Luiz Filipe M. Vieira, Uichin Lee, Youngtae Noh, Mario Gerla Computer Science Department

1. Laser Acoustic Burst 3 Surface Acoustic Burst 1 Acoustic Burst 4 Acoustic Burst 2 Acoustic Burst 5 Under Water Positioning with Lasers Luiz Filipe M. Vieira, Uichin Lee, Youngtae Noh, Mario Gerla Computer Science Department University of California, Los Angeles • MOTIVATION: • Location tagging of events where GPS is not available • Laser Positioning = laser generates acoustic burst when it hits the water [1] • The aircraft fires four unmodulated laser pulses -> four acoustic pulses propagate under water. • The 5th laser burst is modulated with time and previous four pulses impact point coordinates (clock, x, y). • Using 4-MFSK modulation, the modulated acoustic pulse carries up to 160 bits/s to 320 meters underwater. • Each underwater sensor localizes itself via trilateration. Covert: laser cannot be detected above water Coordinates are encrypted: only members can retrieve the position/ time Easy to deploy: no need of support ship, buoy layout or underwater transponder Energy efficient: does not requires sensor node transmissions Compare with current state of the art, eg “Dive and Rise” • RED Beacons are “positioned” at surface; they dive and calibrate BLUE sensors [2]. • Drawbacks: • Not covert • Not precise • Energy inefficient • Reference [1]T.G. Jones et al. Remote underwater ultrashort pulse laser acoustic source. CLEO/QELS 2006. [2]M. Erol et al. Dive and Rise, WUWNET 2007. Supported by NSF Grant: SEA-Swarm: A Rapidly Deployable U/W Sensor Network.