In 2011 AAM was commissioned by the Commonwealth to fly an airborne laser scanning survey (LiDAR) of Christmas Island. The survey was carried out using a fixed wing aircraft between the 24th and 26th of August 2011. All data was captured within approximately 2 hours of low tide. During this period tides ranged from 0.5m to 1.2m.
AAM classified the raw LiDAR points into the following classes using a single algorithm across the project area:
0 Unclassified - Created, never classified
1 Default - Unclassified
2 Ground - Bare ground
3 Low vegetation - 0 – 0.3m (essentially sensor 'noise')
4 Medium vegetation - 0.3 – 2m
5 High vegetation - 2m >
6 Buildings, structures - Buildings, houses, sheds, silos etc.
7 Low / high points - Spurious high/low point returns (unusable)
8 Model key points - Reserved for ‘model key points’ only
9 Water - Any point in water
10 Bridge - Any bridge or overpass
11 not used - Reserved for future definition
12 Overlap points - Flight line overlap points
The raw LiDAR points in the .las format were provided to Geoscience Australia along with 1km ESRI grid tiles generated by interpolation from the points. The tiles were then joined to create a DEM (TIFF) that covers the full extent of Christmas Island. Each cell, 1m x 1m, in the grid contains the height in metres of the ground surface. As a guide, the DEM data is vertically accurate to 15cm and horizontally accurate to 30cm. Manual checking and editing was carried out by AAM to improve accuracy. Positional accuracy has been checked by Geoscience Australia and was found to match the ground surface well.
The DEM data is complete for the full extent of Christmas Island.
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