A doppler radar of the type normally used to measure relative speed between a transmitter and a reflector is mounted so that its antenna is directed toward the surface to be measured. The radar is coupled to a means for de-emphasizing the doppler shift frequencies of the return signal associated with the speed of the vehicle and emphasizing the lower frequency components of the back scattered signal. The energy contained in these components provides an indication of the roughness of the surface which is in relative motion to the radar.