US Patent 9091754 Distance measurement methods and apparatus

Distance measurement methods and apparatus use laser pulse sets having signatures which enable returned pulses to be correlated with emitted pulses. Each pulse set comprises at least one pulse and a signature selected from a set of possible signatures. Pulse sets reflected from at least one surface are detected and, for each set, the signature is recognized and a time of flight is determined. Signatures are defined by one or more of: spacing in time between pulses of a set, wavelength of the at least one pulse of the set, spacing in time between a first subset of a set and a second subset of a set, difference of wavelength between pulses of a set, and difference of wavelength between a first subset of a set and a second subset of a set. Each set can have multiple groups of pulses and pulses within a group can have different amplitudes.