1.2.1 Spectral Density of Road Unevenness
For theoretical investigation of vehicle oscillations induced by road unevenness, the representation of unevenness as a function of time or the distance is usually not of significance. The statistical mean excitations induced by a road of characteristic unevenness is of higher significance. This implies the determination of the amplitudes and frequencies of excitation induced by the road at certain fixed distances.
The slide above shows the derivation of the power spectral densities, both in the distance as well as time domains.