Data Set ID: 
NSIDC-0634

Alaska Tidewater Glacier Terminus Positions, Version 1

This data set contains Alaska tidewater glacier terminus positions digitized from USGS topographic maps and Landsat images.

This is the most recent version of these data.

Version Summary: 

initial release

STANDARD Level of Service

Data: Data integrity and usability verified

Documentation: Key metadata and user guide available

User Support: Assistance with data access and usage; guidance on use of data in tools

See All Level of Service Details

Parameter(s):
  • SNOW/ICE > ICE EXTENT
Data Format(s):
  • ASCII Text
  • ESRI Shapefile
Spatial Coverage:
N: 61.5, 
S: 56.5, 
E: -132, 
W: -151
Platform(s):LANDSAT-5, LANDSAT-7
Spatial Resolution:
  • 30 m x 30 m
Sensor(s):ETM+, MSS, TM
Temporal Coverage:
  • 1 January 1948 to 31 December 2012
Version(s):V1
Temporal ResolutionVariesMetadata XML:View Metadata Record
Data Contributor(s):Robert McNabb, Regine Hock

Geographic Coverage

Once you have logged in, you will be able to click and download files via a Web browser. There are also options for downloading via a command line or client. For more detailed instructions, please see Options Available for Bulk Downloading Data from HTTPS with Earthdata Login.

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.

McNabb, R. W. and R. Hock. 2015. Alaska Tidewater Glacier Terminus Positions, Version 1. [Indicate subset used]. Boulder, Colorado USA. NASA National Snow and Ice Data Center Distributed Active Archive Center. doi: https://doi.org/10.5067/3OOVUDFK3R0W. [Date Accessed].
Created: 
10 October 2018
Last modified: 
10 October 2018

Data Description

This data set allows for the characterization of temporal and spatial variability in Alaska tidewater glacier length and terminus position over timescales ranging from decades to sub-annual. The data set contains glacier terminus positions for 50 Alaska tidewater glaciers. There are from 120 to 327 terminus outlines per glacier, with an average of 205 outlines per glacier, and a total number of over 10,000 terminus outlines (individual glacier fronts) for the study area's six regions including Kenai Peninsula, Western Chugach, Icy Bay, Yakutat, Glacier Bay, and Coast Range.

Parameters

This data set provides glacier terminus positions.

Parameter Description

ASCII text files include decimal date (decdate) and length attributes. The shapefile day of year (doy), Landsat scene (lsat_scene), and projection (proj) attributes are not included in the ASCII files.

Shapefiles of glacier terminus positions for fifty Alaska tidewater glaciers.

Table 1. Primary Data Attributes
Data Field Description
decdate Decimal date
year Year
doy Day of Year
lsat_scene Landsat scene (may also indicate "USGS Map")
proj Projection, e.g. UTM zone 7N
length Glacier length in kilometers

Sample Data Record

Figure 1 illustrates Columbia Glacier terminus positions during select years from 1972 to 2012.

sample data record
Figure 1. Columbia Glacier terminus positions 1972 to 2012

File Information

Format

ASCII text

ESRI ArcGIS Shapefile:

  • .dbf – dBASE table that stores the attribute information of features.
  • .prj – file that stores the coordinate system information.
  • .shp – main file that stores the feature geometry.
  • .shx – index file that stores the index of the feature geometry.

Directory Structure

Data are available via HTTPS in the following directory:

https://daacdata.apps.nsidc.org/pub/DATASETS/nsidc0634_ak_tidewater_glacier_v1/

This directory contains the following folders:

Table 2. Top-Level FTP Directory Structure
Folder Name Description
length_timeseries Measurement time series and length values in ASCII text files for each of the 50 glacier termini in the data set
glacier_bay Shapefiles for Glacier Bay tidewater glaciers subregion
icy_bay Shapefiles for Icy Bay tidewater glaciers subregion
kenai Shapefiles for Kenai tidewater glaciers subregion
west_chugach Shapefiles for West Chugach tidewater glaciers subregion
yakutat Shapefiles for Yakutat tidewater glaciers subregion
coast_range Shapefiles for Coast Range tidewater glaciers subregion

Naming Convention

This section explains the shapefile and text file naming convention used for this data set.

