The maximum range of radial velocity that can be observed without ambiguity by a Doppler radar, sodar, or lidar. Velocities outside this interval are folded into the interval. For a pulsed radar or sodar operating with an interpulse period T, or a lidar with an A/D converter sampling interval T, the unambiguous velocity interval is −λ/4T to +λ/4T, where λ is the operating wavelength. This interval can be extended by the use of dual PRF and other techniques. See velocity aliasing, Nyquist frequency.