README GEOTIFF

The ice concentration data is stored in byte format (0 to 255).
The ice concentrations between 0% and 100%  are scaled to the values 0 to 200. Thus 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 for the hemispherical Arctic and Antarctic maps. In the regional maps land is set to 255 (missing data).

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


Gunnar Spreen, April 2004

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