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CHAPTER XXII

AERIAL FOREST SURVEYS IN BURMA

NOTABLE departure was made in Burma by undertaking the first aerial survey of a forest area ever made in India or, it is believed, the East. The use of the aeroplane in forest work was not unknown. In 1917, during the War, the author had occasion to visit Northern Russia. From Archangel he went up the Northern Dwina River several hundred miles to the foot-hills of the Urals. Nearly the whole distance lies through virgin forests of pine, spruce and birch. Mr. J. L. Bell, now Deputy Conservator of Forests in the Bombay Presidency, accompanied the 1918-19 Expedition to Archangel as an Air Force Officer. On his return to Edinburgh later on he gave the author several aerial photographs taken in the neighbourhood of Archangel. From these it at once became apparent how easy it would be to distinguish and select the most densely stocked areas of pine and spruce. The country is quite flat. In Canada the aeroplane has been employed on fire protection work and the Laurentide Company in Canada have successfully made use of aerial photography in the work of stock-mapping and surveying their forests. In fact it was the assistance and information given by Mr. Ellswood, formerly of this Company, to Mr. Watson whilst on furlough in England, which materially helped in carrying out similar work in Burma,

The forests over which the first aero-photo survey was carried out consisted of the Reserved Forests of the Irrawaddy Delta Division, extending over 1000 square miles. Topographically, except for a low ridge in the Myaungmya District rising to 120 feet, the area is essentially deltaic, being formed by alluvial deposits of the Irrawaddy; the plain is intersected by large and small creeks of the ordinary type met with in such regions. Of the seven forest types including "blanks" the three first are: (1) Pure or almost pure forest of kanazo (Heritiera minor) covering large areas and is the most valuable; (2) mangrove forest containing various species of Rhizo

phoracea, usually confined to mud-banks along creeks; (3) scrub jungle designated as byaik, of three types: (a) characterized by Phoenix paludosa, (b) by Cynometra ramiflora, (c) by absence of tree growth and presence of tall grasses and creepers. Mr. A. W. Moodie had made a Working Plan for these forests in which a full description is given.

Until recently the only map available was Fitzroy's reconnaissance map (4 miles to 1 inch) dated 1864. In 1918-19 a survey, which proved inaccurate and very expensive, was undertaken for 360 square miles. In 1921 Moodie commenced another survey by cutting linear survey lines at 1 mile intervals from north to south and east to west. The forest growth was also noted upon. This work was commenced before the aerial survey was proposed. The difficulties of carrying out such a survey or describing the forests in areas of deltaic nature are well known to anyone acquainted with them. He will appreciate the following: "Wide waterways with a rapid current ebbing and flowing with the tide; mud-banks in which at every step the surveyor sinks to the knees or even further; at high tide large tracts under water too deep to walk in; small creeks only navigable at high tide in small boats; and then, on the so-called land, even at low tide, a mass of aerial roots which makes walking slow and painful, and a dense tangled undergrowth through which every step has to be cut; all this tends to make ground survey on an accurate scale slow and expensive." It is estimated that an accurate ground survey on a scale of 4 inches to 1 mile would have cost fully Rs.500 per square mile and would have taken three to four years. The description of the aerial survey actually undertaken is recorded in Aero-Photo Survey and Mapping of the Irrawaddy Delta, Burma. For. Bull., II (1925). This was compiled by the officers concerned in the work, Mr. R. C. Kemp, Major C. G. Lewis, R.E., Messrs. C.W. Scott, D.F.C., and C. R. Robbins, M.C., D.F.C., the latter two of the Forest Department. Blanford, Conservator, Working Plans Circle, writes an introduction. Reference should be made to this interesting brochure for a full account of the operations. A brief summary is only possible here.

The origin of the idea of undertaking an aerial survey is attributed to Mr. E. F. A. Hay, I.F.S., when in charge of the area. The idea does not appear to have received much consideration until Mr. H. W. A. Watson visited the forests in 1920, when Conservator of the Delta Circle. Watson was

greatly impressed with Hay's suggestion and pointed out that the conditions were ideal for aerial work, the country being absolutely flat, salient points easily picked up, whilst the kanazo stocking, which is abrupt and easily distinguishable in appearance and colouration from other growth, could be laid down without the cumbrous ground stock-mapping. The survey could also be put through in a few weeks instead of years. Both the Government and Colonel Ryder, SurveyorGeneral, were lukewarm. The expert opinion in 1921 with regard to aerial survey work in India seemed to prove that there was a difficulty in flying straight enough to obtain a regular series of strips covering a piece of country. The following year Mr. Kemp, the Chief Inspector of Aircraft in India, visited Burma. Watson discussed the matter with him and a conference was held in August, Mr. Smales, Chief Conservator, Colonel Ryder, Colonel Coldstream, Superintendent Eastern Circle, Survey of India, Mr. Kemp and Watson being present. The proposal was accepted and Mr. Kemp was asked to prepare detailed estimates for the work of 1000 square miles. The estimate was submitted and backed by the SurveyorGeneral, who promised co-operation and undertook: (1) The fixing of the necessary points, (2) the fair drawing of the sheets for publication. These services would not be charged for to the Burma Government as they would be useful for the ordinary 1-inch topographical survey which was an Imperial charge. The arrangements from this point came under Colonel Gunter, in charge of the Burma Circle, Survey of India, and this officer is credited with having finally obtained the assent of the Finance Committee in 1923 to the project being carried out.

