Module 2: Forestry and LiDAR

The purpose of this week's lab was to find and use LiDAR data in an analysis to calculate forest height and biomass. The original .las LiDAR file was acquired from the Virginia LiDAR online application (https://vgin.maps.arcgis.com/home/index.html). The LiDAR Download Grid: N16_5807_20 was downloaded and decompressed using an LAS Optimizer from ESRI. The DEM and DSM were created from the LiDAR layer by changing the appearance to Ground and Non Ground, respectively, using the LAS Dataset to Raster tool in ArcGIS Pro using a sampling value of 6. The original LiDAR scene and derived DEM are below.

To create a forest or tree height layer, the DEM and DSM were used as inputs in the Minus tool in ArcGIS Pro. A tree height distribution chart was created with data from this layer. The chart shows the total count of tree of different heights. It approximates a normal distribution bell curve ranging from -5 (an error value) to 163 feet, with an average of 54 feet. Most of the tree heights are between 27 and 90 feet. The resulting Height layer is below with a distribution chart is below.

Finally, the forest density or biomass was created using the DEM and DSM layers. These layers were inputs using the LAS to Multipoint tool with an average point spacing value of 1 (determined from the LiDAR layer using the Point File Information tool) and class code of 2 (for ground) and 1 (for vegetation) determined from the metadata. The resulting multipoint files were converted to raster using the Point to Raster tool with a cell size of 3. A binary file where 1 is assigned to all values that are not null was created for each raster file using the IS NULL tool, then those files were used in the Con tool so that if a value of 0 was encountered, it was accepted as true. These two files were combined using the Plus tool and converted that result from integer to float using the Float tool. To calculate the final density, the Divide tool was used. The resulting canopy density layer is below.

 

The density map shows the variation in vegetation density throughout the mapped area. It shows foresters areas that are densely forested (values close to 1) and not as densely forested (values close to 0). This would help foresters make important management decisions in terms of what areas might need treatment and for targeting wildlife habitats. From the density map, we can also infer that there are man-made structures in the landscape, although we cannot see those structures as genuine man-made structures using the density map alone. The structures that are most likely man-made are roads, with values close to 0 and yellow in the map above, which are particularly apparent in the southwest and southeast corners of the density map. It would appear that the man-made structures, or roads, affect the vegetation growth in that the density of the vegetation in these areas have zero to very low density. This makes sense as roads do not have vegetation and the areas immediately adjacent to the roads are usually cleared for access, safety and/or utilities.