Example File Names:

  • muir.txt
  • muir.dbf
  • muir.prj
  • muir.shp
  • muir.shx

Convention:

  • glaciername.EXT
Table 3. Naming Convention for Shapefiles
String Description
glaciername Name of glacier
EXT File extension.
.txt (measurement time series and length text file)

Shapefile format includes:
.dbf (attributes)
.prj (projection information)
.shp (shapes)
.shx (feature geometry index)

File Size

The complete data volume is approximately 6.8 MB.

Spatial Information

Coverage

  • Southernmost Latitude: 56.5° N
  • Northernmost Latitude: 61.5° N
  • Westernmost Longitude: 151° W
  • Easternmost Longitude: 132° W

Resolution

Derived from 30 m satellite imagery.

Geolocation

Universal Transverse Mercator (UTM) Zones 6N, 7N, or 8N, depending on glacier location.

Temporal Information

Coverage

01 January 1948 to 31 December 2012

Resolution

Annual terminus positions for each glacier, intermittent from 1948 to 2012.

Data Acquisition and Processing

Background

Terminus outlines of all tidewater glaciers are manually digitized from USGS Topographic Maps and Landsat scenes.

Acquisition and Processing

As described in McNabb and Hock (2014), terminus outlines on U.S. Geological Survey (USGS) 15 minute topographic maps were digitized and georeferenced to provide a base length for glaciers before 1970 (pre-Landsat). Since topographic maps produced by the USGS are dated to the year only, in order to determine the time of year for each map a date was assigned using mean flight dates reported for each map. The nominal horizontal accuracy of the USGS 1:63,360 scale maps used in this study is 53.6 m.

For each glacier between 1972 and 2012 calving front outlines were manually digitized from all available cloud-free Landsat images, resulting in a total of more than 10,000 outlines. Estimated horizontal accuracy for digitized Landsat scenes is 60 m.

This data set contains 50 glaciers identified as existing tidewater glaciers (McNabb and Hock, 2014).

Quality, Errors, and Limitations

Some studies have indicated that errors in map topography can be much larger than the nominal error in Alaska of 53.6 m (Aðalgeirsdóttir et al., 1998; Arendt et al., 2002), though most of these errors occur in areas of low contrast, such as the accumulation zone of glaciers. Because information about potential horizontal errors was not available, it is assumed that the nominal error is correct. Nominal horizontal accuracy for digitized USGS topographic maps is 53.6 m. Horizontal accuracy for digitized Landsat scenes is estimated at 60 m, incorporating both georeferencing errors and errors in the manual digitization (McNabb and Hock, 2014).

Software and Tools

Text data files may be opened by any text editor or word processing program that reads ASCII text files.

Shapefiles can be readily accessed using GIS software such as ArcGIS and QGIS.

Related Data Sets

Related Websites

Contacts and Acknowledgments

Robert W. McNabb
University of Alaska Fairbanks
Geophysical Institute
903 Koyukuk Drive
Fairbanks, AK 99775-7320

Regine Hock
University of Alaska Fairbanks
Geophysical Institute
903 Koyukuk Drive
Fairbanks, AK 99775-7320

Acknowledgments:

This work was funded in part by NSF grant EAR-0943742, NASA grant NNX11AF41G, and NASA grant NNX11A023G.

References

Aðalgeirsdóttir, G., K. A. Echelmeyer, and W. D. Harrison. 1998. Elevation and volume changes on the Harding Icefield, Alaska, Journal of Glaciology, 44:(148):570–582.

Arendt, A., K. Echelmeyer, W. Harrison, C. Lingle, and B. Valentine. 2002. Rapid wastage of Alaska glaciers and their contribution to rising sea level, Science, 297(5580):382–386.

McNabb, R. W., and R. Hock. 2014. Alaska Tidewater Glacier Terminus Positions, 1948–2012, Journal of Geophysical Research Earth Surface, 119:153–167, doi:10.1002/2013JF002915.

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