Click here to download the point cloud data for the North Shore coastline

  DATA ACQUISITION


    Airborne Data Acquisition

  An airborne laser scanner survey was conducted over the North Shore, from North Head to Long Bay
    (approximately 22.5 km following the shoreline). Operations were undertaken on 19th June 2019 in good flying
    conditions. Data were acquired using a Riegl VUX-1LR lidar system, mounted on an EC120 helicopter, operated
    by Christchurch Helicopters. The laser survey was based on the following parameters:



      Parameter


      Parameter



      Scanner
      Riegl VUX-1LR
      Pulse Repetition
      820 kHz


      Flying Height
      50-80 m above ground
      Swath Overlap
      75-100%


      Scan Angle
      180 degrees
      Aircraft speed
      45 knots


      Scan Frequency
      170 Lines per second
      Nominal pulse density
      50 pls/m2 (p/flightline)



  The scanner-IMU was mounted on a front facing boom extending below the cockpit with an unobstructed
    240-degree field of view, with a GNSS antenna mounted on the cockpit. 
  Survey operations were conducted from North Shore Aerodrome, with each survey comprising a sequence of short,
    linear flightlines aligned to the coast. Flightlines were acquired north-south, and then south-north, to
    account for the effects of occlusion during a single overpass. Each return sortie too approximately 70 mins
    of flying time (not including travel time to and from a regional base). Following the first sortie, all
    instrumentation was powered down and dismounted, before being remounted and reinitialized. This approach
    mimics exactly the procedure that would be followed between two widely separately surveys in time.
  Global Navigation Satellite Systems (GNSS) Base Station Data
  GNSS observations were recorded at a 3rd order (2V) LINZ geodetic mark (GSAL) to correct the roving
    positional track recorded at the sensor. This is a continuous operating reference station (CORS) operating
    as part of Global Surveys Leica Geosystems SmartFix network, recording observations at 1 s. The details of
    the reference station are as follows:



      LINZ
        Benchmark Code:
      GSAL (Albany Triton)


      Benchmark Position:

      Latitude:
      36° 44' 27.51079" S


      Longitude:
      174° 43' 23.50966" E


      Ellipsoidal height
        (m):
      88.262


      Antenna:

      Leica AS10



  A further ground survey of check point data was acquired using Leica GS15 GNSS systems operating using
    network RTK GNSS based on the Global Survey SmartFix network. >300 observations were acquired from
    across the survey area, classified by land-cover to include hard surfaces (roads); and short grass pasture.
    Note: network RTK GNSS have typical absolute accuracies of 4-6 cm over the baseline lengths used here (15-25
    km).
  Real Time Kinematic GNSS Checkpoint Data
  A distributed network of 351 checkpoints were acquired as checkpoints to evaluate the vertical accuracy and
    precision of the survey data. All points were collected using network-derived RTK GNSS observations based
    on the Leica Geosystems SmartFix network of broadcasting referencing stations. Measurements were acquired
    with a Leica GS16 receiver on the 24th January 2020, and acquisition settings that enforced a 3D standard
    deviation of < 0.025 m for each observation. To capture any broad scale patterns of georeferencing
    error, the checkpoints were collected in four regional surveys at Browns Bay, Mairangi Bay, Milford and
    Narrow Neck, as shown in Figure 6 overleaf.

  DATA PROCESSING
  Trajectory Modelling
  Lidar positioning and orientation (POS) was determined using the roving GNSS/IMU and static GNSS observations
    acquired using Waypoint Inertial Explorer Software. The resulting solution maintained attitude separation
    of less than +-2 arcmin and positional separation of less than +-1 cm. Trajectories were solved
    independently for each of the two surveys.
  Lidar Calibration
  Swath calibration based on overlap analysis was undertaken using the TerraScan and TerraMatch software
    suite. Flightline calibration was undertaken to solve for global and flightline specific deviations and
    fluctuations in attitude and DZ based on over 100,000 tie-lines derived from ground observations. The
    results of the calibration, based on all used tie-lines is shown in Table 2 below:




      Survey
      Initial mean 3D
        mismatch (m)
      Calibrated mean 3D
        mismatch


      1
      0.055
      0.014


      2
      0.044
      0.011



  Point Cloud Classification
  Data were classified using standard routines into ground, above ground and noise.

    For Survey 1, the point density over the entire area is 97.5 points/m² for all point classes and 44.2
      points/m2 for only ground points.
    For Survey 2, the point density over the entire area is 55.7 points/m² for all point classes and 30.9
      points/m2 for only ground points.

  The difference between the two datasets reflects trimming of Survey 1 to incorporate only the coastal fringe,
    while Survey 2 extends inland by typically 300 m to provide a demonstration of the potential wider coverage
    observable from the flightpath. On the beach areas and along the cliff sections, typical densities are in
    excess of 100 points/m2 in both surveys. The final point cloud classification for each survey is shown in
    Table 3:



      Surface Type
      Classification Code

      Point Class
      Survey 1
        Observations
      Survey 2
        Observations


      Unclassified
      1
      Off-Ground
      204,644,243
      226,749,086


      Ground
      2
      Ground
      143,160,406
      182,111,679


      Total Points


      347,804,649
      408,860,765

Click here to view the point cloud data for the North Shore coastline in a Scene Map.

