Canterbury - Christchurch and Selwyn LiDAR 1m DEM (2015)

Data Acquisition:
Airborne Laser Scanner (ALS) data was acquired from a fixed wing aircraft in October and November 2015, using AAM's Riegl LMS-Q1560 and Leica ALS60 LiDAR systems.

Survey Specification:

Selwyn:
Device Name Q1560
Half Scan Angle 29 degrees
Laser Pulse Rate 800 kHz
Overlap Percentage 20%
Average Point Spacing 3.1 pts/m2
Laser Footprint 0.47m

Christchurch:
 Device Name: ALS60
 Half Scan Angle: 12.5 degrees
 Laser Pulse Rate: 145 kHz
 Overlap Percentage: 20%
 Minimum Point Density: 4 pts/m2


 Laser Return Types: 1st, 2nd, 3rd and last
 Laser Intensity All returns
 File Format: ESRI ASCII Grid, ESRI Shapefile, LAS 1.2
 Horizontal Datum: NZGD2000
 Vertical Datum: NZVD2016
 Map Projection: NZTM
 Vertical Accuracy Specification: ±0.10m Standard Error (68% confidence level or 1 sigma)
 Horizontal Accuracy Specification: ±0.50m Standard Error (68% confidence level or 1 sigma)

Data processing:

Laser strikes were classified into ground and non-ground points using a single algorithm across
the project area. Manual checking and editing of the data classification further improved the
quality of the terrain model.
Further Processing: ArcGIS 10.1 Terrain and Surface Grids were derived using the Natural
Neighbor interpolation. This method uses the closest triangles and applies weights to the
proportionate areas from the grid cell centroid to interpolate the value. It uses known elevation
data, it does not make any predictions regarding the surface and accurately depicts existing
troughs and peaks in the data and supports irregular point spacing, which suits the nature
LiDAR data.

GPS base station support was sourced from Global Surveys CORS
operating in Christchurch. The ground check points were field surveyed by Sounds Surveying
Limited, these allowed an independent assessment of the accuracy of the ALS data..

All product deliverables were initially supplied in terms of NZTM and Lyttelton 1937 height datum.

Classification of the point cloud followed the classification scheme below:
0 - Created, never classified
1 - Unclassified
2 - Ground
7 - Low/high points
9 - Water

Re-processing:
In 2016 the data was reprocessed by AAM for LINZ relative to the NZVD2016 vertical datum, and supplied as 1:1000 nominal scale (2500 720m high x 480m wide subtiles per full NZ Topo50 sheet). Lakes and rivers were hydroflattened in the bare earth digital elevation model.The deliverables to LINZ were:

1m gridded bare earth digital elevation model (DEM)
1m gridded digital surface model (DSM)
Classified point cloud