Documentation for EASE-Grid and EASE-Grid 2.0 Land-Ocean-Coastline-Ice Masks Derived from Boston University MODIS/Terra Land Cover Data, Version 1

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This user guide covers two data sets:

Detailed Data Description

    Format

    Masks are provided as flat binary, 1 byte files stored by row. Quick-look browse images are also available in PNG (.png) format. The masks indicate the location of land, water, coastline, and ice using coded integers. Refer to Table 1 for the key to these values:

    Table 1. Key to Values Stored in LOCI Masks
    Value Description
    0 Land
    101 Ice
    252 Coastline
    254 Off the map
    255 Water

    Note: The software used to generate the LOCI masks sets the width of coastline pixels to a user-specified value. For this data set, the coastline width has been set to zero, i.e. the masks do not contain the value for coastline (252). Masks with non-zero coastline pixel widths are available upon request by contacting NSIDC User Services.

    Each resolution and projection combination is described by a Grid Parameter Definition (GPD). The short name, grid dimensions, and file sizes for each GPD are provided in Table 2 for EASE-Grid and in Table 3 for EASE-Grid 2.0. See Table 4 for the file naming convention.

    Table 2. EASE-Grid Land Classification Resolutions and Grid Sizes
    Projection Available Resolutions Grid Dimensions (r x c) File Size GPD Short Name
    N., S. Hemisphere 25 km 721 x 721 508 KB Nl, Sl
    12.5 km 1441 x 1441 2 MB Nh, Sh
    Global 25 km 1383 x 586 792 KB Ml
    12.5 km 2766 x 1171 3.1 MB Mh

    Table 3. EASE-Grid 2.0 Land Classification Resolutions and Grid Sizes
    Projection Parent Grid Available Resolutions Grid Dimensions (r x c) File Size GPD Short Name

    N., S. Hemisphere

    		 100 km 100 km 180 x 180 32 KB EASE2_N100km, EASE2_S100km
    10 km 1800 x 1800 3.1 MB EASE2_N10km, EASE2_S10km
    5 km 3600 x 3600 13 MB EASE2_N05km, EASE2_S05km
    36 km 36 km 500 x 500 245 KB EASE2_N36km, EASE2_S36km
    9 km 2000 x 2000 3.9 MB EASE2_N09km, EASE2_S09km
    3 km 6000 x 6000 35 MB EASE2_N03km, EASE2_S03km
    25 km 25 km 720 x 720 507 KB EASE2_N25km, EASE2_S25km
    12.5 km 1440 x 1440 2 MB EASE2_N12.5km, EASE2_S12.5km
    6.25 km 2880 x 2880 8 MB EASE2_N6.25km, EASE2_S6.25km
    3.125 km 5760 x 5760 33 MB EASE2_N3.125km, EASE2_S3.125km
    Global 36 km 36 km 964 x 406 383 KB EASE2_M36km
    9 km 3856 x 1624 6 MB EASE2_M09km
    3 km 11568 x 4872 54 MB EASE2_M03km
    25 km 25 km 1388 x 584 792 KB EASE2_M25km
    12.5 km 2776 x 1168 3.1 MB EASE2_M12.5km
    6.25 km 5552 x 2336 13 MB EASE2_M6.25km
    Temperate¹ 25 km 25 km 1388 x 540 750 KB EASE2_T25km
    12.5 km 2776 x 1080 3.0 MB EASE2_T12.5km
    6.25 km 5552 x 2160 12 MB EASE2_T6.25km
    3.125 km 11104 x 4320 50 MB EASE2_T3.125km
    ¹The temperate grid is a subset of the global grid that omits the most poleward latitudes. It extends from 67 N° to 67 S°.
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    File and Directory Structure

    EASE-Grid

    Data are available via FTP in ftp://sidads.colorado.edu/pub/DATASETS/nsidc0607_loci_ease/. This directory contains a subdirectory for each EASE-Grid region: north, south, and global. The available land masks and browse images for a region are stored within the corresponding subdirectory.

