Velocities of Outlet Glaciers, Ice streams, and Ice shelves, Antarctica, From Satellite Images
Entry ID: USGS_outletglaciers

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Summary
Abstract: Changes in global climate and sea level are intricately linked to changes in
the area and volume of polar ice sheets. Thus, melting of the ice sheets may
severely impact the densely populated coastal regions on Earth. Melting of the
West Antarctic ice sheet alone could raise sea level by approximately 5m. In
spite of their importance, the current mass balances (the net gains or losses)
of the Antarctic ice sheets are not known. Because of difficult logistic
problems in Antarctica, field research has focused on only a few major ice
streams and outlet glaciers. Yet, to understand the ice sheet dynamics fully,
we must carefully document all of the coastal changes associated with advance
and retreat of ice shelves, outlet glaciers, and ice streams. A critical
parameter of ice sheets is their velocity field, which, together with ice
thickness, allows the determination of discharge rates. Remote sensing, using
moderate- to high-resolution satellite images, permits glacier movement to be
measured on sequential images covering the same area; the velocities can be
measured quickly and relatively inexpensively by tracking crevasses or other
patterns that move with the ice. Especially important are velocities where the
ice crosses the glaciers' grounding lines (locations along the coast where the
ice is no longer ground supported and begins to float).

Landsat images are particularly useful because they provide synoptic views
covering as much as 185 square km. Thus several fixed points in the scenes,
needed for geometric corrections and coregistration of images, are likely to be
found. On the other hand, Landsat images have disadvantages: the early
Multispectral Scanner (MSS) images have moderate resolution (about 80 m),
permitting tracking of only the larger patterns in the floating part of ice
tongues or shelves. Thematic Mapper (TM) images have high resolution (about 30
m), but digital TM data are very expensive. Also, the long polar winter night
reduces acquisition opportunities, and cloud cover may impede recognition of
features. An alternative is ERS SAR images (European Remote Sensing Satellite,
Synthetic Aperture Radar), which have 30-m resolution and similar viewing
conditions regardless of season or cloud cover. Thus they permit the tracking
of small crevasses and other patterns above or at the grounding line.

An extensive set of Landsat images covering Antarctica was acquired in the
early to middle 1970s. Since 1984, new Landsat images of Antarctica's coastal
regions have been obtained largely through a program sponsored by an
international consortium of nations belonging to the Scientific Committee on
Antarctic Research (SCAR). A period of 20 years between acquisitions of some of
the Landsat images makes them an invaluable resource.

ERS-1 images have been available since mid-1991 in both ascending and
descending orbits. They have repeat orbital cycles varying from 3 days to 35
days, and they cover 100 square km on the ground. We herewith acknowledge the
support of the European Space Agency (ESA), which makes the images (and tapes)
available at no cost to researchers of accepted projects.

Examination of the image pairs showed that many glaciers do not have suitable
floating tongues. Tongues on coastlines where ice shelves are narrow or absent
tend to be short, perhaps due to vigorous ocean-current and wind regimes. Also,
short tongues having distinctive crevasse patterns may break off in a time
frame shorter than that between image acquisitions. For these regions, only
methods that employ high-resolution images that permit recognition of features
near and above the grounding line can be used.

This report summarizes the results of velocity measurements of outlet glaciers,
ice streams, and ice shelves around the Antarctic periphery. For some regions,
where suitable images were available, the same area was measured repeatedly to
validate the data or register changes in velocity with time. The results given
here are a compendium of published papers and work in progress. The results
constitute a data base that will be added to and amended as more velocity
measurements become available.

Related URL
Link: VIEW EXTENDED METADATA
Description: Metadata in Biological Data Profile format.


Geographic Coverage
 N: -67.0 S: -76.0  E: 130.0  W: -142.0

Data Set Citation
Dataset Originator/Creator: B.K. Lucchitta, J.M. Barrett, J.A. Bowell, J.G. Ferrigno, K.F. Mullins, C.E. Rosanova and R.S. Williams
Dataset Title: Velocities of Outlet Glaciers, Ice streams, and Ice shelves, Antarctica, From Satellite Images
Dataset Release Date: 1995
Dataset Release Place: Flagstaff, Arizona
Dataset Publisher: U.S. Geological Survey
Data Presentation Form: landsat images
Online Resource: http://geochange.er.usgs.gov/pub/antarctica/glacier-velocity/Core/m...


