Forestry Tasmania Combines GIS and Lidar to Model Canopy Height

Forestry Tasmania employees input lidar data into a geographic information system (GIS) to model and map forests located on Australia’s southern island state of Tasmania. While they were analyzing tree health, canopy density and standing timber volumes, they discovered the world’s tallest standing hardwood tree.

Foresters measured the Goliath eucalyptus, nicknamed Centurion, at 99.6 meters in height and 405 centimeters in diameter. California coast redwood trees still maintain the record as the world’s highest trees, the tallest of which reaches 115 meters.

Lidar, short for light detection and ranging, is an optical remote-sensing technology that uses laser pulses (strikes) to measure the properties of scattered light to find range or other information about its target. Like radar technology, which uses radio waves instead of light, lidar determines the range to an object by measuring the time delay between transmission of a pulse and detection of the reflected signal.

When a plane equipped with lidar sensors flies over forests and other vegetation, some laser strikes penetrate the canopy and reflect off the ground, while other strikes reflect off vegetation such as trees and shrubs. Engineers separate vegetation strikes and use GIS to process the remaining strike data to create digital  elevation models (DEMs) of floor and canopy heights. These models provide them with three-dimensional visualizations of the terrain and the forest.

“Lidar promises to revolutionize forest mapping and inventory,” says Martin Stone, resources manager, Forestry Tasmania. “With traditional aerial photography, accurate photogrammetry is impossible when the ground is obscured, so we were reliant on skilled but subjective manual interpretation. Lidar provides more accuracy to data for creating visualizations of our forest.”

Passive satellite imagery relies on statistical inference that has relatively low reliability at operational scales. This method leaves foresters guessing about the terrain lying under dense vegetation. Conversely, lidar is an active sensor. It directly measures forest and terrain variations accurately and repeatedly. The lidarbased ground DEMs precisely reveal streams and contours in great detail.

Lidar and GIS technologies are used to create this three
dimensional of the enermous eucalyptus tree  
Lidar and GIS technologies are used to create this threedimensionalmodel of the enormous eucalyptus treeThe forestry staff uses lidar data and ESRI’s ArcGIS to model and map forest features such as tree height, canopy density, and standing timber volumes. It is effective even if the forest cover is highly variable. Forestry Tasmania managers claim that the system enables them to plan access roads, cable harvesting, and silvicultural activities. ArcGIS helps them easily delineate harvest boundaries, improve planning methods, better estimate environmental outcomes, efficiently maintain timber inventories, and accurately map the forest’s spatial variation.

 Lidar forest inventory datasets are quite large. An average of two lidar strikes per square meter of forested land is captured. This is a lot of data to store and process. Forestry Tasmania’s data management system includes an Oracle Spatial relational database. The data in Oracle is efficiently replicated to a separate geodatabase, where ESRI’s ArcGIS Desktop is used to perform advanced geoprocessing and analysis on it. The output is a range of derived products that can be published as GIS layers such as DEMs, timber volume surfaces, contours, and drainage lines.

“Our organization has become spatially aware, and everyone uses GIS in some form, especially in the field offices,” says Luke Ellis, GIS manager for Forestry Tasmania. “Our employees regularly use ArcGIS to browse and query data and publish maps. We use it to per form everyday work tasks such as processing lidar data, modeling and analyzing the state of the forest, computing statistics for spatial analysis, monitoring sustainability indicators for annual reporting, and visualizing our forest’s attributes.”

GIS gives foresters a better picture of what resides in the forest, such as the very special Centurion tree. The tree has lived in the forest for 400 years and survived recent threats such as logging operations in the 1950s and two massive wildfires, one in 1934 that passed just to the west of the tree and another in 1966 on its east side.

“No one was looking out for the tree in those days,” Stone remarks. “We didn’t know it was there. But thanks to lidar and GIS, it now has a name and is, literally, on the map.” Centurion has been formally classified as a giant tree, and the area surrounding it has been designated as a protected reserve.

Allyson Lawson, ESRI Writer/ESRI Forestry GIS Journal, Spring 2010 
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