The North Pole lies in the middle of the Arctic Ocean, which is covered by a sea-ice pack whose thickness is not known accurately. The aim of the Total Pole Airship expedition is to take thickness measurements over wide areas of the ice pack. In April-May 2008, we will fly from one side of the ice pack to the other in an airship carrying underneath it an electro-magnetic device called the EM Bird. This device, developed by Dr Christian Haas of the Alfred Wegener Institut (Germany's polar institute), will measure ice thickness as it flies along 20 metres above the ice.
A year prior to this expedition, we will be carrying out a calibration or “ground-truthing” campaign to determine how accurate EM Bird measurements are. In the region of the Pole, we will select a plot of sea ice 200m x 60m lying across a pressure ridge where the ice thickness is uneven. We will then overfly the zone with the EM Bird slung underneath a helicopter. This will give the “EM Bird” thickness. This data will then be compared with the “real” thickness of the ice plot derived from 3D topography.
Topography of the upper surface of the ice will be carried out by Prof. Yves Egels of France's National Geographic Institute (IGN) using an aerial laser scanner and photo-grammetry. Topography of the under-surface of the sea ice will be carried out using a wire-guided submersible (ROV) equipped with an upward-looking sonar (ULS). The ROV will be piloted by a team on the ice, with the electronics and monitor set up in a heated tent. The exact position of the ROV will be determined using acoustic devices placed under the ice by divers. The ROV will take measurements in a grid pattern yielding an underwater profile of the plot of sea ice being studied.
By superimposing the surface and subsea profiles we can determine the real thickness of the sea ice, which can be fed into a 3D model. Comparing the model with the thickness measurements taken by the EM Bird will give us a “mistake coefficient” to apply to future EM Bird measurements to ensure that they are accurate.
The EM Bird ground-truthing campaign will be conducted from 13 to 27 April, using as a base Russia's Borneo Station located at 89°N.