AERIAL SURVEY WORK

Evening Post, Volume CXI, Issue 17, 21 January 1931, Page 8

AERIAL SURVEY WORK

TRIUMPH OF PHOTOGRAPHY

63,000 SQUARE MILES

. (From "The Post's" Representative.) LONDON,1 4th December. .News about the progress of aerial survey work in Northern Rhodesia provides striking illustration of the superiority of air photography over ground survey methods. The area phot&graphed comprises no less than 63,000 square miles. Experienced surveyors estimate that had ground methods alone been available, the j work.of mapping this immense territory would.have occupied more than ten years. | The air-borne camera has completed the photography of the entire area in the phenomenal time of four months. A mosaic of overlapping photographs, some taken obliquely and some taken- vertically, is providing the basis of detailed maps, which will be finished and delivered next June—less than eighteen months after the air surveyors began work. . ■ From the .information thus gathered, geologists, mining prospectors, tax-gather-ers, road and railway engineers, and power and water experts.will be enabled to draw knowledge to assist them in their diverse tasks. The first step in intensive development of the area, in fact, has been taken by the survey aeroplanes. FIRST SURVEY*'PLANE. The time occupied to picture an area of this size is unusually short even in the annals of air survey. Two years might reasonably have elapsed between the taking of the first photo and the last.' The speeding-up is largely due to the employment of a specially designed British twinengined biplane, the first \urvey 'plane built in the world. ■ An air survey craft should possess an uninterrupted view downwards, both vertically and obliquely, sp that the camera may be operated from the cabin or cockpit without obstruction from any part of the aeroplane. ; The pilot must have unrestricted view; on him rests the responsibility of steering the aircraft accurately up and down over the strips of country photographed. Immunity from forced landings, especially in- desolate or little known territory, is desirable. The British survey 'plane used by the Aircraft Operating Company in "Northern Rhodesia, equipped with two 500 h.p. motors, is able to maintain level flight at a height of 9000 feet on the power of one engine alone. On full power the machine climbs rapidly to 20,000 feet,.and can fly there for as long as seven 'hours at a time without descending to re-fuel. This quality of endurance makes possible the survey of an area of no less than 30,000 square miles from a single ground base; thus iB explained the speed of the work accomplished. Actually the area, the largest ever mapped in a single-air survey enterprise, was photographed from three ground bases only, a feat impossible of achievement without the endurance and safety of the twin-engined machine. British aircraft; are to-day surveying large areas of South America, Africa, Canada, India, Burma, and' Australia. • In South America the successful British survey of Rio de Janeiro and its environs has induced the authorities of Buenos Aires to request tenders for the survey of the great Argentine city and the surrounding territory. AIR MAPS OF SPAIN. In Europe the biggest air survey scheme yet attempted is likely to bo begun next. year in Spain. The project covers more than, one-half of the total area of Spain, I and is to be employed for the production of maps on which to base the incidence of I land tax on all property. It is estimated i that an air -survey could be accomplished i in a quarter of the time taken by ground methods—the Spanish official calculation allots ten years to air survey and forty or fifty to the ground surveyors. Spanish departmental officials have discussed the scheme with British aerial survey eatperts in London. A report is being prepared for "Submission to the Spanish Government, and a meeting to decide final plans will, it is expected, be held in Madrid early in the new year.