Temporal Coverage
Start Date: 1972-01-01
Stop Date: 1992-12-31


Location Keywords
CONTINENT > ANTARCTICA
GEOGRAPHIC REGION > POLAR


Science Keywords
CRYOSPHERE >GLACIERS/ICE SHEETS >GLACIERS    [Definition]
CRYOSPHERE >GLACIERS/ICE SHEETS >ICE SHEETS    [Definition]
TERRESTRIAL HYDROSPHERE >GLACIERS/ICE SHEETS >GLACIERS    [Definition]


ISO Topic Category
GEOSCIENTIFIC INFORMATION
INLAND WATERS


Quality
We use two methods to determine the glacial velocities: an interactive one in
which we visually trace crevasse patterns (Lucchitta and others, 1993) and an
autocorrelation program developed by Bindschadler and Scambos (1991) and
Scambos and others (1992). First, we digitally co-register the images by using
a minimum of three well-dispersed fixed points (such as nunataks or ice walls)
to calculate a least-squares fit to a first-order polynomial equation. This
insures that only a rotational/translational correction is made and no new
internal error is introduced during the geometric resampling. In the
interactive technique, we then match and align the crevasse patterns displaced
with time, and record the starting/ ending image coordinates for each point.
To obtain the distribution of average velocities over the length of the glacier
tongues, we also use the distance from the location of each point on the
earlier image to a base line drawn perpendicular to glacier movement and
ideally lying on the grounding line; where the grounding line is complex, the
base line may only approximate its position. Next, a digitized file is made,
tracing the glacier ice movements and defining the glacier's baseline (or
grounding line). This file is used to calculate the velocity and distance
statistics by measuring the displacements along the curve that approximates the
ices movement per given time interval. For each measured point, a displacement
vector is plotted on the image, commonly the earlier one of the pair, to
illustrate the relative velocities between glaciers and time intervals.

Because the velocity field may also change across the glacier tongues, we
divide the wider glaciers into several longitudinal paths. Next we obtain an
estimate of the spread of measured points by performing a regression analysis
on the data. This includes an option to cull bad data points by inputting a
variable for the standard deviation. If used, the mean absolute deviation of
the points about this line is calculated and any points lying outside that
distance are disregarded during the statistical analysis. Calculations are
made for the entire glacier as well as for each individual path. The 95%
confidence interval for the regression coefficient is calculated along with the
correlation coefficient.

The files contained in this data base are the output ASCII files
generated by this statistical software. Each file identifies the
images used, their dates, and resolutions, the time interval
between image acquisitions and the statistical variables used to
make the calculations. These data are followed by a table of the
distance and velocity values for each point and the statistics
calculated per path. The measurement results are shown in graphs
that display average velocities per given time interval versus the
distance from the base line for all points in each field (not
included in this data base).

In the auto-correlation method we use the same techniques for coregistration
and graphic and statistical display. However, we may not divide the glaciers
into segments and paths, but instead combine all velocities and show variations
across the glacier by color contours (also not shown in this report).


Access Constraints
None


Use Constraints
None


Keywords
glacier
glacier tongues
glacier velocity
Antarctica
TEMS
GTOS
G3OS


Data Set Progress
COMPLETE


Data Center
Publications and Data, Global Change Research Program, Eastern Region, Geology Division, U.S. Geological Survey, U.S. Department of the Interior    [Information]
Data Center URL: http://geochange.er.usgs.gov/pub/info/holdings.html

Data Center Personnel
Name: PETER N. SCHWEITZER
Phone: (703) 648-6533
Fax: (703) 648-6252
Email: pschweitzer at usgs.gov
Contact Address:
Mail Stop 954 National Center
U.S. Geological Survey
12201 Sunrise Valley Drive
City: Reston
Province or State: VA
Postal Code: 20192
Country: USA


Personnel
BAERBEL K. LUCCHITTA
Role: TECHNICAL CONTACT
Phone: 928-556-7176
Email: blucchitta at usgs.gov
Contact Address:
U.S. Geological Survey
Branch of Astrogeology
City: Flagstaff
Province or State: Arizona
Postal Code: 86001-1689
Country: USA


TYLER B. STEVENS
Role: DIF AUTHOR
Phone: (301) 614-6898
Fax: 301-614-5268
Email: Tyler.B.Stevens at nasa.gov
Contact Address:
NASA Goddard Space Flight Center
Global Change Master Directory
City: Greenbelt
Province or State: MD
Postal Code: 20771
Country: USA



Creation and Review Dates
DIF Creation Date: 2003-04-29
Last DIF Revision Date: 2012-12-12
Future DIF Review Date: 2004-04-29

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