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Data Set ID:
NSIDC-0646

MEaSURES Greenland Ice Velocity: Selected Glacier Site Velocity Maps from Optical Images, Version 2

This data set, part of the NASA Making Earth System Data Records for Use in Research Environments (MEaSUREs) program, consists of mean monthly velocity maps for selected glacier outlet areas. The maps are generated by tracking visible features between optical image pairs acquired by the Landsat 7 Enhanced Thematic Mapper Plus (ETM+), the Landsat 8 Operational Land Imager (OLI), and the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER).

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

Version Summary:

Changes for Version 2 include:
1. a correction in the processing, which caused error values to appear as NaNs in some of the data
2. a more aggressive filtering method was applied to remove small, isolated clusters of data,
3. cross-path Landsat pairs were used to fill in temporal gaps in the 2016 data. These use the MEaSUREs Greenland Ice Mapping Project (GIMP) Digital Elevation Model from GeoEye and WorldView Imagery and the orthorectifcation algorithm of Rosenau 2012
4. spatial coverage expanded to include the Wcoast-80.75N grid
5. temporal coverage expanded from September 2015 to September 2016
6. to reduce overall size of the data set, GeoTIFFs are produced using Lempel–Ziv–Welch LZW lossless compression

Geographic Coverage

Parameter(s):
  • Snow/Ice > Ice Velocity
Spatial Coverage:
  • N: 82, S: 60, E: -20, W: -70

Spatial Resolution:
  • 100 m x 100 m
Temporal Coverage:
  • 1 July 1999 to 30 September 2016
Temporal Resolution: 1 month
Data Format(s):
  • GeoTIFF
  • PNG
Platform(s) LANDSAT-7, LANDSAT-8, TERRA
Sensor(s): ASTER, ETM+, OLI
Version: V2
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 Velocity: Selected Glacier Site Velocity Maps from Optical Images, Version 2. [Indicate subset used]. Boulder, Colorado USA. NASA National Snow and Ice Data Center Distributed Active Archive Center. doi: http://dx.doi.org/10.5067/VM5DZ20MYF5C. [Date Accessed].

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Detailed Data Description

Format

This data set is organized into 50 study sites. Study sites in this data set correspond to geographical sub-regions of Greenland. The name of each sub-region reflects its center latitude. Table 2 under the Spatial Coverage section of this document lists the name (center latitude) of each sub-region, the latitude and longitude of its lower left corner, and the geographical features it contains.

The following files are provided for each site:

  • velocity browse image (PNG)
  • component velocity in the x-direction (GeoTIFF)
  • component velocity in the y-direction (GeoTIFF)
  • error estimates in the x-direction (GeoTIFF)
  • error estimates in the y-direction (GeoTIFF)
  • metadata file (ASCII text)
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File and Directory Structure

Data are available via HTTPS in the https://daacdata.apps.nsidc.org/pub/DATASETS/nsidc0646_MEASURES_greenland_vel_optical_v2 directory. In this directory, there are 50 folders, 1 for each study site, and within each of these folders are subfolders for each date of acquisition.  These subfolders each contain six data files.

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File Naming Convention

This section explains the file naming convention used for this data.

Example File Names:

  • OPT_E61.10N_1999-09_v2.png
  • OPT_E61.10N_1999-09_vx_v2.tif
  • OPT_E61.10N_1999-09_vy_v2.tif
  • OPT_E61.10N_1999-09_ex_v2.tif
  • OPT_E61.10N_1999-09_ey_v2.tif
  • OPT_E61.10N_1999-09_v2.meta

File Naming Convention:

  • OPT_[sub-region]_[date]_[datum]_[v2].[ext]

The following table describes the variables used in this data set's file naming convention:

Table 1. File Name Variables and Descriptions
Variable Description
OPT Velocities derived from optical image pairs acquired by Landsat 8 OLI, Landsat 7 ETM+, ASTER, or a combination.
sub-region  Sub-region names are defined as follows:
  • E, W, or S: East, West, or South Coast
  • Center latitude in degrees, minutes
date Date of acquisition (YYYY-MM)
datum Component velocity or component error estimate:
  • vx: x component of velocity
  • vy: y component of velocity
  • ex: x component of error
  • ey: y component of error
v2 version number
ext File extension:
  • png: Portable Network Graphic file
  • tif: GeoTIFF-formatted file
  • meta: ASCII text file. Contains image dates, production date, sensor combinations, and geographical information.
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File Size

The data files range in size from 0.3 MB to 5.1 MB.

