Read Ebook: Balloon observation and instructions on the subject of work in the basket by United States War Department Division Of Military Aeronautics

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SPOTTING OF POINTS.

The best method of work will be, then, that which suppresses as quickly as possible one of these dimensions and to conduct the research on a straight line.

Any point can be placed on the terrain or on the map if you know the following elements:

LOCATING ON THE GROUND AN OBJECT SEEN ON THE MAPS.

If it is a question of a very visible point , the spotting can be done almost immediately, it was found in the general reconnaissance of the terrain, which was discussed in chapter 1.

If, on the contrary, the point under consideration is difficult to find , we must have recourse to a precise method.

Identify on the map two points, one situated over and one short of the objective. Narrow down this bracket step by step until the object is recognized.

As this investigation of the range is the more difficult, observers must be warned against certain methods which are to be absolutely avoided--

If these two points are not at exactly the same height, the deformations due to oblique vision can falsify their apparent relative range. The point farthest away can even seem nearer, and the nearest point farther away.

EXAMPLE .--Suppose there are two trees, A and B, A being nearer the balloon and higher than B. It can happen that, in oblique vision , B having its image B? and A its image A?, the depression of the image B? is more than that of A?. In this case, the observer will be tempted to believe that the tree B is nearer him than the tree A.

Oblique alignment means a line connecting two points on the map and not passing through the horizontal projection of the balloon.

You might be tempted to use an alignment to find the range of an objective after having determined the direction. The process would consist in finding on the map two points so placed that the straight line between them passes through the objective, visualizing this line on the terrain, and placing the objective at the intersection of this visualized line and the direct alignment. This result, which would be accurate if the ground were absolutely flat, is made erroneous by the unevenness of the terrain. On account of this, the oblique alignment does not pass, in oblique vision, through the same points as its horizontal projection on the map.

EXAMPLE .--On the map C is the objective, A and B two points so situated that the line AB passes through C, and EF the direct alignment, or the line balloon objective. The line AB coincided on the terrain, with the trace of the vertical plane passing through A and B. In oblique vision it is different. The line A?C?B? is a curve which follows the irregularities of the ground, and the point C? is not on the oblique alignment A?B?.

LOCATING ON THE MAP AN OBJECT SEEN ON THE GROUND.

A result which you can obtain very quickly, thanks to the points which you had found in your first reconnaissance of the terrain.

This operation consists in determining the alignment of the objective. As this alignment is a straight line, you only have to know two points. One of them could be the horizontal projection of the balloon; but you must realize that this position is always changing a little, and it is hard to determine it with absolute precision. It is better to carry on the operation independent of this position, which means applying the following method:

This direction can be approximated to the extent of the thickness of the pencil mark. On its accuracy the final result depends. The difficulty lies in materializing the alignment--that is, the vertical line through the center of the objective--in order to lessen the chances for mistakes. Student observers should have frequent practice in this exercise.

When the point to be found is near the edge of the map it is sometimes necessary to take both reference points between the balloon and the objective; this should be avoided as much as possible, because it is apt to be less exact than when the objective is bracketed by its reference points.

Thus , two reference points A and B determine the alignment AB, O, the objective, is situated at some point between A and B. An error AA? in the spotting of one of these points leads to a smaller error in the position of the objective OO?--that is, smaller than AA?.

On the other hand, let both the reference points "a" and "b" be situated short of the objective O, "a" being nearer the objective and "b" nearer to the balloon. An error aa? in spotting "a" leads to an error OO? in the objective greater than aa?. Notice that this error diminishes as "A" approaches O, thus "a" being as a?, the error a?a?? equal to aa? leads to an error OO??, in the objective, less than OO?. We would thus obtain an analogous result if we would move the point "b" farther away.

Identify details of the terrain situated over and short of the objective on the alignment. Narrow this bracket down step by step; situate the objective on the map according to its relative distance from the two nearest identifiable reference points, taking into account the deformations due to the laws of perspective and the relief of the ground.

If you have a vertical photograph of the region, trace the alignment on this photograph and make the investigation in range by the same means.

The dangers against which I warned you before in connection with the investigation of range apply in this case also, so it is unnecessary to repeat them.

When the two last identifiable reference points are some distance from each other, the situation of the objective has a possible error, of which you know the size according to the distance between the two reference points; it might be interesting to remember this in case different information is obtained on this objective from that obtained in the balloon.

This error can be considerably diminished if you use a vertical photograph; the investigation can then be carried on by the same method as on the map, with greater precision. In the case of a battery, particularly, it is for the observer to find the position of each piece.

In case, on account of dead ground or of a mask before the battery, the observer sees the flashes or the smoke without seeing the battery itself, he should mark the exact alignment in which the flashes or smoke are seen, and determine the bracket in range--that is, the reference points nearest the objective which are clearly over and short. This document compared with other information can facilitate the identification of the battery.

