Fig. 1. Feature maps of swept frequency BOTDR signal. (a) Raw BGS data of swept frequency BOTDR; (b) 3D-BGS; (c) BGS-Distance matrix; (d) groups of similar blocks

Fig. 2. BOTDR denoising flow based on BM3D algorithm

Fig. 3. System diagram of long-range BOTDR

Fig. 4. Experimental optical fiber schematic diagram

Fig. 5. BGS-Distance matrix before and after denoising. (a) Before denoising; (b) after denoising

Fig. 6. BFS curves before and after denoising

Fig. 7. BGS curves before and after denoising

Fig. 8. RMSE curves before and after denoising

Fig. 9. BFS curves before and after denoising under different temperatures. (a) BFS curves for raw data (Avg10000); (b) BFS curves for denoised data

Fig. 10. Spatial resolution analysis before and after denoising

Fig. 11. Comparison of different denoising methods. (a) BFS; (b) analyses of fluctuation range and RMSE