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Volume

The total data volume is approximately 5.8 GB.

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Spatial Coverage

This data set contains velocity maps for most of the outlet glaciers on the Greenland Ice Sheet. The study area lies within the following bounding box:

  •  Southernmost Latitude: 60° N
  •  Northernmost Latitude: 82° N
  •  Easternmost Longitude: 20° W
  •  Westernmost Longitude: 70° W

Spatial Resolution

100 m

Projection and Grid Description

Data are organized into 50 sub-regions of a 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. Table 2 lists the name (center latitude) of each sub-region, the latitude and longitude of its lower left corner, and the glaciers it contains.

Table 2. Sub-Region Names, Locations, and Geographical Features

Sub-Region Name

  • Latitude, Longitude (lower left corner)
Geographical Features in Grid
E61.10N
  • 60.8004, -43.9589
  • Unnamed glacier near Danell Fjord
  • Danells
  • Kanderdluluk Fjord
  • Cape Herluf Trolle
  • Cape Tordenskjold
E61.70N
  • 61.3903, -43.7671
  • Anorituup Kangerlua Fjord
  • Napasorsuaq Fjord
E62.10N
  • 61.801, -43.2149
  • Puisortoq Glacier (north)
  • Puisortoq Fjord (south)
E62.55N
  • 62.2422, -43.6371
  • Mogens Heinesen Fjord
  • Timmiarmiut Fjord
E63.00N
  • 62.7212, -43.5332
  • Heimdal Glacier
E63.35N
  • 63.0911, -42.5656
  • Thrym Glacier
  • Sehested Fjord
  • Skinfaxe Glacier
E63.85N
  • 63.5620, -42.4419
  • Bernstorffs Fjord
E64.35N
  • 64.0768, -42.2688
  • Gyldenlove Fjord
E64.65N
  • 64.3291, -41.7539
  • Fridtjof Nansens Peninsula
E65.10N
  • 64.7987, -41.8569
  • Koge Bay
E65.55N
  • 65.2242, -40.5156
  • Ikertivaq Sound
  • Pamiatig
E66.50N
  • 66.1973, -39.1116
  • Fenris Glacier
  • Helheim Glacier
E66.60N
  • 66.3305, -37.4428
  • Midgard Glacier
  • Midgard North
E66.90N
  • 66.5045, -36.2923
  • Kruuse Fjord
  • Steenstrup Glacier
  • Tasiilaq Fjord
E67.55N
  • 67.2762, -34.9643
  • Norde Parallel Glacier
  • Nordre

E68.05N

  • 67.9148, -33.9170
  • Hutchinson Glacier
E68.50N
  • 68.3044, -31.1040
  • Courtauld Glacier
  • Frederiksborg Glacier
  • Christian IV Glacier
  • Sorgenfri Glacier

E68.52N

  • 68.3044, -31.1040
  • Schjelderup Glacier
  • Sorgenfri Glacier
E68.80N
  • 68.4663, -34.3672
  • Kangerdlussuaq Glacier
  • Nordfjord Glacier

E69.90N

  • 69.8224, -29.5537
  • unnamed glaciers

E70.10N

  • 70.0023, -26.7390
  • Syd Glacier

E70.40N

  • 70.0488, -30.6613
  • Rolige Glacier
E71.75N
  • 71.4887, -30.9758
  • Daugaard-Jensen Glacier

