LPS: Laser Positioning System for Underwater Networks

Underwater Sensor Networks (UWSN) have many potential applications, such as ocean exploration, pollution monitoring, public safety and military underwater surveillance [1]. In all of these applications, localization plays an important rule since detected events must be tagged with position information. Moreover, position may also be required for geographical routing. GPS is not available in underwater because the signal does not propagate through water. Alternative schemes have been proposed, as discussed later. However, in underwater sensor networks battery power limitations are critical. Protocols must economize message exchange to save power. Existing positioning schemes take a toll on power because of frequent transmissions. Based on recent laser acoustic technology, we propose LPS, a Laser Positioning System for Underwater Networks. Recent experiments [2] have shown that a laser pulse can propagate underwater and at the end ”burst” into an acoustic pulse at a predetermined distance from surface. Jones et al. [2] measured pulse durations on the order of 1 μs and sound pressure levels up to 170 dB. The laser source can be above water, i.e. on an airplane. We propose to use this laser/acoustic pulse as a localizating beacon. By hearing the beacon, and knowing the exact burst time and position, sensor nodes can get localize themselves via trilateration. The benefits of LPS are: