Survey Specification:

-Scanner: Optech Sensor

-Flying Height: 900m above lowest ground

-Scan Angle: ±20 degrees

-Scan Frequency: 40Hz

-Pulse Rate: 70 or 75kHz

-Points Per M2: 1.4

Data Acquisition:

The LiDAR was acquired between 23 to 28 February 2014 and on 3 May 2014

using NZAM’s Optech LiDAR sensor systems.

The data in the tidal influence area was collected within 2 hours either side of low tide.

The data was collected flying 900 metres above lowest ground, and using a

scan angle of 20 degrees either side of nadir. The outgoing laser pulse rate

(PRF) was set at either 70kHz or 75kHz and mirror scan frequency 40 Hz. The

settings were selected to create a dataset with a minimum 1.4 point per square

meter pulse density in open ground.

New Zealand Aerial Mapping used a reference mark we established at

Woodbourne (NZAM0161) for the collection of GNSS base station data

during the aerial data acquisition.

Independent of the aerial survey work Sounds Surveying Ltd field surveyed a

series of topographic features in open ground, to be later used to verify the

accuracy of the processed ground dataset. This field survey work was

conducted between 10 and 13 March 2013. The field survey work is in terms

of LINZ geodetic marks AB83, AD84, BE0G, AD5R, A3TV, B3ED, A7GH,

BAK6, A867, ACYW, APW4 and BH3D.

Data processing:

The LiDAR sensor positioning and orientation (POS) was determined using

the acquired GPS/IMU datasets and Applanix POSPac software. This work

was all undertaken in NZGD2000 geodetic reference system using the data

collected at the LINZ geodetic reference marks for the differential processing.

The POS data was combined with the LiDAR range files and used to generate

LiDAR point clouds in NZTM map projection. This process was undertaken

using Optech LiDAR Mapping Suite software. As well as creating the point

clouds this software also checks the relative fit between points in the

individual swath overlap areas. All subsequent data processing steps were

undertaken using TerraSolid’s LiDAR processing software modules TerraScan

and TerraModeler.

The point cloud was checked for completeness of project coverage and pulse

density. Automated routines tailored to the projects land cover and terrain

were then setup and run on the data to create a ground classified point cloud.

This data was converted from ellipsoidal heights to Nelson 1955 vertical datum

using the LINZ NZGeiod09 grid and offset model.

Comprehensive manual editing of the LiDAR point cloud data was

undertaken to improve the quality of the automatically classified ground

point dataset. This editing involved visually checking over the data and

changing the classification of points into and out of the ground point dataset.

As part of this process LiDAR returns from water bodies were removed from

the ground point dataset and supplementary points were added to help support

hydro flow characteristics around and along water bodies.

The positional accuracy of the processed data has been checked by overlaying

the Sounds Surveying field surveyed features on the LiDAR dataset displayed

with its intensity values. The data was found to fit well in position. The

height accuracy of the classified ground points were checked by calculating

height difference statistics between a TIN of the LiDAR ground points and the

field surveyed points. The standard deviation statistic for the data is +/-0.06m.

The data from New Zealand Aerial Mapping was supplied in NZTM map projection

and the Nelson 1955 vertical datum, the point cloud datasets had been

tiled into NZTopo50 1:2000 tiles.

Classification of the point cloud followed the classification scheme below:

1 - Unassigned

2 - Ground

14 - Above_Ground

Data Reprocessing:

In 2017 the data was reprocessed by AAM New Zealand for LINZ relative

to the NZVD2016 vertical datum, NZGD2000 horizontal datum, NZTM map projection, with the NZGeoid2016. This data was supplied as 1:1000 nominal scale

(720m high x 480m wide tiles per full NZ Topo50 sheet).

Sounds Surveying Ltd undertook ground surveying to support the original work.

For this project, the Sounds Survey converted this dataset to NZVD2016. When doing so, they took accord of any local adjustments to geodetic marks that had been applied to the original field surveying coordinates.

Classification of the point cloud followed the classification scheme below:

2 - Ground

14 - Non Ground

The starting point for processing was the Classified point clouds produced for

Marlborough DC based on NZGeoid09. This data has been reverted to ellipsoidal

heights, then NZGeoid2016 has been applied to convert the data to orthometric

heights. The data was then compared to the ground surveying NZVD2016 test

points, and an appropriate final Z shift applied to each block.

Ground point data had been checked to check site data obtained by the field survey, this was assumed to be error free. The test points were distributed across the mapping area and located on clear open ground. Difference statistics yielded for Reference Project Site Awatere: RMS 0.035m and for Wairau: RMS 0.045m

All point attribute data (intensity, return number, GPS time) in the original data

points have been imported into the new las file dataset. 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

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