Oceania Geodetic Data - Page 4

The NSN55-NZVD2016 grid enables the conversion of normal-orthometric heights from the Nelson 1955 local vertical datum to the New Zealand Vertical Datum 2016 (NZVD2016).

The conversion value is represented by the attribute “O”, in metres.

This conversion and NZVD2016 are formally defined in the LINZ standard LINZS25009.

NSN55-NZVD2016 is published on a two arc-minute grid (approximately 3.6 kilometres) extending over the benchmarks that nominally define the extent of the Nelson 1955 vertical datum (171.3° E to 174.4° E, 40.4° S to 42.7° S).

The height conversion grid models the difference between the Nelson 1955 vertical datum and NZVD2016 using the LINZ GPS-levelling marks. From the GPS-levelling marks the expected accuracy of NSN55-NZVD2016 is better than 2 centimetres (95% Confidence interval).

More information on converting heights between vertical datums can be found on the LINZ website.

The Nelson 1955 to NZVD2016 Conversion Raster provides users with a two arc-minute (approximately 3.6 kilometres) raster image of the conversion of normal-orthometric heights from the Nelson 1955 local vertical datum to the New Zealand Vertical Datum 2016 (NZVD2016).

The conversion value is represented by the attribute “O”, in metres.
This conversion and NZVD2016 are formally defined in the LINZ standard LINZS25009.

The height conversion grid models the difference between the Nelson 1955 vertical datum and NZVD2016 using the LINZ GPS-levelling marks. From the GPS-levelling marks the expected accuracy is better than 2 centimetres (95% Confidence interval).

More information on converting heights between vertical datums can be found on the LINZ website.

The national airborne gravity dataset is comprised of more than 50,000 linear km of flight observations, covering the three main islands of New Zealand and up to 10km offshore.

This dataset provides a 1 arc minute raster image of the Bouguer anomalies, which have been downward continued to the ground surface (McCubbine et al, 2017).

The national airborne gravity dataset was collected as a joint project between Land Information New Zealand (LINZ), GNS Science (GNS) and Victoria University of Wellington (VUW). The airborne survey was completed in a total of eight months, over two campaigns: August – October 2013, and February – June 2014.

Users may also be interested in other layers created for the free-air anomalies at ground surface and the along track observations from the gravity flight lines at flight elevation NZ Airborne Gravity Free-Air Anomalies at Ground Surface (2013-2014) and NZ Airborne Gravity Flight Lines at Elevation (2013-2014).

McCubbine, J. Stagpoole, V. Caratori-Tontini, F. Amos, M. Smith, E. and Winefield, R. (2017). Gravity anomaly grids for the New Zealand region. Manuscript submitted for publication New ZealandJournal of Geology and Geophysics.

Introduction
This dataset provides gravity observations, reductions and metadata for New Zealand’s national airborne gravity survey at flight elevation. A full description of each field in this dataset is available in the accompanying pdf NZ Airborne Gravity Flight Lines at Elevation (2013-2014) Description.

Description
New Zealand’s national airborne gravity dataset is comprised of more than 50,000 linear km of flight observations, covering the three main islands of New Zealand and up to 10km offshore.

Gravity observations can be used to compute gravity anomalies: differences between measured gravity and an ellipsoidal model of the Earth’s gravity field. Gravity anomalies correspond to un-modelled density variations within the Earth’s crust and upper mantle. They are used to investigate concealed geological structures and for quasigeoid modelling.

The national airborne gravity dataset was collected as a joint project between Land Information New Zealand (LINZ), GNS Science (GNS) and Victoria University of Wellington (VUW). The airborne survey was completed in a total of eight months, over two campaigns: August – October 2013, and February – June 2014.

Users may also be interested raster layers created for each of the free-Air and Bouguer Anomalies which have been downward continued to ground surface NZ Airborne Gravity Free-Air Anomalies at Ground Surface (2013-2014) and NZ Airborne Gravity Bouguer Anomalies at Ground Surface (2013-2014).

Introduction
This dataset provides a 1 arc minute raster image of the free-air gravity anomalies, which have been downward continued to the ground surface (McCubbine et al, 2017).

Description
Gravity anomalies are differences between measured gravity (from the airborne gravity dataset) and an ellipsoidal model of the Earth’s gravity field (GRS80). Gravity anomalies correspond to un-modelled density variations within the Earth’s crust and upper mantle. They are used to investigate concealed geological structures and for quasigeoid modelling.

These free-air anomalies show values which include gravitation impact of the topography.

The national airborne gravity dataset is comprised of more than 50,000 linear km of flight observations, covering the three main islands of New Zealand and up to 10km offshore.

As the airborne gravity dataset was measured at flight altitude, the observations have been reduced to the ground surface (a process known as downward continuation).

The national airborne gravity dataset was collected as a joint project between Land Information New Zealand (LINZ), GNS Science (GNS) and Victoria University of Wellington (VUW). The airborne survey was completed in a total of eight months, over two campaigns: August – October 2013, and February – June 2014.

Users may also be interested other layers created for Bouguer anomalies at ground surface and the along track observations from the gravity flight lines at flight elevation NZ Airborne Gravity Bouguer Anomalies at Ground Surface (2013-2014) and NZ Airborne Gravity Flight Lines at Elevation (2013-2014).

