= +3 br 
As far as the errors which may be found in radar 
profiles are concerned, a definite distinction may be made 
between errors in the barometric determination of the 
differences in aircraft height and errors arising from the 
use of electronics in measuring distance. In order to give 
a clearer picture of the method itself, we will enumerate the 
most important errors of these two groups. 
To the first group belong: 
1) the error in determining the 
differences in aircraft altitude with reference 
to the isobaric surface. This error probably 
amounts to l meter (3 feet). 
2) local anomalies and lack of 
parallelism between the isobaric surface and the 
geoid. By choosing a suitable flying altitude 
the effect of local atmospheric disturbances, 
which are concentrated in relatively limited areas 
above the earth's surface, are almost eliminated. 
The minimum flying altitude is therefore 700 - 1300 
meters (about 2000 - 4000 feet), depending on the 
nature of the terrain. The fact that the elevation 
is measured by means of a barometer at a certain 
altitude in the atmosphere is one of the most 
important characteristics of the radar profile method. 
Any further differences in atmospheric pressure which 
may be encountered during flight can be compensated in two ways: 
a) by applying the formula derived in 
connection with the development of the radar profile 
method, with which it is possible to calculate the 
gradient of the barometric air pressure during 
flight as a function of the angle of drift and other 
known factors, and 
b) by making, if possible, corrections 
after comparing the profile with actual spot heights 
on the ground. 
The formula used in calculating the air pressure 
gradients, in its abbreviated form. is: 
& This formula was evolved by T. J. G. Henry of the Meteorolo- 
gical Branch of the Department of Transport