THE AIRWAY

Sun (Auckland), Volume III, Issue 770, 17 September 1929, Page 14

THE AIRWAY

(By THE

ROC.

Surveying from the Air

THE airplane, combined with the aerial camera, has opened np a new field which, in the near future, will be extended to New Zealand, when a Dornier Libelle all-metal flyingboat, purchased by a newly-formed Auckland company, will arrive and commence operations. For the most part this machine will be used in aerial surveying and photography, two highly specialised ai-ts which go hand in hand, and the company is establishing a staff of experts in order to obtain the best results possible.

Aerial surveying and photography has been carried out in the Dominion on previous occasions, but it is doubtful whether it has been done so on quite the scientific lines as intended by the newly-formed Auckland company, with its Dornier Libelle flyingboat. On various occasions in the past useful work has been carried out in the surveying of the Waimakariri watershed and the Southern glacier region, while a complete aerial survey of Christchurch was made two years ago by Captain J. L. Findlay, of the Wigram airdrome. This was the first survey of a New Zealand city from the air. CAMERA HAS MEMORY It can readily he understood that although the human mind can record with a fair degree of accuracy images within the limited view on the ground, the memory may become confused when the range of view is increased, as in the air, and is changing' ht the rate of 100 miles an hour. The

aerial camera serves as the eyes and memory of the airplane and the aerial surveyor.

Aerial photography is a child of the world war. Subsequent developments have established aerial photography as the most expeditious and economical surveying method. The modern aerial camera is constructed with the same precision as the surveyor's instruments. Many of its parts are fitted to a fraction of a thousandth part of an inch. It is automatic in operation. The lenses have great rapidity and are freed from all possible aberrations. A roll of liypersenitised panchromatic film, 70 feet long and nine inches wide, is about the average used in aerial work. From 110 to 120 exposures are taken on one roll, making it possible to cover a large area without changing the film. There are two general types of aerial photographs—the vertical and the oblique. The vertical photograph is taken with the camera pointed straight down and through the aperature in the floor of the airplane. The oblique is taken downward at an angle between the horizontal and the vertical. Obliques produce a perspective with which every one is familiar, resembling a picture of the lowlands taken from a mountain. As the oblique covers a much larger area than the vertical photograph it has been decided that it is better suited for exploration mapping. TWO METHODS IN MAPPING Two general methods are used in applying aerial photography to mapping, namely, making a map with the photographs and constructing a map from the photographs. That is, a line or photographic map can be produced.

When Captain Findlay surveyed Christchurch from the air he flew at a comparatively low speed—6s miles an hour. Exposures were made every 20 seconds, and 18 plates were carried in each magazine of the camera, 72 plates being carried on each trip. The chief factors that the pilot had to contend with were the necessity of keeping the same altitude and the danger of drifting off the course through the action of the wind. A start was made at Papanui, and

the machine was flown on a compass bearing, the route being a straight line over the city to the hills. The machine then flew back on a parallel course, allowing sufficient space to ensure an overlap on one edge of the picture. The height maintained was 5,400 feet, and after each batch of 72 plates was taken they were developed and pieced to gether to see that nothing had been missed. IN THE ANTARCTIC According to Captain McKinlej’, of the Byrd Expedition, it is startling how much the airplane adds to one’s conception of the vastness of this great ice-covered land. The eye looks over hundreds of square miles of territory at a glance. The work of gigantic forces which twist and break the barrier into deep and awful chasms is apparent as it can never be the lonely traveller who may stand in awe on the brink of t? great precipice, but who cannot see the many miles of similar upheavals and open-

ings on either side of him. But to one in an airplane, all the magnificent vista is exposed at once in all its intricate relationship. THE EYE OF THE CAMERA So with the aerial camera. The machine registers such a view in an instant that it may be returned to the laboratory and there carefully studied at leisure. And it records much more faithfully than the eye and retains all the marvellous outlines of the manifestations of nature which can only be understood when studied in their entirety. Already these photographic maps have indicated lines of pressure and force which may be full of meaning to the expert-glaciologist. When the work of next year is completed and the entire map of formations about the Bay of Whales is made from the air, it may be possible for the first time to learn some of the at present unknown causes for this unusual indentation in an otherwise smooth barrier edge. When looking at a photographic map of the Antarctic one feels much as though one were in reality over the ice and snow, although one is probably somewhat warmer. The photographs for such maps are made at a high altitude and may be pieced together to form a large mosaic which portrays the terrain, as it could be shown in no other way. Air views are taken from a lower altitude, and with a camera of greater focal length than the mapping photographs. These latter are single shots and are instructive, and may often be artistic. Among them are photographs of icebergs, unusual pressure conditions which may be selected for study, deep crevasses, dog teams on the trail and our camp, Little America- The aerial camera gives Commander Byrd a photographic history of the expedition’s work from the vantage point of the air, where everything within a large area may be included.