Fig. 1. Diagram of optical fiber temperature sensing system based on BOTDA

Fig. 2. Diagram of Brillouin scattering signal

Fig. 3. Algorithm flow of AdaGrad

Fig. 4. Flowchart of extracting BFS by AdaGrad

Fig. 5. Experimental block diagram of fiber optical temperature sensing system based on BOTDA

Fig. 6. Diagram of pulse peak power measurement

Fig. 7. Relationship between pulse peak power and Brillouin scattering signal. (a) Ps=17.3 dBm; (b) Ps=14.5 dBm

Fig. 8. Three dimensional map of Brillouin scattering spectrum

Fig. 9. Two dimensional map of Brillouin scattering signal

Fig. 10. Brillouin scattering spectrum fitting curves with assignment of initial value deviating from real value. (a) General gradient descent method; (b) AdaGrad

Fig. 11. Brillouin scattering spectrum fitting curves with assignment of initial value close to real value. (a) General gradient descent method; (b) AdaGrad