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Data Set ID:
NSIDC-0714

MEaSUREs Greenland Ice Mapping Project (GIMP) Land Ice and Ocean Classification Mask, Version 1

This data set, part of the NASA Making Earth System Data Records for Use in Research Environments (MEaSUREs) program, provides a complete land ice and ocean classification mask for the Greenland ice sheet that was mapped using a combination of Landsat 7 ETM+ panchromatic band imagery, and RADARSAT- 1 Synthetic Amplitude Radar (SAR) amplitude images.

See Greenland Ice Mapping Project (GIMP) for related data.

Geographic Coverage

Parameter(s):
  • Glaciers/Ice Sheets > Ice Sheets > Land Ice/Ocean Classification
Spatial Coverage:
  • N: 82, S: 60, E: -20, W: -70

Spatial Resolution:
  • 15 m x 15 m
  • 30 m x 30 m
  • 90 m x 90 m
Temporal Coverage:
  • 1 July 1999 to 30 September 2001
Temporal Resolution: 2 year
Data Format(s):
  • GeoTIFF
Platform(s) LANDSAT-7, RADARSAT-1
Sensor(s): ETM+, SAR
Version: V1
Data Contributor(s): Ian Howat
Data Citation

As a condition of using these data, you must cite the use of this data set using the following citation. For more information, see our Use and Copyright Web page.

Howat, I. 2017. MEaSUREs Greenland Ice Mapping Project (GIMP) Land Ice and Ocean Classification Mask, Version 1. [Indicate subset used]. Boulder, Colorado USA. NASA National Snow and Ice Data Center Distributed Active Archive Center. doi: http://dx.doi.org/10.5067/B8X58MQBFUPA. [Date Accessed].

Literature Citation

As a condition of using these data, we request that you acknowledge the author(s) of this data set by referencing the following peer-reviewed publication.

  • Howat, I., A. Negrete, and B. Smith. 2014. The Greenland Ice Mapping Project (GIMP) land classification and surface elevation data sets , The Cryosphere. 8. 1509-1518. http://dx.doi.org/10.5194/tc-8-1509-2014

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Detailed Data Description

This data set provides complete land ice and ocean classification masks posted at 15-m, 30-m and 90-m for the Greenland ice sheet. Ice cover was mapped using a combination of orthorectified panchromatic (band-8) imagery from the Landsat 7 Enhanced Thematic Mapper Plus (ETM+), distributed by the USGS, and RADARSAT-1 Synthetic Amplitude Radar (SAR) amplitude images produced and distributed by I. Joughin at the Applied Physics Laboratory, University of Washington. The Landsat imagery was acquired for the months of July through September in 1999, 2000 and 2001 (mostly 2000) and the RADARSAT imagery was acquired in fall of 2000.

Format

Data are available in GeoTIFF (.tif) format.

The 15 and 30 m resolution masks are distributed as sets of 36 tiles, as shown in Figure 1. Additionally, a complete 90 m resolution ice-sheet-wide mask is also provided, and is comprised of the following: a grounded ice mask, an ice mask, and an ocean mask.

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File and Directory Structure

Data are available via HTTPS in the https://daacdata.apps.nsidc.org/pub/DATASETS/nsidc0714_MEASURES_gimp_mask_v1 directory.

There are two folders in this directory: 15m and 30m.

Within the 15m and 30m folders, there are 72 files each: one GeoTIFF for the land ice mask and one GeoTIFF for the ocean mask for each of the 36 tiles.

Also, this directory has three GeoTIFF files and one text file:
GimpGroundedIceMask_90m_v1.1.tif
GimpIceMask_90m_v1.1
GimpOceanMask_90m_v1.1
README_v1.1.txt

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File Naming Convention

The following tables explain the file naming convention for the mosaics included in this data set. See Table 1 for an explanation of the variables for file names for the 15 m and 30 m files and Table 2 for the 90 m files.

