SECTION VI
METHODS OF ALTIMETRY
15.
General
This section outlines the methods of altimetry used in conjunction with surveying altimeters manufactured by
Wallace & Tiernan. The altimetry methods described herein are confined to three: the single-base, the two-base, and the
leapfrog. The single-base method requires a minimum of observers and equipment. However, because it requires the
application of many correction factors it is not the most practical or accurate of the three methods. The two-base method
is the most widely used and is generally accepted as the standard for accuracy. It does not require the application of all
the correction factors needed in the single-base method. Instead, a calibration is made which compensates for air density
over the area to be surveyed, and, through the use of two-base altimeters, a highly accurate altimeter survey is possible.
The leapfrog method again requires the use of the same series of correction factors used with the single-base system.
However, the leapfrog method has an advantage over both the other fixed-base methods in that the altimeters used are
always in close relationship to each other and therefore operate under reasonably similar atmospheric conditions. This
contrasts with fixed-base methods where the roving altimeters move continually away from the base station and perhaps
encounter pressure and temperature conditions which do not
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