A novel signal encoding and decoding method for laser ranging is described. The coherent burst method achieves high precision ranging based on simultaneous analysis of time-of-flight and phase shift of an amplitude modulation pattern that is electronically coherent with a master oscillator. High frequency modulation provides high absolute precision, while measured temporal delay from transmission to reception eliminates uncertainty from aliasing. Demodulation of the coherent burst signal is achieved using quadrature analysis. Electronic coherence between the coherent burst modulation pattern and a master oscillator is used to generate analytic signals representing the real and imaginary components of the demodulated return signal. These components are used to determine magnitude and phase of a vector representing the signal from the target. The phase of this vector provides an estimate of phase shift between the return signal and the master oscillator, while the leading edge of the magnitude envelope is used to obtain an estimate of time-of-flight.
Eric A. Wachter,
Walter G. Fisher,
Michael L. Keltos,
"Coherent burst laser ranging", Proc. SPIE 3380, Laser Radar Technology and Applications III, (8 September 1998); doi: 10.1117/12.327198; https://doi.org/10.1117/12.327198