High Precision Positioning for Searching Airborne Black Boxes Underwater Based on Acoustic Orbital Angular Momentum

The search for flight data recorders (“black boxes”) is a worldwide problem when the plane falls into the sea after air crash. The underwater locator beacon built in the black box is an active-passive composite sonar, which can help locator in the Unmanned Underwater Vehicle (UUV) detect the approximate distance between the black box and the detection point by underwater communication. However, it is hard to give the exact azimuth of black box, which has brought great difficulties for searching. To solve this problem, a new underwater black box search system is proposed. It can narrow the searching range to hundreds of meters area. Besides, to further improve the positioning accuracy of the near range searching, angle detection based on acoustic Orbital Angular Momentum (OAM) is introduced into the system for azimuth measurement. The whole underwater black box search system includes 4 parts, namely the shipborne data processing and control center, UUV, Global Navigation Satellite System (GNSS) reference stations and GNSS intelligent buoys. They form an efficient search network entirely, which can determine the approximate area where the black boxes falls. Under this framework, the acoustic OAM is introduced for azimuth direction measurement of the black box. The traditional black box positioning results and acoustic OAM angle measurement information can be integrated based on the Extended Kalman Filter (EKF) method. Simulation results have shown great perspectives of this positioning system. Compared with the positioning results of the existing black box, which can only get the distance information by the pulse signal, the use of acoustic OAM angle measurement information reduces the positioning error of the black box by more than one order of magnitude. It greatly improves the positioning accuracy of the black box and reduces the search cost underwater in the deep sea.