# Positioning Systems for Unmanned Underwater Vehicles: A Comprehensive Review
## 1 Introduction
### Positioning Systems of UUVs
#### 2.4.1 Primary Positioning Systems
However, it can be affected by magnetic interference from natural or man-made sources, limiting its effectiveness in certain conditions [61; 62]. Hydrostatic Pressure Sensors (HPSs) measure the pressure exerted by the surrounding water to determine the depth of a UUV. These sensors are crucial for maintaining depth control in underwater operations. They are simple, reliable, and effective for depth measurement but provide limited information on horizontal positioning or orientation. They are typically used in conjunction with other systems for comprehensive navigation [63]. Satellite Navigation Aided Systems use signals from satellites to aid in the navigation of UUVs, often in conjunction with surface support vessels [64]. These systems leverage GPS or other satellite signals to provide accurate positioning data on the surface, which can be relayed to the UUV. They are highly accurate when the UUV is close to the surface but are less effective underwater, where satellite signals cannot penetrate [13]. * Synthetic Aperture Sonar (SAS) is an advanced sonar technology that creates high-resolution images of the underwater environment by processing sonar data collected over a wide area [65]. SAS provides detailed imagery and is useful for seabed mapping, underwater inspections, and object detection. However, it requires significant data processing capabilities and can be affected by water conditions [66]. * Beacon-based Localization uses acoustic or electromagnetic beacons deployed at known locations to provide reference points for positioning [67]. UUVs communicate with these beacons to determine their location based on the received signals. This method is effective for precise localization and tracking but requires the deployment of multiple beacons, which can be logistically challenging [68]. * Photogrammetry involves using high-resolution images to create detailed 3D models of underwater environments [69]. By analyzing overlapping images taken from different angles, photogrammetry can provide accurate spatial information. This technique is useful for detailed surveys and inspections but is limited by visibility and lighting conditions [70]. * SLAM (Simultaneous Localization and Mapping) is a method that allows a UUV to build a map of its environment while simultaneously determining its location within that map [71]. SLAM combines sensor data, such as sonar or cameras, with algorithms to continuously update the vehicle's position and map. It is effective for exploring unknown environments but can be computationally intensive and requires sophisticated processing [72]. * Electromagnetic Positioning systems utilize electromagnetic fields to determine the position of a UUV. These systems can be particularly useful in environments where acoustic methods may be less effective, such as in areas with high levels of ambient noise. However, electromagnetic positioning is influenced by the conductivity of the water and the presence of other electromagnetic sources [73; 74]. * LIDAR (Light Detection and Ranging) uses laser pulses to measure distances and create detailed 3D maps of underwater environments. LIDAR systems are highly effective for capturing fine details and generating accurate models. However, they are limited by the penetration depth of laser beams in water and are typically used in conjunction with other sensors [15; 75]. * Buoy-based Positioning involves using surface buoys equipped with positioning systems to provide reference points for UUVs. These buoys can relay position data via acoustic or other communication methods, helping to track and guide UUVs. This method is useful for surface-tracked missions but may have limited effectiveness in deep or remote locations [76; 77; 78]. * Fiber Optic Gyroscope (FOG) provides precise measurements of angular rotation by detecting changes in light polarization through fiber optics. FOGs are known for their high accuracy and stability, making them suitable for advanced navigation systems.