Conventional Localization Localization is any method used in determining an object’s position. Conventional localization is implemented through Global Position System (GPS) technology. How GPS works Commercial GPS works by having satellites send out electromagnetic signals with a center frequency of 1575.42 Mhz to a receiver whose position is unknown. Electromagnetic waves work in air because the conductivity of air is very low. Air has a conductivity varying from 3×10−15 to 8×10−15 Siemens per meter at 20 C° so signal degradation is negligible. Why GPS isn’t applicable Fresh water’s conductivity ranges from 1×10−2 to 2×10−1 Siemens per meter. Due to the higher conductivity of water electromagnetic waves quickly lose strength so they cannot propagate long distances. Acoustic signal testing site: Mansfield Hallow lake, CT Acoustic Signal Transmission To circumvent the issues affiliated with Transducers generate acoustic signals. electromagnetic signals in conventional localization, AUV localization uses acoustic signals instead. Acoustic signals are advantageous because their signal strength loss is not related to the conductivity of the medium that they traverse. Acoustic Signal Application Commercial localization methods: Long base line (LBL) Short base line (SBL) Ultra short base line (USBL) GPS intelligent buoys (GIBS) Research localization methods: Synchronous localization Asynchronous localization Long Baseline Schematic Node response AUV AUV signal Acoustic signal Node 1 Node 2 Node 3 Sea Floor Node 4 Signal Time Diagram (LBL) Node 4 Node 3 Node 2 Node 1 AUV Time Long Baseline Localization (LBL) Advantages of LBL: Very high Positioning accuracy and stability Observation Redundancy Disadvantages of LBL: Complex system requiring expert operators Large arrays of expensive equipment Short baseline Schematic Boat Transducers A B C Acoustic signal AUV Transducer signal AUV signal Sea Floor Pinger Signal Time Diagram (SBL) Transducer C Transducer B Transducer A AUV Time Signal Time Diagram (SBL) Transducer C Transducer B Transducer A AUV Time Short Baseline Localization (SBL) Advantages of SBL: Low system complexity Ship-based system (no transducers deployed on sea floor) Disadvantages of SBL: Larger baseline needed for accuracy in deep water (>30m) Position accuracy depends on additional sensors Ultra Short Baseline Schematic Boat Transducer Array A B C Acoustic signal AUV Transducer signal AUV signal Sea Floor Signal Time Diagram (USBL) Transducer A Transducer B Transducer C AUV Time Ultra Short Baseline (USBL) Advantages of USBL: Low system complexity makes USBL and easy tool to use. Ship based system means no need to deploy a transponder array on the seafloor. Disadvantages of USBL: Position accuracy may be greatly affected by slight variations. Calibration of the receivers and AUV require that their clocks be synchronized when using time of arrival estimates GPS Intelligence Buoys Schematic GPS Surface Vehicle Radio signal Node 1 Node 2 Synchronizes Nodes Node 3 Acoustic signal AUV Sea Floor Node 4 Signal Time Diagram (GIBs) Node 4 Node 3 Node 2 Node 1 AUV Time GPS Intelligent Buoys (GIBs) Advantages of GIBs: No calibration other than communication with the satellite is needed Easy to deploy and recover Disadvantages of GIBs: If water is too deep, buoys could drift Their position would have to be controlled to maintain array Synchronous Localization Schematic Node 1 GPS Node 2 Node 3 Acoustic signal AUV 2 AUV 1 AUV 3 Signal Time Diagram (sync) Node 4 Node 3 Node 2 Node 1 AUV Time Synchronous Localization (sync) Advantages of synchronous localization: Able to service multiple AUV at once Does not require continuous GPS signal to synchronize surface nodes Disadvantages of synchronous localization: Nodes must be on the surface initially to receive a GPS signal initially. Any missed node signal means position can not be computed if working with the minimum node schematic. Asynchronous Localization Schematic Node response AUV initiator signal Node 1 Node 3 AUV Node 2 Node 4 Signal Time Diagram (Asynch) Node 4 Node 3 Node 2 Node 1 AUV Time Asynchronous Localization Advantages of Asynchronous Localization: Node clocks do not require synchronization with each other. Extra timing measurements sent from other nodes can be factored into to calculations to provide better position accuracy. Disadvantages of Asynchronous Localization: The initiator signal must send out a delay factor long enough so no nodes send out signals at the same time. Never field tested so actually accuracy improvement is unknown. Objective Design a highly accurate localization system capable of being used on underwater vehicles. Conduct joint testing with the AUV senior design group to implement an effective localization schematic. Timeline of Events September October • Project Statement. • Localization research. January • Hardware setup of nodes. • Field testing of algorithms . November • Project specifications. • Additional localization research • Coding DSP C February • Field testing of algorithms. • Algorithm comparison analysis. December • Coding DSP C • Finalize implementation plans. March • Field testing of algorithms. • Algorithm comparison analysis. April • Integration of localization with other groups. • Algorithm comparison analysis. • Hardware setup of nodes. • Coding DSP C algorithms. May • Complete integration of localization. Questions?