## 3 Results
### Hydrographic Surveys  
Conducting data acquisition in designated areas (see Figure 2, Table 1), the measuring system on the hydrographic boats was configured to acquire all kinds of hydrographic and topographic data from the installed lidar systems at one time. The dual head of the multibeam echosounder provided information on bathymetry--the shape of the bottom, backscatter--data on the intensity of acoustic signal reflection, used for bottom classification, and water column data. The solution used, compared to the preparatory work (the first stage in Figure 4) with a single head, has the advantage of wider coverage of the bottom with data in a similar measurement time. This was made possible by using two heads and angular inclination of the sonar heads by \(\pm 20\) degrees outwards. Figure 7 compares data from the same area for one and two measuring heads. The use of two heads, at depths of 7-8 m, increased the range twice: from 26 m to 54 m (Figure 7). \begin{table}
\begin{tabular}{c c c} \hline \hline \multirow{2}{*}{**Accuracy Estimation**} & \multicolumn{2}{c}{**Coordinates’ Accuracy After Transformation [m]**} \\ \cline{2-3}  & **Calculated for Total Station** & **Calculated for TLS** \\  & **Point Cloud** & **Point Cloud** \\ \hline Mean error & \(1.4\times 10^{-3}\) & \(4.5\times 10^{-3}\) \\ Total error & \(1.4\times 10^{-3}\) & \(4.7\times 10^{-3}\) \\ (of point) & \(1.4\times 10^{-3}\) & \(4.7\times 10^{-3}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Coordinates of geodetic–photogrammetric control points. Figure 6: Offsets’ measurements from the point cloud: **(a)** HYDROMAPPER survey boat, **(b)** GNSS antennas, **(c)** MBES. With this configuration, improvements in scanning underwater vertical surfaces, i.e., quay walls, bridge pylons, are also apparent. The heads are physically tilted, so their point cloud collection capability is close to the water surface, which, in conjunction with laser scanning, results in an integral situational model (Figure 8). The hydrographic data underwent processing consisting of alignment of navigation data, removal of outliers, and cleaning of depth measurement interference. This was performed using manual and automatic techniques implemented in the hydrographic software (Kuda Processing 4.8.1). Finally, processing quality control was performed by comparing the mapped areas to the requirements of the IHO special category S-44. Table 4 shows the percentage of mapped areas that meet the IHO accuracy criteria for area type: Exclusive and Special. The green colour indicates achievement of accuracy in accordance with the standard. Figure 8: Quay wall (double MBES head) with a minimum depth of 0.0 m.  
Figure 7: Echosounder measurements: (**a**) one head, (**b**) two heads (MBES). \begin{table}
\begin{tabular}{c c} \hline \hline
\begin{tabular}{c} \hline \hline Survey Accuracy: Standard = Exclusive Order, \\ a = 0.150, b = 0.004 \\ Footprints conform with survey accuracy: \\ 21,263,698 (98.27\%) \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Evaluation of compliance of bathymetric data with the s-44 standard. Analysing the differential model (Figure 9) from the two measurement stages (equipment setup and data acquisition), it is clear that the configured bathymic system has repeatability in the same area. Cross-sectional profiles on the bathymic surface from the two stages showed slight deviations within the measurement error. The models were created one year apart, where bottom migration of the material has an influence. Subsequent models in designated areas confirm the repeatability of the system at intervals of several days. The occurrence of larger differences is within the limits of error. Figure 10 shows graphs for the accuracy of TVU (Total Vertical Uncertainty) and THU (Total Horizontal Uncertainty), which are part of the Total Propagated Uncertainty (TPU). The input data for the calculations were the measurement uncertainties of the individual sensors at a confidence level of 68% included in the MBES R2 Sonic dual-head measurement system.