# Autonomous Underwater Vehicle Localization Using Sound Measurements of Passing Ships
## 1 Introduction  
The localization problem of an Autonomous Underwater Vehicle (AUV) is a critical problem for the navigation of the AUV. This paper presents the localization of an AUV in environments (such as harbors or ports) where there can be passing ships near the AUV. In practice, there may be ships with known trajectories. We assume that the AUV can access the trajectory and approximate Source Level (SL) of a passing ship, while identifying the ship by processing the sound of the ship. The proposed localization method uses sound bearing measurements of a passing ship moving along a known trajectory (planned routes). We use the planned routes of large commercial ships. Large commercial ships make large noise, thus their sound signals travel a long distance in underwater environments. Hence, the sound information of large commercial ships is valuable for the proposed localization. The information of ships' trajectories is accessible, since a ship uses Automatic Identification System (AIS) nowadays. AIS records the position, routes, destinations of large commercial ships worldwide. The AIS of commercial ships is available using the following website: [[https://www.marinetraffic.com/](https://www.marinetraffic.com/)]([https://www.marinetraffic.com/](https://www.marinetraffic.com/)). It is feasible that the AUV can access approximate Source Level (SL) of a passing ship, while identifying the ship by processing the sound of the ship. [PERSON] et al. [1] introduced metrics of ship noise, including spatial radiation patterns, source levels, spectral characteristics, and sound exposure levels for seven merchant ship-types: container ships, vehicle carriers, bulk carriers, open-hatch cargo ships, and chemical, crude oil and product tankers. It is feasible to gather the SL information of large commercial ships using the estimation approach in [2]. [PERSON] et al. [3] acquiredthe noise data from a large number of individual ships, and calculated sound transmission loss (TL) to estimate ship source levels. Then, the relationship between ship noise source level and different parameters was analyzed; the mean source spectrum curve of selected ships was fitted; and the source spectrum model for merchant ship-radiated noise was established. The authors of [4] provided frequency analysis methods for estimating ship machinery sources and propeller noise. In the past, various localization techniques (acoustic, geophysical, optical, or sensor fusion methods) were used for underwater localization [5]. To localize an AUV by processing signal measurements, Time-Of-Arrival (TOA) [6; 7; 8; 9], Time-Difference-Of-Arrival (TDOA) [10; 11; 12], or Angle-Of-Arrival (AOA) [13; 14] can be used. In practice, short-BaseLine (SBL) [15], Ultra-Short-BaseLine (USBL) [16], and Long-BaseLine (LBL) [17] were widely used to track underwater vehicles and divers. However, SBL, USBL, or LBL require additional facilities, such as signal transmitters and receivers. Many papers [18; 19; 20; 21] discussed Cooperative Localization (CL) of an AUV assisted by a surface vehicle, say Communication Navigation Aid (CNA), which can utilize Global Positioning Systems (GPS) to localize itself. [PERSON] et al. and [PERSON] et al. [18; 22] handled the case where the AUV's motion is constrained by the CNA's motion. The CNA locates an AUV by measuring the relative position (or distance) of the AUV in [18; 19]. Several papers discussed cooperative localization of AUVs based on bearing-only [23; 24] or range-only measurements [25]. However, this paper handles the case where only one AUV exists, thus no CNA can be used for the AUV's localization. Consider the case where only one AUV exists, as in this paper. [PERSON] et al. [26; 27] integrated propeller and Inertial Measurement Units (IMU) for localization of the AUV. In the case where the AUV moves close to the sea bottom, Doppler Velocity Log (DVL) can be integrated to measure the AUV speed with respect to the ground [26; 27; 28].