A próxima DEEC Talk (também ISR Seminar) terá lugar no dia 22 de Janeiro, no Ea4, 17:00, e será proferida por Lee Freitag, da Woods Hole Oceanographic Institution (WHOI), onde trabalha há 25 anos em comunicações para veículos submarinos autónomos, testados em cenários deslumbrantes.
Title: Underwater Acoustic Communications in the Arctic
The effects of climate change are accelerating the loss of ice in the Arctic and as a result there is a need to understand the processes that drive the changes in ice cover and thickness, and to do so at range scales of meters to hundreds of kilometers. Further, the reduction in the amount and extent of ice has encouraged expanded tourism and industrial activities that may result in the need for under-ice exploration and survey by autonomous vehicles. Unfortunately, unlike in temperate climates, ice-cover precludes easy access to the surface for both GPS navigation and Iridium communications, thus there is a need for a replacement that will allow command and control, plus geo-referenced data collection by unmanned underwater vehicles (UUVs).
There are multiple range scales that are important for UUV operations and these depend on the persistence, sensors and spatial scale of the mission. In addition, there are many different Arctic regimes as well, each with a different feasible propagation range. There are at least four distinct Arctic and under-ice propagation environments, Central, Beaufort, continental shelf and shore-fast, though with seasonal and location-dependent variability. The Central Beaufort has rough (though decreasingly so) ice with downward refracting propagation, which limits range at practical frequencies. The Beaufort has a shallow acoustic duct, minimizing surface interaction and providing ranges of hundreds of kilometers. The Arctic continental shelf, at least north of Alaska, can seasonally support long ranges when low frequencies are used, while in shore-fast ice conditions in Alaska or Greenland the maximum range is highly dependent on ice type and bathymetry and varies from hundreds of meters to at least 30 km as achieved recently in Greenland.
The talk will review the missions that UUVs have done and will soon do in the Arctic, present the acoustic conditions in the different environments, and show results from multiple experiments. In addition, some of the practical issues associated with traveling and working in the Arctic in Alaska, Greenland and Norway will be illustrated in photos and video.