Aerial photography at BAS
BAS uses a Zeiss RMK aerial photography camera with a 153 mm (6") focal length lens for aerial photography. Two of the four Twin Otter aircraft are fitted to take the camera system.
The camera sits in a pit near the rear cargo doors, pointing vertically downwards through a hole in the aircraft belly. A motorised mounting ring keeps the camera level during flight and rotates it to compensate for any crabbing of the aircraft due to side winds. A navigation periscope looks downwards and forwards through a hole near the front of the aircraft. The whole system weighs about 165 kg - it's not a 'Box Brownie'!
Above: Left - the BAS Zeiss aerial photography camera, comprising of a mounting ring, camera body, film magazine and control box (back left) fitted in a Twin Otter. Right - the navigation periscope. Note the 'magic eye' just behind the front wheel.
Each aerial photograph is 23 cm x 23 cm and we use 80 m of film in each reloadable magazine. For mapping and fieldwork reconnaissance photography we normally fly at 15,000 feet, so that each photo covers a ground area of 6.9 x 6.9 km. This means that clear weather with no cloud below 15,000 feet is needed! We usually take the photos with 60% overlap and 20% overlap between adjacent strips to allow stereo-viewing and map compilation using photogrammetry. The photography is usually panchromatic (black and white) but colour and infra-red film may be used for special purposes. Sometimes aerial photography is acquired at lower altitudes for other projects such as detailed mapping of the BAS bases or penguin census.
Sorties are flown following a flight plan prepared on 1:100,000 scale extracts from Landsat satellite imagery because there are usually no good maps of the target areas. One team member operates the navigation periscope, communicating with the pilot to keep on the flight line, controlling the interval between the photos and applying corrections for crab. The other team member keeps a detailed record of the sortie, changes the film magazine when required and monitors the camera.