We would like to thank the UCLA Greenland team for sharing their study and photography through Mission: Water magazine. MISSION: WATER 30 FEATURE STORY A LOT AT STAKE During the survey, the RiverSurveyor-M9 was mounted on a HydroBoard, which is pulled from bank to bank to gather data along a transect. The Greenland team gathered at least four transects each hour. That was a challenge in itself—the river banks were nearly vertical, and a few hundred meters downstream, the river dropped into a moulin that would have swallowed the RiverSurveyor forever. "We knew if we lost it, it wasn't coming back," says Pitcher, who worked with Overstreet and HydroBoard II designer Bob Carlson on designing and rigging an anchoring system that could be operated from one side of the unfordable stream and would remain rooted in place as the surface of the ice dropped up to 5 centimeters (2 inches) per day due to melting and sublimation. "Once we set up on a river, we only had access to one side," Pitcher explains. The helicopter that ferried the team and their gear could shuttle Pitcher and the rest of the set-up crew across the river a time or two, but once the chopper left, there was no way to cross again. For a short deployment, ice screws could suffice. But as a day wore on, the metal screws would have conducted solar energy into the ice and melted their anchorages. Instead, Pitcher and Overstreet borrowed a trick from ice climbers, drilling a meter-deep "V" into the dense ice below the crumbing surface and threading thick webbing through the channel to anchor the rigging that secured and controlled the floating RiverSurveyor. The team also planted an upright bamboo pole deep into the ice to serve as a stable, known georeferencing point for periodic calibration of location tracking data. IMPROVING THE SCIENCE In late 2017, the team published its 2015 Rio Behar data alongside the predictions generated by five leading ice melt models. The authors of the paper, which was published in the Proceedings of the National Academy of Sciences, represented a large and diverse group of investigators—not only geologists and hydrologists like Smith, Rennermalm, and the hardy grad students who gathered the measurements, but also Jenner and a group of other leaders in climate science and modeling. "This isn't 'our camp against their camp,'" emphasizes Pitcher. "This is a big collaboration. They're interested in how our ground truth data can be used to improve and explain what they're modeling." For Brandon Overstreet, multiple trips to the Greenland Ice Sheet sum up the value—and the thrill—of fieldwork. It's a level of detail that can't be found in satellite imagery or fly-by science. "My initial impression of the Greenland Ice Sheet was a large, featureless landscape that was only exciting at the edges where the icebergs were calving," he says. "But on the ice surface, you have this incredible, dynamic system of rivers that behave like terrestrial rivers—in some ways, that are terrestrial rivers in overdrive. "I don't want to live in a world where you collect everything you need by looking at a satellite image," he adds. "I don't want to live in a world where you collect everything [with] a satellite image." The RiverSurveyor M-9 uses two frequencies to ensure optimum signal for velocity, depth and direction measurements. Photo Courtesy: Johnny Ryan