Mr. Kemp's engagement with the Government of India having come to an end, he contracted with the Burma Government to undertake the work, the terms being the payment of Rs.2,75,000 for the first 1000 square miles and Rs.28,000 for a further 350 square miles if required to be undertaken later. The work to be carried out was briefly : The production of vertical and oblique photographs suitable and necessary for the compilation of a 4-inch I-mile scale map of the area. For the full detailed conditions reference should be made to Major Lewis' Note in the Bulletin. He also details the ground control undertaken by his party in December, 1923, and January, 1924.

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A base for the aeroplanes was formed in Rangoon at Monkey

Point, some 90 miles by air line from the centre of the area to be surveyed. A moveable emergency and advance base was formed by a launch with a motor-boat and sampans (native boats). The type of seaplane used was a D.H. 9 Puma engined service type aeroplane converted to a seaplane by the fitting of floats designed by Mr. Kemp. Flying Officer Mr. J. Durward was lent on leave by the A.O.C., Royal Air Force (India), for employment as photographer, and Major C. K. CochranPatrick, D.S.O., M.C., late R.A.F., acted as pilot.

Photography was commenced in February, 1924, and completed early in April of the same year. Owing to the delays in settlement of the contract the start was not made as early as contemplated. January and February would, it is said, have been the best months, weather and visibility both being better.

The important part of the work which fell to the Forest Department to carry out was the examination of the forest with a view to settling how the different types of forest growth could be determined from the photographs. Fortunately in Messrs. Scott and Robbins the Department in Burma possessed two young officers who had made their names in the Royal Air Force during the War. They were deputed for short periods to examine the photographs and compare them with the actual types of forest on the ground. Both officers made trial flights over the area and visited parts of the forest. Their Reports are included in the Bulletin. As soon as the prints were available the preparation of rectified mosaics and the compilation of the maps were undertaken by Major Lewis' Party (No. 18) at Maymyo. As the actual scale of the photographs proved to be about 3-4 inches = 1 mile, it was agreed to alter the final scale to 3 inches I mile since it would be easier to work up the rectified mosaics, from which the final map would be prepared. From the Reports of Scott and Robbins it appeared that eight to ten different types of forest could be distinguished on the photographs, and that it was possible to distinguish between fully stocked kanazo forest and the same forest which had been heavily worked. They were also of opinion that they could determine at least two quality classes of this type of forest from the photographs.

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Blanford summarises the Reports of the officers as given in the Bulletin, from the Forest Department's point of view, as follows: "(1) Cost. The cost including ground work and mapping has worked out to about Rs.293.7 per square mile.

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A ground survey on the same scale would have cost in the neighbourhood of Rs.500 per square mile, without giving an indication of the types of forest growth. (2) Rapidity. The actual survey was completed in five months and the whole period taken from the commencement of the fixing of the ground control to the completion of maps and stock maps should not greatly exceed one year. Ground survey would have taken three to four years. (3) Accuracy. This is far in excess of anything that could have been obtained by ground survey in this type of country except at a further increase in cost and time. (4) Details available. The areas and distribution of the different types of forests are not only obtainable at no increase of cost but with an accuracy that it would have taken years and a considerable expenditure to have equalled."

At the same time Blanford points out that both the country and type of forest were exceptionally easy and quite unlike the usual character of forest country throughout India and Burma where hills would predominate and where, moreover, the prevalence of a mixed deciduous forest might not prove easy to determine accurately. Scott made one flight over the Pegu Yoma. The season of the year was unfavourable as the deciduous forests were leafless and "looked very bare and featureless." Robbins says that 8000-10,000 feet is probably the best height from which to take photographs, taking all considerations into account including the cost, and remarks that "comparison of photographs with the ground from the air is a great help to their interpretation.'

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THE AERIAL SURVEY OF THE SOUTH
TENASSERIM DIVISION

The second survey projected was a far more ambitious undertaking. It was recognized that the success of the Delta Survey was no criterion that such work would be possible in the case of the more ordinary type of forest country. Owing to the delayed start in 1923-4 it was not possible to carry out, as intended, a series of experiments over different types of forest on the hills, Scott's single flight over the Pegu Yomas being the only one attempted, owing to the lateness of the season. Proposals were, however, accepted by the Local Government to carry out a second season's work in 1924-5. This second survey related to over 14,000 square miles of unexplored forests in the South Tenasserim Division which were

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