Marin Dahl and Jarle Krisitansen have to place the calibration sphere within a circle 2,5 meters wide at 30 meters depth.
- Preferably, you should calibrate in the waters where you do the measurements. The conditions might differ from one place to another. Also, things might have happened on the long journey from Norway to the Antarctic Ocean that might have influenced the instruments, Rolf Korneliussen says. He is responsible for the acoustic measurements on this research cruise.
After our visit to the old whaling station at Grytviken, we have relocated to another fjord along the South Georgia rugged coastline. We have anchored up outside another old whaling station, Stromness. This is where the Germans stop to calibrate their acoustic equipment when they are on research cruises in this area.
Different echo sounders must be calibrated using different spheres. Martin Dahl is about to swap spheres.
A major challenge is to get the boat to be as still as possible in the water. During the calibration, spheres are lowered 30 meters below surface, or 20 meters below the hull. The researchers know the echo of this sphere, which is then compared with the measured echo. The echo is measured directly below the boat and in a horizontal circle 2.5 meters in diameter. Different spheres are used for different frequencies.
There are several potential sources of disturbance. Gusts of wind coming down the valley make the ship move. Curious seals can move the sphere around in the water and even run of with the thing. Calibration made slow progress in the beginning, but picked up speed towards the night.
The volunteers from Husvik whaling station visiting G.O. Sars: Thorfinn Myhre, Colin Doole, Henrik Kulms, Hans Kristian Røkenes og Eirik Myhre (left to right).
This morning we had visitors. In Husvik, a whaling station close by, five Norwegians are doing maintenance work on the whaling manager’s house. A few cruise participants from G.O. Sars went ashore in Stanley on the Falkland Islands where they ran into one of the volunteers spending three weeks doing maintenance work in Husvik. He invited them to visit.
- This morning there were several Zodiacs transporting tourist to and from their cruise ship. Amongst these zodiacs came another boat with different people. We assumed this would be some Russians who had promised over the radio to deliver a weather forecast. But when we approached them, we were greeted in a distinct northern Norwegian dialect, Thorfinn Myhre says.
The five are not paid for their work, but the South Georgia Heritage Trust covers expenses and supplies. Local businesses from Sandefjord, where several of them are from, sponsor them with equipment, food and more.
They did not hesitate for one second when the first officer of G.O. Sars invited them to visit the research vessel. They got the full tour of the ship, had a shower and ate a warm lunch before returning to Husvik.