The effect of atmospheric temperature and elevation on the v

The effect of atmospheric temperature and elevation on the velocity of the electromagnetic energy propagated by the EDMI is typically adjusted by inputingppm into the instrument based on a chart termed a______________________________

Solution

ans: Refractive Index Ratio

All electromagnetic waves travel with the same velocity in a vacuum. The velocity of the waves is reduced when travelling through atmosphere due to retarding effect of atmosphere. Moreover, the velocity does not remain constant due to changes in the atmospheric conditions. The wavelength ? of a wave of frequency f has the following relationship with its velocity V.
? =v/f
EDM instruments use electromagnetic waves, any change in V will affect ? and thus the
measurement of the distance is also affected because the distance is measured in terms of wavelengths.
The changes in velocity are determined from the changes in the refractive index ratio (n). The refractive index ratio is the ratio of the velocity of electromagnetic waves in vacuum to that in atmosphere. Thus
V=C₀/n
The value of n is equal to or greater than unity. The value depends upon air temperature,
atmospheric pressure and the vapour pressure.