NASA Distributed Active Archive Center (DAAC) at NSIDC

Polar Stereographic Data

Data Sets in the Polar Stereographic Projection

Masks and Overlays

The masks and overlays provided here supply the user with many options for concealing unwanted regions or overlaying coastlines and latitude/longitude grids; they are divided into the following categories:


Land Masks

The land masks are useful for concealing the land of the Northern and Southern Hemispheres prior to processing of the data. The files are divided into two categories: Northern Hemisphere and Southern Hemisphere.

Note on Land Masks

Several versions of the land masks have been developed, though NSIDC only distrubutes the most current masks.

Beginning with the SMMR era, the first masks NSIDC developed were landmask.ntb and landmask.stb. Other masks were later added for use with SSM/I F8 data. The last set of masks to be added to the series are those beginning with gsfc, which were originally developed for use with SSM/I F11 and F13. However, all of the masks provided here will work across all platforms (SMMR and SSM/I).

The relatively slight differences in numbers of SSM/I-grid pixels masked as land can introduce discrepancies in analyses of time series spanning the SMMR and SSM/I period. One method of addressing this issue is to generate a composite mask in which all pixels mapped as land in any of the masks are coded as land pixels in the composite mask. Use of such a composite mask improves the consistency of the SMMR and SSM/I record at the expense of masking additional ocean areas as land. A composite of the CIA World Data Bank I and II (GSFC-1 and JPL-1) has been produced by J. Maslanik at NSIDC.

Another issue is the effect of contamination of coastal ocean pixels by their proximity to land. Such proximity can modify the brightness temperatures of coastal ocean pixels, producing false ice concentration values along some coasts. These pixel mixing errors are considered in the summer 1996 issue of NSIDC Notes (Issue no. 18). Maslanik et al. (1996) discuss the effects of such land contamination in introducing differences between SMMR and SSM/I time series, and they describe the use of a modified land mask where land areas are extended to mask substantial contamination.

The land masks that are availabe are the following:


Tool Name amsr_gsfc_6n.hdf and amsr_gsfc_6s.hdf
Applicable Data Sets AMSR-E/Aqua Daily L3 6.25 km 89 GHz Brightness Temperature Polar Grids
Description 6.25 km AMSR-E land mask for both hemispheres (n: Northern Hemisphere, s: Southern Hemisphere). Although the AMSR-E land masks are more current than those NSIDC uses for SSM/I data, they have not been updated since 1997 to account for many iceberg calvings. A 1-byte integer array is included in each HDF file. Values are 0 (water), 3 (coast), and 216 (land).

amsr_gsfc_6n.hdf:1216 columns x 1792 rows
amsr_gsfc_6s.hdf: 1264 columns x 1328 rows
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Tool Name amsr_gsfc_12n.hdf and amsr_gsfc_12s.hdf
Applicable Data Sets AMSR-E/Aqua Daily L3 12.5 km Brightness Temperature, Sea Ice Concentration, & Snow Depth Polar Grids
Description 12.5 km AMSR-E land mask for both hemispheres (n: Northern Hemisphere, s: Southern Hemisphere). The North 12.5 km AMSR-E land mask is identical to gsfc_12n.msk, while the South land mask is based on data from the 1997 RADARSAT Antarctic campaign. Although the AMSR-E land masks are more current than those NSIDC uses for SSM/I data, they have not been updated since 1997 to account for many iceberg calvings. A 1-byte integer array is included in each HDF file. Values are 0 or 1, where 1 is the mask.

amsr_gsfc_12n.hdf: 608 columns x 896 rows
amsr_gsfc_12s.hdf: 632 columns x 664 rows
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Tool Name amsr_gsfc_25n.hdf and amsr_gsfc_25s.hdf
Applicable Data Sets AMSR-E/Aqua Daily L3 25 km Brightness Temperature & Sea Ice Concentration Polar Grids
Description 25 km AMSR-E land mask for both hemispheres (n: Northern Hemisphere, s: Southern Hemisphere). The North 25 km AMSR-E land mask is identical to gsfc_25n.msk, while the South land masks are based on data from the 1997 RADARSAT Antarctic campaign. Although the AMSR-E land masks are more current than those NSIDC uses for SSM/I data, they have not been updated since 1997 to account for many iceberg calvings. A 1-byte integer array is included in each HDF file. Values are 0 or 1, where 1 is the mask.

amsr_gsfc_25n.hdf: 304 columns x 448 rows
amsr_gsfc_25s.hdf: 316 columns x 332 rows
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Tool Name gsfc_12n.msk and gsfc_12s.msk
Applicable Data Sets DMSP SSM/I Daily Polar Gridded Brightness Temperatures
Near Real-Time DMSP SSM/I Daily Polar Gridded Brightness Temperatures
Description 12.5 km land and coast mask for both hemispheres (n: Northern Hemisphere, s: Southern Hemisphere). A 1-byte integer array is included in each file. Values are 0 or 1, where 1 is the mask.

