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FEATURE MAPPING


Putting lidar on the map


From the depths of the ocean to outer space, Rachel Berkowitz looks at the latest developments and applications of lidar technology


E


arly efforts to map topographical features involved measuring tapes, compasses and aneroid barometers. But then came ‘light detection and


ranging technology,’ or lidar, and a new era of geospatial surveying capabilities. Meteorologists used this new technology in the 1960s to map cloud patterns from aircraft. Then, in 1971, lidar went into space to map the moon’s surface during the Apollo 15 mission. Now, lidar gives new perspectives on landslides on Terra Firma, sets the stage for autonomous vehicles, and is used to investigate undersea topography. Meanwhile, meteorologists are continuing to develop techniques that will eventually provide a satellite’s view of wind speed over the entire globe.


While the basic concept of lidar is simple – illuminating a target with laser light and measuring how long it takes for the reflected signal to return to the source – this technology is evolving to address problems never envisioned by the original developers.


Lenses for landslides


In 2014, a mudslide south of the British Columbia border in Oso, Washington State claimed the lives of 43 people. Weeks after the landslide, University of Washington geomorphologist David Montgomery became aware of data from a 2003 airborne lidar survey collected by the Puget Sound Lidar Consortium. An additional survey detailing the slopes of the major landslides in 2006 showed previous slides and erosion chipping away at a shelf that had long buttressed the upper slope and the plateau near Oso. These new lidar images showed in striking detail that older and very large landslides exist


18 ELECTRO OPTICS l OCTOBER 2016


elsewhere in the region in and around Oso. ‘[Lidar] is like a brand new pair of glasses,’ said Montgomery. ‘The level of resolution we can get relative to what we had in old topography maps is like night and day. If you look at old hazard maps for that area, the nature of previous existing landslides doesn’t pop out, but you look at lidar terrain maps and go, Oh! This has happened before.’ Lidar technology motivated efforts to explore the age of old landslides, and their frequency of occurrence. State agencies contracted surveyors to collect lidar data as soon as possible at the 2014 landslide site, which Montgomery and colleagues then used to develop a method for determining the age of these landslides and, therefore, a metric for landslide risk. Their results were published this year in the journal Geology. Commercial airborne lidar systems have been available for two decades. The simple ‘linear’ beam systems offer high power but low sensitivity. For the new Washington surveys, lidar systems mounted in Cessna aircraft surveyed the landslide area from 900 metres altitude. The bidirectional or polygonal scanning mirror system measures one point on the ground for each firing of the near-infrared 21cm-diameter laser beam, with a sensor set to acquire eight points per square metre. GPS units continuously record the aircraft’s position and altitude to define the laser point position accurately and continuously, and new classification algorithms can distinguish ground vegetation, buildings, and water. While Montgomery was thrilled when lidar came into use, ‘for students now, this is a new normal. They don’t know what you’d do without it,’ he remarked.


Lidar scanner surveys the seafloor from a Remotely Operated Vehicle


Truly 3D


New lidar technology also contributes to many day-to-day activities. The growth of cities has brought about a corresponding need to refine routes that reduce travel time for both emergency and civilian vehicles. And refined navigational data is necessary for the successful deployment of newly-developed autonomous vehicle navigation systems. Old estimates of the effect of sea level rise and flooding are being refined, and power companies are seeking better ways to manage vegetation encroachment on their distribution networks. Improved data acquisition speed and spatial


resolution lets lidar play a role in these and other fields. Much of this new technology is not ‘new’, but has been available to the defence industry for 15 years. It was unveiled commercially in 2015 with ‘Geiger-mode’ lidar offering the most accurate elevation data available. When


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