Data Acquisition:

Airborne Laser Scanner (ALS) data was acquired from a fixed wing aircraft on 3 September 2021, using ASL's Optech Galaxy Prime LiDAR system.

Survey Specification:

- Scanner: Optech Galaxy Prime

- Flying height: 2850 m AMGL

- Scan angle: 25 degrees

- Pulse rate: 400 kHz

- Swath overlap: 30%

- Swath points per M^2: 4.17 pts per sq m.

Data Processing:

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

Base Station Positions: PPRTX

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 0.02m; a RMS of0.02m and the average difference is 0m. LiDAR is relative to the control check points.

The positional accuracy of the LiDAR data has been checked by overlaying Sounds Surveying Ltdsurveyed 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 with TerraSolid LiDAR processing software into ground and above ground returns using a sparse triangular irregular network (TIN) from the supplied LiDAR points and then classified according to required classes by using automatic iterative process followed by manual correction.Terrascan’s inbuilt macros with different parameters were used to classify low points, ground points, buildings, temporary features and finally vegetation.

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

Classification of the point cloud followed the classifications scheme below:

1- Unclassified

2 - Ground

3 - Low Vegetation

4 - Medium Vegetation

5 - High Vegetation

6 - Buildings

7 - Low Noise

9 - Water

18 - High Noise

The Digital Elevation (DEM) was derived using a point to TIN and TIN to Raster process, using a Natural Neighbour interpolation. Hydro flattening was performed as per part 7 of PGF version New Zealand National Aerial Lidar Base Specification Jan 2020.

The deliverables to LINZ were:

1m gridded bare earth digital elevation model (DEM)

1m gridded digital surface model (DSM)

Classified point cloud