Sea Technology

OCT 2013

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

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surement allows the team to determine directly how much meltwater is conveyed through the hydrologic system of the Greenland Ice Sheet and how quickly it moves toward the ocean. Most days started with a helicopter commute from the team base at the Kangerlussuaq International Science Support facility in southwest Greenland to sampling sites, often as far as 120 kilometers away. The researchers outftted a drone boat with an echosounder, GPS and spectroradiometer to measure the depth and optical characteristics of glacial lakes and slow-moving streams. Where the current was too fast for the drone boat, the group deployed a RiverSurveyor S5 acoustic Doppler Next Challenge: Pure Water After providing for the safety of the scientists and instruments, the next challenge was a surprising one: ultrapure water. The RiverSurveyor S5 uses fve acoustic beams to analyze (Photo Credit: Brandon Overstreet and Dr. Carl Legleiter) (Photo Credit: Brandon Overstreet and Dr. Carl Legleiter) (Photo Credit: Brandon Overstreet and Dr. Carl Legleiter) profler (ADP) by SonTek (San Diego, California). Using fve acoustic beams and multiple frequencies, the ADP provided depth and velocity measurements. Built-in software also computed discharge. On one side of a sampling location, the team secured a vertical mast into the ice with a series of ice screws. Team members few across the stream by helicopter to anchor a second mast and receive a weighted fshing line thrown across the stream. Using that line to pull a cable across the river, they anchored the cable to the mast and tightened it with a hand crank. At each sampling site, the cable provided a track to pull the SonTek Hydroboard-mounted ADP across the river. Whitewater conditions and heavy slush fows threatened to capsize or sweep away the RiverSurveyor, but the StreamCraft cable system, which was designed by University of Wyoming graduate student Chip Rawlins, kept the unit steady throughout the team's weeks of feldwork. "In some cases, the ADP and Hydroboard actually became airborne," Overstreet said. "To keep the Hydroboard upright in high-velocity conditions, we had StreamCraft modify its harness to prevent the board from becoming unstable, which would have been catastrophic in those conditions." A second cable point near the bow of the Hydroboard changed the direction of pull in very fast-moving streams while allowing the RiverSurveyor S5 to accurately profle channels and measure velocity. During the data-gathering phase, it was vital to keep the scientists out of harm's way. Because RiverSurveyor Live software feeds data through a mobile phone connection, team members could operate the ADP from a safe distance away from the stream's edge. (Top) The RiverSurveyor was operated via mobile phone while being slowly pulled across the stream. (Middle) A second operator was fown across the stream by helicopter, and a second anchor system was installed. (Bottom) Most supraglacial streams abruptly transition into deeply incised canyons with powerful hydraulics. Even low-gradient streams can spontaneously be captured by crevasses or form moulins. October 2013 / st 11

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