University of Idaho School of Forestry - Forester Yearbook (Moscow, ID)

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42 more than a photographic flight, but with the qualification in each case, that ground trips do not aHord the advantages previously enumerated. ' It appears, then, that up to the point of actual maps and surveys, aerial methods offer a great advantage not only in time, but in returns from the cost, and further, that there is a credit balance to carry over and apply on the cost of ground control and mapping. AERIAL RECONNAISSANCE The effectiveness of the reconnaissance and photographic flights on the Lewis and Clark project over that of ground reconnaissance was evidenced in many ways. On the Hrst flight the Bitter Root Mountains were crossed over the Lochsa River Route and recrossed over the North Fork Route. The Ridge Route lying between the above mentioned routes was observed at the same time. The flying time was three hours, over diiiicult mountain coun- try, and the distance flown, about three hun- dred miles. The main streams were in deep narrow recesses and the high ground was sharp and ragged in form. The flight was made at an elevation of from 1,000 to 5,000 feet above the ground. The highest elevation reached was 10,000 feet and in only one case did the plane descend within a few hundred feet of the ground. It was naturally supposed that the general course and relation of the routes as well as the drainage systems would show clearly, but a surprising amount of detail proved to be ascertainable at the same time. The plane was held to one side of the objective rather than immediately above it in order to permit of the ground view in perspective. STREAMS SHOW PLAINLY In the burned areas, ground details showed with a great clearness and the nature of the material was evident. On fully timbered sec- tions where the trees rose tier on tier from narrow bottoms, and the river seemed to fill the channel, the details were not so readily ascertained. In this case, judgment could be rendered only from the general steepness of the side slopes, the bald rocky spots and masses of rock that had rolled into the river. The general configuration, however, was readily observed. The heavily timbered sec- tions were not extensive in the canyons and offered little interruption. The various routes flowed by with such rapidity that the outstanding differences were presented with emphasis and comparisons were readily made. Secondary streams could, in many cases, be seen from their sources to their mouths. The side of the main rivers having the least tributary streams was easily selected. The requirements for bridges were evident. The varied characters of ground along the river bank were easily segregated. Slopes and cliffs and the main trails showed THE IDAHO FORESTER clearly, as well as fluffs of dust stirred by a plodding pack train, with which, perchance, there traveled some engineer on ground re- connaissance. The position of the pack train indicated to a certain degree the nature of the ground near the river by its occupancy or its avoidance. TREES lVlARK HIGH WATER In many cases a line of isolated trees stood at highwater line along the rivers and so showed that the area between them and the water was a bar, and not tenable. Steep sections of the main streams were in- dicated by narrow channels and white water, and slack sections by Wide channels and black water. The scars of snow slides and cloud bursts led down the slopes to fantails of debris on the river bank and bars in the stream. The entire panorama lay spread beneath in all its detail and close or distant observation was accomplished by a word to the pilot. Mountains led away on both sides and wide deflections in the courses of river and streams were seen in their true relations and in some cases invited cut-offs by the use of more ascent and descent. The top of the divide was viewed for many miles and the passes lay spread out for observation. There is slight likelihood of missing a hidden pass from the air. Out from the divide ran slopes and ridges of varied ground which told much of their texture by their form. Basins were viewed from all sides and peaks are circled with celerity. A remark to the pilot, and distant ground is quickly close by and then swept away as ,questions are answered visually. An effortless investiga- tion conducted by a seemingly detached intel- lect that requires no endurance for its trans- portation. ROUTES EASILY COMPARED FROM AIR The examination of routes lying reasonably close to main streams is comparatively simple as the actual position of the line is determinate within narrow limits. The position of a sup- ported line that may loop about is not so readily decided upon from the air as a wide area may be occupied and the elevation line can not be determined. In such cases, the ex- amination becomes more general. The con- figuration and formation of the country over which a descent is proposed, is open to con- sideration as a whole. Desirable ground for development or support is much more readily located from the air, although ground work would be required to prove its utility and co- incidence with the desired grade line. In any case, the general character of sup- porting ground on any route or routes is readily open to comparison. Aerial recon- naissance eliminates that ever present fear on ground work of overlooking something by not knowing what lies just beyond one more hill. From the air, the entire area and many miles on each side are examined in a few ef-