    EASE-Grid 2.0

    Data are available via FTP in ftp://sidads.colorado.edu/pub/DATASETS/nsidc0609_loci_ease2/. This directory contains a subdirectory for each EASE-Grid region: north, south, and global. The available land masks and browse images for a region are stored within the corresponding subdirectory.

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    File Naming Convention

    EASE-Grid

    Example File Name: Nl.LOCImask_land50_coast0km.721x721bin
    Generic File Name: Pr.LOCImask_landTT_coastZkm.colxrow.ext

    Refer to Table 4 for the valid values for the file name variables listed above.

    EASE-Grid 2.0

    Example File Name: EASE2_N25km.LOCImask_land50_coast0km.720x720.bin
    Generic File Name: EASE2_PRRkm.LOCImask_landTT_coastZkm.colxrow.ext

    The following table describes this data set's file name variables:

    Table 4. File Naming Convention for the Land Classification Files
    Variable Description
    EASE2_ File contains EASE-Grid 2.0 data. Files without this variable contain EASE-Grid data.
    P Projection. Values: N = N. Hemisphere; S = S. Hemisphere; M = global; T = temperate

    EASE: r

    EASE 2.0: RRkm

    Resolution (EASE-Grid). h = 12.5km, l = 25km

    Resolution in km (EASE-Grid 2.0). For example: 03km = 3 km; 3.125km = 3.125 km; 05km = 5 km..
    LOCImask File contains the LOCI mask
    landTT Identifies the land threshold used in the processing of these files (50: 50% cut off used).
    coastZkm Identifies the width of the coast used in the processing of these files. Coastlines = 0 px for this data set, i.e. value for coastline not present in data.
    colxrow Grid dimensions in pixels, column x row.
    .ext

    File extension. .bin = binary data file, .png = PNG browse image.

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    Spatial Coverage and Resolution

    EASE-Grid

    These data cover the entire globe and are provided in projections for the entire globe and for the Northern and Southern Hemispheres. See Table 2 for a complete listing of the projection/resolution combinations.

    EASE-Grid 2.0

    These data cover the entire globe and are provided in projections for the entire globe and for the Northern and Southern Hemispheres. See Table 3 for a complete listing of the projection/resolution combinations.

    Projection and Grid Description

    These data are provided in both the EASE-grid projection and the EASE-Grid 2.0 projection. The grid sizes are given in Table 2 and Table 3, respectively. For complete details on these two projections, see the EASE-Grid Format Description and the EASE-Grid 2.0 Format Description web pages.

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    Temporal Coverage

    The LOCI masks are derived from MODIS (Version 4) data obtained between July and December, 2000 (Friedl et al. 2002).

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    Software and Tools

    See the EASE-Grid | Geolocation Tools page for links to software and tools that geolocate and display EASE-Grid data sets.

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    Data Acquisition and Processing

    Processing Steps

    The LOCI masks were generated from the following input data:

    These EASE-Grid and EASE-Grid 2.0 land cover data sets were derived from the Boston University MODIS/Terra 1 km Land Cover Product (MCD12Q1, V004). MCD12Q1 utilizes the 17 International Geosphere Biosphere Programme (IGBP) land cover classes in Table 5.

    LOCI masks were generated using the follow algorithm:

    1. For each grid cell, calculate the percent land by summing the percent of IGBP non-water classes (1-16).
    2. Cells with >= 50% ice are classified as ice.
    3. Cells with >= 50% land and < 50% ice are classified as land
    4. Any remaining cells are classified as ocean (including lakes and inland water).

    Note: The LOCI masks available as part of this data set have their coastline widths set to zero pixels. As such the files do not include the value for coastline. To obtain masks with custom coastline widths, please contact NSIDC User Services.

