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Aviation History
1924
1924 - 0135.PDF
MARCH 6, 1924 maps—one from a ground survey, the other from an air survey. The new Point was photographed three times in 1921—in May, October and December—and each time appreciable changes were noticed especially in the refiexed part of the hook of the new Point, which moved nearly 100 yards between October and December. The importance of a rapid means of survey of the kind which can be carried out in a few hours is obvious, for though the sea-going traffic from the village of Blakeney is not large, there may be many other parts of the world in which similar changes are going on which are vital to navigation and sea-borne commerce. " In this connection I may point out that the approach to one of our greatest ports is at present in need of a survey which can only be done from the air without very great labour. " Southampton Water and the neighbouring shores are being invaded by a salt marsh grass Spartina Toumsendi, which was unknown till 1870. Appearing at first in a few clumps, it has spread with astonishing rapidity, and now covers great areas which were formerly mud flats exposed at low water. It has spread into Poole Harbour, where it covers large areas, and eastward as far as Rye, while across the Channel it is establishing itself in France. While I do not anticipate that this rapid growth of vegetation will influence greatly the main Channel to Southampton in the near future, it may ultimately do so, and it considerably alters the appearance of the banks. An annual aerial survey which could be put into the hands of those who are studying such tidal lands would be of great scientific interest and perhaps of ultimate commercial importance, since nobody really knows what will be the results of this remarkable growth of the Spartina grass. " Geology.—The scientific study of the structure of the earth's crust will be greatly assisted by the execution of aerial photographic surveys. The geologist has two sides to his work—one the study of the surface features and the recognition of the causes which have brought about the present topography, and secondly the study of the underlying rocks and their contents. This scientific study has a practical outcome in the investigation of water supply and of the distribution of deposits of coal, oil, ores and other mineral substances. " The value of the air picture in the study of surface features is obvious. Not only does it display the main features of the ground, but also the smaller details such as would seldom be shown even on a good topographical map. The investigation of these features on the ground would require a very laborious and long-continued survey, which in many parts of the world would be almost out of the question on account of the difficulty of maintaining an expe dition in the field for a sufficiently long period. " In this connection I may mention that the aerial survey of Palestine has provided data for the scientific exploration of many of the complicated and difficult points in the surface features of this country. As an example, we may notice the geology of the Jordan Valley. It would appear that the present Dead Sea is the last remnant of a very much larger sheet of water which once spread upwards and was connected with the Sea of Galilee. The floor of the Valley is now filled with flat beds of calcareous mud laid down on the bed of this great inland sea. What has been the cause of this great diminution of the area of the water ? " The aerial survey shows that the drainage system of the large part of Central Syria with its high mountains once flowed into the Jordan Valley, but the channel along which this drainage passed in bygone times is now empty. The water which once poured down through it in a great stream has been captured by a smaller river, and is now led directly to the coast, and so the water supply of the Jordan has been very greatly diminished and is restricted to streams arising in its own vicinity. " We may pass from this example to consider how aerial survey may help the progress of knowledge as to the structure of the earth, and we must first note that this knowledge depends very largely on geological mapping. A geological map shows the distribution of the outcrops of the various types of rock on the surface, and thus, with a knowledge of the dip and the nature of the rock, goes a long way in the elucidation of structure and the explanation of what happens underground. Obviously we cannot at once turn an air survey map into a geological map, but the air survey will very much lighten the work of the geologist and enable him to cover large areas of ground in a more detailed manner. In the first place, the photographs willl show exactly where outcrops of the underlying rock are to be found, and the geologist can proceed to them without having to spend much time in searching through a large area mostly covered with soil and vegetation. Then in the same way as mentioned in the case of vegetation surveys, the geologist will often be able to get a map of extent of country occupied by outcrops of a particular kind of rock after a short exploration and comparison of the photographs with the actual rock features in any district. In more exceptional cases, such as in manv parts of Palestine, the individual beds of rock in a formation may be recognised in the photographs and render their mapping a much easier matter. In all cases an air survey will greatly facilitate the first investigation of the geology of a country, which is a preliminary to the location of deposits of mineral wealth. This has been recognised by the Canadian Department of Mines and by the United States Department of Mines. " In the investigation of water supply problems, progress will be facilitated not only by the accurate portrayal of the courses of streams and rivers by aerial survey, but also owing to the fact that the position of springs is very readily located by the camera. " Archeology.—I have above touched on the application of aerial survey in two branches of science which have in many respects important practical application, and I should finally mention one further study which has already derived some benefit from air work, and will in the future derive more, but which has less bearing on the economic development of a country. The study of archaeology has, however, a great fascination for the average civilised man, and it has long been the practice to show in our English ordnance maps features of archaeological interest. " There is no need to refer to the interesting discoveries at Stonehenge resulting from aerial survy, but I should like to mention how in many places at home and abroad an air survey will bring to light features of historical and archaeo logical importance in a striking way. In the case of the remains of ancient buildings, the air photograph gives their ground plan, without a prolonged series of measurements being taken on the ground. In other cases remains of historic or prehistoric buildings are buried under an accumula tion of soil and debris, and may escape the notice of the traveller on the ground. In such cases the aerial survey photograph may reveal the presence of these buried structures, for when viewed from above we can quickly recognise any symmetry that may occur in mounds of earth which often cover old sites which, when examined on the ground, appear without order and show little trace of man's handiwork. " One of the most striking examples of this was seen in the vertical photographs of the ancient ninth century city at Samarra in Mesopotamia. Here the ground plan of large areas could be clearly, seen with the sites of the streets, buildings and houses perfectly outlined. It is hard to believe that these are not distinctly seen on the ground, but yet it is said by those who have been there that the site appears to show in most places nothing but a vast series of shapeless and irregular mounds of earth. This example is provided by the ruins of a comparatively recent city, but it serves to illustrate the general principle. In many parts of the world aerial survey should, if carried out, be of very great help in the study of ancient monuments, cities and civilisations. " One further example may be given. At the present day all the southern part of the Jordan Valley north of the Dead Sea is a very arid and desolate region, with very little cultivation and very few inhabitants. Yet according to the Biblical story it was once a very fertile district, and one wonders what could have given rise to this idea. It was interesting to find as the result of air survey that in some parts of the eastern side of the valley there are remains of an extensive system of irrigation channels arranged in regular lines, which watered the ground with water from the hills of Moab. These channels are shown owing to the fact that they are filled with scrub-like plants which are less regularly arranged and less abundant in the surrounding country and in the flats between the channels. We cannot tell, of course, what is the age of these irrigation systems, but they are probably of considerable antiquity. " There is always a possibility that areas like these which have been cultivated in ancient times might be again opened up and brought under cultivation, and so discoveries of antiquarian interest might become of modern economic importance. Conclusion " We have seen in the first part of the lecture how progress has been made in the working out of methods of aerial survey on a basis of vertical photographs, and how it has become possible to carry out reconnaissance surveys over great tracts of country with extraordinary rapidity and probably in the end with considerable economy. While in some cases the filling in of the topographical details will be best done \
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