Double peak-induced distance error in short-time-Fourier-transform-Brillouin optical time domain reflectometers event detection and the recovery method

Abstract

The measured distance error caused by double peaks in the BOTDRs (Brillouin optical time domain reflectometers) system is a kind of Brillouin scattering spectrum (BSS) deformation, discussed and simulated for the first time in the paper, to the best of the authors' knowledge. Double peak, as a kind of Brillouin spectrum deformation, is important in the enhancement of spatial resolution, measurement accuracy, and crack detection. Due to the variances of the peak powers of the BSS along the fiber, the measured starting point of a step-shape frequency transition region is shifted and results in distance errors. Zero-padded short-time-Fourier-transform (STFT) can restore the transition-induced double peaks in the asymmetric and deformed BSS, thus offering more accurate and quicker measurements than the conventional Lorentz-fitting method. The recovering method based on the double-peak detection and corresponding BSS deformation can be applied to calculate the real starting point, which can improve the distance accuracy of the STFT-based BOTDR system.

Dynamic Strain Measurement Using Small Gain Stimulated Brillouin Scattering in STFT-BOTDR

“…The rising edge for the case of 1.2W peak pulse power is further delayed. This is the distance error in time domain due to the double-peak effect of the BFS spectra in frequency domain with large BFS change [14]. With a worse SNR in the case of 1.2W, compared with that for the other two profiles, the distance error is more obvious due to the amplitude error of detected BFS by small SNR and the double-peak effect.…”

“…However, BOTDR usually needs a large number of averaging due to the weak power of spontaneous Brillouin scattering (SpBS) and the conventional frequency scanning method [13]. Recently, Short-time Fourier transform (STFT) algorithm is replacing the frequency scanning in BOTDR [12], [14]. STFT can reduce the averaging times and realize the dynamic strain measurement [12], [14], whose performance is limited by the signal-to-noise ratio (SNR) that is usually low in BOTDR [13].…”

Reconstruction of Distributed Strain Profile Using a Weighted Spectrum Decomposition Algorithm for Brillouin Scattering Based Fiber Optic Sensor

“…When the true strain profile varies within the given spatial resolution (like a crack or a sudden spatial change in strain), the Brillouin spectrum becomes distorted or contains additional peaks [5]. As the measured Brillouin spectrum is a superposition of all spectrum components with different peak frequencies, evaluating the peak frequency of the superposed T his paragraph of the first footnote will contain the date on which you submitted your paper for review.…”

Brillouin Scattering Spectrum Analysis Based on Auto-Regressive Spectral Estimation

“…Currently, FFT-based schemes can achieve high resolution in spatial and in accuracy. However, the measurement speed remains a problem [3][4][5][6][7].…”