## 2 Materials and Methods
### Measurements  
The assessment of the effect of the conducted unmanned vessel modernisation on the operational properties was carried out based on experimental testing. On 7 March 2019, hydrographic measurements were performed to assess the accuracy of steering an ASV/USV in automatic mode along sounding profiles (Figure 7) designed in accordance with the principles included in the IHO S-44 standard [6]. Since the hydrometeorological conditions are an important factor affecting the obtained results, the measurements were performed in windless weather and the sea state was equal to 0 according to the Douglas scale (no wind waves or sea currents). The waterbody selected for the study was a small storage reservoir located in Gdarsk with a constant depth of 1.5 m, an orthophotomap of which was obtained from the Google Earth platform. The study used an USV modernised to include automatic mode and equipped with a low-cost multi-GNSS receiver, whose task was to sail along the pre-set test routes. The sounding profiles were designed in four variants. For the first two routes (Figure 7a,b), they were designed in such a manner \begin{table}
\begin{tabular}{c c c c} \hline \hline
**A/O** & **Functionality** & **Before Modernisation** & **After Modernisation** \\ \hline A & Control & Direct RC & Direct RC, semi-automatic, \\ A & RC operation range & 300 m (2400 MHz) & 1 km (868 MHz) \\ A & Telemetry monitoring & Additional PC & Integrated with the RC equipment \\ A & Positioning system & u-box NEO-7: 56 channels; GPS, & u-box NEO-M8N: 72 channels, GPS, \\  & & GLONASS, Galileo, QZSS, SBAS & GLONASS, BDS, Galileo, QZSS, \\ O & Possibility for hull & & SBAS \\ O & replacement & No & Yes \\ O & Type of drive & Engines, main engine & Integrated pushing propellers \\  & & shafts, screws & \(2\times 50\) N \\ O & Engine cooling and ESC & Yes - forced, water & Not required \\ O & Battery bank & \(2\times 9\)Ah AGM (\(2\times 108\) Wh) & \(2\times 22\) Ah LiPo (\(2\times 326\) Wh) \\ O & Time of operation until & 1.5 h & 6 h \\ O & battery replacement time & & 25 kg & 18 kg \\ O & Ingress protection class & IP44 & IP56 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: A summary comparison of the USV functionality parameters before and after the modernisation. Figure 6: A schematic diagram of the main components subjected to the USV modernisation. that the sounding lines were parallel to each other. The mutual distance between the profiles was assumed to be 5 and 10 m. The arrangement of the sounding profiles of two other routes (Figure 7c,d) resembled \"narrowing squares\" (a spiral of) towards the centre of the waterbody being sounded. The distance between the successive polygons was constant and amounted to 5 and 10 m for both variants, similar to the first two routes. The test routes, i.e., hydrographic sounding profiles along which the USV moved, were planned using a typical geodetic software, Trimble Business Center, and satellite images obtained from the Google Earth platform. The coordinates of the route turning points were then exported to *.knl files. They were recorded as geodetic coordinates, referred to the WGS84 ellipsoid with a precision of nine decimal places. The planned USV routes set in this manner were converted to *.shp files dedicated to the ArduPilot Mission Planner software operating the 3 DR PX4 Pixhawk autopilot installed on the vessel, thanks to telemetry (TBS Crossfire TX LTE). A navigation multi-GNSS receiver NEO-M8N (GPS, GLONASS (GLObal NAvigation Satellite System), BDS (BeiDou Navigation Satellite System), Galileo, QZSS (Quasi-Zenith Satellite System), SBAS (Satellite Based Augmentation System)), which was installed along the vessel's axis, was connected to the autopilot. In order to assess the steering accuracy, a geodetic receiver (Trimble R10) using the GNSS geodetic network was applied.