FlightGlobal.com
Home
Premium
Archive
Video
Images
Forum
Atlas
Blogs
Jobs
Shop
RSS
Email Newsletters
You are in:
Home
Aviation History
1951
1951 - 0702.PDF
438 FLIGHT, 13 April 1951 CIVIL AVIATION . . . MAPPING THE FUTURE The ImportcuKe of Aerial Methods in Surveying the World's Undeveloped Areas IN a paper read befipfe a rriefcting of the Royal Society of Arts inLondon on Thursday, March 29th, Mr. T. D. Weatherhead, Q.B.E., M.A., general manager of Hunting Aerosurveys, Ltd., dealt witit the application of aerial methods in the science of sur- veying the world's agricultural and mineralogical resources. The subject is one which is B^cdming increasingly important in view of the current rapid exploitation of so-called undeveloped areas; Mr. Weatherhead's lecture—which we summarize belcw—was intended as a brief outline of the ways in which recently developed techniques can be used to assist in mapping these relatively in- accessible regions. Hunting Aerosuryeys, incidentally, have already done a great deal of work in this field, their most recent contract being for a survey of 6,477 square miles in Fiji.* Introducing his paper, the speaker pointed out that the world's population, which has doubled in the past century, is now esti- mated to be increasing at the rate of 20,000,000 per year. With the rapidly increasing speed and ease of communications there was a universal demand for a higher standard of living. "There are at present," he said, "many areas within the British Com- monwealth and Empire where over-population, poverty, hunger, disease and low standards of living provide ready breeding grounds for discontent, revolt and Communism. To rectify this instability, full use must be made of each country's natural resources." The lecturer pointed out that 2,000 years ago Plato had recog- nized what was insufficiently appreciated by many people even today—namely, that forests, water-supply and fertile soils were intimately related and were, in fact, a unity and not independent elements. Recently, he said, there had been many examples cf official recognition of this problem. In 1949 the United Nations Scientific Conference on the Conservation and Utilization of Resources, held at Lake Success, brought together 700 scientists from 50 countries to consider this problem. They dealt with such diverse resource aspects as minerals, fuels and energy, water, forests, land, fish and wild life; in each of these fields the deficiency of basic data on resources was emphasized and the need to provide systematic inventories stressed. On mineral resources very meagre information was available and in only a few countries had there been systematic and detailed geological and mineralogical surveys. In most parts of the British Commonwealth and Empire, development had taken place prior to survey and many serious mistakes had been made. The advent of aeriil techniques, however, now made it possible to survey before any development took place. The lecturer went on to show that a resources inventory must always be carried out by a combination of ground and air methods and, in an undeveloped area, would usually divide itself into four roughly defined stages. In the preliminary stage all existing in- formation about the area was collected, studied and co-ordinated, so that priority areas could be decided upon. Secondly, there was the reconnaissance stage, in which small-scale air photography was used to examine the entire area, to prepare topographic maps and to plan further detailed investigation. In the third stage large-scale air photography was used to prepare inventory maps of the various potential resources. In the final "construction- planning" stage large-scale contour maps were prepared by photo- grammetric methods. Before it was possible to produce a soils map, a forest inventory or a geological map, the planimetry and topography had to be accurately compiled as a base. This, said the speaker, had hitherto involved the slow and costly method of geodetic triangulation, but two major developments had recently taken place which, after more practice and research, should hasten considerablv this vital stage in survey work. The first was the helicopter, which in Canada—in 1949—had enabled each ground-survey party so equipped to achieve eight-and-a-half times its previous output at one-third of the cost per station. The second aid to geodetics came from the use of radar for the measurement of long lines on the earth. The method was to fly a suitably equipped aircraft between two ground stations and to record the minimum trans- mission time of pulses from the aircraft. The readings were cor- rected for temperature, humidity and barometric pressure varia- tions, and the lines, which might be up to 500 miles in length, would then be broken down into shorter legs by ground parties using helicopters; photogrammetric bridging followed. Air-survey methods for map compilation varied considerably