  DATA ACQUISITION


    Airborne Data Acquisition

  An airborne laser scanner survey was conducted over the North Shore, from North Head to Long Bay
    (approximately 22.5 km following the shoreline). Operations were undertaken on 19th June 2019 in good flying
    conditions. Data were acquired using a Riegl VUX-1LR lidar system, mounted on an EC120 helicopter, operated
    by Christchurch Helicopters. The laser survey was based on the following parameters:



      Parameter


      Parameter



      Scanner
      Riegl VUX-1LR
      Pulse Repetition
      820 kHz


      Flying Height
      50-80 m above ground
      Swath Overlap
      75-100%


      Scan Angle
      180 degrees
      Aircraft speed
      45 knots


      Scan Frequency
      170 Lines per second
      Nominal pulse density
      50 pls/m2 (p/flightline)



  The scanner-IMU was mounted on a front facing boom extending below the cockpit with an unobstructed
    240-degree field of view, with a GNSS antenna mounted on the cockpit. 
  Survey operations were conducted from North Shore Aerodrome, with each survey comprising a sequence of short,
    linear flightlines aligned to the coast. Flightlines were acquired north-south, and then south-north, to
    account for the effects of occlusion during a single overpass. Each return sortie too approximately 70 mins
    of flying time (not including travel time to and from a regional base). Following the first sortie, all
    instrumentation was powered down and dismounted, before being remounted and reinitialized. This approach
    mimics exactly the procedure that would be followed between two widely separately surveys in time.
  Global Navigation Satellite Systems (GNSS) Base Station Data
  GNSS observations were recorded at a 3rd order (2V) LINZ geodetic mark (GSAL) to correct the roving
    positional track recorded at the sensor. This is a continuous operating reference station (CORS) operating
    as part of Global Surveys Leica Geosystems SmartFix network, recording observations at 1 s. The details of
    the reference station are as follows:



      LINZ
        Benchmark Code:
      GSAL (Albany Triton)


      Benchmark Position:

      Latitude:
      36° 44' 27.51079" S


      Longitude:
      174° 43' 23.50966" E


      Ellipsoidal height
        (m):
      88.262


      Antenna:

      Leica AS10



  A further ground survey of check point data was acquired using Leica GS15 GNSS systems operating using
    network RTK GNSS based on the Global Survey SmartFix network. >300 observations were acquired from
    across the survey area, classified by land-cover to include hard surfaces (roads); and short grass pasture.
    Note: network RTK GNSS have typical absolute accuracies of 4-6 cm over the baseline lengths used here (15-25
    km).
  Real Time Kinematic GNSS Checkpoint Data
  A distributed network of 351 checkpoints were acquired as checkpoints to evaluate the vertical accuracy and
    precision of the survey data. All points were collected using network-derived RTK GNSS observations based
    on the Leica Geosystems SmartFix network of broadcasting referencing stations. Measurements were acquired
    with a Leica GS16 receiver on the 24th January 2020, and acquisition settings that enforced a 3D standard
    deviation of < 0.025 m for each observation. To capture any broad scale patterns of georeferencing
    error, the checkpoints were collected in four regional surveys at Browns Bay, Mairangi Bay, Milford and
    Narrow Neck, as shown in Figure 6 overleaf.

  DATA PROCESSING
  Trajectory Modelling
  Lidar positioning and orientation (POS) was determined using the roving GNSS/IMU and static GNSS observations
    acquired using Waypoint Inertial Explorer Software. The resulting solution maintained attitude separation
    of less than +-2 arcmin and positional separation of less than +-1 cm. Trajectories were solved
    independently for each of the two surveys.
  Lidar Calibration
  Swath calibration based on overlap analysis was undertaken using the TerraScan and TerraMatch software
    suite. Flightline calibration was undertaken to solve for global and flightline specific deviations and
    fluctuations in attitude and DZ based on over 100,000 tie-lines derived from ground observations. The
    results of the calibration, based on all used tie-lines is shown in Table 2 below:




      Survey
      Initial mean 3D
        mismatch (m)
      Calibrated mean 3D
        mismatch


      1
      0.055
      0.014


      2
      0.044
      0.011



  Point Cloud Classification
  Data were classified using standard routines into ground, above ground and noise.

    For Survey 1, the point density over the entire area is 97.5 points/m² for all point classes and 44.2
      points/m2 for only ground points.
    For Survey 2, the point density over the entire area is 55.7 points/m² for all point classes and 30.9
      points/m2 for only ground points.

  The difference between the two datasets reflects trimming of Survey 1 to incorporate only the coastal fringe,
    while Survey 2 extends inland by typically 300 m to provide a demonstration of the potential wider coverage
    observable from the flightpath. On the beach areas and along the cliff sections, typical densities are in
    excess of 100 points/m2 in both surveys. The final point cloud classification for each survey is shown in
    Table 3:



      Surface Type
      Classification Code

      Point Class
      Survey 1
        Observations
      Survey 2
        Observations


      Unclassified
      1
      Off-Ground
      204,644,243
      226,749,086


      Ground
      2
      Ground
      143,160,406
      182,111,679


      Total Points


      347,804,649
      408,860,765