    Table 5. IGBP Land Cover Classes
    Class Number Category Class Number Category
    01 Evergreen needleleaf forest 10 Grasslands
    02 Evergreen broadleaf forest 11 Permanent Wetlands
    03 Deciduous needleleaf forest 12 Croplands
    04 Deciduous broadleaf forest 13 Urban and built-up
    05 Mixed forests 14 Cropland/natural vegetation mosaic
    06 Closed shrublands 15 Snow and ice
    07 Open shrublands 16 Barren or sparsely vegetated
    08 Woody savannas 17 Water bodies
    09 Savannas
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    Error Sources

    Errors in the input data represent the primary source of error in this data set. See Data Corrections Applied in the User Guide for EASE-Grid and EASE-Grid 2.0 Land Cover Classifications Derived from Boston University MODIS/Terra Land Cover Data.

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    Version History

    The following tables show the version history for these data sets.

    Table 6. Version History for EASE-Grid LOCI Masks Table 7. Version History for EASE-Grid 2.0 LOCI Masks
    Version Date Description Version Date Description
    V1.0 2004 The EASE-Grid LOCI masks were created as an ancillary data set, not part of the official NASA DAAC data catalog. Instead, some of the data were distributed as ancillary data via a web page and others via personal communication with the authors. V1.0 2011 The EASE-Grid 2.0 LOCI masks were created as an ancillary data set, not part of the official NASA DAAC data catalog. Instead, the data were distributed via personal communication with the authors.
    V1.1 2014

    These data were accessioned into the NASA DAAC catalog and given a data set ID number. During this process, NSIDC changed the title, filenames, and organization of the data to improve usability. For example, the file name for the Northern Hemisphere 25 km LOCI mask was changed as follows:

    • Nl_loci_land50_coast0km.721x721.bin (old name)
    • Nl.LOCImask_land50_coast0km.721x721bin (new name)
    		 V1.1 2014 These data were accessioned into the NSIDC system and given a data set ID number. During this process, NSIDC changed the title, filenames, and organization of the data to improve usability. For example, the old file name for the Northern Hemisphere 25 km mask was changed as follows:

    • EASE2_N25km_loci_land50_coast0km.720x720.bin (old name)
    • EASE2_N25km.LOCImask_land50_coast0km.720x720.bin (new name)
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    References and Related Publications

    References

    General
    Friedl, M. A., et al. 2002. Global Land Cover Mapping from MODIS: Algorithms and Early Results. Remote Sensing of the Environment 83: 287-302.

    EASE-Grid
    Brodzik, M. J. and K. W. Knowles. 2002. "EASE-Grid: a versatile set of equal-area projections and grids" in M. Goodchild (Ed.) Discrete Global Grids. Santa Barbara, CA, USA: National Center for Geographic Information & Analysis.

    EASE-Grid 2.0
    Brodzik, M. J., B. Billingsley, T. Haran, B. Raup, M. H. Savoie. 2012. EASE-Grid 2.0: Incremental but Significant Improvements for Earth-Gridded Data Sets. ISPRS International Journal of Geo-Information, 1(1):32-45. doi:10.3390/ijgi1010032. http://www.mdpi.com/2220-9964/1/1/32.

    Brodzik, M. J., B. Billingsley, T. Haran, B. Raup, M. H. Savoie. 2014. Correction: Brodzik, M. J. et al. EASE-Grid 2.0: Incremental but Significant Improvements for Earth-Gridded Data Sets. ISPRS International Journal of Geo-Information 2012, 1, 32-45. ISPRS International Journal of Geo-Information, 3(3):1154-1156. doi:10.3390/ijgi3031154. http://www.mdpi.com/2220-9964/3/3/1154.

    Related Data Collections

    Contacts and Acknowledgments

    Mary J. Brodzik
    National Snow and Ice Data Center
    CIRES, 449 UCB
    University of Colorado
    Boulder, CO 80309-0449 USA

    Kenneth W. Knowles
    Operational Systems, Inc.
    6514 Fairways Dr.
    Longmont, CO 80503 USA