Harvest planning goes high tech
From the Summer 2007 edition of Bush Telegraph Magazine.
Left: A 3D view of canopy height with the tallest trees coloured yellow.
Right: Digital Elevation Model showing creek lines (blue) and slopes greater than 30 degrees (red).
Left: A 3D ‘point cloud’ visualisation of raw lidar point.
Right: A crown map of a eucalypt regrowth forest showing values for each crown. Generated and captured by Russell Turner
A range of cutting edge technologies are now having a major impact on how our native forests are managed. Sarah Chester reports.
Dr Russell Turner, Forests NSW’s first lidar specialist, firmly believes that new technology has powerful applications for harvest planning.
He said among the next generation of high tech tools were the latest airborne laser scanners (ALS) also known as lidar (Light Detection and Ranging).
“In particular, these scanners are seen as a breakthrough technology for harvest planning, as they provide unprecedented three-dimensional information on ground terrain and forest structure,” Russell said.
“Airborne laser scanners operate by firing high-repetition, short duration laser pulses at ground targets. The time it takes for the light to be reflected back to the sensor is used to calculate the target’s distance below the aircraft.”
Russell said because the position of the aircraft was accurately known in ‘real time’, based on a highly precise onboard Global Positioning System and Inertial Navigation System, the horizontal and vertical position of ground targets could also be accurately calculated.
The current systems are capable of recording up to 100,000 data points a second, each point tagged with an x, y and z coordinate.
“It doesn’t take very long to record millions of data points, which look like ‘point clouds’ across the landscape,” Russell said.
This capability means that, unlike conventional optical remote sensing systems, lidar scanners can actually measure the 3-D position of forest objects.
In addition, because lidar systems provide their own light illumination they are independent of natural sunlight, and can operate day or night, or under cloud cover, which is a major advantage over traditional aerial photography.
Russell is currently trialling lidar applications in forests of the Watagan Mountains with Paul McBain, an experienced Forests NSW harvest planner from Central Region.
They hope to develop new methods for integrating lidar derived forest measurements into existing Geographic Information System planning processes.
“As a direct sampling tool, lidar can capture a range of terrain and forest measures more rapidly, objectively and cost effectively than current ground based survey techniques,” Russell said.
“The three dimensional measurements of forest structure can be used to measure tree heights, spacing and position in the terrain, all of which are indicators of whether a tree is of a merchantable size or accessible for harvesting crews.”
Lidar can also provide incredibly detailed Digital Elevation Models of the ground surface for accurately locating creek networks and steep slopes which need to be reserved from harvesting.
In mountainous terrain like the Watagans, Russell said the ability to map cliff lines also helped in planning road and fire trail networks.
Paul said knowing this information in advance will greatly assist harvest planners in designing the most efficient harvesting method, while avoiding more sensitive forest areas such as steep slopes and drainage buffers.
“This new technology will considerably increase the accuracy of harvesting plans and at the same time significantly reduce the time it takes to develop the plans,” he said.
Sarah Chester Public Affairs & Media, Albury
