## 4 Discussion
### Localization Accuracy and Precision
Overall, the quasi distributed sensor configuration tends to produce smaller localization uncertainties, especially at longer pulse lengths than the fully distributed one for the setup with a short pipe segment used here. This is attributed to the possibility of signal averaging over a certain bin range and resulting higher signal-to-noise levels. However, for longer pipes it is expected that \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**No.**} & **Sensor Design** & **Position of Impact** & **Optical Pulse Length/ns** & **Evaluation Procedure** & **Localization Uncertainty/cm** \\ \hline \multirow{2}{*}{1} & fully & \multirow{2}{*}{A} & \multirow{2}{*}{100} & \multirow{2}{*}{differentiation, direct} & \multirow{2}{*}{51} \\  & distributed & & & & \\ \hline \multirow{2}{*}{2} & fully & \multirow{2}{*}{B} & \multirow{2}{*}{100} & \multirow{2}{*}{differentiation, direct} & \multirow{2}{*}{51} \\  & distributed & & & & \\ \hline \multirow{2}{*}{3} & fully & \multirow{2}{*}{B} & \multirow{2}{*}{50} & \multirow{2}{*}{differentiation, direct} & \multirow{2}{*}{32} \\  & distributed & & & & \\ \hline \multirow{2}{*}{4} & fully & \multirow{2}{*}{B} & \multirow{2}{*}{30} & \multirow{2}{*}{differentiation, direct} & \multirow{2}{*}{19} \\  & distributed & & & & \\ \hline \multirow{2}{*}{5} & quasi & \multirow{2}{*}{A} & \multirow{2}{*}{50} & \multirow{2}{*}{differentiation and summation, signal onset (automatically)} & \multirow{2}{*}{20} \\  & distributed & & & & \\ \hline \multirow{2}{*}{6} & quasi & \multirow{2}{*}{B} & \multirow{2}{*}{100} & \multirow{2}{*}{differential and summation, signal onset (automatically)} & \multirow{2}{*}{22} \\  & distributed & & & & \\ \hline \multirow{2}{*}{7} & quasi & \multirow{2}{*}{B} & \multirow{2}{*}{50} & \multirow{2}{*}{differentiation and summation, signal onset (automatically)} & \multirow{2}{*}{21} \\  & distributed & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Summary of the localization uncertainties obtained in DAS measurements for different sensor configurations, optical pulse lengths and evaluation procedures. Positions of mechanical impacts are either on the front face (A) or on the side of the pipe (B). Uncertainty is given as twice the standard deviation (confidence interval of 95.5%). signal intensities and localization precision will deteriorate if the distance between disturbance and the localized sensors increases. This effect was also observed by [PERSON] et al. (2018) for localization on a pipe with acoustic emission sensors. For the fully distributed fiber-optic sensor configuration this effect is irrelevant so that the localization precision should be only influenced by the effect of overall signal attenuation along the optical fiber which is present for any sensor configuration. For selection of an optimal application geometry in an industrial environment these advantages and disadvantages must be considered alongside issues concerning accessibility of pipes, overall range to be monitored and the required spatial resolution. Moreover, for practical pipes, which often have a larger diameter than the ones inspected here, the localization precision and accuracy would increase when employing similar fiber pitch as in the experiments shown here. However, in this case the monitoring distance along the pipe would be decreased and/or the bandwidth restricted further. Therefore, it is expected to be favorable to adjust the fiber pitch to larger values in order to cover longer stretches of pipeline, as in many practical cases lower spatial resolution than the one reached here should be sufficient.