A subharmonic detrending or data-smoothing approach for longitudinal road profile measurements

Commonly used figure-of-merits for longitudinal road profiles such as the International Roughness Index (IRI) and the Ride Number (RN) are based on statistical properties. Raw measured longitudinal road profile data may contain large trending components especially when the measurements are made with walking profilers in hilly regions. To obtain approximate stationary data suitable for statistical processing measurements should be subjected to detrending before calculating the IRI- or RN- value. In this paper a novel detrending method is proposed which is well suited for removing large profile trends without significantly corrupting the short wavelength content of the profile data. The method called sub-harmonic detrending works by fitting sub-harmonic sinusoids to the data followed by circular filtering in order to remove the trend. The method is also well suited for data-smoothing.