gsfc_12n.msk: 608 columns x 896 rows
gsfc_12s.msk: 632 columns x 664 rows
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Tool Name gsfc_25n.msk and gsfc_25s.msk
Applicable Data Sets DMSP SSM/I Daily Polar Gridded Brightness Temperatures
Sea Ice Concentrations from Nimbus-7 SMMR and DMSP SSM/I Passive Microwave Data
Nimbus-5 ESMR Polar Gridded Brightness Temperatures
Bootstrap Sea Ice Concentrations from Nimbus-7 SMMR and DMSP SSM/I
Near Real-Time DMSP SSM/I Daily Polar Gridded Brightness Temperatures
Near Real-Time DMSP SSM/I Daily Polar Gridded Sea Ice Concentrations
Description 25 km land and coast mask for both hemispheres (n: Northern Hemisphere, s: Southern Hemisphere). A 1-byte integer array is included in each file. Values are 0 or 1, where 1 is the mask.

gsfc_25n.msk: 304 columns x 448 rows
gsfc_25s.msk: 316 columns x 332 rows
Access Brightness Temperature Data Sets: FTP
Sea Ice Data Sets: FTP


Tool Name landmask.ntb and landmask.stb
Applicable Data Sets Nimbus-5 ESMR Polar Gridded Brightness Temperatures
Description Northern (ntb) and Southern (stb) Hemisphere land mask at a 25 km resolution. Note: These have been superseded by the gsfc_25n.msk and gsfc_25s.msk but may be more appropriate for the ESMR data sets.

landmask.ntb: 304 columns x 448 rows
landmask.stb: 316 columns x 332 rows
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Tool Name pole_n.msk
Applicable Data Sets Sea Ice Concentrations from Nimbus-7 SMMR and DMSP SSM/I Passive Microwave Data
Bootstrap Sea Ice Concentrations from Nimbus-7 SMMR and DMSP SSM/I
Near Real-Time DMSP SSM/I Daily Polar Gridded Sea Ice Concentrations
Description Circular mask that symmetrically covers the observed maximum extent of the missing data (resulting from the orbit inclination and instrument swath) near the North Pole. This is a 1-byte array with no header. The area of the SSM/I hole has a value of 1. The additional area of the SMMR hole (a ring around the SSM/I hole) has a value of 2. All other pixels have a value of 0.

pole_n.msk: 304 columns x 448 rows
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Land Overlays

The land overlays are useful for overlaying coast line and latitude/longitude grids on top of images and processed data. The files are broken down into two categories: Northern Hemisphere and Southern Hemisphere.

The land overlays that are availabe are the following:


Tool Name coast_12n.msk and coast_12s.msk
Applicable Data Sets DMSP SSM/I Daily Polar Gridded Brightness Temperatures
Near Real-Time DMSP SSM/I Daily Polar Gridded Brightness Temperatures
Description 12.5 km coastline grid overlay for both hemispheres (n: Northern Hemisphere, s: Southern Hemisphere). Format is 1-byte integer arrays. Values are 0 or 1, where 1 is the mask.

coast_12n.msk: 608 columns x 896 rows
coast_12s.msk: 632 columns x 664 rows
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Tool Name coast_25n.msk and coast_25s.msk
Applicable Data Sets DMSP SSM/I Daily Polar Gridded Brightness Temperatures
Sea Ice Concentrations from Nimbus-7 SMMR and DMSP SSM/I Passive Microwave Data
Nimbus-5 ESMR Polar Gridded Brightness Temperatures
Bootstrap Sea Ice Concentrations from Nimbus-7 SMMR and DMSP SSM/I
Near Real-Time DMSP SSM/I Daily Polar Gridded Brightness Temperatures
Near Real-Time DMSP SSM/I Daily Polar Gridded Sea Ice Concentrations
Description 25 km coastline grid overlay for both hemispheres (n: Northern Hemisphere, s: Southern Hemisphere). Format is 1-byte integer arrays. Values are 0 or 1, where 1 is the mask.

coast_25n.msk: 304 columns x 448 rows
coast_25s.msk: 316 columns x 332 rows
Access Brightness Temperature Data Sets: FTP
Sea Ice Data Sets: FTP


Tool Name ltln_12n.msk and ltln_12s.msk
Applicable Data Sets DMSP SSM/I Daily Polar Gridded Brightness Temperatures
Near Real-Time DMSP SSM/I Daily Polar Gridded Brightness Temperatures
Description 12.5 km latitude/longitude grid overlay for both hemispheres (n: Northern Hemisphere, s: Southern Hemisphere). Format is 1-byte integer arrays. Values are 0 or 1, where 1 is the mask.

