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‘If a Tree Falls in a Forest’ –

Change Detection with 3D Sensors

Toby Clewett (Presenter)

Sunshine Coast Council

Geospatial Information Services

Toby.Clewett@SunshineCoast..au

Executive Summary

1940’s Wartime development of aerial photography instigated a paradigm shift in earth observation and mapping. So common is it now, that imagery is available globally. In essence, this change is captured by subtleties in the thought experiment, “If a tree falls in a forest and no-one is around to hear it…”. This presentation investigates an equivalent shift being brought about by airborne Light Imaging Detection And Ranging (LiDAR) and Computational Photogrammetry technologies. A visual demonstration will showcase their inherent strength for detecting change through quantitative analysis in the third dimension.

LiDAR provides a fantastic new capability for vegetation health monitoring and compliance by way of mapping change over time. Traditional ‘Air Photo Interpretation’ provides an undeniable visual description of change, but it is limited to a planimetric two dimensional landscape view. LiDAR creates Three Dimensional (3D) forest maps, and derives vegetation height from forest penetrating laser pulses that strike both the ground and the tree tops. Processing of this native 3D point cloud data delivers extremely valuable Canopy Height (CHM) and Foliage Cover Models (FCM).

Computational Photogrammetry technology mapping products are interpreted easily, and this has proven exceptionally valuable. Generation of a Digital Surface Model (DSM) with photogrammetry is a rapid and cost-effective mapping process, in part due to rapidly improving Unmanned Aerial Vehicle (UAV) technology. A plethora of software products automate the data management pipeline helping with photo-mosaicing, 3D processing, and Ground Control Point (GCP) calibration. Best of all, photogrammetry provides a result that is visually rich and measurable, and the natural colour improves interpretation during a fly-through!

Comparison of fine-scale forest height maps over time is an astounding capability. Maps clearly highlight structural change within a forest, with the differentiating factor being the inherent 3D quantitative nature of the data. ‘LiDAR’ and ‘Computerised Photogrammetry’ help by providing an accurate, measurable, and undisputable record of vegetation structure.

In this presentation, you’ll see how LiDAR technology has helped Sunshine Coast Council to

• Find ‘Big Bob’, Queensland tallest measured tree, and watch the other giant candidates grow, age and fall;

• Compare how Vegetation Change is detected;

• See how software is used to dynamically compare 2008 v 2014 LiDAR derived Canopy Height, and Foliage Cover Models;

• Find and map vegetation clearing for compliance;

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