File Naming Convention: Gimp[Ice/Ocean]Mask_[RR]m_tile[C_R]_v1.1.ext

Example File Names for 15 m and 30 m for tile 0_5:

  • GimpIceMask_15m_tile0_5_v1.1.tif
  • GimpOceanMask_15m_tile0_5_v1.1.tif
  • GimpIceMask_30m_tile0_5_v1.1.tif
  • GimpOceanMask_30m_tile0_5_v1.1.tif
String Description
Table 1. Naming Convention Description for 15 m and 30 m files
Gimp Greenland Ice Mapping Project
Ice/Ocean IceMask indicates glacier ice, OceanMask indicates ocean and all other terrain
RR Resolution (15m or 30m)
C_R Column and row of mosaic tile. Tile 0_0 is in the lower left corner, Tile 5_5 is in the upper right (see Figure 1)
v1.1 version 1.1
.tif File name extension for GeoTIFF-formatted file

File Naming Convention for 90 m files: Gimp[GroundedIce/Ice/Ocean]Mask_[RR]m_tile[C_R].ext

File Names for 90 m:

  • GimpGroundedIceMask_90m.tif
  • GimpIceMask_90m.tif
  • GimpOceanMask_90m.tif
Table 2. Naming Convention Description for 90 m files
String Description
Gimp Greenland Ice Mapping Project
GroundedIce/Ice/Ocean GroundedIceMask indicates grounded glacier ice; IceMask indicates glacier ice, and OceanMask indicates ocean and all other terrain
RR Resolution (90m)
v1.1 version 1.1
.tif File name extension for GeoTIFF-formatted file
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File Size

The 15 m resolution files are each approximately 6-8 MB and the 30 m resolution files are each approximately 2-3 MB. The 90 m resolution ice and ocean masks are approximately 951 MB each and the grounded ice mask is approximately 7.3 MB.

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Volume

Total volume of the complete data set is 2.5 GB.

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Spatial Coverage

Spatial coverage is:
Southernmost Latitude: 60° N
Northernmost Latitude: 82° N
Easternmost Longitude: 20° W
Westernmost Longitude: 70° W

Spatial Resolution

The data are available in 15 m, 30 m, or 90 m resolutions.

Projection and Grid Description

Data are provided in standard NSIDC polar stereographic north grid (EPSG 3413) centered on Greenland.

The 15 m and 30 m masks are provided as sets of 36 tiles of 6 rows by 6 columns, numbered from 0-0 in the lower left corner to 5-5 in the upper right (see Figure 1). Each tile has dimensions of 249.3 by 450 km. These dimensions were selected because they are divisible by 15 m, which is the resolution of Landsat-7 Enhanced Thematic Mapper Plus (ETM+) panchromatic (band-8) imagery.

Additionally, lower resolution masks (90 m) are provided.

Figure 1. GIMP Landsat-7 ETM+ band-8 and RADARSAT-1 ice mask (90 m resolution) of Greenland with tile boundaries and tile numbers overlain. The map projection is polar stereographic (EPSG 3413).

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Temporal Coverage

Temporal coverage is 1999 through 2001

Temporal Resolution

The temporal resolution is 2 years.

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Parameter or Variable

The parameter is Land Ice/Ocean Classification. Depending upon the specific mask, the data values (0 or 1) indicate glacier ice or ocean and all other terrain.

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Software and Tools

A variety of Geographical Information System (GIS) software packages will work with GeoTIFF files, including ArcGIS, ENVI, GDAL, and QGIS.

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Data Acquisition and Processing

Theory of Measurements

Land classification masks provide a method of co-registration of repeat imagery and elevation data to track changes of the ice surface, which can change with time, while areas of exposed bedrock provide a control for measuring the changes. In addition, masks provide an accurate delineation of ice boundaries, which become a benchmark for measuring future ice margin changes. Landsat-7 ETM+ data are commonly used for mapping snow and ice.

