in their originally intended use, aircraft employ dme to determine their distance from a land-based transponder by sending and receiving pulse pairs. the ground stations are typically collocated with vors or vortacs. a low-power dme can be collocated with an instrument landing system, ils localizer, or microwave landing system (mls) where it provides an accurate distance to touchdown, similar to that otherwise provided by ils marker beacons (and, in many instances, permitting removal of the latter).