Data Acquisition:

Airborne Laser Scanner (ALS) data was acquired from a fixed wing aircraft on between 16 and 18 April 2019, using Aerial Surveys Optech Galaxy Prime LiDAR system.

Survey Specification:

• Scanner: Optech Galaxy Prime

• Flying Height: 2500 m AMGL

• Scan Angle: ±20 degrees

• Scan Frequency: 47.5Hz

• Pulse Rate: 300kHz

• Swath Overlap: 35%

• Points Per M2: 2

The scan angle is ±20 degrees per the data supplied to us not ±10 degrees referenced in the survey reports.

Data Processing:

The LiDAR sensor positioning and orientation (POS) was determined using the collected GPS/IMU datasets and Applanix POSPac software.

Base Station Positions: PP-RTX

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 Sounds Surveying Ltd. This was done by calculating height differences statistics between a TIN of the LiDAR ground points and the checkpoints.The standard deviation statistic is 0.030 m; a RMS of 0.033 m and the average difference is 0.012 m. LiDAR is relative to the control check points

The positional accuracy of the LiDAR data has been checked by overlaying Sounds Surveying 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 then classified withTerraSolid LiDAR processing software into ground and above ground returns using automated routines tailored to the project landcover and terrain.

All product deliverables supplied in terms of NZTM map projection and NZVD2016 height datum.

Classification of the point cloud followed the classification scheme below:

1 - Unclassified

2 - Ground

7 - Noise

12 - Overlap

14 - Above Ground

10 - Rail points were also found in the data not mentioned in the survey report.

Rail (10) and Above_Ground (14) points were reclassified by LINZ as Unassigned classification (1) before providing the classified point cloud data to Open Topography.

Lakes and large 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