How new computational methods will improve the accuracy of satellite navigation
In a time where global positioning devices are cheap and plentiful, it’s actually becoming harder than ever to define where exactly ‘here’ is. For example, global processes such as plate tectonics ensure that ‘here’ is never quite in the same place. As demand for centimetre precision increases, this position discrepancy from year to year is unacceptable.
Over the last three years, Geoscience Australia has been utilising the NCI supercomputer to reprocess the national Global Navigation Satellite System (GNSS) data archive, representing over twenty years of global positioning data. This activity will produce a consistent time series for datum definition, and includes both position and velocity estimates for stations in Australia and around the world.
“Australia is moving seven centimetres a year,” explains Geoscience Australia’s Geodesy Section Leader Dr John Dawson, in reference to the shift of tectonic plates.
“This ultimately is creating an issue for us. When people use GPS in their everyday lives, they are measuring their location today but using spatial data from 25 years ago.”
By using modern computational techniques to process the GNSS data archive, changes due to tectonic shift can be estimated, as well as other distortions in the Australian Plate that were not detectable previously. It is only possible to carry out the reprocessing on a large compute system, such as those located at NCI, due to the high computational load.
This level of positional accuracy opens up a wealth of opportunities for new technology, such as the next generation of driverless cars, aircraft navigation and airborne package deliveries using drones.
“There are a whole range of applications that require two centimetre positioning, for example, precision farming,” explains Dr Dawson. With that level of accuracy, farmers could deploy fertiliser more efficiently using unmanned aerial vehicles, using the new coordinate models.
Dr Craig Harrison of Geoscience Australia’s Geodesy Section elaborates further. “This is really a readjustment of GDA94 – the Geocentric Datum of Australia”. GDA94 is Australia’s national coordinate system, and is part of a global coordinate reference frame. “We are moving forward to GDA2020, removing the 1.5 meters of tectonic plate shift and removing distortions.”
“We’ve never done such a comprehensive national adjustment before. Due to the limitations of computers we previously used a less rigorous approach which introduced distortions and unrealistic uncertainties.”
Reprocessing the GNSS data archive will allow all of these adjustments to be brought together for the first time. This precision will allow Australia’s GNSS data archive to more accurately align with the international reference frame.
“We will continue to do these adjustments. Coordinates will always be the same across all devices and internationally” explains Dr Harrison.