Difficult Calibration Campaign for the EM-Bird

Published on 09.05.2007 - Total Pole Airship

The calibration campaign that was envisaged for this Spring 2007 has just been finished by Jean-Louis Etienne and his team prior to the delivery of the airship and its first test flights. The Total Pole Airship's first steps were beset with problems.

Before being able to hang the EM-Bird below the airship and to fly over the Arctic pack ice in order to measure its thickness, Jean-Louis Etienne had wanted to go to the North Pole in order to calibrate what he calls the "electromagnetic bird" (EM-Bird) and thereby to satisfy himself that his measurements were correct.

For this calibration to be accurate, it was naturally necessary to have an accurate knowledge of the pack ice sample (an ice slab of 200 metres by 60) that was going to be used as the yardstick for the experiment. A simple mapping of the underneath of the pack ice. The enterprise was no easy matter to achieve because the information collected beneath the pack ice can change at a rate of knots. As proof, the fault that abruptly opened in the pack ice on April 26th last at the Barneo station, which saw a Russian bulldozer sink 4,000 metres to the bottom.

In fact, things started pretty badly for Etienne and his team. Hardly arrived at Barneo (Sunday April 15), they saw the Antonov that had deposited them there taking off earlier than envisaged and bumping into the crates in which two and a half tons of the expedition's equipment were stacked. Result: a night of repairs for the EM-Bird, which had been violently shunted between two blocks of ice, and ditto for the little ROV robot (Remote Oceanographic Vehicle) envisaged for photographing and measuring the underneath of the pack ice!

On April 17th, Etienne and Christian Haas of the Alfred Wegener Institute (which had developed the EM-Bird) flew off aboard an MI8 (below) from which the EM-Bird has hanging at the end of a 30-metre rope. They were due to take the first measurements at 350 km from the pole. But the bad weather had made them turn back.

The following day, the first dives were made beneath the selected pack ice sample, intended to prepare for the ROV's dive. Then, there was the fine-tuning of another robot, the "Super Achilles┬╗, which had to guide the ROV beneath the ice. In short, several days of preparation were necessary for testing the EM-Bird's qualities. But at the moment of the first actual overflight of the pack ice (Thursday, April 26th), another major setback: the device broke down because of an electrical problem that had occurred on the MI8 helicopter that was transporting it. Jean-Louis Etienne's team then had to call upon a lighter instrument, the EM Turtle, which takes the same ice measurements, but from a sledge.

Here in any event are the results of this first phase of the Total Pole Airship Expedition, as published by Jean-Louis Etienne's website: "For Christian Haas, the results of this mission are unique: he has never had so much time and as many means at his disposal for modelling the pack ice, essential for the validation of his measurements. Jerome Boutain has put the topography of the lower surface on to his computer screen, on the basis of the points read by the altimeter installed on the ROV. According to the divers, who were able to find all the breaks of terrain under which they had been diving for ten days, the rendition was surprisingly accurate. The accuracy of the mapping of the pack ice's upper surface reflects the constancy, application and time that Yves Egels has spent alone, in the cold and in winds of every kind, at the foot of his laser scanner. He still had to traverse the pack ice with the thickness-measuring instrument. For want of the EM-Bird, damaged by an electrical charge accident, Christian Haas and Samuel Audrain covered the area with the EM-Beetle (the name preferred by Christian to EM-Turtle). The correlation between the measurements of the airborne device and the one used on the ground is known, which has enabled the EM-Bird to be validated despite this incident."

"The results are then going to be correlated and interpreted (surface, underwater part, and the thickness of the snow). Christian Haas considers that this will be a significant contribution to the interpretation of the Cryosat measurements, the European Space Agency satellite that will be launched in 20O9 March in order to measure the thickness of the ice. He is also confirming that the ice is thinner compared to the measurements that he took in 2001. The melting of the pack ice over the years is confirmed."

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