OBSERVATION OF FIRE.

The observation of fire is essentially the following operation, repeated for each shot or salvo: Locating on the ground the position of one point, which is the point of burst, and announcing its situation in reference to another point, which is the target.

But it has been demonstrated that it is impossible, without using the map, to determine the error in range of one point relatively to another point not on the same alignment.

The operation must consist in:

The observation of the burst--that is, the spotting of the point of impact--is the same whether the observation is direct or lateral.

To draw the line balloon target, it is not necessary to know the horizontal projection of the balloon. It is enough to find on the ground a point situated directly on the alignment of the center of the objective.

The delicate part of the operation consists in seeing the shot at the moment of burst. One must try to spot the apex of the inverted cone formed by the burst, without paying any attention to the more or less considerable cloud of smoke which follows and which will cause mistakes if the burst was not seen immediately. The method of situating the point is the same as that described above.

For the direction, one reference point is enough, because one can consider the alignment of the point as practically parallel to the balloon-target. For the range, a rapid study of the terrain before the fire is sufficient to allow the observer to know the reference points by which he can guide himself. His eyes must never leave the point of burst until he has fixed well in his mind its situation in reference to appropriate reference points. Not to do this would lead to errors and to loss of time while he has to find the point again with his glasses to study it some more.

Particularly around batteries, the ground is often very irregular. There may even be little spaces of dead ground, caused by hollows which the map does not always show. The above method, applied with the help of photographs, allows you to avoid errors resulting from the existence of these hidden parts.

PRACTICAL ADVICE.

This position is preferable to all others, because it allows the observer--

To correct with his head and shoulders the movements of the basket.

To have the map always before him. He can consult it at any moment, mark the necessary alignments without loss of time, use it as a desk for drawing or taking notes, or as a wind shield when looking at photographs.

The observer who works standing up must either pick up his map from the bottom of the basket every time he needs it, which is out of the question, or fasten it outside the basket; the latter solution is inadvisable, it necessitates working in the wind when the map is referred to, and every time the observer turns to look at his map he disturbs the equilibrium of the basket.

It is advisable to work standing up only on days when there is practically no wind, and the balloon is continually turning and never becomes oriented.

To be able to trace an alignment on the map with precision, the rule must rest on a firm surface. This happens when the map is mounted on a drawing board; when it is mounted on a frame with rollers, the frame should have, between the two thicknesses of the map, a board level with the edges of the frame on which the rule can slide with its whole length on the map.

With a hard pencil, well sharpened, precise and neat alignments can be drawn.

The duodecimeter rule is for measuring distances on photographs and on the map; chiefly in observations of fire.

This advice, sometimes ignored by observers without expedience, has a great influence on the accuracy of information. When an observer holds the glasses in one hand, it is much more difficult for him to correct the movements caused by the balloon and to concentrate on a point. It is very important, therefore, to hold the glasses firmly with both hands, especially when you are making a delicate observation or when you wish to study an "objective" in detail.

NOTE 1.--All observations of rounds refer to the line battery target and a line perpendicular to same passing through the target. Observations are given in meters right and left and whether the round is over or short. Indications as to deflection are given before those of range. Indications as to the amount of error precede those as to the sense of the error. Example, 50 meters "Right," "over." Owing to the dispersion of fire when adjusting fire for field artillery or howitzer, it is unnecessary and of little value to the battery to give the amount of the error in range except when asked for by the battery commander or when the error in range is abnormal .

When the target is clearly visible and the effect of a round hitting a target is evident, the observation "Target" is reported. Unless the observer is certain of having seen the bursts "Unobserved" will be sent. If, however, after a few seconds smoke can be seen rising from trees, houses, etc., in proximity to the target, the observation "Unobserved, but smoke seen rising left and over," may be given.

NOTE 2.--Observers must beware of being over-confident in their own powers of observation. True confidence only comes with experience, and this is best attained by making ascents with a trained observer when ranging a battery and checking one's own observations with those given by him. An observation must never be given unless the observer is quite certain as to its correctness. It is essential to good results that the artillery may be able to rely absolutely on the observations sent down. The observer must watch the target but must avoid straining his eyes by putting up his glasses as soon as a round is fired. He should arrange for the chart room to inform him when a shell is about to fall. The latter must know the time of flight. Observers must learn to distinguish readily the bursts of different kinds of shells.

NOTE 3.--If the balloon-target line makes an angle with the battery-target line of more than 30? with field artillery and 20? with heavy, the balloon position will be given to the battery, and all observations will be given with reference to the balloon-target line and the battery will replot accordingly.

PLEASE READ THIS BEFORE YOU DISTRIBUTE OR USE THIS WORK

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