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Data Set ID:
NSIDC-0724

MEaSUREs Greenland Monthly Image Mosaics from MODIS, Version 1

This data set, part of the NASA Making Earth System Data Records for Use in Research Environments (MEaSUREs) program, consists of monthly image mosaics of the Greenland coastline and ice sheet periphery constructed from composited MODIS imagery.

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

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Geographic Coverage

Parameter(s):
  • CRYOSPHERIC INDICATORS > ICE EDGES > Ice Edges
  • Glaciers/Ice Sheets > Ice Sheets > Surface Morphology
Spatial Coverage:
  • N: 85, S: 57, E: 11, W: -109

Spatial Resolution:
  • 100 m x 100 m
  • 500 m x 500 m
Temporal Coverage:
  • 1 March 2008 to 30 September 2016
(updated 2018)
Temporal Resolution: 1 month
Data Format(s):
  • GeoTIFF
Platform(s) AQUA, TERRA
Sensor(s): MODIS
Version: V1
Data Contributor(s): Terry Haran, Jennifer Bohlander, Ted Scambos, Ian Joughin

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.

Haran, T., J. Bohlander, T. Scambos, and I. Joughin. 2017, updated 2018. MEaSUREs Greenland Monthly Image Mosaics from MODIS, Version 1. [Indicate subset used]. Boulder, Colorado USA. NASA National Snow and Ice Data Center Distributed Active Archive Center. doi: https://doi.org/10.5067/6L166FFRPCPP. [Date Accessed].

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Detailed Data Description

This data set consists of monthly image mosaics of Greenland that include surface morphology derived from high-pass filtered MODIS Band 1 (red light) images. Scenes were selected to provide nearly cloud-free views of the coastal and ice front calving areas of the main ice sheet, including the ice caps on Baffin Island, Devon Island, Axel Heiberg Island, and Ellesmere Island. Each of the monthly mosaics were assembled from between 5 and 56 (typically 10) MODIS scenes (five-minute segments of swath data) selected from the MODIS/Aqua and MODIS/Terra Calibrated Radiances 5-Min L1B Swath 250 m data sets (MYD02QKM and MOD02QKM) for each day-lit month (March – September). Scenes were manually cloud masked and then mosaicked using:

  • A stacking technique (data cumulation) that allows multiple images to contribute to a single grid cell's representation.
  • A weighting scheme that favors near-nadir views and feathers the edges of contributing images.
Format

The files in the data set are provided in GeoTIFF (.tif) format.

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File and Directory Structure

Data are available via HTTPS in the following directory:

https://n5eil01u.ecs.nsidc.org/MEASURES/NSIDC-0724.001/

Within this directory, the folders are named for each year, month, and day of the data collection, for example: /01.03.2008/.

The directory contains 126 files: 2 files for the months of March through September for each year from 2008 to 2016. One file provides the mosaic at a spatial resolution of 100 m and the other file provides it at a resolution of 500 m.

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File Naming Convention

This section explains the file naming convention, with examples, of the files in this data set. Table 1 describes the variables of the naming convention.

Example File Names

mog100_200806_hp1_v01.tif
mog500_200806_hp1_v01.tif

File Naming Convention

mog[resolution]_[YYYYMM]_v01.[ext]

    Table 1. File Naming Convention
    Variable Description
    mog[resolution] Mosaic of Greenland at either 100 m or 500 m resolution
    YYYY Year
    MM Month
    hp1 Surface morphology (high-pass filtered Band 1) image map
    .v01 Version number
    .tif GeoTIFF file extension
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    File Size

    The 100 m resolution .tif files range from 104 MB to 486 MB and the 500 m resolution .tif files range from 5.5 MB to 25.2 MB.

    The total data volume of this data set is approximately 24 GB.

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    Spatial Coverage

    Spatial coverage for this data set includes Greenland, as noted by the coverage below.

    • Northernmost Latitude: 85° N
    • Southernmost Latitude: 57° N
    • Easternmost Longitude: 11° E
    • Westernmost Longitude: 109° W

    Spatial Resolution

    The data are provided at both 100 m and 500 m resolutions. The underlying MODIS Band 1 and 2 swath data have a nominal resolution of 250 m; however, the image stacking scheme used to assemble the mosaics increases the resolution of the final product beyond that of individual MODIS scenes to between 150 m and 250 m, depending on the number of images that were stacked and how the images were weighted. See the Surface Morphology Image Map section of this document for information on Compositing via Data Cumulation.

    Projection and Grid Description

    GeoTIFFs are provided in a WGS84 polar stereographic grid with a standard latitude of 70° N and rotation angle of -45° (sometimes specified as a longitude of 45° W). With this convention, the y-axis extends south from the North Pole along the 45° W meridian (EPSG 3413).

    Table 2 lists the dimensions (in pixels) for the 100 m and 500 m grids and the locations (in meters from the origin) of the upper left corner of the upper left cell:

    Table 2. Grid Dimensions
    Grid x y Upper Left Corner, Upper Left Cell
    100 m 21000 px 28000 px -1200000.0 m from origin
    500 m 4200 px 5600 px -600000.0 from origin
    Note: For both the 100 m and 500 m grids, the upper left corner of the upper left cell is located 1,200,000 m west and 600,000 m south of the origin, (i.e. the North Pole). Grids do not include the North Pole.
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    Temporal Coverage

    01 March 2008 to 30 September 2016

    Temporal Resolution

    Monthly

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    Parameter or Variable

    The image mosaics report surface morphology, and the glacier ice edge at the calving fronts in fjords, derived from brightness variations in MODIS Band 1 red light images. Many processing steps were required to create a seamless and uniform surface morphology mosaic from the numerous images that contributed to each grid cell. As such, the image values no longer have a clearly quantifiable relationship to the top-of-atmosphere, red light reflectance, from which they were derived. Instead, the mosaics provide semi-quantitative but highly consistent approximations of the surface shape and reflectivity, as illuminated by the sun across all surface types.

