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Glacier Scanning

Peter Johnston, I-SiTE Product Manager, Sydney

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In December 2004, a laser scanner was used to map the position of an Antarctic glacier. The project's aim was to investigate the possibility of monitoring long-term glacier movement using terrestrial laser scanners. This was done as part of the ongoing research being carried out by Assoc. Prof. Sean Fitzsimons of the University of Otago, New Zealand, who has been looking into the mechanisms of several Antarctic glaciers.

glacierscanning2Similar glacial measurements have been collected in the past using terrestrial photogrammetry or by monitoring a small number of discrete reference points adjoining the glacial apron. Two of Assoc. Prof. Fitzsimons' research sites had been monitored using these methods. It was hoped to compare this data, thus proving the reliability of the technique, and also providing immediate comparison with past movement for both glaciers. The research sites are in the McMurdo Dry Valleys, Victoria Land. Most research in this area is supported from New Zealand's Scott Base, or USA headquarters, McMurdo Station.

Travel to these distant sites is primarily by helicopter, with local travel on foot. The compact size and ease of deployment of the scanner (an I-Site 4400) was well suited to this challenging environment. The Victoria Upper Glacier in the Victoria Valley was the site of the first scan.

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In the 1980s, Trevor Chinn, of the then NZ Ministry of Works, undertook research here using a Wild photo-theodolite. One of his survey control points was located by Assoc. Prof. Fitzsimons and Shelley MacDonell in 2003, and was used in this project to provide a common reference system. A second point used for the 1980s projects can be linked indirectly via the 2003 research.

Eight scans were recorded in around three hours, covering approximately 1 km of the 35 m high glacier face. The second site, the Suess Glacier, is in the Taylor Valley. This was the first of the dry valleys to be discovered, by accident in the early 1900s when members of Captain R. F. Scott's party became lost. After walking down the valley past Suess Glacier, they retraced their steps to the head of the valley and continued on their way. Today, the same area is serviced by Bell 212 helicopters.

At this site, two existing control points were able to be used, one of which is known to have been used by T. Chinn, while the second is presumed to have been.

A total of five scans was recorded in around 2.5 hours to cover approximately 500 m of the glacier face and surrounding terrain. The laser scanner provided a motorised survey telescope which enabled accurate and easy backsighting for alignment, as well as automated scan data geo-location when the existing survey control was used. At both sites, scanner locations were selected to provide coverage along the ice cliff. Each station was fixed by survey for later combining of adjoining scans.

The original intention was to collect a dataset during the summer season, with a proposal to revisit the sites in May 2006 or June 2007 for a comparative survey.

However, on the third day in the Victoria Valley, a significant icefall from the glacier provided an opportunity to measure the volume of ice which fell. On a small scale this would simulate the expected situation on follow-up visits. The area of the fall was rescanned from approximately the same location as before thus providing a record of the event. A tense 30 minutes followed while the scanner was set up and orientated, and the scan was carried out with the sound of cracking ice directly above. The efficiency of the scanner was greatly appreciated!

Modelling of the surveyor laser scan data was completed entirely in Studio 2.4 software. Individual scans were modelled to preserve overhanging areas common in the ice structures and a pair of fusion surfaces were created with triangle sizes of 0.5 m and 1 m. The resulting two surfaces covered the total 1,500 m of glacier face, composed of data from 13 different scans. The volume of ice which slipped was calculated to be 1,400 m³.

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Scanning was carried out by Measurement Solutions of NZ and all results were generated using I-SiTE Studio 2.4 software. Thanks to Jofe Jenkins, Measurement Solutions NZ and Assoc. Prof. Sean Fitzsimons, Geography Department, University of Otago.

© 2009 Department of Geography, University of Otago, Dunedin, New Zealand