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Applications of ERS satellite radar altimetry in the Lambert Glacier-Amery Ice Shelf system, East Antarctica


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Phillips, Helen Amanda 1999 , 'Applications of ERS satellite radar altimetry in the Lambert Glacier-Amery Ice Shelf system, East Antarctica', PhD thesis, University of Tasmania.

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The Lambert Glacier-Amery Ice Shelf system is a major component of the East
Antarctic ice sheet. Few accurate elevation data exist for the system, and many of
its important glaciological parameters remain uncertain, including the mass
budget and location of the grounding zone. This study uses European Remote
Sensing satellite (ERS) radar altimeter waveform data to expand knowledge of the
system's structure and surface properties.
Surface elevations are derived by retracking ERS-1/2 altimeter waveforms,
making corrections for slope-induced error and tides, and are validated against insitu
Global Positioning System (GPS) observations. Elevation differences, at the
intersections of the ERS-1 ground tracks with the GPS survey, have a mean of
, 0.0 ± 0.1 m and RMS of 1.7 m, and are spatially correlated with topographic
variations. Two Digital Elevation Models (DEMs) are constructed from the
calibrated altimeter heights: one on a 1-km grid for the Amery Ice Shelf only
(AIS-DEM), which exhibits unprecedented resolution, and another on a 5-km grid
for the entire basin (LAS-DEM). The altimeter DEMs allow new insight into the
glaciology of the system.
The AIS-DEM is combined with measured ice thicknesses and a simple density
model to derive a 'hydrostatic height anomaly' term (i.e., the excess height above
that required for buoyancy). Where this term is close to zero indicates floating
ice; this occurs over most of the ice shelf and up the trunk of the Lambert Glacier.
Significantly positive values of the term occur around the, margins of the floating
ice, identifying the location of the grounding zone. A region in the north-west of
the shelf, where the ice is known to be afloat, displays anomalous values of the
hydrostatic height anomaly term. This is an area of marine ice accretion, where
the ice thickness sounder only detected the upper boundary of the accreted layer.
These results reveal that the Amery Ice Shelf extends much further south than
previously reported, and that the marine ice is up to 200 m thick, oriented along
the ice flow direction and restricted to the west of the shelf.
The LAS-DBM is used to define flowlines for the grounded ice within the
drainage basin, where the average surface slope determines ice flow direction.
These are combined with accumulation distributions to derive balance fluxes for
the system. Comparison with flux measurements from a traverse program
suggests that the interior of the system has a slightly positive mass budget. The
DEMs also provide reference surfaces against which to monitor any future
Near-surface snow parameters are estimated from the ERS waveform data using a
surface arfd volume scattering model in the retracking. These indicate that surface
scattering dominates the altimeter return power over most of the ice shelf, whilst
volume scattering predominates elsewhere. Standing water is detected on the ice
shelf by the occurrence of specular returns. This melt-water flowed along surface
troughs observed in the AIS-DEM. Backscatter observations along a 3-day repeat
track of ERS-1 showed variations in meltstream onset, extent and duration
between the 1991-92 and 1993-94 summers.
This study, using derived high-precision altimeter products, has quantified many
parameters of the Lambert-Amery system that were previously unknown, and
provided a reference against which to monitor any future change in the system.
The new findings are consistent with observed in situ data and sub-ice shelf model
results, and provide credence for the long-term use of altimetric data for ice sheet

Item Type: Thesis - PhD
Authors/Creators:Phillips, Helen Amanda
Keywords: Ice sheets, Ice sheets, Ice sheets, Ice sheets, Sea ice, Sea ice
Copyright Holders: The Author
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Additional Information:

Thesis (Ph.D.)--University of Tasmania, 1999. Includes bibliographical references

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