## 2 Materials and Methods
### GNSS > Sonar > Phone System Implementation  
#### 2.2.1 Devices and Apps  
The \(\mathrm{G>S>P\) Sys consists of a hardware part and a software part. The hardware components forming the \(\mathrm{G>S>P\) Sys and tested, also individually, in this work were the Deeper Smart Sonar Pro+ 2 (Deeper UAB, Vilrius, Lithuania), the Deeper Smart Sonar CHIRP+ (Deeper UAB, Vilrius, Lithuania), the SimpleRTK2B (ArduSimple, Principality of Andorra) and the Huawei P30 Pro (Huawei Technologies Co., Ltd., Shenzhen, China). The Deeper Smart Sonar Pro+ 2 and CHIRP+ are two Single Beam Echo Sounders [29; 30] operating at frequencies of 100 kHz, 240 kHz and 675 kHz and with scan cones of 47\({}^{\circ}\), 20\({}^{\circ}\) and 7\({}^{\circ}\) respectively. The devices perform about 15 scans per second and cover a depth ranging from a minimum of 0.15 m to a maximum of 100 m.  
The Deeper Smart Sonars have an internal GNSS receiver that enables geolocation. Alternatively, they can geolocate themselves via the GNSS receiver of the smartphone. The Sonars connect to the smartphone via Wi-Fi and are controlled by an app called Fish Deeper--Fishing App. This allows Sonars to transmit their data to the smartphone (Sonar data in Figure 1). Due to geolocation, the Sonars produce 2D maps with the bathymetric information obtained while scanning the bottom. The products of a survey immediately available to a user consist of a georeferenced sonar scan of the bottom and a 2D bathymetric map. The products are displayed in real-time on the smartphone and, after the survey, are also available via the web platform of Deeper UAB. Instead, the raw data, downloadable from the smartphone and the web platform, consist of a text file (*.csv) containing the latitude and longitude of the acquired points, the depth values recorded from the bottom scans (in metres), the water temperature values (in \({}^{\circ}\)C) and the acquisition time of the sonar scans (in UNIX format). The difference between the Deeper Smart Sonar CHIRP+ and the Pro+ 2 consists of the CHIRP technology. CHIRP stands for \"Compressed High Intensity Radar Pulse\" and sonar with CHIRP technology, unlike a classic sonar, scans the bottom by sending multiple pulses simultaneously. This provides more information and allows it to create more accurate scans, better detect the bottom and better separate targets. Table 1 shows the technical features of the Deeper Smart Sonar Pro+ 2 and the Deeper Smart Sonar CHIRP+. The SimpleRTK2B is an external GNSS receiver based on the ZED-F9P GNSS module made by U-Blox (U-Blox, Thalwil, carton of Zurich, Switzerland) that can be connected to various devices including smartphones allowing more precise geolocation [31]. The SimpleRTK2B allows observation of GPS, GLONASS, Galileo and Beidou constellations and reception of the L1C/A L2C, L1 OF L2 OF, E1-B/C E5b, B1I B2I frequencies. In this work, a Bluetooth data transmission module (AS-XBEE-BT-2.4-INT-00) and a Helical multiband GNSS antenna (IP67) were added to the receiver. Using U-Center (software to manage U-Blox GNSS), the receiver was programmed to transmit via Bluetooth the real-time position in Single Point Positioning (GNSS-SPP data Real-time in Figure 1) and transmit via USB On-The-Go (USB OTG) connection the GNSS raw data in *.ubx format (GNSS-Raw data in Figure 1).