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THE IDAHO FORESTER 41 Th-e form of the information lends flexibility to it and its completeness instills confidence by removing uncertainties. Group decision and the elimination of the personal equation will tend to strengthen judgment and are a natural outcome of aerial examination and surveys. DIVERSITY OF USE The diversity of use of aerial photographs and mosaics, particularly when made under government or public auspices, enhances their economic value and conversely reduces the ultimate cost, as the information is applicable to many purposes. Aerial photographs and mosaics embody the possibility of being de- veloped into topographic maps. In addition they depict a replica of every ground feature and can be used for all purposes, including forestry, agriculture, reclamation, and state and government highways projects. This adaptability enhances very materially the value of the resulting information by eliminat- ing duplication of effort. Ground survey maps would indicate and emphasize only the fea- tures or subjects directly applying to the par- ticular purpose under consideration. NONTECHNICAL In many cases it is essential that certain technical aspects of projects be discussed with and made clear to nontechnical persons, for purpose of financing and appropriations. To many of these persons maps, profiles, and dia- grams are not readily comprehensible. A pic- ture or a mosaic with the project indicated up- on it brings ready comprehension and when supplemented with oblique pictures, affords understanding and eliminates long complicated explanations. A common ground of under- standing is thus provided and any tendency to- ward an individual uncertainty is removed, to the end that negotiations can proceed with more assurance and confidence in both the project and the representative. The preceding general statements introduce a few engineering aspects of aerial surveys and some of the resulting advantages. The scale of the pictures and the extent of the de- tail depend only upon the height from which the picture was taken and the extent of it is later enlargement. The map scale will vary similarly. GENERAL COMPARISON A comparison of relative values between ground and aerial examination, particularly on preliminary Work, is not readily present- able with brevity inasmuch as the aerial method introduces new elements of great val- ue that are not obtainable by ground methods. A dollar for dollar comparison is not equit- able as the advantage of the a-erial method in providing a quicker and broader understand- ing of the entire situation is infinitely gI'eater than the ground method. Similar results might be obtained by either method by the same in- dividual provided he covered the country on the ground with a thoroughness equal to the plane in the air, took enough time, and made a decision that his superiors would approve if they had seen everything that he had seen. This is a rather heavily qualified statement and the result of that procedure would be to again become subservient to the personal equa- tion and delete all of the fundamental advan- tages and assurances previously enumerated. The sole advantage would be that the man had been upon the ground and would be in a better position to classify the material. Upon returning from a reconnaissance, he would bring no corroborative evidence to support his opinion. Upon the return of the plane, a series of photographs of each route considered would be available for d-etailed study and con- sideration and would constitute a permanent record available at any time for any purpose affecting the area covered. For an explora- tory flight as compared to a ground trip, the flight would cost the least. For a photographic flight as compared to a ground trip on trails, the cost would be about the same, as the ground trip would require much more travel to gain the sam-e understand- ing and assurance. In certain very difficult areas, the ground reconnaissance would cost A Forest Survey Party Makes Use of Pack Horses to Ca.r1'y Men and E'qnfipment into Inaccessible Regions Where There Are No Roads and Often Few Trails.

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THE IDAHO FORESTER 43 fortless minutes and conclusions are reached that are qualified by few mental reservations! The flights, both reconnaissance, photo- graphic and reflights for the Lewis and Clark Highway, were completed in twelve hours of fiying time and about 1,000 miles were flown. A ground party would occupy that period in traveling ten miles along the trail and mak- ing camp. The films were sent to Washing- ton, D. C. by airmail for development and printing. In ten days from the date of taking, the pictures were received and the stereoscopic study began. From the air, the alternate routes are con- sidered close together and no term of time or effort lies between the observations to dull the impression derived, as is the case when travel- ing laboriously along faint trails upon the ground. When observed information is sup- ported and supplemented by continuous photo- graphs, the aerial method far outstrips ground reconnaissance in every respect. In addition, the resulting record is of much greater value, due to its increased scope and versatility of use. It is, in fact, visual proof of the condi- tions, while that of ground reconnaissance is simply verbal and subject to the personal equation. PRELIMINARY ESTIMATE After the photographs of the various routes have been studied under a stereoscope and a tentative route has been indicated upon the mosaics, the pictures are again studied and a preliminary cost estimate is made. This preliminary or reconnaissance estimate is made just as it would be by a man upon the ground. The ground conditions show clearly under the stereoscope. Some distortion occurs in the steepness of the slopes due to variation in the overlap of the pictures, but the same condition obtains on all the routes so the result balances suhiiciently for comparison purposes. Stream crossings are more readily determi- nate upon the pictures than upon the ground. Advantageous breaks in the slopes above the rivers are located at once and not passed by as when traveling below. The choice of ground along the main streams is readily made as the pictures show half a mile on each side. Cliffs and slopes are easily distinguishable, particu- larly in open country, and large boulders in the rivers are discernible. BEST ROUTE READILY ASCERTAINED When the line leaves the rivers and supports along the slope, the procedure does not con- tinue with as much confidence as along the river as there is no gauge of elevation except by estimating the height of the trees and step- ping off the ascent or descent accordingly. The character of the country shows, however, and the gross ascent is usually known, so the distance across each type of ground is de- terminate and the cost is estimated. The pur- pose at this time is to arrive at comparative costs and so know the relative value of alter- nate routes. With these figures are placed the physical values of rise and fall, curvature and distance, together with climatic, political, maintenance, and economic values, the most suitable route becomes evident. To the engineer making a ground recon- naissance in heavy country, the matter of dis- tance is usually approximated, but on the air pictures that difficulty does not appear, as they can be measured on the photograph and the mosaic. ' In making these approximate reconnaissance estimates, the ground method has the advan- tage in a more detailed classification of the material. It contains, however, the more seri- ous possibility of overlooking the opportuni- ties of more favorable ground that is plainly evident from the air. Estimates of this type are visual approximations based on previous knowledge of similar conditions and little variation in judgment should occur. GROUND CONTROL The completion of the reconnaissance Hights and the photography concludes one complete section of aerial work. The choice of routes has been made and the remainder of the work re- quired is the making of a topographic map of the accepted route and the actual staking of the located line upon the ground and final esti- mating of cost. From this point, then, two courses are open. The topographic map can be made from the photographs after a ground control has been placed, or it can be made from measure- ments taken on the ground after a staked preliminary line has been established. The desired end is to obtain topography and tie it into a base line. This is required in order that the center line when projected upon the topography may be transferred to the ground in the same relation to the base or preliminary line that it occupies upon the map. Ground control consists of elevations on certain dis- tinguishable points at random on the picture and also the length and bearings of the courses between the points. This information may be secured by stadia or otherwise as the condi- tions warrant. A preliminary line would be a precise staked line close to the position that the highway was expected to occupy and form the base from which the topography would be taken and from which the projected center line would be located upon the ground. GROUND CONTROL IMPORTANT In mountain country such as that under consideration the preparations for doing either would be similar. The size of the party for ground control was less on the Lochsa than would have been the case for a preliminary line and the time taken for the fifty miles of canyon was less. Survey points upon the