bild

Weather balloon. Meteorologist launching a weather balloon. The balloon, which is made of rubber and filled with helium, carries aloft an ozonesonde, an instrument that detects ozone in the atmosphere and sends its measurements back to a base station using a radio transmitter. As the balloon gains altitude, and the local pressure drops, the balloon expands. Eventually, at around 35,000 metres, the balloon bursts and the ozonesonde is returned to Earth by a small parachute. The measurements will be used to study the depletion of the polar ozone layer. Helium is used for night launches, but hydrogen is used in the day. Photographed at the Arctic Research Centre, Sodankyla, Finnish Lapland. (KEYSTONE/SCIENCE PHOTO LIBRARY/DAVID HAY JONES)