Fig. 1. Schematic diagram of principle analysis of back Rayleigh scattering. (a) Back Rayleigh scattering discrete model diagram; (b) back Rayleigh scattering light detection optical path

Fig. 2. Schematic diagram of modulation system

Fig. 3. Time domain waveform of linear sweep signal

Fig. 4. Echo signal strength versus sensing distance

Fig. 5. Modulation system structure diagram

Fig. 6. Time domain waveform of echo signal

Fig. 7. Frequency domain waveform of linear sweep signal

Fig. 8. Frequency domain waveform of echo signal. (a) Unamplified echo signal frequency domain waveform frequency domain waveform; (b) (c) (d) frequency domain waveform of echo signal amplified at different times