New Zealand Vertical Datum 2016 (NZVD2016) provides the ability to determine accurate and reliable heights anywhere within New Zealand.
New Zealand Vertical Datum 2016 (NZVD2016)
Traditional precise levelling networks required extensive re-levelling to re-establish after an earthquake. In contrast, NZVD2016 is a geoid-based vertical datum which means that if a reliable ellipsoidal height can be measured in terms of New Zealand Geodetic Datum 2000 (NZGD2000), then a reliable NZVD2016 height can be calculated.
New Zealand Geodetic Datum 2000 (NZGD2000)
Find out more about converting between NZVD2016, NZGD2000 and local vertical datums
A useful application of this would be to use NZVD2016 height to re-establish critical infrastructure such as water supplies, stormwater drains, sewerage systems, roads, bridges and tunnels after a significant event such as a cyclone or earthquake. In these scenarios the geodetic control marks may be disturbed, destroyed, or unreliable as the surrounding environment has been impacted.
For example, the ground level prior to an event might have been 2.50 metres above NZVD2016, but after flood damage the same location could be only 2.11 metres above NZVD2016. By reobserving the location using GNSS, the new height of 2.11 metres can be determined almost immediately. NZVD2016's stability plays a vital role in the recovery process, making it a critical reference for resilience.
Findings from the 2016 Kaikōura earthquakes
As a geoid is derived from gravity data, it is influenced by factors that result in changes in gravity such as the density and shape of the Earth’s surface, and distance from the centre of the Earth. The magnitude 7.8 Kaikoura earthquake (and subsequent aftershocks) of 2016 appeared to cause significant changes on the Earth’s surface, including hundreds of thousands of landslides and uplift of up to 10 metres. This has provided an opportunity to investigate the impact of such changes on the geoid. Our findings confirmed the ongoing reliability of NZVD2016 even after such a large seismic event.
Changes in the gravity field following the event were modelled using satellite-based observation and checked against ground-based control marks. The most significant modelled changes in the geoid were between 5 and 7 millimetres.
More information about this project can be found in a paper published in the Geophysical Journal International: McCubbine, J., Stapoole, V., Caratori Tontini, F. et al. Evaluating temporal stability of the New Zealand quasigeoid following the 2016 Kaikōura earthquake using satellite radar remote sensing. Geophysical Journal International (2019). https://doi.org/10.1093/gji/ggz536