Acoustic Transponders Essay

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Acoustic Transponders
Three main acoustic positioning systems (Fig. 3) used for localization of AUVs are introduced and discussed. They are short baseline (SBL) systems, ultra-short baseline (USBL) systems and long baseline (LBL) systems. The transponders of SBL and USBL systems are deployed on a anchored ship or pier before the start of mission. LBL systems require transponders to be mounted on the seafloor before localizing AUVs. These three acoustic positioning systems are stated as below.
1) Short Baseline: Short baseline (SBL) systems deter- mine the position of a tracked AUV by measuring its distance from three or more transducers that are mounted under a ship or pier. For improving the accuracy of positioning system, a pressure sensor
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A virtual SBL algorithm that minishes the computation without increasing any instruments is presented in [15] and the positioning accuracy is improved. The virtual SBL algorithm forms the virtual pair of hydrophones by con- sidering the virtual source which emits the surface reflection signal as a virtual hydrophone.
2) Ultra-short Baseline: Ultra-short baseline (USBL) sys- tem has been used on many popular AUV platforms due to its advantage that it just needs a compact space to deploy. A USBL system is composed of a transceiver and a transponder. The transceiver is mounted on a ship or
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The drift error of DVL and the low rate measurements of USBL are fused using the proposed filter and a more precise estimate of velocity, position and orientation of this vehicle is produced. The USBL measurements and the DVL measurements are fused using a particle filter to give a geo-referenced position estimate without drifting in [17]. An information filter is used in [18] for USBL and DVL data fusion while dealing with the delays caused by the acoustic communication
3) Long Baseline: Long Baseline (LBL) system is dif- ferent from the deployment of SBL and USBL systems. The beacons of LBL system need to be deployed around the work area before starting the mission. The positions of these transponders are known in advance and this feature contributes to very high positioning accuracy and robustness that is independent of water depth. LBL system is especially suitable for such situation where position stability for SBL and USBL systems cannot

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