Chapter 1.ORIENTATION AND GENERAL RECONNAISSANCE OF THE TERRAIN.
This is the operation which the observer executes on his first ascension in a new sector; this is how it should be conducted.
1.Rapidly look over the terrain around the ascensional point in order to orient the map.
This is done by finding in some direction from the ascensional point a line giving an easily identifieddirection (a road, an edge of woods, etc.). Orient the map so as to make this line on the map parallel to the line on the ground.
The map can also be oriented by means of the compass.
2.Locate the horizontal projection of the balloon.
The observer may know already the winch position, but the balloon is carried off horizontally from the winch sometimes as much as 400 or 500 meters (436 to 545 yards). Thus it is essential not to confuse the winch position with the horizontal projection of the balloon. If this is done, errors will be made in the operations which we are going to discuss later, where we make use of this known point.
It is pretty hard to materialize definitely the vertical line passing through the basket. The effect of the wind and the movements of the balloon make it impossible to use a plumb line. The observer has to find his projection on the ground by leaning first from one side of the basket and then from the other in order to diminish the chances of error. An approximation of 25 or 50 meters is sufficiently accurate for the general reconnaissance which it is necessary to make.
3.Leaving the region beneath the balloon, acquaint yourself, step by step, with the most prominent points in different directions—masses of woods, villages, etc.
There are two methods—by the process ofcheminementor tracing landmarks and by the process of direct alignment.
The process of “cheminement” or tracing consists in following outlines, such as roads, streams, or hedges, identifying as you go along details of the terrain which these lines pass through or near. On account of the deformations due to the effect of perspective and to the unevenness of the ground, and particularly on account of the deformation of angles, if it is a winding road, this method often leads to errors; it should be employed only in certain cases defined below:
The process of “direct alignment” consists of studying the terrain by following successive directions from the balloon position.
We call the “alignment” of a point the trace, on the terrain, of the vertical plane passing through this point and through the eye of the observer; in perspective vision, when the observer determines the point in question, this alignment would appear to him a vertical line. On the map it is nothing more than the straight line joining the point under consideration to the vertical projection of the balloon.
The method of alignment, then, consists in first identifying the most prominent points near the balloon and finding, bycheminementor tracing, the lines running from these points.A point found directly by cheminement should not be considered as definitely determined until its alignment has been verified.
This first reconnaissance is not to study the terrain in all its details, but only to fix in the memory a certain number of prominent points scattered throughout the sector in order to facilitate later work.
These points should be very distinct, visible to the naked eye, and of characteristic forms, so that there will be no danger of confusing them with others—masses of woods, important villages, etc. Roads with borders of trees, large paths for hauling supplies, when taken together, are very valuable for quickly finding others.