Glenn Hyland

Examining the interaction between multi‐year landfast sea ice and the Mertz Glacier Tongue, East Antarctica: Another factor in ice sheet stability?

The Mertz Glacier tongue (MGT), East Antarctica, has a large area of multi-year fast sea ice (MYFI) attached to its eastern edge. We use various satellite data sets to study the extent, age, and thickness of the MYFI and how it interacts with the MGT. We estimate its age to be at least 25 years and its thickness to be 10-55 m; this is an order of magnitude thicker than the average regional sea-ice thickness and too thick to be formed through sea-ice growth alone. We speculate that the most plausible process for its growth after initial formation is marine (frazil) ice accretion. The satellite data provide two types of evidence for strong mechanical coupling between the two types of ice: The MYFI moves with the MGT, and persistent rifts that originate in the MGT continue to propagate for large distances into the MYFI. The area of MYFI decreased by 50% following the departure of two large tabular icebergs that acted as pinning points and protective barriers. Future MYFI extent will be affected by subsequent icebergs from the Ninnis Glacier and the imminent calving of the MGT. Fast ice is vulnerable to changing atmospheric and oceanic conditions, and its disappearance may have an influence on ice tongue/ice shelf stability. Understanding the influence of thick MYFI on floating ice tongues/ice shelves may be significant to understanding the processes that control their evolution and how these respond to climate change, and thus to predicting the future of the Antarctic Ice Sheet.

Digital elevation models for the Lambert Glacier-Amery Ice Shelf system, East Antarctica, from ERS-1 satellite radar altimetry

The Lambert Glacier-Amery Ice Shelf system is a major component of the East Antarctic ice sheet. This paper presents two digital elevation models (DEMs) that have been generated for the Lambert-Amery system from validated European Remote-sensing Satellite (ERS-1) radar altimeter waveform data. The first DEM covers the Amery Ice Shelf only, and was produced using kriging on a 1 km grid. The second is a coarser (5 km) DEM of the entire Lambert-Amcry system, generated via simple averaging procedures. The DEMs provide unprecedented surface elevation information for the Lambert-Amery system and allow new insight into the glaciology of the region.

ARISE (Antarctic Remote Ice Sensing Experiment) in the East 2003: Validation of Satellite-derived Sea-ice Data Product

Abstract Preliminary results are presented from the first validation of geophysical data products (ice concentration, Snow thickness on Sea ice (hs) and ice temperature (TI) from the NASA EOS Aqua AMSR-E Sensor, in East Antarctica (in September–October 2003). The challenge of collecting Sufficient measurements with which to validate the coarse-resolution AMSR-E data products adequately was addressed by means of a hierarchical approach, using detailed in situ measurements, digital aerial photography and other Satellite data. Initial results from a circumnavigation of the experimental Site indicate that, at least under cold conditions with a dry Snow cover, there is a reasonably close agreement between Satellite- and aerial-photo-derived ice concentrations, i.e. 97.2±3.6% for NT2 and 96.5±2.5% for BBA algorithms vs 94.3% for the aerial photos. In general, the AMSR-E concentration represents a Slight overestimate of the actual concentration, with the largest discrepancies occurring in regions containing a relatively high proportion of thin ice. The AMSR-E concentrations from the NT2 and BBA algorithms are Similar on average, although differences of up to 5% occur in places, again related to thin-ice distribution. The AMSR-E ice temperature (TI) product agrees with coincident Surface measurements to approximately 0.5˚C in the limited dataset analyzed. Regarding Snow thickness, the AMSR hs retrieval is a Significant underestimate compared to in situ measurements weighted by the percentage of thin ice (and open water) present. For the case Study analyzed, the underestimate was 46% for the overall average, but 23% compared to Smooth-ice measurements. The Spatial distribution of the AMSR-E hs product follows an expected and consistent Spatial pattern, Suggesting that the observed difference may be an offset (at least under freezing conditions). Areas of discrepancy are identified, and the need for future work using the more extensive dataset is highlighted.

External influences on the Mertz Glacier Tongue (East Antarctica) in the decade leading up to its calving in 2010

This work was supported by the Australian Government’s Cooperative Research Centre (CRC) program through the Antarctic Climate & Ecosystems CRC, and Australian Antarctic Science Projects 3024 and 4116 and contributes to WCRP Climate and Cryosphere (CliC) project Targeted Activity Interactions Between Cryosphere Elements.

Interannual variability of Antarctic snow melt events derived from scatterometer data

Microwave backscatter from the Antarctic snow cover depends on the surface roughness, properties and structure within the snow cover, and moisture content. Small increases in moisture content produce a significant reduction in backscatter. This acts as a sensitive indicator of the occurrence of snow melt conditions. The ERS wind scatterometers provide an almost continuous sequence of observations of microwave backscatter coefficients over Antarctica north of latitude 79/spl deg/S since August 1991. Normalised values of the backscatter coefficient are calculated by removing the anisotropic contributions, mainly from a dependence on incidence angle. Depression of these values below a long term dry snow average indicates occurrence of snow melt. The results show a large variability between summer seasons of melt extent and duration. There was very extensive and intense melting in 1991-92, with much less melt in following seasons probably in response to a cooling following the Pinatubo eruption. 1997-98 has extensive melt with a total area approaching that for 1991-92.

A Semi-Automated Line Tracing Technique for Monitoring Ice Margins in Antarctic Images

The current shape and rate of change of the margins of the Antarctic ice sheet are poorly known. Since polar regions are inhospitable, remotely sensed images provide an invaluable data source for studying the ice margin. These images can be examined by a human expert or processed automatically by a computer. This paper describes the design and implementation of a semi‐automated technique to trace ice margins in Synthetic Aperture Radar images. The technique is based on a deformable contour model derived from the Kass et al. active contour model and Lobregt and Viergevers discrete dynamic contour. The contour is initialized by the user, to approximate the margin, and the deformation process causes the contour to accurately mould itself to the shape of the margin. The technique has been tested on a number of different images, with acceptable results in most cases.

Mapping the Antarctic ice sheet margin and grounding zone for change detection

We have undertaken mapping of the ice sheet margin and grounding zone in East Antarctica using Landsat TM and ERS SAR images in order to establish an accurate baseline for the detection of future change. As part of this work we have implemented a computer-aided edge-following algorithm to provide an objective and consistent mechanism for analysis of different images. Accurate geocoding of the images is achieved with sparsely distributed ground control points and a transformation of the images which preserves their inherent geometric properties and internal positioning accuracy. An initial comparison with published maps has identified significant changes in several large ice shelves.