Lidar Applications
Introduction
Lidar data can be used in a wide variety of application. Some of the applications include base mapping and cartography. Lidar is frequently used to create high resolution digital elevation mode (DEMs). Lidar is used extensively in flood modeling, as the high resolution data provides extremely accurate data. The ability of lidar data to separate ground and above ground features make it particularly useful in forestry. Lidar data can be used to map and measure the structure of forests and even measure individual trees.
Surface Models
Lidar data is most commonly used to create Digital Surface Models (DSMs). DSM is a generic term for any file or raster that represents the features on the Earth's surface. DSMs generally include both the ground and any features on the surface including trees and buildings. A DEM is a type of surface model that only represents the ground or the bare earth, sometimes this is referred to as a bare earth model. Because lidar data has multiple returns we can easily create highly accurate, detailed digital elevation models. The ground returns, which are usually the last returns are used to create the DEMs.
A 30m resolution DEM on the left and a high resolution 1m lidar derived DEM hillshade on the right If both a DEM and DSM are generated from the lidar data it is possible to estimate the canopy height above the ground. The DSM essentially represents the height of the canopy above sea level while the DEM represents the height of the ground above sea level. A canopy height model (CHM) can be generated by subtracting the the DEM from the DSM to produce a files where the pixel values represent the maximum height of the canopy.
Forestry
In addition to creating canopy height models, lidar can be used to obtain or estimate a variety of forest parameters. Individual trees can be measured and easily identified using lidar data. Lidar data can even be used to help identify individual tree species, particularly if intensity data is available for the points. Direct measurements from lidar include: Stand Density, Tree Height, Crown Width, and Crown Length. Other forest parameters can be estimated using regression models. Estimates include: Volume, Biomass, Basal Area and DBH (diameter at breast height).
Lidar point cloud for an individual tree. Image Credit: USFSBathymetry
Bathymetry is the study of underwater depth of lake or ocean floors. Basically, bathymetry is the underwater equivalent to topography. Bathymetric lidar is used to determine water depth. Most bathymetric systems use lasers at two wavelengths: a near near infrared pulse which reflects off the sea surface, and green-blue wavelength laser which can penetrate through the water column to reflect off the bottom. The combination of these two wavelengths are used to establish water depths and shoreline elevations. When water is clear water the systems can reach measure depths of 50 meters.
Lidar Bathymetry Data Image Credit: USGSArcheology
Since lidar penetrate vegetation is can be used to reveal features that are normally hidden by vegetation. This is particularly useful in archeology because it is non-invasive and destructive. It can also be used to create precise models of ancient structures and civilizations. In the below image lidar data was used to reveal farm walls, roads and homesteads hidden within Connecticut's Pachaug State Forest. The homesteads dating from the 1700s were abandoned in the 1950's and long since covered in vegetation.
