FROM THE AIR

Ashburton Guardian, Volume 50, Issue 261, 18 August 1930, Page 8

FROM THE AIR

MAPPING AUSTRALIA. HOW PHOTOGRAPHY HELPS. Tremendous strides have been made in recent years -in aerial survey, and Australia is to reap the benefit, for the Air Force is about to commence a survey of about 500 square miles of land that . has mever before been mapped. Other areas will be tackled subsequently, and it is likely that before the end of the year 3000 square miles will be surveyed from the air. A considerable amount of this class ot work has already been done by the Australian Air Force, the jobs including ordinary topographical mapping, photographs for the Navy Department for charting purposes, town surveying for municipal purposes, forestry survey work for oil research at Papua, and the photographing of areas in South Australia to ascertain the geological structure of the earth. The camera used for the work is of a special type which is mounted in the observer's cockpit in the plane, with the lens pointing through a hole in the floor. Each picture taken is 7ii». by 7in., and is adaptable for scale of from one in 2000 to one in 25,000. Most of the work is done with the aeroplane at a height of 12,000 ft. The pictures are taken in parallel strips on a film, one of which is sufficient to photograph a total area of nearly 200 square miles. This area can. lie photographed completelv in about two and a-half hours. Each picture on the film is an individual one, the outer portions of which overlap a portion of the picture on the previous film. This ensures that no part of the territory is left unphotographed. No Margin for Error. Every picture taken, is automatically numbered by the special apparatus m the camera, which also records on the film the height at which it was taken, the levels of the plane, the date, and the time to the nearest second, lhrs leaves no margin for error when the photographs are being pieced together lor the completed mosaic. A special stereoscopic instrument enables contours to be correctly indicated. Ihe temperature at 12,000 ft. is usually about zero or below, and botii pilots and photographers have to be expertly trained to carry out the work successfully. The plane has to be kept on a straight course up and down the area being photographed,' and must be kept level and at" a uniform height. Flight-lieutenant G. Packer, the Air Force expert on aerial survey work, who explained the process of operation, said that bying was not as expensive as was generally thought. J lie cost for continuous operation m aerial survey was about 10s a square mile. He added that a certain amount oi ground work was usually necessary for the most successful survey. One of the biggest aerial jobs done recently by the Air Force was the mapping of t>UU square miles in the vicinity of Sydney. This was done for the local authorities to help them when making sewerage and water connections. The Air J'orce was paid for the actual cost of the work, and benefited from the experience given to pilots and photographers.