Abstract
The navigation of autonomous underwater vehicles is a major scientific and technological challenge. The principal difficulty is the opacity of the water media for usual types of radiation except for the acoustic waves. Thus, an acoustic transducer (array) composed of an acoustic sonar is the only tool for external measurements of the AUV attitude and position. Another difficulty is the inconstancy of the speed of propagation of acoustic waves, which depends on the temperature, salinity, and pressure. For this reason, only the data fusion of the acoustic measurements with data from other onboard inertial navigation system sensors can provide the necessary estimation quality and robustness. This review presents common approaches to underwater navigation and also one novel method of velocity measurement. The latter is an analog of the well-known Optical Flow method but based on a sequence of sonar array measurements.
Highlights
GPS intelligent buoy (GIB) systems can be regarded as inverted long baseline (LBL) devices, where the transducers are replaced by floating buoys, self-positioned through GPS [25,26]
Since the most accessible means of external sensing is acoustic, we present various approaches, which are used in combination with acoustic means with inertial navigation system (INS) and correct biases inherent to its functioning
In addition to the approaches well-presented in the literature and practice of underwater research, we suggest a method that is an analog of the optical flow known in the video navigation of the unmanned aerial vehicles
Summary
Autonomous underwater vehicles (AUV) or “underwater drones” [1] constitute a significant class of robots that has many applications in various areas from commercial to military [2], including, e.g., marine archeology [3] and geoscience [4]. Direct positioning is achieved by the measurement of the time of acoustic signal propagation from the vehicle to some objects with a known position. One possible way to measure velocity is based on the Doppler effect, which manifests as the frequency shift proportional to the relative velocity Special devices, such as acoustic Doppler current profilers (ADCP). Underwater measurements are indirect: instead of coordinates, they yield distances and/or bearing angles For this reason, some of the mentioned methods have limited applicability, and more specialized approaches to estimation are necessary.
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