    Sample Data Record

    Figure 1. Sample mosaic of data collected for March 2008.

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    Software and Tools

    GeoTIFF files can be viewed with a variety of Geographical Information System (GIS) software packages including:

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    Data Acquisition and Processing

    Theory of Measurements

    Since the 1990s, studies have demonstrated that carefully processed satellite radiometry, most notably from the Landsat series and NOAA's AVHRR instruments can reveal unprecedented details about the surface morphology of ice sheets.

    The twin MODIS instruments on board NASA's Terra and Aqua satellites provide an opportunity to exploit two active sensors during the compilation period with a higher spatial and radiometric resolution than AVHRR. In addition, this data set improves the accuracy, detail, and seamlessness of the final products by combining new methods with several preexisting techniques.

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    Data Acquisition Methods

    The MODIS scenes were selected to maximize clear-sky area and coverage of the Greenland coastline.

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    Derivation Techniques and Algorithms

    Geolocation and Processing

    The scenes used to create the image maps were selected from a combination of Collections 4, 5, and 6 MODIS/Aqua and MODIS/Terra data sets (MYD02QKM and MOD02QKM). Band 1 and Band 2 scenes from MYD02QKM and MOD02QKM, together with illumination and viewing angles from MYD03 and MOD03¹, were geolocated and resampled onto the projection grid using NSIDC's MODIS Swath-to-Grid Toolbox (MS2GT). The software interpolated the MYD03 and MOD03 latitude/longitude data from 1 km resolution to 250 m and then resampled the MODIS/Aqua and MODIS/Terra Level-1B calibrated radiances to the grid using a forward elliptical weighted average algorithm (Greene et al., 1986).

    ¹MODIS Level 1A Geolocation Fields from EOS Aqua and EOS Terra

    Destriping of MODIS Image Data

    The MS2GT algorithm was modified to remove MYD02QKM and MOD02QKM striping artifacts, a known problem with all Terra and Aqua MODIS 250 m Level-1B data, by adding a Lambertian solar zenith angle normalization on the swath data for both bands. Telemetry noise and line drops, which have the appearance of chads in the projected images, were reset to zero (treated as masked cloud areas). This procedure is discussed in detail in the Destriping of MODIS Image Data section of the MOA2004 documentation.

    Cloud Masking

    The geolocated scenes were manually masked to remove clouds, cloud shadows, fog, blowing snow, and heavy surface frost. Refer to the Cloud Masking section of the MOA 2004 documentation. The final image maps are nearly perfectly cloud-cleared, except for some areas of thin clouds, cirrus cloud shadows, and fog or low-lying small clouds.

    Surface Morphology Image Map

    Geolocated and destriped Band 1 images were high-pass filtered to reduce non-Lambertian illumination and to reset the mean grayscale range to a common value for compositing. For each gridded image, the investigators created a corresponding weight image in which each non-masked pixel is assigned a scalar value or weight. Weights were computed based on proximity to the nadir track, favoring near-nadir areas, and proximity to an image or mask edge to feather the edges of the component images. Finally, weight images were then combined using stacking techniques called image super-resolution or data cumulation. These techniques allow multiple images to contribute to how a single grid cell is represented in the final composite.

    The algorithms used to compute and combine the weight images into the final mosaics are provided in the MOA2004 Compositing the Image Swaths documentation.

    Error Sources

    Wolfe et al. (2002) estimated the accuracy of the MYD03/MOD03 Level-1A geolocation data to be 50 m, considerably better than the MYD02QKM/MOD02QKM ground-equivalent nadir pixel size of 250 m. The accuracy and precision of this geolocation was also tested for the MOA2004 using known surface sites, such as South Pole Station, Vostok Station, Siple Dome camp and traverse trail, and areas of well-mapped coastline such as Ross Island and the northern Antarctic Peninsula. The investigators did not find discrepancies greater than 125 m in the projected location of any fixed object.

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    Sensor or Instrument Description

    The MODIS instruments collect 12-bit radiometric data in 36 spectral bands, ranging from 0.4 µm to 14.4 µm in wavelength. Bands 1 and 2 are imaged at a nominal resolution of 250 m at nadir. The Terra satellite crosses the equator from north to south (descending node) at 10:30 AM local time; Aqua crosses from south to north (ascending node) at 1:30 PM local time. Both satellites occupy sun-synchronous, near-polar, circular orbits at an altitude of 705 km. The MODIS instruments' ±55 degree scanning pattern produces a 2330 km cross-track by 10 km along-track swath with nearly complete global coverage every one to two days.

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    References and Related Publications

    Contacts and Acknowledgments

    Ted Scambos
    National Snow and Ice Data Center
    449 UCB, University of Colorado
    Boulder, CO 80309-0449 USA

    Acknowledgments: 

    These data were generated through a grant from the NASA MEaSUREs program.

    Document Information

    DOCUMENT CREATION DATE

    July 2017

    DOCUMENT REVISION DATE

    June 2018

    FAQ

    Do you have sample code to read GeoTiffs?
    Sample image ouput from Python code. Below you will find  sample code in IDL, MATLAB, and Python to read in a GeoTIFF file, extract the metadata, and create an image. The code has been tested with... read more