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Sensor or Instrument Description

This data set was produced from images acquired by Landsat 7’s Enhanced Thematic Mapper Plus (ETM+) and Synthetic Aperture Radar (SAR) from the RADARSAT-1 satellite.

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Data Acquisition Methods

The mask files included in this data set were derived from the GIMP 2000 Image Mosaic, created using Landsat 7 ETM+ and RADARSAT-1 SAR imagery. The Landsat imagery was acquired for the months of July through September in 1999, 2000 and 2001 (mostly 2000) and the RADARSAT imagery was acquired in fall of 2000.

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Processing Steps

The mask files included in this data set were created from manual digitization of the panchromatic and pan-sharpened multispectral GIMP 2000 Image Mosaic. Using manual methods, the ice margin can be difficult to locate visually in areas of abundant debris and snow cover. Margins of debris-covered ice were identified by breaks in surface slope, emerging melt water streams, color differences and the presence of small melt water ponds typical of debris-covered glaciers. Similarly, glaciers were differentiated from perennial snowfields by visible crevassing, surface moraines and the existence of a visible toe. Snowfields without these features were not classified as glaciers. Using the same method, the coastline is digitized to produce an ocean mask, with the null of the ice and ocean masks being ice-free terrain (Howat, et al., 2014).Please see Howat et al., 2014 for more information regarding processing methods.

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Error Estimates

Uncertainty in these classification masks arise from three sources of error: (1) image pixel resolution, (2) image geo-registration and (3) erroneous selection or non-selection of pixels (i.e., mapping error). All error sources are expected to vary randomly in space. However, there is likely a systematic component of error source (2) over distances equivalent to the size of a single image (e.g., 185 km for Landsat 7). This is due to errors in the registration model used to orthorectify the image, which typically is ±5 m, or one third of a pixel for L1T-processed imagery.

Error source (1) contributes a random error of one pixel for each ice boundary pixel. The position of any point of the ice margin has an uncertainty of 21 m while the total error for a given area of ice is then (8N)1/2x2, where N is the number of boundary pixels and x is the pixel posting in meters. Erroneous selection or non-selection of pixels (error source 3) can be due to debris cover, shadows and misidentification by the operator, as well as the ambiguity of delineating an ice boundary at glacier fronts ending in packs of icebergs. Without ground control, delineation of the ice edge in areas of debris cover, terminal moraines and persistent snow cover is subjective. These errors are difficult to quantify. Due to ambiguity in the ice edge and operator error, estimations were done by comparing mappings performed by three different operators over the same area. On average, each operator identified 24.21 km (1614 pixels) of ice margin over the common area, with a 660 m (44 pixels) difference between the maximum and minimum mappings, giving an estimated error of ±3 percent. This error, however, is expected to vary widely by particular location and size of area considered (Howat et al., 2014).

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Quality Assessment

Please see Howat et al., 2014 for more information regarding the quality and processing methods used to produce this data set.

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Version History

Version 1.1 was released April 2017. Refer to Table 1 for this data set's version history:

Table 1. Version History
Version Description
V1.1 This version corrects the location of the upper left pixel in each GeoTIFF file. The previous version incorrectly specified the location of the upper left pixel as the distance in meters from the north pole to the center of the upper left pixel. The corrected location of the upper left pixel is the distance in meters from the north pole to the upper left corner of the upper left pixel. This correction effectively shifted the location by one-half pixel to the upper left relative to their positions in the previous version. Only the geolocation metadata in each GeoTIFF has changed; the data array is the same as in the previous version.
V1 Initial version (February 2017)
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References and Related Publications

Contacts and Acknowledgments

Dr. Ian Howat
Ohio State University
Byrd Polar Research Center
Scott Hall Room 108
1090 Carmack Road
Columbus, Ohio 43210
USA

Acknowledgments: 

These data were generated through a grant from the NASA Making Earth System Data Records for Use in Research Environments MEaSUREs Program.

Document Information

DOCUMENT CREATION DATE

February 2017

DOCUMENT REVISION DATE

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Email: nsidc@nsidc.org