By Brian Anderson and Susannah Erwin
March 21, 2019
USGS scientists are using laser technology to collect topographic data along the Upper Missouri River. The laser, a lightweight and portable LiDAR (Light Detection And Ranging) system, is approximately the size of a hockey puck and transmits up to 300,000 laser pulses per second. A sensor on the instrument precisely measures the time it takes each pulse of the laser light to be reflected back from the surrounding river bank and vegetation. Using the speed of light (186,00 miles per second or 0.3 meters per nanosecond) and precise Global Navigation Satellite System (GNSS) positions the the LiDAR system calculates the distance and elevation of every reflective surface in the surrounding area. These reflected pulses from the laser are processed into a point cloud (fig. 1), which provides a three-dimensional topographic map of river banks, bars, and vegetation. The topographic data from LiDAR complements bathymetric data collected by survey boats, allowing scientists to generate detailed digital models of the entire river channel. These data are then used to develop flow and particle track models to simulate downstream dispersal of pallid sturgeon free embryos.
In September 2018, CERC scientists travelled to Glasgow Montana to collect LiDAR data along a 20+ kilometer section of the Upper Missouri River. The LiDAR system was mounted in a jon boat (fig. 2) and each river bank was scanned. Each pass was collected in a single day. By comparison, a standard survey with handheld GNSS equipment would have taken several days to complete and collected only a small percentage of data acquired using the LiDAR system.