McCubbine, J. Stagpoole, V. Caratori-Tontini, F. Amos, M. Smith, E. and Winefield, R. (2017). Gravity anomaly grids for the New Zealand region. Manuscript submitted for publication New Zealand Journal of Geology and Geophysics.

This dataset provides information about the position, position accuracy, mark name, mark type, condition and unique four letter code for geodetic marks in terms of a New Zealand's official geodetic datum.

The dataset only contains marks that are within the New Zealand mainland and offshore islands. These positions have been generated using geodetic observations such as precise differential GPS or electronic distance and theodolite angles measurements. The positions are either 2D or 3D depending of the availability of this measurement data.

The source data is from Toitū Te Whenua Land Information New Zealand's (LINZ) Landonline system where it is used by Land Surveyors. This dataset is updated daily to reflect changes made in the Landonline.

Accuracy

Geodetic marks with a coordinate order of 5 or less have been positioned in terms of NZGD2000. Lower order marks (order 6 and greater) are derived from cadastral surveys, lower accuracy measurement techniques or inaccurate historical datum transformations, and may be significantly less accurate.

The accuracy of NZGD2000 coordinates is described by a series of 'orders' classifications. Positions in terms of NZGD2000 are described by three-dimensional coordinates (latitude, longitude, ellipsoidal height). The accuracy of a survey mark is indicated by its Order. Orders are classifications based on the quality of the coordinate in relation to the datum and in relation to other surrounding marks. For more information see

Note that the accuracy applies at the time the mark was last surveyed. Refer to the web geodetic database for historical information about mark coordinates.

Note also that the existence of a mark in this dataset does not imply that there is currently a physical mark in the ground - the dataset includes destroyed or lost historical marks. The geodetic database provides more information on the mark status, valid at last time it was visited by LINZ or a maintenance contractor.

This dataset provides information about the position, height, height datum, height accuracy, mark name, mark type, condition and unique four letter identifier for geodetic marks that have an authoritative height in terms of a vertical datum. Heights are in datums defined at www.linz.govt.nz/guidance/geodetic-system/coordina... .

All marks will have positions in terms a 3D New Zealand official geodetic datum. The horizontal positions of marks are provided for approximate location purposes only .

This dataset only contains marks that are within the New Zealand mainland and offshore islands. The height data for these marks have been generated using precise levelling from datum tide gauges, or has been acquired by 3rd party sources either as levelling observations or direct heights.

The source data is from Toitū Te Whenua Land Information New Zealand's (LINZ) Landonline system where it is used by Land Surveyors. This dataset is updated daily to reflect changes made in the Landonline.

Accuracy

The accuracy of normal-orthometric heights are described by height orders.

For more information see www.linz.govt.nz/guidance/geodetic-system/coordina... .

Note the accuracy applies at the time the mark was last surveyed - see the geodetic database for historical information about height coordinates.

The New Zealand Quasigeoid2009 (NZGeoid2009) can be used to convert GPS derived ellipsoidal heights to New Zealand Vertical Datum 2009 (NZVD2009) normal-orthometric heights that relate more closely to mean sea level and the local gravity field. NZGeoid2009 can also be used to transform heights to any of the 13 official local vertical datums used across New Zealand, more information on this transformation is available at www.linz.govt.nz/geodetic/conversion-coordinates/h....

NZGeoid2009 is formally defined in the LINZ standard LINZS25004 which can be obtained from www.linz.govt.nz/geodetic/standards-publications/s.... NZGeoid2009 models the difference between the GRS80 ellipsoid and the geoid over the New Zealand region. The geoid is a theoretical surface of equal gravity that roughly approximates the mean level of the sea across the Earth.

NZGeoid2009 is published by LINZ and was computed by enhancing the EGM2008 global gravity model with terrestrial gravity observations over New Zealand and DNSC08 satellite altimetry data over the oceans. The model is published on a one arc-minute grid covering New Zealand's extended exclusive economic zone.

The accuracy of NZGeoid2009 is nominally ±0.08 metres across New Zealand. More information on the accuracy in relation to the 13 local vertical datums is provided in LINZS25004.

The NZGD2000 Government CORS provides the locations of GNSS Continuously Operating Reference Stations operated by GNS Science under the GeoNet project (www.geonet.org.nz). Coordinates are from the LINZ Geodetic Database, in NZGD2000.

These are split into several different networks:

• PositioNZ - stations predominantly funded by LINZ, with some GeoNet funding. These provide a nationwide coverage of ~120km spacing. More info here
• GeoNet - stations funded by the GeoNet project. These are located in areas of geophysical interest, usually on the East Coast of the North Island. More info here
• SAGENZ - stations funded by the University of Otago, GNS Science, MIT, University of Colorado and UNAVCO. These Southern Alps Geodetic Experiment - New Zealand stations are generally semi-continuous sites.
• Tide Gauge - stations co-located with tide gauges at major ports. Data is managed through the GeoNet project also.

30" RINEX data from all of these sites is available from the GeoNet website

Real Time data is available from all PositioNZ stations, and some GeoNet stations. For more information, see the PositioNZ-RT website