POLOR PHOTOGRAPHY

Evening Star, Issue 20375, 6 January 1930, Page 9

POLOR PHOTOGRAPHY

SURVEYING THE ANTARCTIC CAPTAIN M'KINLEY'S METHODS [By Captain Ashley C. M'Kxnlev, Aerial Surveyor of the Byrd Antarctic Expedition.] LITTLE AMERICA (Antarctica), November 10. The photographic survey during the flight to the South Pole from Little America will, if successful, make a record of this region which can be returned to civilisation and studied at leisure by those who are interested in the formation of the South Polar Continent. Such a survey is difficult because elevations will be constantly changingThe work must be done in cold more severe than is usually encountered at home in a surveying flight, and every moment in the photographer s time must be utilised to the best advantage. Such flights are not repeated, and there will be no opportunity to make good deficiencies in the record. Probably no flight ever offered so great an opportunity to demonstrate the value of aerial photography as a surveying method. Here is a virgin country, a vast unknown plain, upheaved ice showing the presence of land beneath it, and a rampart of mountains, of which almost nothing is known. MOSAIC STRIP MAE OF 1,600 MILES. We hope all this will be recorded, made into a mosaic strip map, and brought back for the geologist, the .glaciologist, and others to pore over and decipher the meaning of its contours; , „ . Aside from the pleasure of flying over such an unknown land there is the pleasure of contributing something new and of value to scientific knowledge, even though the one who records it, as in this case, is incapable of interpreting ifcs symbols. As a task it should probably be unique, as there has never_ been made a single-strip map 1,600 miles long on one flight. One must keep one’s fingers crossed and hope that nothing jams, for a defect in the mechanism of the camera a.t such a critical time or some other interruption would be quite- sufficient to impel a harassed surveyor to jump out on the nearest peak', and, as our columnists say, end it all. But if everything goes well it will be a map which in length and content will bo new and of great value. It is always rash to predict what may be doue in exploration. AIMING OP CAMERA ON ANGLE The camera is aimed through noles in either side of the plane, where canvas flaps have been made to fasten around it to keep out the icy wind. Pictures will be made of one side of the route going out- and of the otner coming back if the same route is taken, and as they are taken at an angle they will cover a largo territory. The photographs will be obliques taken at 20deg from the horizontal and overlapped so as to give a continuous strip from our base, which is on the coast, to the South Pole,,about bOO miles inland. ' . , From these photographs additions and verifications can be made on the existing line maps or hand drawn, and a photographic mosaic can be constructed. The mosaic is made of overlapping photographs laid and pasted on a mount or base on which has been plotted all existing control data. Controls may be defined as all data used to fix points on which to construct a mosaic or line map. These, data are always related to some point located on the earth’s surface, and an exactly accurate survey cannot be made with it. The images on each photograph are matched with like images contained on the next photographic strip, in this manner forming a composite picture of the entire area contained in, the exposed film. BARRIER DETAIL TO BE PICTURED.

The first picture of this loug mosaic, vre hope, will show the great Ice Barrier and Little America. Then the strip starts across the Barrier, While most of the Barrier is flat there are many rises and depressions, crevasses and sasturgi, all of which will help the glaciologists to determine the general character of this great sheet of ice and possibly what underlies it. A<l details will be shown to scale m the aerial photographs. At about 400 miles from the base the glacerised mountains with bare rock ■stending through the ice will appear iu the photographic strip.' These photographs will greatly interest geologists. The photographs, taken at 20deg from the horizontal, will include the horizon appearing about 12deg from the top of each photograph. The length of the area covered on each picture wu- > * I,oooft altitude to 132 miles at 10,000 feet. The flight, as planned, will average about 5,000 ft above the surface, so that the strip will cover an area about 800 miles long and 81 miles wide. DIFFICULTIES OF POLAR PHOTOGRAPHY.

Exploration aerial mapping is neoessarily conducted under much more difficult circumstances than mapping in a civilised country. The polar flight will' bo especially complicated in this way, as the plane will fly at varying altitudes, necessitating a varying time interval between exposures so as to obtain the proper overlap. In other words, the surveyor must calculate his altitude and make adjustments between each picture, and the intervals between exposures are only two minutes long. To obtain sufficient data to control the maps to be made from the photographs there must be recorded between the exposures the altitude temperature, ground speed, dead reckoning, any observations Commander Byrd makes and bases laid by the dog teams as they are passed. Between times one can take a nap or look at the scenery. And when possible the hands must be warmed m fur bags fastened to one’s legs so as to keep the fingers from becoming entirely rigid. Fortunately the flight passes over Captain Roald Amundsen’s old route to the Pole, so that his records of ground elevations can be used to determine approximately, in conjunction with our barometric readings, our height above the earth’s surface. - Captain Amundsen’s observations are being checked as far as the by Dr Laurence Gould, of the geological party. The strips being started at Little America, which is accurately located, and ending at the Pole, the two points will serve tb control the,ends of the strip. USING ARMY AIR CORPS CAMERA. 1 The aerial camera used on this flight is the regulation • United States Army

Air Corps camera containing a long roll of paper for recording data, a thermometer, a barograph, and a stop-watch-Covers have been attached from the camera - apertures to the plan© to the cover of tte camera to keep out the sub-zero air, which would otherwise come ir at 100 miles an hour. These covers may keep the aerial surveyor from ending up with frozen hands, as most of the work must he don© without gloves Convenient devices have been made in Little America to meet the unusual conditions under which the survey is made. Among them is a stand attached to the camera containing instruments for recording data. , This camera contains in each magazine, three of which will b© carried, 75ft of hpyersensitised panchromatic film 9in wide, and takes 110 exposures, 7in by 9in on each roll. The camera is semi-automatic, a crank being turned for each exposure, exposed film being passed in to place, a pressure plate released to allow, the film to move freely and reset to hold the film in a perfect focal plane. It also sets the shutter.

The camera weighs 341 b, and is con* structed of aluminium. It is made with the same precision as any other sur* veying instrument. The usual 12in local length lens has been replaced by one of 9Jin focal < length in order that the greatest cover* age for the size of the exposed film can be obtained. Three extra rolls of film and a changing bag are being carried, in order that pictures can be taken on the return flight. This will make it possible to.take 660 pictures during the flight. [Captain M'Kinley accompanied Rear-admiral Byrd on his successful flight to the Pole at the end of November.] £