Fig. 1. Frequency spectrum characteristics of laser signal. (a) Result of time-frequency analysis; (b) profile of time-frequency analysis; (c) frequency spectrum

Fig. 2. Phase characteristics of laser signal. (a) Phase introduced by frequency with sinusoidal variation; (b) phase introduced by frequency with random variation; (c) random phase noise

Fig. 3. Diagram of phase estimation method

Fig. 4. RMSE of the phase estimation result

Fig. 5. (a) Phase estimation result and (b) phase estimation error with the delay of 700 m; (c) phase estimation result and (d) phase estimation error with the delay of 5000 m; (e) phase estimation result and (f) phase estimation error with the delay of 7500 m

Fig. 6. Low spectrum of echo signal. (a) Original frequency spectrum; (b) frequency spectrum after local oscillator digital delay processing; (c) main lobe of the frequency spectrum after local oscillator digital delay processing