E71.95N

  • 71.7410, -29.9742  
  • Daugard-Jensen Glacier

E78.95N

  • 78.7851, -22.2120
  • Gammel Hellerup Glacier
W61.70N
  • 61.4746, -48.4912
  • Sermiligarssuk Fjord
W62.10N
  • 61.8077, -49.0172
  • Nigerdlikasik Glacier
  • Avangnardleq Glacier
  • Ukassorssuaq
W64.25N
  • 63.9263, -49.8721
  • Kangiata Nunata Sermia Glacier
  • Quamanarssup Glacier
W64.75N
  • 64.4610, -50.1732
  • Ujarassuit Paauat Fjord
  • Narsap Sermia Glacier
W69.10N
  • 68.7418, -50.4126
  • Alangordliup Sermia Glacier
  • Jakobshavn Isbræ Glacier
  • Torsukattak Glacier
W69.95N
  • 69.6356, -50.6122
  • Kangilerngata Sermia Glacier
  • Kujatdleq Glacier
  • Torsukattak Fjord
W70.55N
  • 70.2285, -50.9177
  • Lille Glacier
  • Sermilik Glacier
  • Kangilleq Glacier
  • Store Glacier
W70.90N
  • 70.7542, -50.9613
  • Perdlerfiup Sermis Glacier
  • Silardleq
W71.65N
  • 71.3100, -51.8327
  • Kangerluarsuk Glacier
  • Rink Glacier
W72.00N
  • 71.6540, -52.8014
  • Inngia Fjord
  • Umiammakku Glacier
W72.90N
  • 72.5829, -54.8293
  • Alangorssup Sermia Glacier
  • Upernavik Isstorm Glacier
W73.45N
  • 73.1520, -55.6912
  • Kakivfait Sermiat Glacier
  • Giesecke Glacier
  • Nutarmiut Glacier
  • Tuvssaq (populated area)
W73.75N
  • 73.1520, -55.6912
  • Cornell Glacier
  • Sugarloaf Bugt (sound)
  • Ussing Glacier
W74.50N
  • 74.1506, -56.4843
  • Cornel Glacier
  • Alison Bugy (bay)
  • Illulik (populated area)
W74.95N
  • 74.5750, -57.6463
  • Hays Glacier
  • Kjer Glacier
  • Jensen Glacier
W75.50N
  • 75.1264, -58.5281
  • Dietrichson Glacier
  • Steenstrup Glacier
  • Sverdrup Glacier
W75.85N
  • 75.4736, -59.2722
  • Nansen Glacier
  • Nordenskiold Glacier
W76.10N
  • 75.7205, -60.0987
  • Kong Oscar Glacier
  • Nordenskiold Glacier
  • Nutarmiut
W76.25N
  • 75.9067, -61.2365
  • Balgoni
  • Docker Smith Glacier
  • Fisher
  • Igssuarssuit Sermia Glacier
  • Leven

W76.33N

  • 76.1538, -64.2165
  • Yngvar Nielsen Glacier
  • Mohn Glacier
W76.35N
  • 75.7416, -63.3988
  • Mohn Glacier
  • Gade Glacier
  • Meteor Bay
  • Yngvar Nielson Glacier
W80.75N
  • 81.1505, -46.6109
  • Chow
S44.84W
  • 61.0923, -45.3465
  • Kiattuut Sermiat glacier
  • Qooroq Fjord
S45.43W
  • 61.2196, -45.8994
  • Equlorutsit Kangigdlit
  • Sermia
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Temporal Coverage

Data are available July 1999 through September 2016.

Temporal Resolution

Monthly

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Parameter or Variable

Parameter Description

This data set reports the following parameters:

  • Ice velocities (x- and y-components)
  • Error estimates (x- and y-components)

Corresponding ASCII text metadata files (.meta) are also provided and contain geographical information plus dates and codes that reveal the sensor combinations of the images used to create the monthly mean. The sensor combination key is provided in Table 3.

Table 3. Sensor Key for Metadata Files
Sensor Code
Landsat 8 OLI LC8
Landsat 7 ETM+ LE7
ASTER AST

The following sensor combinations are possible: LE7/LE7, LE7/LC8, AST/AST, LC8/LC8.

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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

Data Acquisition Methods

Level 1 imagery for the Landsat 7 ETM+ and Landsat 8 OLI was obtained from the U. S. Geological Survey (USGS | Landsat Level 1 Standard Data Products). ASTER (AST14DMO) imagery was obtained from the NASA Land Processes Distributed Active Archive Center (LPDAAC).

