NSIDC Polar Stereographic Grid Definitions

Projection Details

Projection details vary by region. Older passive microwave data sets archived at NSIDC use the NSIDC Sea Ice Polar Stereographic projections described in Table 1 (Northern Hemisphere: EPSG 3411) and Table 2 (Southern Hemisphere: EPSG 3412). These are based on the Hughes 1980 ellipsoid. There are two other Polar Stereographic projections, described in Table 3 (Northern Hemisphere: EPSG 3413) and Table 4 (Southern Hemisphere: EPSG 3976), that newer NSIDC data sets use. These projections are based on the WGS 1984 ellipsoid (WGS 84/NSIDC Sea Ice Polar Stereographic North and WGS 84/NSIDC Sea Ice Polar Stereographic South). The differences between the two projection pairs (EPSG 3411/3412 and EPSG 3413/3976) are minimal - the diagonal distance across a WGS 84/NSIDC Sea Ice Polar Stereographic 25 km grid cell differs about 1 m from the original NSIDC Sea Ice Polar Stereographic grid cell. However, users should note that EPSG codes 3411 and 3412 are deprecated, and NSIDC encourages all new products to use EPSG codes 3413 and 3976.

Table 1. Northern Hemisphere Projection Based on Hughes 1980 Ellipsoid
Geographic Coordinate System Unspecified datum based upon the Hughes 1980 ellipsoid
Projected Coordinate System NSIDC Sea Ice Polar Stereographic North
Longitude of True Origin -45
Latitude of True Origin 70
Scale factor at longitude of true origin 1
Datum Not_specified_based_on_Hughes_1980_ellipsoid
Ellipsoid/spheroid Hughes 1980
Units meter
False Easting 0
False Northing 0
PROJ4 String +proj=stere +lat_0=90 +lat_ts=70 +lon_0=-45 +k=1 +x_0=0 +y_0=0 +a=6378273 +b=6356889.449 +units=m +no_defs 
EPSG Code https://epsg.io/3411
Table 2. Southern Hemisphere Projection Based on Hughes 1980 Ellipsoid
Geographic Coordinate System Unspecified datum based upon the Hughes 1980 ellipsoid
Projected Coordinate System NSIDC Sea Ice Polar Stereographic South
Longitude of True Origin 0
Latitude of True Origin -70
Scale factor at longitude of true origin 1
Datum Not_specified_based_on_Hughes_1980_ellipsoid
Ellipsoid/spheroid Hughes 1980
Units meter
False Easting 0
False Northing 0
PROJ4 String +proj=stere +lat_0=-90 +lat_ts=-70 +lon_0=0 +k=1 +x_0=0 +y_0=0 +a=6378273 +b=6356889.449 +units=m +no_defs 
EPSG Code https://epsg.io/3412
Table 3. Northern Hemisphere Projection Based on WGS 1984
Geographic Coordinate System WGS 84
Projected Coordinate System WGS 84 / NSIDC Sea Ice Polar Stereographic North
Longitude of True Origin -45
Latitude of True Origin 70
Scale factor at longitude of true origin 1
Datum WGS 1984
Ellipsoid/spheroid WGS 84
Units meter
False Easting 0
False Northing 0
PROJ4 String
+proj=stere +lat_0=90 +lat_ts=70 +lon_0=-45 +k=1 +x_0=0 +y_0=0 +datum=WGS84 +units=m +no_defs 
EPSG Code http://epsg.io/3413
Table 4. Southern Hemisphere Projection Based on WGS 1984
Geographic Coordinate System WGS 84
Projected Coordinate System WGS 84 / NSIDC Sea Ice Polar Stereographic South
Longitude of True Origin 0
Latitude of True Origin -70
Scale factor at longitude of true origin 1
Datum WGS 1984
Ellipsoid/spheroid WGS 84
Units meter
False Easting 0
False Northing 0
PROJ4 String
+proj=stere +lat_0=-90 +lat_ts=-70 +lon_0=0 +k=1 +x_0=0 +y_0=0 +datum=WGS84 +units=m +no_defs 
EPSG Code http://epsg.io/3976

Grid Dimensions

The grid size varies depending on the region and channel, as shown in Table 5. Latitude/longitude pairs are geodetic, with positions on the Earth based on an ellipsoid rather than a sphere.

Table 5. Grid Dimensions
Region
Nominal Gridded Resolution (km)
Number of Columns
Number of Rows
North 6.25 1216 1792
North 12.5 608 896
North 25 304 448
South 6.25 1264 1328
South 12.5 632 664
South 25 316 332

Grid Coordinates

The origin of each x, y grid is the respective pole. The approximate outer boundaries of the Northern and Southern grids are defined in Table 6 and Table 7, respectively. Corner points are listed and should be read clockwise from the upper left. Interim rows define boundary midpoints.

Table 6: Northern Hemisphere Grid Coordinates
X (km)
Y (km)
Latitude (deg)
Longitude (deg)
Description
-3850 5850 30.98 168.35 corner
0 5850 39.43 135.00 midpoint
3750 5850 31.37 102.34 corner
3750 0 56.35 45.00 midpoint
3750 -5350 34.35 350.03 corner
0 -5350 43.28 315.00 midpoint
-3850 -5350 33.92 279.26 corner
-3850 0 55.50  225.00 midpoint
Table 7. Southern Hemisphere Grid Coordinates
X (km)
Y (km)
Latitude (deg)
Longitude (deg)
Description
-3950 4350 -39.23 317.76 corner
0 4350 -51.32  0.00  midpoint
3950 4350 -39.23 42.24 corner
3950 0 -54.66 90.00 midpoint
3950 -3950 -41.45 135.00 corner
0 -3950 -54.66 180.00 midpoint
-3950 -3950 -41.45 225.00 corner
-3950 0 -54.66 270.00 midpoint

Grid Distortion

To minimize distortion in the (typical) marginal ice zones, the Polar Stereographic projections are true at 70 degrees, which translates to a 6% distortion at the poles. Distortion in the rest of the grid increases as the latitude decreases because more of the Earth's surface falls into a given grid cell. This distortion can be quite significant. In the Northern Hemisphere, there is a 31% distortion around the grid edge, while in the Southern Hemisphere the maximum distortion is 22%.