Data Acquisition:

Airborne Laser Scanner (ALS) data was acquired from a fixed wing aircraft on July 10 and 17

2012, using Aerial Surveys' Optech ALTM 3100EA LiDAR system.

Survey Specification:

 Scanner: Optech ALTM 3100EA

 Flying height: 1250m AMGL

 Scan Angle: +/- 14.9 degrees

 Scan Frequency: 47.3Hz

 Pulse Rate 70kHz

 Swath Overlap: 35%

 Points Per Sqm: 1

Data processing:

The LiDAR sensor positioning and orientation (POS) was determined using the collected GPS/IMU datasets and Applanix POSPac software. This work was all undertaken in NZGD2000 coordinate system using the data collected from Aerial Surveys basestation:

Benchmark : A79B

Base Station Position: 42 15 55.52400 S 173 48 23.40990 E 18.425 Ell Height

Antenna Height: 216mm, 218mm, 218mm

The POS data was combined with the LiDAR range files and used to generate LIDAR point clouds in NZTM and ellipsoidal heights. This process was undertaken using Optech LMS LiDAR

processing software. The data was checked for completeness of coverage. The relative fit of data in the overlap between strips was also checked.

The height accuracy of the ground classified LiDAR points was checked using open land-cover

survey check site data collected by C & R Surveyors Ltd. This was done by calculating

height differences statistics between the checkpoints and a TIN of the LiDAR ground points. A -0.188m vertical offset was applied to the data to bring it into terms with the survey check site data. The standard deviation statistic is 0.041 m and a RMS of 0.089m.

C & R Surveyors Ltd field surveyed check sites that were used to verify the accuracy of the processed ground dataset. The positional accuracy of the LiDAR data has been checked by overlaying C & R Surveyors Ltd surveyed data over the LiDAR data displayed coded by intensity. The data was found to fit well in position.

The point cloud data was classified with TerraSolid LiDAR processing software into ground and above ground returns using automated routines tailored to the project landcover and terrain.

Classification of the point cloud followed the modified ASPRS classification scheme below:

0 - Created, never classified

1 - Unassigned classification

2 - Ground

9 - Water

14 - Above_Ground

Re-processing:

In 2016 the data was reprocessed by Aerial Surveys for LINZrelative 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

Data hosted by OpenTopography was re-classified: the Above_Ground (14) points were reclassified as Unassigned classification (1)