21 Dec to 4 Jan - GPS Surveying
Map of the Antarctic Peninsula showing locations referred to in the diary.
21 December: Some problems with the cable connections in the aircraft had caused camera failure on the December 19 test flight, but a second short test flight over Rothera station showed that these problems had been resolved. We sliced about two metres of film from the end of the 80 metre film roll and hand-developed it in the Rothera darkroom to establish that the camera was now working correctly.
The Rothera area is breathtaking viewed from the air. Today the shifting brash ice off the Rothera wharf made fascinating patterns. The illustration shows a mosaic of test aerial photography over Rothera Research Station, taken on 21 December 2000, showing the base buildings, wharf and offshore brash ice.
22 December: Giles Wilson (BAS pilot) laid a depot of ten drums of aviation fuel in eastern Palmer Land for later use during our air-supported GPS surveying project.
23 December: Technical problems have been discovered with both the Twin Otter aircraft fitted with the adaptations necessary for aerial photography. Both aircraft need repairs by a specialist engineering team flying in from Canada, but they are not due to arrive until January 7. This means that the aerial photography work has to be suspended until one of the aircraft is flying again.
24 December: A third Twin Otter aircraft was brought back from Halley research station today. Whilst this aircraft is not suitable for aerial photography it can be used for the air-supported GPS work. However there were inevitably heavy demands on this aircraft which was now doing a double workload moving and resupplying field parties as well as cargo and depot tasks. It was clear that it would be after Christmas before the MAGIC team would be able to use the aircraft for GPS survey work.
This provided a welcome opportunity for some recreational skiing and mountaineering in the Rothera local area, including building an igloo! and meant that we were at Rothera for an excellent traditional Christmas dinner of turkey with all the trimmings.
31 December: The availability of an aircraft together with the forecast of good weather finally allowed us to begin our air-supported GPS survey task, working as a team of four; Adrian Fox and Olivier Cottray (MAGIC), Florian Piper (GA) and Giles Wilson (pilot). The image shows the GPS surveying team - left to right AF, OC, FP & GW.
The geology of eastern Palmer Land is an important area of BAS research involving an extensive fieldwork programme in forthcoming field seasons. However the area between 72°30' and 75°30' South and 61° to 64° West, about 350 km north to south, (further than London to Leeds) is very poorly mapped and MAGIC will be producing a series of maps based on Landsat Thematic Mapper (TM) satellite imagery to support field travel and geological mapping. The first stage of this process is to 'georeference' the satellite imagery (adjust the raw imagery to its correct scale and orientation). This requires the use of features which can be identified on the satellite scene and whose positions are accurately known by surveying. In this area there are only three accurately surveyed points, from a joint BAS/United States Geological Survey (USGS) expedition in 1976.
The MAGIC survey work involves using these existing surveyed points as a starting point for generating a large number of new accurately surveyed points using 'Differential GPS surveying'. Using this technique one receiver collects GPS data at a known point (the 'base station') whilst a second 'roving' receiver simultaneously records GPS signals at a new point. The ideal location for a new point is on a small conspicuous nunatak (rock outcrop); candidate nunataks in the optimum positions for georeferencing the TM scene had been previously identified on the imagery. Later analysis, relating the two sets of readings, allows many of the errors, for example those due to atmospheric effects, to be largely eliminated, so that a position for the new point can be calculated with an accuracy of better than a metre. The image shows a GPS base station, linked to one of the BAS/USGS survey points on a nearby mountaintop.
Our initial plan was to start at the northern end of the area, and work southwards to finish at the BAS Sky-Blu field station. Landing a Twin Otter aircraft on skis in open, unvisited country, on an unprepared surface is a difficult and highly skilled operation, which requires good light conditions so that the pilot can accurately perceive the snow-covered surface. Today rapidly deteriorating weather forced a move to Sky-Blu without achieving any survey, but the aircraft was kept busy moving a glaciology field party to a new site to the south-east.
After a long but disappointing day, New Year's Eve was celebrated at Sky-Blu field station with the small team of BAS staff who maintain the blue-ice runway and give regular weather reports for aircraft movements.
1 January 2001: Today thick cloud, indicating poor visibility, showing on the meteorological satellite imagery received at Rothera precluded survey landings in eastern Palmer Land.
2-3 January: Clear skies today at last allowed us to start the survey work but, after achieving one northernmost survey point, encroaching cloud and deteriorating visibility forced us to the southern part of the area, effectively racing ahead of the incoming poor weather. Working in Antarctica sometimes means changing plans at short notice and making the most of limited good weather by working round the clock. We finished surveying at 2 am having achieved all the points from the southernmost base station, and then camped there overnight. It was a satisfying feeling having achieved a substantial portion of the project at last.
In previous field seasons similar work has been approached by travelling overland between the points using skidoos and sledges, which is time consuming and sometimes arduous. Using the aircraft to hop between the new survey point locations, covering 50 km in only a few minutes allowed much more work to be achieved in a day.
We spent the early part of January 3 at Sky-Blu downloading the GPS data to a laptop computer ready for post-processing. Meanwhile the aircraft flew to Haag Nunataks at 77° South to bring out a depot of equipment left there by a previous field party. In the late afternoon we headed north to Fossil Bluff field station (71°30' South) hoping for clearer weather at the northern end of our survey area so that work could continue the next day.4 January: After staying overnight at Fossil Bluff it was clear that the weather in eastern Palmer Land was deteriorating rather than improving, so we returned to Rothera to process our work so far and await the next spell of good weather to continue with the survey.