Table of Contents

1. Contacts and Acknowledgments
2. Detailed Data Description
3. Data Access and Tools
4. Data Acquisition and Processing
5. References and Related Publications
6. Document Information

Citing These Data

The following example shows how to cite the use of this data set in a publication. For more information, see our Use and Copyright Web page.

Smith, B. E., I. R. Joughin, and S. Tulaczyk. 2012. Antarctic Active Subglacial Lake Inventory from ICESat Altimetry. [indicate subset used]. Boulder, Colorado USA: National Snow and Ice Data Center. http://dx.doi.org/10.7265/N57M05WS

Overview

Platform	ICESat (Ice, Cloud,and Land Elevation Satellite)
Sensor	GLAS (Geoscience Laser Altimeter System)
Spatial Coverage	Northernmost Latitude: 60° S Southernmost Latitude: 90° S Easternmost Latitude: 180° E Westernmost Latitude: 180° W
Spatial Resolution	Ranges from 1 to 50 km
Temporal Coverage	1 September 2003 to 1 November 2009
Temporal Resolution	2 to 3 measurements per year
Parameters	Lake Boundaries Lake Volume Change (km³) Ice Surface Elevation Changes (m)
Data Formats	KML CSV GeoTIFF
Metadata Access	View Metadata Record
Data Access	FTP

1. Contacts and Acknowledgments

Investigators

Benjamin E. Smith
University of Washington
Applied Physics Laboratory
Polar Science Center
1013 NE 40th St
Box 355640
Seattle, WA 98105-6698

Ian R. Joughin
University of Washington
Applied Physics Laboratory
Polar Science Center
1013 NE 40th St
Box 355640
Seattle, WA 98105-6698

Slawek Tulaczyk
University of California, Santa Cruz
Department of Earth and Planetary Sciences
Earth & Marine Sciences A208
Santa Cruz, CA 95064

Technical Contact

NSIDC User Services
National Snow and Ice Data Center
CIRES, 449 UCB
University of Colorado
Boulder, CO 80309-0449  USA
phone: +1 303.492.6199
fax: +1 303.492.2468
form: Contact NSIDC User Services
e-mail: nsidc@nsidc.org

Acknowledgements

This work was supported by National Science Foundation (NSF) grant ANT-0636719 to Joughin and Smith, NSF grant ANT-0636970 to Tulaczyk, and National Aeronautics and Space Administration (NASA) grant NNX07AL18G to Helen A. Fricker.

2. Detailed Data Description

Format

Data are provided in the following formats:

• Keyhole Markup Language (.kml)
• Comma-separated value (.csv)
• GEOTiff (.tif)

File and Directory Structure

Data are available on the FTP site in the ftp://sidads.colorado.edu/pub/DATASETS/AGDC/nsidc0523_smith_V01/ directory. Within this directory, the /NSIDC_Lakes/ folder contains Antarctic_lakes.kml, an index file of outlines, names, and volume histories for all of the lakes in the data set. KML files can be opened with Google Earth or similar GIS software.

In addition, each of the 124 lakes has its own subdirectory within /NSIDC_Lakes/ that houses additional lake-specific data files. Figure 1 below illustrates this directory structure.

Table 2 details the contents of the lake subdirectories using the example name Bindschadler_1:

Table 2. Contents of the Lake Subdirectories

Name	Description
¹Difference estimates represent changes relative to the first campaign for which an adequate number of measurements were available (defined as 50% of the maximum number of measurements in any campaign).
Bindschadler_1_z_range_thumb.tif	GEOTiff thumbnail image showing the difference between maximum and minimum ICESat-measured heights within the lake polygon.
Volume_history.csv	Comma-separated value text file with volume-difference estimates for each ICESat campaign.¹
z_grids	Folder that contains a set of GEOTiff gridded elevation-difference estimates for the elevation difference between each campaign and the first valid campaign.¹

File Size

Antarctic_lakes.kml is 305 KB. Data files for individual lakes range from 100 KB to 4 MB. The complete data set is approximately 100 MB.

