Predicting disaster before it strikes: InSAR in Australia

By on 28 June, 2017

Displacement in the Perth basin, as observed by InSAR. See annotated figure below for details.

The very first InSAR results using the new Sentinel-1 satellite over Australia have recently been published. The results reveal displacements related to groundwater and land use changes in Western Australia’s Perth Basin, and shows promise for a roll out for additional applications in other locations.

Interferometric Synthetic Aperture Radar (InSAR) uses two or more Synthetic Aperture Radar (SAR) images of an area to identify surface movements through time. Also referred to as Differential InSAR (DInSAR), the approach is a promising and relatively new method to measure land use changes, evaluate natural land disasters and even to predict earthquakes before they happen.

InSAR has revolutionised the way we measure changes of the Earth’s surface.”

Past evidence from continuous GPS and repeat levelling identified subsidence in Perth, but these measurements were limited to discrete points or traverses. However, with InSAR the team was able to investigate displacements over a much larger area, and will be able to repeat the process to monitor ongoing changes.

The Researchers from Perth’s Curtin University used the European Space Agency’s newly launched InSAR sensor as part of the Sentinel mission. By comparing information from time-separated Sentinel-1 radar images, the team have mapped ground displacements over the entire greater Perth region, offering new insights into groundwater extraction and natural processes in the region.

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The Sentinel-1A satellite (pictured) was used for InSAR measurements over Australia.

A game-changing approach

The teams’s observations were recently published open access in the journal Remote Sensing, and presented at the European Space Agency’s Fringe 2017 workshop in Helsinki, Finland. The research team made use of nine months of imagery that was collected by the European Union’s Sentinel-1A satellite. By validating the results with a second satellite, and continuous GPS, the authors showed how this approach offers a useful tool for identifying sub-centimetre displacements.

“It is incredible that by measuring millimetre or centimetre scale movements of Earth’s surface, we can learn about fluid flow in subsurface aquifers and reservoirs, discover unmapped faults, and understand how magma is stored beneath volcanoes before eruptions,” said Dr Amy Parker, lead author of the study.

“The results will now be used to guide further focused studies on urban subsidence and the links to groundwater extraction from the city’s aquifers”

Map of vertical displacements over Perth from the new European Space Agency Sentinel-1 satellite. Profile (left) shows broad-scale features and the zoomed in boxes (right) show wetlands. Displacements are largely attributed to seasonal changes in groundwater. Source: Dr Amy Parker et al, Curtin University.

Previous SAR satellite missions have offered sporadic data coverage over Australia.  “This has limited the uptake of SAR and InSAR as a remote-sensing tool in Australia, especially for science applications, which rely heavily upon open access to data,” explained Dr Parker.

“For large and inaccessible areas (so much of Australia) this method is the only viable option for monitoring surface displacements.”

Sentinel-1 A and B are the Synthetic Aperture Radar component of the pioneering Copernicus earth observation program. This European initiative aims to provide global information for land management, marine environment, atmosphere, emergency response, security, and climate change, using 6 ‘families’ of Sentinels, each with different imaging capabilities.

“The Sentinel-1 satellites are complete game changers for InSAR, providing imagery over the whole of Australia every 12 days and allowing investigations into much larger regions for the first time”, Dr Parker continued. “Now there is access to a consistent and regular data source, these measurements can be routinely used for monitoring and understanding natural and anthropogenic processes”.

Predicting disaster before it strikes

Parker listed a bevy of high value applications where InSAR could be applied. This includes ground displacements associated with geohazards, such as earthquakes, landslides and nearby volcanoes, plus resource extraction and carbon sequestration, and also changes in the reflectively of Earth’s surface due to fire and flood damage.

The Curtin team plan to extend the measurements over Perth using a longer time-series of data. This will help to differentiate between seasonal and long-term effects of changes in groundwater.

Elsewhere, they are looking to apply Sentinel-1 to other displacement ‘hotspots’ in Australia and surrounding regions, where this type of information is useful for hazard monitoring, industry and urban planning.

The team will also be working with Geoscience Australia to test the government agency’s new open source InSAR software, PyRate.

“These types of open-source initiatives will help users maximise the potential of the huge Sentinel-1 data archive, which is increasing by 10 terabytes per day,” said Parker.

“InSAR has revolutionised the way we measure changes of the Earth’s surface.”

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