according to the type of terrain. In rugged country and in areas where precise contours were required, the use of three-dimen- sional plotting-machines, such as the Williamson Multiplex and the Wild A.5, was essential. Before accurate topographical maps could be plotted with the aid of these instruments, however, a considerable amount of height-control data had to be produced, and until recently the only method available for this was that of using ground-survey parties. The development in Canada of an instrument known as the Airborne Profile Recorderf enabled height control for 50ft contour maps to be obtained entirely from the air. With this device the continuous recording of the time of return of a narrow-beam radar pulse directed vertically down- wards from the aircraft gave an actual profile of the ground. Although the idea was by no means new, it was only within the last two years that the A.P.R. had reached the stage of being a practical operating tool. The operation of the instrument de- pended upon the ability to establish a barometric datum. It was necessary in this method to record throughout the flight the air- craft-drift angle, which could be obtained or checked from the photographs. The machine was flown over a known datum at the beginning of the flight—and subsequently, whenever possible— . so that a mean could be obtained of the various errors. By having a grid pattern of A.P.R. profiles, with crossings over well-defined flat features, it was possible to take a large area and reduce the whole grid to a common datum. Value of Aerial Photographs The cost and time involved in establishing height control for the basic mapping required for resources surveys was one of the most important factors affecting the whole cost of the operation and often caused serious delays. It would, however, be consider- ably hastened by the use of the A.P.R. which, said the lecturer, seemed to have an interesting potential application in the pro- • vision of scale-control for mapping. For this purpose the A.P.R.7 gave precisely the type of information which was required, i.e.,; the perpendicular distance from the apex of a "radar air triangle" : so that, angles being known, the triangles could actually be scaled.;; Mr. Weatherhead was of the opinion that the primary im- portance of the air photograph was its use in compiling "land-' use" maps and in helping to delineate the perimeters of soil types. One of the main factors in determining soil-types from air photo- graphs was the drainage pattern, which showed up readily and could be used to identify soils and bed-rocks on a regional basis. Another field of survey work m which aerial methods were invaluable was the provision of overall inventories of our forest resources; the recent Empire Forestry Conference had called for their completion before 1957. Again the application of aerial methods in this field-had been exploited mainly in Canada. For an appraisal of various resources and the preparation of a manage- ment-plan, mapping at a scale of 1:15,000 approximately was required. The inventory would be required to include such data as forest types, tree heights, density, site_ classification, acreage and timber volume—and a great deal of this information could be obtained from aerial photographs. In temperate forests "species composition" could be inter- preted very accurately, while in open forests the height measure- ment of trees was possible by using photogrammetric methods. Aerial methods, said the lecturer, were also the key to compiling the geological maps which were essential in providing an inven- tory of mineral resources. From the stereoscopic study of photo- graphs, angles of dip could be determined, faults and dykes traced, and frequently, inter-relationships of structures could be noticed which would be easily missed on the ground. By pre- selecting the points to be visited by ground parties, the best use could be made of the geologist's time. In the same way airborne geophysical studies were now being made over likely oil-producing areas. The main method used was that of aeromagnetic survey, in which the magnetometer record was related to ground positions by air photographs. A continuous magnetic profile was obtained by flying in parallel lines along the area to be surveyed. These profiles were subse- quently reduced to a common datum and contoured; the resultirg maps not only revealed geological structures to a remarkab e extent, but sometimes even gave a direct indication of the Pr°'"" able location of ore bodies. The airborne magnetometer nra many advantages, not the least of which was its accuracy, speed and low cost as compared with ground survey methods. 'See "Flight" of March 2nd, 1951. tDescribed in "Flight" of February 9th, 1951. See also article, "The World in Camera," April nth, I951
Sign up to
Flight Digital Magazine
Flight Print Magazine
Airline Business Magazine
E-newsletters
RSS
Events
