2002-2003 Part 2
Mapping and Geographic Information Centre (MAGIC) Diary
After a few days of bad weather at Rothera spent checking and modifying our GPS equipment, on January 6 we were able to undertake aerial photography and GPS survey of the Corner Cliffs/Citadel Bastion area of southern Alexander Island, about 2 hours flying time south of Rothera. This is preparatory work for a large-scale topographic map of this unmapped but scientifically important area. A horseshoe ridge of fossil-rich sedimentary rocks encloses a 90 metre-deep lake. A programme studying the lake sediments promises to reconstruct the past climate of the area and the history of the major George VI Ice Shelf nearby.
Above: Citadel Bastion and Corner Cliffs from over the George VI Ice Shelf. The mountains of Alexander Island are beyond. Click the images to enlarge it.
Our project involved establishing a GPS base station at the aircraft landing site and then travelling over the area collecting decimetre accuracy GPS surveyed points on conspicuous ground features, and measuring the altitude of the lake surface.
Working as two teams, helped by field assistant Neil Stevenson and Operations Manager Mike Dinn, we were able to do all the survey work in one very long day. Progress between the survey points was slow; trudging through above-the-knee soft snow and traversing unstable scree covered slopes. There are no paths in Antarctica! We were surprised to find occasional patches of luxuriant lichen growth in this otherwise barren but starkly beautiful landscape.
On our return to Rothera, David Lee the weather forecaster, who is on loan to BAS from the Meteorological Office, was predicting improving conditions for the northern Antarctic Peninsula and on the 8 and 9 of January we were able to acquire aerial photography of the Grandidier Channel, about 300 Km north of Rothera. This work is part of cooperation between BAS and the UK Hydrographic Office. The photography will be used for updating hydrographic charts of this region.
This area has some of the most spectacular scenery in Antarctica with towering mountains rising 2000 metres directly from the sea and iceberg choked bays backed by sweeping glaciers and tumbling chaotic ice falls. Interestingly, we were easily able to see significant changes in the coastline since the 1989 satellite image we had used for our flight plan. In many places glaciers have retreated hundreds of metres creating new bays, and rocky headlands previously connected to the mainland by ice are now true islands.
For logistical reasons mid-January was an ideal window for us to go over to tackle our aerial photography project on the Brunt Ice Shelf, operating out of Halley research station. Halley sits on the floating ice shelf and there is concern over its long-term stability and thus the future of the station. Our main task was to fly high-altitude aerial photography of the ice shelf to give an up-to-date, high-resolution overview to complement airborne geophysical studies and ground measurements.
A secondary task was to take low-altitude aerial photographs of the base itself. At Halley the main buildings are several metres clear of the ground on jackable legs, but all objects on the surface, such as subsidiary buildings, shipping containers, vehicles and drum depots have to be spread out to minimise drifting by blowing snow. A large-scale plan of the base area with a photographic backdrop will assist management of the wider base area.
To emphasise the subtle surface features the ice shelf photography was undertaken during the night when there is a low sun-angle and shadows are at a maximum. There is no darkness at Halley until February 15. We used differential GPS to track the flight path of the aircraft during the sortie and generate scene-centre coordinates so that each photograph could be tied to its geographic position on the ice shelf.
Above: Adrian setting up the differential GPS system prior to take-off . The receiver is connected to a GPS antenna mounted on the aircraft roof directly above the camera. The airborne positions are referenced to a ground base station to achieve accuracy of a few metres.
Seeing from the air every feature of the ice shelf, ice cliffs and canyons and shattered ice features of the 'hinge zone' (where the floating ice shelf meets the grounded continental ice sheet) in high relief by the late evening light was a magical and unforgettable experience. At 15,000 feet Halley is just a tiny speck in a vast white wilderness and really brought home to me the isolation of this most remote BAS station.
The interaction of the ice shelf, open sea and enormous continental ice mass is 'meteorology in action' and one could often see clouds forming and dissipating before your eyes. Sometimes there were five different types of cloud in the sky, or at ground level, at once! However we did eventually get the required clear skies and captured the aerial photography over three nights between 16 and 23 January.
The flight between Halley and Rothera needs two refuelling stops en route, each of which have to have good weather. It is common to wait for days before setting out on this journey, but we were lucky and were able to fly back to Rothera on January 26. One of our refuelling stops was at a small depot on the Ronne Ice Shelf. The only sign on the ground was an empty fuel drum on a pole, but this marker showed up clearly on the aircraft's radar. We then had to dig up four drums of fuel, buried under a metre of snow and pump them into the aircraft, using a small pump carried for this purpose, before proceeding on our way.
When we returned to Rothera the US Coastguard vessel Laurence M. Gould was visiting Rothera for some collaborative work with BAS marine biologists and to take part in an oil-spill response exercise. As it was Saturday night a lively party was underway, with a performance by the Rothera band for the visitors, but we had been warned to expect good weather for aerial photography the next day and so retired early!
On Sunday 27 the meteorological satellite imagery received at Rothera each morning showed our remaining eastern Palmer Land target to be clear, probably for the first time this summer. A long, but successful day of aerial photography under an azure sky in this area notorious for cloudy weather capped a very productive January for the MAGIC team.
Alison Cook and Adrian Fox