Maximum unambiguous range

From Glossary of Meteorology

maximum unambiguous range

The maximum range from which a transmitted radar, lidar, or sodar pulse can be reflected and received before the next pulse is transmitted. This range, rmax, is given by rmax = cT/2, where T is the interpulse period and c is the speed of light (or speed of sound in the case of sodar).

Range is measured by the time delay between pulse transmission and reception, ordinarily assuming that the received pulse is associated with the most recent transmitted pulse. Targets at ranges beyond rmax therefore appear at ranges closer than rmax because of range folding. Special coding of the pulses permits discrimination between echoes from the most recent transmitted pulse and earlier ones, enabling the measurement of ranges beyond rmax.
See also second-trip echo, range aliasing.