## 2 Materials and Methods
### Features of AUV Performance and AUV-Based Side-Scan Sonar Operations
#### 2.1.3 Differences between Shipborne and AUV-Mounted Side-Scan Sonar Operations  
Shipborne side-scan sonar systems are typically classified into two installation modes: hull-mounted and towed. The hull-mounted configuration offers enhanced positional accuracy by aligning the sonar system's attitude with the vessel's. However, its practicality is limited to shallow waters, with the attainable depth range depending on the device's measuring capabilities. Conversely, the ship-towed sonar system can operate in deeper waters, with the attainable operational depth dependent on the length of the tow cable.  
Figure 5: Constant-altitude and constant-depth motion control modes. The top blue line represents the sea surface, the second blue line represents the track line for constant-depth, and the third yellow line represents the track line for constant-altitude mode. The yellow filling represents the seabed.  
Nonetheless, this configuration has limitations, including limited cable length, uncertainties arising from imprecise depth control, and reduced positional accuracy caused by the simplified reduction model required to locate the system. Furthermore, underwater attitude hinges on a separately built-in attitude sensor, which is not a standard feature in side-scan sonar equipment. The sonar system's altitude or depth is influenced by velocity, a parameter that does not always align with the vessel's speed, consequently leading to inertial delays.  
When deploying an AUV for side-scan sonar payload operations, it is imperative to consider both the fundamental principles of these operations and the vehicle's performance characteristics. The submersible has the potential to outperform shipborne side-scan sonar while remaining aligned with the principles of side-scan sonar operations [30]. Unlike shipborne side-scan sonar, its AUV-based counterpart is incorporated with its carrier, ensuring remarkable consistency in speed and attitude. As the AUV system combines satellite navigation, inertial navigation, and bottom-tracking navigation, reinforced by high-precision attitude sensors, it exhibits precise satellite positioning capabilities on the sea surface, along with robust attitude measurements underwater, complemented by altitude and depth measurement functions. Beyond that, the vehicle's ability to maintain a consistent attitude and vertical position enables it to perform vertical motion, a capability absent in shipborne operating modes. Nevertheless, given its inability to receive satellite signals underwater, the AUV primarily navigates through underwater regions via a combination of inertial and bottom-tracking navigation. Underwater acoustic communication-based positioning can also be an option, though it is infrequently employed due to precision limitations.  
In essence, the AUV-mounted side-scan sonar differs from its conventional shipborne equivalent. These two systems exhibit distinct operational characteristics, differing significantly in many aspects such as localization, navigation, operational depth, sea area coverage, underwater attitude, survey line deployment, and data characteristics. These disparities underscore the divergence in their operational requirements and mission planning considerations.