Grounding line mapping in
Antarctica using 15 years of
DInSAR data
Jérémie Mouginot1
Eric Rignot1,2, Bernd Scheuchl1
1
University of California, Irvine
2 Jet Propulsion Laboratory
Outline
• Introduction
– Definition
– Why grounding lines delineation is important ?
• DinSAR mapping
– Methodology
– Datasets
– Results
– Comparisons & Discussion
Grounding Lines - Definition
• Grounding lines (GL) are the
boundary between grounded
and floating ice.
• Different flow regimes of
grounded and floating ice are
coupled across the GL.
Huybrechts (2009)
• InSAR is making an immense
contribution, with its ability to map
and monitor GL location on a
large scale and to unprecedented
horizontal accuracy.
Grounding lines dynamic
• The ice sheet–ice shelf transition zone are a
key parameter for marine ice sheet
dynamics.
• It may allow especially rapid response if the
ice sheet to changes in climate
Van der Veen, Fundamental of Glacier Dynamics
Methodology
• Same time interval with the exact same imaging
geometry, i.e. same satellite track.
• To form the interferogram, we migrate image
pixels by calculating the motion field using a
speckle tracking technique [Michel and Rignot,
1999]
• Interferogram = range displacements
surface topography
+ imaging geometry
+ glacier flow
+ tidal flexure of floating ice
ALOS 2007 Track171
Methodology
• Differencing interferogram removes the
glacier flow signal
• Surface topography (or short differential
baseline) is used to remove topography.
Tidal motion has a distinct signature of elastic
bending
 GL are mapped in range domain with a
horizontal precision of 100 m.
Methodology - Mapping
• limit of tidal flexing (F)
• grounding line (G)
• line of first hydrostatic
equilibrium (J)
• break in surface slope (I)
• maximum extent of the
flexure zone (H)
Data – ERS-1 & -2
•
Earth Remote Sensing Satellite 1 and 2
(ERS‐1/2):
– years 1992, 1994, and 1996
– Antarctic Peninsula, West Antarctica
north of 81°S, Victoria Land and Wilkes
Land in East Antarctica:
– 1 day repeat cycle
– Best for GL mapping strong tidal signal
compared to ice motion
Spaatz Island
En
sh
gl i
Co
as
t
Data - RADARSAT‐1
• RADARSAT-1
–
–
–
–
Year : 2000
East Antarctica
24 day repeat cycle.
Decorrelation is a bit bigger that with ERS
Data - RADARSAT‐2
• RADARSAT-2
• 2009
• areas south of 81°S
• 24 day repeat cycle.
Siple Coast
Data - ALOS
• ALOS PALSAR
– 2007– 2008
– select areas north of 77.6°S
– 46 days
– L-band ; good correlation even
if the repeat cycle is large
Results
Green : ALOS
Blue : R2
Pink : R1
Red : ERS
• We mapped 1.4 million
grounding line points
experiencing tidal
flexure.
• Ice reaches the ocean
at over 28,600 km of
the coastline, or 76% of
Antarctica, of which
22,600 km experiences
tidal flexure.
• Currently working with
NSIDC to make this
dataset available.
Comparison - Region1
Siple Coast
• Excellent agreement between
DInSAR and ICESat
• Same detection principle, but :
ICESat noise of 10–20 cm
[Brunt et al., 2010] vs 1 cm with
DInSAR.
• On Mercer Ice Stream,
DInSAR GL extends 50 km
farther south than delineated
by MOA  break in slope is
not a reliable indicator of GL.
Comparison -Region 2
Victoria Land
• Disparity between DInSAR
and MOA exceeds 50 km on
many glaciers:
– seaward on Aviator,
Borchgrevink, and Tucker
glaciers;
– landward on Lille, Rennick and
Matusevitch glaciers.
• On Rennick Glacier, ICESat &
MOA detects grounding in
the middle of the ice shelf.
DInSAR however reveals that
this is only an ice rise.
Comparison -Region 3
• On Pine Island Glacier, MOA places G
at the inner edge of an already
identified ice plain, 20 km upstream of
the 1996 DInSAR position, in a region
where no tidal motion is detected.
• On Slessor Glacier, the ICESat
delineation agrees with DInSAR,
while MOA’ s is 100–150 km too far
inland.
Grounding Lines retreat
•
Strong evidence that GL is moving
(Rignot, 1998) and that melting is
related to inland thinning (Shepherd et
al, 2004)
PIG 2011 from ERS-2 ice phase
Conclusion
•
•
•
•
First, complete, high‐precision, uniform sampling, seamless mapping of GL
around Antarctica based on 15 years of DInSAR data.
MOA delineation is in large disagreement with tidal motion recorded by DInSAR
in areas of fast flow.
A single interferogram yields errors in GL mapping of several km on fast‐
moving ice  DInSAR method is essential.
Errors yield large biases :
–
–
–
–
in calculated ice fluxes.
in the set up of numerical ice flow models.
in the analysis of ice ocean interactions
or simply the selection of a drill site near an ice stream grounding zone
•
We detected the rapid GL retreat of several major glaciers that drive a large part
of the ice sheet mass budget (e.g., Pine Island, Thwaites, Smith gl.)
•
DinSAR based Grounding Line will be soon available at NSIDC for the science
community
Recommendation
• Acquisition of 3 consecutive cycles is critical
for grounding line mapping.
• Routinely observations over super-sites are
recommend to follow the evolution of major
sea level contributor (Pine Island, Thwaites,
Jakobshavn gl., …)
THANK YOU !
Jeremie Mouginot
Department of Earth System Science
University of California, Irvine
Croul Hall
Irvine, CA 92697-3100
[email protected]