What is LiDAR?
LiDAR stands for “light detection and ranging” where, like radar, a burst of laser energy is repeatedly directed at the ground, up to hundreds of thousands of pulses per second. A light sensor records the travel time and converts it to an elevation. The laser scanner is mounted on a moving aircraft and collects points with a X, Y (coordinate position) and Z value (elevation or height). The laser sweeps back and forth across the track of the which creates overlapping coverage to make sure nothing on the ground is missed. LiDAR systems can achieve vertical accuracies of 10 cm (less than one-half foot) over non-vegetated ground, or twice that in vegetated areas. The laser light does not penetrate water or buildings, and returns multiple reflections off vegetation— branches, leaves, tree trunks. All these reflections must be classified and filtered in order to produce a highly accurate representation of the ground surface.
*Illustration of Airborne LiDAR
-From "Integration of LiDAR and IfSAR for Mapping", Ian Dowman 2004
What is available in the LiDAR viewer?
- 2018 Point Clouds - Classified point groups
- High Vegetation
- Buildings - Colorized
- Buildings - Red
- Culvert Lines - locations of flow paths under roads and driveways
- One-Foot Contours - topographic contours at one-foot intervals
- Closed Depressions - Boundaries, identified Low Points and Depth Shading
- Orthoimagery - 2017
- Terrain - Hillshade and Slope Shade generated from Digital Elevation Modeling
What is a closed depression?
A closed depression is an area of land surface that drains internally and has no surface outlet for the runoff of water. In order to leave a closed depression, runoff water must enter the groundwater system through direct conduits or infiltration, or leave through evaporation.
Careful consideration of land use activities must be taken in areas that drain to closed depressions, as potential contaminants have the ability to reach groundwater, and the regional drinking water supply, with little to no filtration. Because of the fragile nature of Door County’s groundwater resources, knowledge of the location of closed depressions and careful land use planning where they are present is crucial.
*Closed Depressions and Conduits to Groundwater - From 2018 LiDAR Derivatives