '_visual.png' use a colortable which
     represents the visible spectrum. Additional topographic data
     is shown.

The last two files are more for visualization purposes and not for scientific 
interpretation.


III. Contact Information

     Dr. Christian Melsheimer
     e-mail: melsheimer@uni-bremen.de 
or
     Dr. Gunnar Spreen
     e-mail: gunnar.spreen@uni-bremen.de

     Institute of Environmental Physics
     University of Bremen
     P.O. Box 330440
     D-28334 Bremen
     GERMANY
     Phone:  +49 (0)421 / 218 - 62158

     http://www.seaice.uni-bremen.de
     http;//www.iup.uni-bremen.de