Patent ID: 8451433

Claim:
A range-finding method comprising the steps of: (i) dividing a beam of pulsed radiation into first and second portions at a division point; (ii) directing the first portion from the division point to a remote target along a first path; (ii) directing the second portion from the division point to a local retro-reflector along a second path; (iii) adjusting the repetition rate of the beam of pulsed radiation to a first value f1 such that pulses of radiation retro-reflected from the remote target spatially coincide at the division point with pulses of radiation reflected from the local retro-reflector; (iv) increasing or decreasing the repetition rate of the beam of pulsed radiation to a second such value f 2 ; and (v) finding the frequency difference±(f 1 −f 2 ) and hence the range of the remote target.