19.
Two-Base Method of Altimetry
In the application of the two-base method of altimetry, it is not necessary to apply the correction factors for temperature,
relative humidity, latitude, or altitude as required in other altimetry methods. The application of these correction factors is
obviated by calibrating the density of the column of air over the area which is to be surveyed. This is done by reading base
altimeters located at the vertical extremities of the area at same time the field altimeter (at the unknown elevation) is read.
To find the elevation of the field station, the difference in altitude readings which are taken simultaneously at the field
station an(l the lower base (F' and L', fig. 8) is determine(l, as well as the difference in altitude between the
Figure 8. Two-base method.
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