Fig. 1. Block diagram of experimental system

Fig. 2. Measurement results of dynamic strain applied on 84.3 km position of sensing fiber. (a) DAS waterfall plot using NLL; (b) DAS waterfall plot using ITLA without PNC; (c) DAS waterfall plot using ITLA with PNC; (d) amplitude spectral density curve of measured dynamic strain signal using ITLA with PNC; (e) distribution of effective signal amplitude along distance near the position where strain is applied using ITLA with PNC

Fig. 3. Variation of strain resolution with fiber distance

Fig. 4. Strain resolutions achieved by DAS system under different bit depths of data acquisition card. (a) 0‒1 km potision of fiber; (b) 50‒51 km potision of fiber; (c) 83‒84 km potision of fiber

Fig. 5. Effect of bit depth on strain resolution. (a) Strain resolutions at 0‒1, 50‒51, and 83‒84 km of fiber with Bits (PDR) varying from 2 to 16 when Bits (AUX) is fixed at 8; (b) raw data segment extracted near 50 km of fiber (16-bit quantized), and corresponding 6-bit and 4-bit quantized results (where half of quantization step is subtracted to remove direct current component for better comparison); (c) demodulation results of sinusoidal strain applied by PZT at 84.3 km of fiber under Bits (PDR) of 2, 8, and 16