NSW gov to capture gravity data for better GPS elevation accuracy

The NSW government will use an airborne gravity sensor to improve the accuracy of real-world heights from GPS positioning to just a few centimetres.

The project, which will be conducted over the next 18 months, will result in a gravity model that spans an 800,000 km² area, with data to be captured in five stages, starting in Western NSW.

Acting NSW surveyor-general Thomas Grinter said the NSW Gravity Model is expected to “provide more accurate date to better manage resources, infrastructure projects and natural hazards”.

The gravity data is a “critical building block” for the development of digital twins, replacing datasets that predate Global Navigation Satellite System (GNSS) positioning.

Last year, the government set aside $40 million over three years to extend its digital twin across the entire state.

NSW has been developing its digital twin with Data61 since at least 2018, with a proof-of-concept covering eight local government areas debuting in February 2020.

The NSW Gravity Model will also “help land managers understand their groundwater stores, allow engineers to identify where major natural hazards may occur and help surveyors measure height”.

“Existing geophysical and geodetic data, which looks at the Earth’s shape, orientation and gravity field, is out of date, incomplete and inconsistent,” Grinter said.

“Much of the data includes a combination of land-based, satellite and airborne gravity data collected across several decades.”

In order to capture the data, NSW Spatial Services said an “aircraft equipped with an airborne gravity sensor will fly lines in two-plus kilometre spacings across NSW measuring extremely small variations in the Earth’s natural gravitational pull”.

All flights will be operated in accordance with Civil Aviation Safety Authority guidelines, meaning above the required height of 300 metres in populous areas and 160 metres in other areas.

NSW Spatial Services executive director Narelle Underwood said that the gravity sensors would “not be capable of capturing images of property, infrastructure, or individual people”.

“The gravity measuring instruments do not emit any signals, or impact people, animals or infrastructure and have been used for decades throughout both Australia and globally,” she said.

Data captured during the project is expected to become freely available through the government's open data platform.