## 6 Conclusions  
This article presents the possibility of using CNN to identify the structure of liquid-gas flow in a horizontal pipeline based on the analysis of signals from a radiometric measurement system. The tests were performed for four types of flows: slug, plug, plug-bubble, and bubble. At the input of the VGG-16 network, available in the MATLAB environment, histogram images with a size of 224 \(\times\) 224 pixels, built for signals from the scintillation detector, were used as predictors. To compare the results, histograms were made for different numbers of classes: 28, 56, 112, and 224. For all four types of flows and all numbers of classes, good recognition results were obtained, which is confirmed by the calculated indices (values above 0.8). The best recognition (values of all indicators equal to 1) was obtained for the slug flow.  
The classification results obtained may be useful in radiometric measurements of two-phase liquid-gas flows in pipelines, in which the velocities (or flow rates) and the  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Number of Classes** & **28** & **56** & **112** & **224** \\ \hline bubble & 0.889 & 0.917 & 0.909 & 0.917 \\ \hline slug & 1 & 1 & 1 & 1 \\ \hline plug–bubble & 0.826 & 0.808 & 0.840 & 0.875 \\ \hline plug & 0.909 & 0.955 & 0.960 & 0.958 \\ \hline \hline \end{tabular}
\end{table}
Table 4: Values of the “precision” indicator.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Number of Classes** & **28** & **56** & **112** & **224** \\ \hline bubble & 0.958 & 0.972 & 0.972 & 0.972 \\ \hline slug & 1 & 1 & 1 & 1 \\ \hline plug & 0.944 & 0.931 & 0.944 & 0.958 \\ \hline plug & 0.972 & 0.986 & 0.986 & 0.986 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Values of the “specificity” indicator.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Number of Classes** & **28** & **56** & **112** & **224** \\ \hline bubble & 0.941 & 0.917 & 0.869 & 0.917 \\ \hline slug & 1 & 1 & 1 & 1 \\ \hline plug–bubble & 0.809 & 0.840 & 0.857 & 0.875 \\ \hline plug & 0.869 & 0.913 & 0.980 & 0.958 \\ \hline \hline \end{tabular}
\end{table}
Table 5: Values of the “\(F1\)” indicator.  
share of individual components of the mixture are determined. Identification of the flow regime is another piece of information that is important for controlling industrial processes and is additionally obtained from recorded measurement signals.  
Conceptualization, R.H. and P.O.; Methodology, R.H. and P.O.; Software, P.O. and M.A.; Validation, M.Z. and M.A.; Formal analysis, M.Z. and M.A.; Investigation, R.H. and P.O.; Data curation, M.Z. and P.O.; Writing--original draft, R.H.; Writing--review & editing, R.H., M.Z. and M.A.; Visualization, M.Z. and P.O.; Supervision, R.H. All authors have read and agreed to the published version of the manuscript.  
This research work is co-financed from the state budget under the program of the Polish Minister of Education and Science under the name Polska Metrologia, project no. PM/SP/0020/2021/1, co-financing amount PLN 975,590, total value of the project PLN 975,590.  
The raw data supporting the conclusions of this article will be made available by the authors on request.  
Author [PERSON] was employed by the company Bury Technologies. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.