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GCN : April 2013
the returning light with accuracy. LIDAR systems vary in the wavelengths of light and the power of the pulses em- ployed. High-energy pulse systems, for example, typically are used for atmo- spheric research, while lower-powered micropulse systems are more often em- ployed for downward scanning, since they are considered "eye safe." And although most airborne LIDAR sys- tems use 1064-nanometer laser beams, bathymetric LIDAR systems --- those used to penetrate water --- employ a narrower 532-nm beam. Bathymetric LIDAR also transmits two light waves, one infrared and the other green. As a result, it can de- tect two returning signals, one off the wa- ter surface and the other from the seabed. Other critical elements in the develop- ment of LIDAR systems have been the en- hancements in the production of higher- resolution and more flexible scanners, optics and photoreceptors. Finally, collecting LIDAR data from aircraft involves a few additional chal- lenges. Because the LIDAR sensor is moving, the changes in location between the firing of the pulse of light and its re- turn must be accounted for in making any measurement. That required the de- velopment of fast, high-resolution GPS devices and inertial measurement units that measure velocity and orientation. Coordinating of this, of course, is no mean feat, nor is digesting the massive amounts of data that are produced. According to Waters, NOAA's LIDAR scans are shooting between 100,000 and 200,000 points per second with about up to 10cm of error. "The rest is math," Waters said. "Lots of math, but it's still just math." RED RIVER BASIN CRISIS Sometimes it takes a crisis to spur innovation. Such was the case with creation of the Red River Basin Decision Informa- tion Network (RRBDIN), and its LIDAR mapping of large swaths of North Dako- ta, Minnesota and central Canada, said Charles Fritz, director of the International Water Institute. "In the Red River basin we had a major flood back in 1997. That's when Grand Forks went under," Fritz said. "My orga- nization actually was one of the outcomes from that flood." In the wake of the flood, the Federal Emergency Management Agency took action that resulted in the creation of the RRBDIN, which is man- aged by the International Water Institute with support from the U.S. Army Corps of Engineers, North Dakota State University Extension and other partners. "When the 1997 flood hit, we had a huge problem because the only things we had to work with were old USGS maps," Fritz said. Even with the obvious need for better information, FEMA and state funding weren't enough to do the job. "At the time, in 2000, we knew LI- DAR was available. We were looking at different technologies to acquire better elevation data, but the numbers were as- tounding. I mean, we were talking about $35 million." By 2005, however, costs had dropped considerably. "Costs were coming down, and the technology was improving," Fritz said. "We said OK, let's move on this." By 2009, the RRBDIN finished its first pass, collecting LIDAR data covering 54,000 square miles. The result was 8 terabytes of data that the team needed to make available in a useful form. Since then, the team has been working to develop and deploy a series of online tools. "We did not want have a situation where everybody in the basin had to know ArcView if they want to use the LI- DAR data, so we put together the online viewer," Fritz said. "There are some really cool tools in there." RRBDIN's LIDAR viewer allows users to create and customize maps with el- evations down to 2-foot contours or spot elevations. There's also a forecast display tool. When the National Weather Service generates a forecast of a flood in Fargo of, say, 38.5 feet, "What does that mean from an inundation and extent standpoint?" Fritz asked. " We can take the LIDAR data, combine it with that 38.5 feet forecast and produced an interactive map that 24 GCN APRIL 2013 • GCN.COM FEATURE 3-D DATA GATHERING Oregon has amassed a database of LIDAR data covering 26 percent of the state, grist for the 25 GIS analysts working with the data for a variety of agencies and purposes.