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Derivation Techniques and Algorithms

Processing Steps

These data were created using orthorectified Landsat Level L1T or L1G and ASTER (AST14DMO) imagery. Orthorectified images were received in UTM projection and converted to Polar Stereographic using Geographic Data Abstraction Library (GDAL) software. ASTER visible bands 1-3 were reduced to a single grayscale principle component image. The panchromatic band was used for Landsat. Velocity fields were constructed using images from the same sensor or combinations of Landsat 7, Landsat 8, and ASTER images. In the case of Landsat pairs, only images from the same path/row were used to reduce the impact of terrain-dependent errors. For Version 2, to fill in temporal gaps in the 2016 coverage, cross path/row Landsat images were used. For these we used the MEaSUREs Greenland Ice Mapping Project (GIMP) Digital Elevation Model from GeoEye and WorldView Imagery and orthorectifcation algorithm of Rosenau et al. (2012).

Velocity fields were produced by an automated cross-correlation of sequential images using the Multi-Image Multi-Chip (MIMC) algorithm described in Ahn and Howat (2011) and updated in Jeong et al. (2017). The MIMC utilizes a range of image filters and search window sizes as well as both backward and forward matching to generate 64 matches per sample. Neighborhood statistics and an a priori velocity field, consisting of radar-derived velocities closest in time to the image dates from the MEaSUREs Greenland Ice Sheet Velocity Map from InSAR Data data set, were used to select the highest confidence solution and its uncertainty.

This velocity field was then corrected for image re-registration errors by subtracting the average displacement over bedrock or very slow moving ice (< 10 m/yr), which is located using the a priori velocity field. The residual deviation of velocities over bedrock then provides the registration error (see Error Sources). Individual velocity image pairs within each region were sampled to the same grid and stacked into monthly medians at each grid point, providing a monthly sampling. The median error was also obtained.

Note: Monthly means are calculated from images, which may have acquisition dates from the preceding or succeeding month. For the naming convention, the month is determined from where the midpoint Julian dates fall. For example, September monthly means may have been generated from images that were acquired in August or in October but the midpoint Julian date between the images falls within September. The exact dates used are included in the meta file.

Error Sources

Uncertainty in the velocity solution results from uncertainty in the match solution and uncertainty in image co-registration. Match solution uncertainty is estimated at each grid point from the sample of individual velocity solutions that results from the MIMC procedure. This error is typically on the order of one-third of a pixel. Co-registration error, the dominant source of uncertainty, is estimated from the residual velocities obtained over bedrock and very slow ice after the mean is removed. These errors vary considerably, but are typically on the order of 100 m/year.

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Sensor or Instrument Description

The Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) obtains high-resolution (15 to 90 square meters per pixel) images of the Earth in 14 different wavelengths of the electromagnetic spectrum, ranging from visible to thermal infrared light. ASTER was launched in December 1999 onboard Terra, the flagship satellite of NASA's Earth Observing System (EOS). For more information, see Terra | ASTER.

The Enhanced Thematic Mapper Plus (ETM+) instrument on board Landsat 7 is a fixed “whisk-broom,” eight-band, multispectral scanning radiometer capable of providing high-resolution imaging information of the Earth’s surface. Orbiting at an altitude of 705 km, the instrument detects spectrally-filtered radiation in visible near-infrared, short-wave near-infrared, long-wave near-infrared, and panchromatic bands from the sun-lit Earth in a 183 km wide swath. Visit NASA Landsat Science | The Enhanced Thematic Mapper Plus for more information.

The Operational Land Imager (OLI) on Landsat 8 is an enhanced version of Landsat 7’s ETM+ that adds two new spectral bands: a deep blue visible channel (band 1) specifically designed for water resources and coastal zone investigation; and a new infrared channel (band 9) to detect of cirrus clouds. For more information, see USGS | Landsat 8.

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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 MEaSUREs program.

Document Information

DOCUMENT CREATION DATE

May 2017

No FAQs or How Tos available for this data set.

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