Spatial Coverage

• Northernmost Latitude: 60° S
• Southernmost Latitude: 90° S
• Easternmost Latitude: 180° E
• Westernmost Latitude: 180° W

Spatial Resolution

Ranges from 1 to 50 km

Temporal Coverage

Data were obtained berween 1 September 2003 and 1 November 2009 by NASA's ICESat Mission.

Temporal Resolution

2-3 measurements per year

Parameter or Variable

Parameter Description

Lake locations and volume changes were derived from elevation changes observed by ICESat. For additional details, see Derivation Techniques and Algorithms.

Sample Data Record

Figure 2 is a screen capture of Antarctic_Lakes.kml viewed with Google Earth. In the image, Foundation_12 has been selected to show the lake's location and volume history.

Figure 3 shows the GEOTiff thumbnail image Recovery_1_z_range_thumb viewed with Exelis ENVI.

3. Data Access and Tools

Data Access

Data are available via FTP.

Software and Tools

A variety of options are available to work with these data. KML files can be opened with Google Earth or similar Geographical Information Systems (GIS). Comma-delimited text files may be opened with standard spreadsheet software. GEOTIff files can be accessed with tools ranging from simple image viewers to advanced software packages that read, process, and analyze geospatial imagery.

4. Data Acquisition and Processing

Data Acquisition Methods

This data set presents a comprehensive study of lakes beneath the Antarctic ice sheet north of 86° S that fill and drain on time scales of months to years. Based on 4.5 years (2003-2008) of ICESat laser altimetry data, the investigators identified 124 lakes that were active during this period.

Derivation Techniques and Algorithms

Areas with anomalous changes in elevation, or Elevation Change Anomalies (ECAs), were identified from ICESat maps of apparent multi-year surface roughness. When an ECA signature was consistent with an underlying subglacial lake, the investigators digitized a boundary around the lake and calculated gridded patterns of elevation changes for additional ICEsat campaigns. Volume changes were computed by taking the spatial integral of the gridded elevation changes within the boundary. For additional details about how these data were derived, see Smith et al., 2009.

Sensor or Instrument Description

The ICESat mission's primary goal was to observe and quantify ice sheet mass balance, to gain insight about how changes in Earth's atmosphere and climate affect polar ice and global sea level. For more information about ICESat, visit NASA's ICESat Web site. The sole scientific instrument onboard ICESat was the Geoscience Laser Altimeter System (GLAS), a next-generation space lidar that combined a precision surface lidar with a sensitive dual wavelength cloud and aerosol lidar. For more information about the GLAS instrument, see NASA's ICESat Fact Sheet (PDF).

5. References and Related Publications

Smith, B. E., H. A. Fricker, I. R. Joughin, and S. Tulaczyk. 2009. An Inventory of Active Subglacial Lakes in Antarctica detected by ICESat (2003-2008). Journal of Glaciology, 55(192):573-595. doi: 10.3189/002214309789470879.

Related Data Collections

• Antarctic Glaciological Data Center at NSIDC
• ICESat/GLAS Data at NSIDC
• Borehole Optical Stratigraphy Modeling, Antarctica

6. Document Information

Acronyms and Abbreviations

The acronyms used in this document are listed in Table 3.

Table 3. Acronyms and Abbreviations

Acronym	Description
AGDC	Antarctic Glaciological Data Center
CSV	Comma Separated Value
DOI	Digital Object Identifier
ECA	Elevation Change Anomaly
GEOTiff	Geographic Tagged Image File Format
GIS	Geographic Information System
GLAS	Geoscience Laser Altimeter System
ICESat	Ice, Cloud, and Land Elevation Satellite
KML	Keyhole Markup Language
Lidar	Light Detection And Ranging
NASA	National Aeronautics and Space Administration
NSF	National Science Foundation
NSIDC	National Snow and Ice Data Center

Document Creation Date

October 2012

Document URL

http://nsidc.org/data/docs/agdc/nsidc0523-smith/index.html