Bare Earth LiDAR

Light Detection and Ranging

LiDAR is fundamentally a distance technology. From an airplane, drone, or helicopter, LiDAR systems send light to the ground. This pulse hits the ground and returns to the sensor. Then, it measures how long it takes for the light to return to the sensor.

Recording the return time is how LiDAR measures distance. In fact, this is also how LiDAR got its name – Light Detection and Ranging. Trees and vegetation make an area challenging to map.

Trees block terrestrial GPS antennas and hide the details of the terrain. By getting above the trees we can get excellent GPS signals and, by using laser scanning equipment we can shoot down in between the trees and get bare earth measurements.

LiDAR samples by sending 160,000 pulses per second. This means that each 1-meter pixel gets about 15 pulses. Typically, linear LiDAR has a swath width of 3,300 ft. New technologies can scan widths of 16,000 feet.

If you can walk through a forest, look up and see the light, the LiDAR can hit the bare Earth. As the scan tries to reach the ground there will be multiple returns. For example, you’ll get the 1st, 2nd, and 3rd returns until it finally hits the bare ground. If there’s no forest in the way, it will just hit the ground surface. This makes LiDAR valuable for interpreting the forest structure and shape of the trees.

Digital Elevation Models (DEM) are bare earth (topographic) models of the Earth’s surface. By using only ground returns, you can build a DEM. Using DEM you can create:

  • Slope (rise or fall expressed in degrees or percent)
  • Aspect (slope direction)
  • Hillshade (shaded relief considering illumination angle)

LiDAR data is a rare, precious resource. But thanks to open data programs, they are becoming more widely available. If you can’t find what you’re looking for, then most likely you will have to purchase LiDAR data. Vendors generally fly LiDAR commercially by helicopter, airplane, and drone.

So where is the LiDAR data?

Here is a list of the top 6 free LiDAR data sources
for you to get a jump-start on your search.


GIS Geography

Author: Doyle

I was born in Atlanta, moved to Alpharetta at 4, lived there for 53 years and moved to Decatur in 2016. I've worked at such places as Richway, North Fulton Medical Center, Management Science America (Computer Tech/Project Manager) and Stacy's Compounding Pharmacy (Pharmacy Tech).

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