Sea Technology

MAY 2018

The industry's recognized authority for design, engineering and application of equipment and services in the global ocean community

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12 ST | May 2018 now routinely recover and reuse tags, achieving cumulative deploy- ments of years. Solar energy collec- tion is possible even underwater to a typical depth of twice the vertical visibility, but energy collection here becomes quite small, so the tag uses minimal power. Running the base profile of wake-up housekeeping every 16 sec. and full sensor scan- ning and flash memory archiving once every 4 min., averaged pow- er consumption is only about 0.1 mW. Compare this to about 1,200 mW for a smartphone in typical use, meaning the draw of the phone in your pocket could alternatively power 12,000 tags. Thus, battery endurance in complete darkness and running the standard sampling and archiving profile is more than four years. Even a tag configured without a battery and using only its capacitor will maintain full opera- tion for 30 hr. in darkness, plus an- other two weeks in standby mode. Yet, recharging requires only about 30 min. at the surface. The tag's in- ternal sensor suite again resembles that of a smartphone, including a three-axis accelerometer and mag- netic sensor, temperature sensor and light and depth sensors. Ar- chived data are stored on an inte- grated microSD flash card, its 2-GB memory enough for four years' worth of archived data at a full set of sensor scans every 2 sec. Reporting is based on the Argos satellite constellation, far slower than any cell phone connection but with global availability from pole to pole. Argos transmissions are short bursts of 0.91 sec. during which data are transmitted at 400 bits/ sec. Yet given system-enforced min- imum transmit intervals and sporad- ic satellite availability in the sparse constellation, effective throughput of user data is on the order of 1 bit/ sec, i.e., slow even by Morse code standards. Still, the solar-powered tag manages to transmit an Argos packet with 31 user bytes a little faster than once every 2 min. when floating at the surface in broad sun- light. A packet is enough to trans- mit, for example, a full scan of all 10 sensor channels, including a time stamp and auxiliary informa- tion. Ocean Dashboard: Toward a Fully Instrumented Ocean The U.S. Navy Strategic Stud- ies Group (SSG) was a think tank charged to generate revolutionary naval warfare concepts. During the 2012 group review, Director Adm. James R. Hogg predicted that the Navy would become obsolete in its current composition within the next few decades. In the abstract, a navy might be considered a set of actuators, e.g., weapons linked to, and informed by, a sensor system. These include sonar, remote im- aging, intelligence reports and the like. Hogg argued that while the Navy has very sophisticated sensors hosted on its ships, aircraft, drones, submarines, AUVs, satellites, etc., it also has very few of these platforms in relation to the size of the oceans. In fact, the detection range of un- derwater sounds and sonar is fre- quency dependent. Smaller targets such as speed boats or AUVs/UUVs tend to produce sounds at high- er frequencies and lower source levels, thus limiting the detection range to a few kilometers or even into the tens or hundreds of me- ters. As asymmetric threats such as swarming attacks, piracy by speed- boats or the use of AUVs/UUVs, etc. increases, the Navy's fleet of sensor platforms are becoming mere pixels of knowledge in the ocean. An early warning may be the maritime pira- cy situation in African waters. While piracy offshore Somalia declined to zero after the 2010 deployment of the international navy task force CTF-151, there was a spate of new attacks in 2017. Meanwhile, piracy incidents in West Africa increased from 54 in 2015 to 95 the follow- ing year. And, in California, cartels are using panga boats to land large quantities of drugs along the rugged Big Sur coast. These trends indicate that in- struments capable of more exten- sive sensing are needed for defense and law enforcement applications, such as detecting illegal fishing in remote waters. These instruments

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