Autonomous underwater vehicle navigation by means of a bottom imaging sonar

Emerging applications of AUV´s demonstrate a need for increasingly precise navigation systems GPS-based solutions are accurate but, in many underwater military applications, as mine warfare, the use of an external system is not affordable in view of the surfacing constraint or risks of loss of covertness it implies. Hybrid inertial navigation systems (INS) offer a good short term accuracy, but are subject to long term drift. This paper concerns bottom imaging sonar using synthetic aperture sonar (SAS) algorithms. We propose a combined approach based on an attitude and heading response system (AHRS) and an SAS algorithm. The synthetic aperture self-calibration parameters obtained are the basis of our method; the result of synthetic aperture processing is filtered, giving an estimation of the motion in the antenna coordinates, then the motion in the absolute reference coordinates is computed using the attitude assessment. This paper first reviews the SAS fundamentals; then the filtering method is defined. Finally, our approach is tested on simulations. The accuracy we obtain is about 0.5 ⁰/₀₀ of the travel length