ltln_12n.msk: 608 columns x 896 rows
ltln_12s.msk: 632 columns x 664 rows
Access FTP


Tool Name ltln_25n.msk and ltln_25s.msk
Applicable Data Sets DMSP SSM/I Daily Polar Gridded Brightness Temperatures
Sea Ice Concentrations from Nimbus-7 SMMR and DMSP SSM/I Passive Microwave Data
Nimbus-5 ESMR Polar Gridded Brightness Temperatures
Bootstrap Sea Ice Concentrations from Nimbus-7 SMMR and DMSP SSM/I
Near Real-Time DMSP SSM/I Daily Polar Gridded Brightness Temperatures
Near Real-Time DMSP SSM/I Daily Polar Gridded Sea Ice Concentrations
Description 25 km latitude/longitude grid overlay for both hemispheres (n: Northern Hemisphere, s: Southern Hemisphere). Format is 1-byte integer arrays. Values are 0 or 1, where 1 is the mask.

ltln_25n.msk: 304 columns x 448 rows
ltln_25s.msk: 316 columns x 332 rows
Access Brightness Temperature Data Sets: FTP
Sea Ice Data Sets: FTP



Missing Data Mask

The circular section over the Northern Hemisphere pole (known as the pole hole) is never measured due to orbit inclination. The following mask is available for the pole hole region not covered by the SMMR and SSM/I instruments.

Tool Name pole_n.msk
Applicable Data Sets Sea Ice Concentrations from Nimbus-7 SMMR and DMSP SSM/I Passive Microwave Data
Bootstrap Sea Ice Concentrations from Nimbus-7 SMMR and DMSP SSM/I
Near Real-Time DMSP SSM/I Daily Polar Gridded Sea Ice Concentrations
Description Circular mask that symmetrically covers the observed maximum extent of the missing data (resulting from the orbit inclination and instrument swath) near the North Pole. This is a 1-byte array with no header. The area of the SSM/I hole has a value of 1. The additional area of the SMMR hole (a ring around the SSM/I hole) has a value of 2. All other pixels have a value of 0.

pole_n.msk: 304 columns x 448 rows
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Region Masks

The region masks are smaller areas than the land masks although they can be used as land masks using the pixel value of 11.

Tool Name region_n.msk and region_s.msk
Applicable Data Sets Sea Ice Concentrations from Nimbus-7 SMMR and DMSP SSM/I Passive Microwave Data
Bootstrap Sea Ice Concentrations from Nimbus-7 SMMR and DMSP SSM/I
Near Real-Time DMSP SSM/I Daily Polar Gridded Sea Ice Concentrations
Sea Ice Trends and Climatologies from SMMR and SSM/I-SSMIS
Description Region masks for the Northern (n) and Southern (s) Hemisperes. The files contain a 300-byte header, followed by a two-dimensional byte array stored by rows in column order. Regions are assigned different pixel values as shown in the following table. The methods and sources for how these regions were geographically defined are discussed in Parkinson and Cavalieri (2012), Cavalieri and Parkinson (2008), and Parkinson et al. (1999).

region_n.msk: 448 rows x 304 columns
region_s.msk: 316 rows x 332 columns

Regions are assigned different byte values as follows:

Pixel Value Arctic Region Antarctic Region
1
Non-regional ocean  
2
Sea of Okhotsk and Japan Weddell Sea
3
Bering Sea Indian Ocean
4
Hudson Bay Pacific Ocean
5
Baffin Bay/Davis Strait/Labrador Sea Ross Sea
6
Greenland Sea Bellingshausen Amundsen Sea
7
Kara and Barents Seas  
8
Arctic Ocean  
9
Canadian Archipelago  
10
Gulf of St. Lawrence  
11
Land Land
12
Coast Coast
0
Lakes, extended coast  
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Ocean Masks

Tool Name For a full list of ocean masks and maximum extent masks, refer to the Monthly Ocean Masks and Maximum Extent Masks Web page.
Applicable Data Sets Sea Ice Concentrations from Nimbus-7 SMMR and DMSP SSM/I Passive Microwave Data
Sea Ice Trends and Climatologies from SMMR and SSM/I
Description Monthly Ocean Masks and Maximum Extent Masks are available for the Northern (n) and Southern (s) Hemispheres. For more information and a description of the files, refer to the Monthly Ocean Masks and Maximum Extent Masks Web page.

Access See the Data Access section of the Monthly Ocean Masks and Maximum Extent Masks Web page for FTP access.