Satellites scan the Earth in bands. Every 12 days, a Sentinel-1 satellite passes Tasmania and scans a new band.
"The problem is no data is received from the oceans because the satellites can’t get a reflection back," University of Tasmania geodesist Dr Lucia McCallum said.
“We need this data to accurately measure sea level rise, which is especially important with ice caps melting due to climate change.”
To calculate and model sea level rise, ocean tides or plate tectonics, scientists need a complete set of global data – a global coordinate system. This system, currently in development, is known as the UN Global Geodetic Reference System.
A bit of theory
One method to detect ground change and distortion is called Interferometric Synthetic Aperture Radar (InSAR). This involves using satellites to bounce microwaves off the Earth’s surface while measuring their travel time and return signal.
Dr McCallum and the team used a combination of the InSAR technique and the University’s VLBI-capable radio telescopes, to connect the satellite data to the global coordinate system.
VLBI refers to interferometry done over very large distances or ‘baselines’ including across continents. Astronomers use the light gathered by up to 30 radio telescopes, combined with precise timing, to build a network of telescopes. Using VLBI, the relative distance between them can be measured to within a few millimetres.
Trialling the new technique
To carry out the research, the team used three University of Tasmania radio telescopes in Cambridge Tasmania, Western Australia and the Northern Territory. Operation of these telescopes is funded by GeoScience Australia’s Positioning Australia program as part of AuScope's VLBI program.
“With our VLBI telescopes, we normally use black holes – assumed to be static points in space – from which to measure the speed of satellites and the Earth,” Dr McCallum said.
For this research, the team used the telescope dish to create a bright reflection in the satellite images.
Over the past year, each time the satellite passed the radio telescope, we pointed it towards the satellite flight path.
To visualise the data, the University of Tasmania geodesists teamed up for the first time with satellite image experts at Curtin University.
From the InSAR images, the team identified where there were bright reflections from the telescopes. They could then assign precise geographical locations or 'georeference' the images in the global coordinate system.
Once in the global system, images from different continents could in fact be connected, thus producing a complete global set of measurements. However, this requires collaboration among the world's VLBI-capable radio telescopes.
Over the next 3-5 years, the team will continue to trial the new approach with an aim to demonstrate consistently accurate results and build a case for global collaboration.
Potentially massive impacts
Dr McCallum said access to this data could improve our understanding of the highly dynamic Earth System.
“With the radio telescopes, we get distinct points on the Earth’s surface so we can model ground motions due to displacement of air and water, including tides.
This could lead to progress towards Earthquake prediction or better tsunami warning systems.
If we can get a few more minutes warning there would be enough time to shut down a nuclear plant, for example, and that would prevent extraordinary damage,” she said.
The solution is so simple it can be implemented into routine telescope operation. This has been successfully tested by international collaborators at the Onsala Space Observatory and the Chalmers University of Technology in Sweden.
Confirming the team’s innovative work, last year a long-term contract of $850,000 per year was signed between Federal Government entity Geoscience Australia and the University for continued contributions towards Positioning Australia – a program that supports UN sustainability goals.
Recognition for innovative research
Originally from Austria, 6 years ago Dr McCallum relocated to Hobart for a University of Tasmania postdoctoral position so that she could contribute to the Positioning Australia program.
“By instigating and running the Positioning Australia program, Australia has now really taken a lead in the global science of geodesy, and it’s great to be part of it,” she said.
At the University of Tasmania, we’re fortunate having access to five University-owned radio telescopes purely for research. It means we’re able to try new things and really innovate.
In recognition of her contribution to Australian research, Dr McCallum was awarded the Royal Society of Tasmania Peter Smith Medal and an ARC Discovery Early Career Researcher Award (DECRA). The DECRA is regarded as one of the most prestigious sources of postdoctoral funding for non-medical scientists in Australia.
An article about the collaborative discovery was recently published in Earth & Space Science News.
About Dr Lucia McCallum
Dr Lucia McCallum is a geodesist in the School of Natural Sciences' radio astronomy group. Her field of research is the Very Long Baseline Interferometry (VLBI) technique, using signals from far distant radio galaxies to measure the Earth. After finishing her PhD at the Technische Universität in Vienna (Austria), she joined the University as a postdoctoral researcher in 2014.View Dr Lucia McCallum's full researcher profile