EarthWord–Lidar

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It’s not a radar for liars, it’s this week’s Earthword...

EarthWords is an on-going series in which we shed some light on the complicated, often difficult-to-pronounce language of science. Think of us as your terminology tour-guides, and meet us back here every week for a new word!

A multicolored lidar image of the Great Sand Dunes
3D lidar representation of bare earth data of the Great Sand Dunes National Park and Preserve, Colorado. Credit: USGS.

The EarthWord: Lidar

Definition:

  • Although it sounds like a radar-based version of a lie-detector, lidar is actually a type of remote-sensing equipment that works by sending out laser pulses. The lasers, ranging from 50.000 to 200,000 pulse per second  reflect off of various surfaces and are read by a scanner. Using GPS and directional data, the laser scans are then used to create an extremely accurate and precise model of the scan.

Etymology:

  • Lidar is an acronym of LIght Detection And Ranging.

Use/Significance in the Earth Science Community:

  • Lidar has quite a few uses in regard to Earth science. Its most common use is high-precision elevation mapping, since its accuracy can get down to 10cm. That elevation data can then be used for any number of purposes, such as building infrastructure, precision agriculture, planning flood prevention, etc.

  • Lidar can also provide insights into what the ground looks like beneath vegetation, since the laser pulses can fit between leaves and tree branches. This is useful for finding structures from the air that might otherwise be invisible. Quite a few archaeological sites have been found this way.

  • Finally, lidar has some useful properties when it comes to determining landslide risk, damage to infrastructure from earthquakes or storms, or even sinkhole risk, since it maps surfaces so precisely. Slopes that are becoming destabilized; bridge supports that are being scoured; land that is beginning to sink at an almost imperceptible rate--all are detectable using lidar.

USGS Use:

  • USGS uses lidar for a number of purposes, but the biggest use is currently the USGS 3DEP program. Standing for 3D Elevation Program, 3DEP is a project of The National Map to cover the conterminous United States, Hawaii, and U.S. territories with lidar mapping to give the best quality elevation maps for the country. Alaska will be mapped too, as part of this, but its cloud cover and remote locations make lidar difficult to use, so we’ll map Alaska with IfSAR instead (which we’ll define in a future EarthWord!).

  • In addition to 3DEP, we’ve used lidar to study river scour after big floods or hurricanes, as well as to study landslide risk in places like Pennsylvania.

Next EarthWord: It’s not flirting for submarines, but it does involve the ocean...

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