AIR SURVEY

Evening Post, Volume CVII, Issue 107, 7 May 1924, Page 18

AIR SURVEY

EXTENSION OF ITS USES

WORK PROCEEDING IN VARIOUS

PARTS

' The British Air Ministry have recently completed for another Department of the Government a photographic survey by aeroplane of a region of about fifty square miles, taking in..the town and castle of Windsor. The whole of this work was completed in a few hours, states Major C. C. Turner in the "Daily Telegraph." The value of such a survey in the case of country already ground-surveyed and mapped is that it shows the exact condition of roads'and woods, and even the. distribution of arable and pasture land, at a given moment. This information would take long to collect and apply. without air survey, but with this the details cah;'be superposed upon the already : existing ordnance .map. The ■■wealth of detail is shown by the fact that in a picture taken from 10,000£t, if examined .through a glass, pigeons on the ground can be distinguished.. The; air survey, while"in many ways to be regarded as complementary to ground survey, can be so closely accurate that it may have high value, even without ground survey, and certainly: it can often with advantage precede the".1 latter-.

The art of the aerial surveyor is rapidly advancing; and by the methods now in use, the result chiefly of the work of the Royal Aircraft Establishment and of Professor B. Melville Jones, Professor, of Aeronautics at Cambridge sity, and ;of the: special, cameras and aeroplane" equipment now available, a survey of fiat' or moderately hilly country, (the hills not exceeding 3Qoft) is so true that maps can be constructed straight; from contact, prints and without any help '/from the'ground survey 'maps. S.uch ah air survey'■_ shows' no' more distortion than. 100 yards -in ICO scyiare. miles. An area of 100. square miles can .-'be surveyed and the maps made in thirty-six hours.. HiUy"country also: can be surveyed, but naturally there is greater room for error. In making the photographs it is necessary that thevcamera should be'vertical, but this is now secured% automatically. It is .possible also to keep an aircraft on a calculated course by aid of a gyro rudder control. The altitude of the aircraft cannot be kept constant, but since each exposure automatically records the altitude at ..the moment, it is an easy- matter: to-make the necessary alterations afterwards. Each; .exposure also,; records the time and.the compass bearings, of the picture.. ;: • ■,"'.-'■•■ : ■;. ■, .:■"■ , 1 THE IRRAWADDY DELTA; - Before mentioning a few of the air surveys now in progress it may.be explained that the vertical exposure for the purposes of .a. mosaic map can be supplemented by oblique photographs revealing the general lie of, the- country: This is necessary. for hilly country; and when surveying new lands it is an indispensable to moro detailed work, rfln general ground surveyors and the airman are working in close accord. To countries ■which, unlike the British Isles, have not been completely ground surveyed, the art of the air surveyor is of the greatest value. The Government' .of/Bgrmah has arranged for an air survey of the- Delta of .the 'Trra'waddy/ and the work has actually begun. .The area includes much forest and malarial., counjtry; and the machines employed are sear planes, there being no land aerodromes, The operations are being directed by Mr. Ronald C. Kemp', Chief Inspector of Aircraft in India. Mr. Kemp was one of 'the earliest British 'pilots, having in May, 1911; secured" the. eightieth certificate, issued by the Royal Aero Club. The estimated cost of the survey, if limited to 777 square miles of the Delta, is £22 per square; mile; but it is- expected that a further 1000 miles will be included,, in which, case the cost per square mile would be much' less. The Spanish Government is making inquiries with,a view to a complete aerial surrey of Spain, in..order to regularise land taxatipn,: which at the present time is too often evaded with impunity. Air survey, ■ besides- being nearly ".perfectly accurate, has the advantage "of freedom from deliberate falsification. - It is probable that the French project for building a railway across the Sahara from Oran to the great Niger Bend will be accelerated by -air* survey, which would save great preliminary, expenditure that otherwise would be necessary, besides doing the work quicker and better. There are various alternative routes from which to, choose,' but the line would terminate .at Wagadugu, in tho fertile, region of the, Niger Bend, a-re-gion with a population of 7,000,000. Another part of tho world in which a certain, amount of air survey is already in progress is' Now Guinea, and the results of Captain F. Hurley.'s expedition aro awaited with interest. WORK. IN-CANADA. Canada has already made extensive use of air survey. '-.Mr.'»A M. Narraway, Controller of Surveys of the Topographical Branch of'the D.1., in a single hour's flight covered terrain that would have taken m&re than a month for a good journey by land and stream, and he obtained, moreover, • very much more valuable results. In another flight, which took an hour and a half out 'and an hour and a half home,- taking him beyond civilisation in Northern Manitoba, Mr. Narraway did ' work that would have taken six week^ by ordinary methods, at the same time "spotting" two forest: fires and'securing their limitation. As is well known, the United States and Canada have saved millions by the. "spotting" and: restriction of forest ; fires by means •of aircraft. Not only is " information conveyed exactly and swiftly, but aircraft themselves can |- be employed to supplement the labour of the fire-fighters by dropping quenching gases. The. number of square miles' patrolled, surveyed, and photographed in Canada by -aircraft in 1922 was 19,678, 19,235, and 791 respectively. This work was carried out by three'companies, two of which were operating under contract with.the Ontario Government and sev-. oral of' the large pulp and paner companies,, and .the- third,- a lumber company', employing aircraft as a subsidiary to their-niaiii'operations'; . ■'!