For over three decades, Synthetic aperture radar (SAR) has been a popular choice for Earth remote sensing. With its high resolution and day-and-night/weather-agnostic monitoring, SAR is utilized in an array of applications - ranging from geoscience and climate research to environmental and Earth system observation, from 2-D and 3-D mapping to 4-D mapping (involving the combination of space and time); from security measures to planetary exploration. Additionally, SAR is especially suitable for surveillance of areas that lack clearly delineated features on a ground level, such as deserts and glaciers, as it can penetrate clouds and be used in the absence of sunlight.
In his PhD, Andrew Hooper, Professor of Geodesy and Geophysics and Co-Director of the Leeds Institute of Geophysics and Tectonics, used SAR satellite data to understand volcanoes better.
“Radar can measure surface movement, helping understand what is going on at depth. When applied to volcanoes, you can infer something about what’s going on beneath the ground. If you get magma moving around, or any kinds of fluids, it forces the earth to bulge up or down depending on which way they are moving, and we can measure that with surprisingly good accuracy.”
Keeping an eye out
Hooper and the team at COMET (Centre for Observation and Modelling of Earthquakes, Volcanoes and Tectonics) are utilizing recent SAR satellite missions, such as Sentinel-1, launched in 2014, to observe more than 1,500+ volcanoes above sea level for indications of ground deformation. This serves as an indication of possible magma activity. “We plan to monitor all volcanoes situated above sea level; when something out of the ordinary occurs, we'll take notice and inform the relevant country's authorities,” he said.
Hooper and his colleagues have observed for years beforehand signals of deformation associated with volcanic eruptions, earthquakes, and other tectonic circumstances. There is a strong connection between deformations in a volcano and an impending eruption. The timing of these events can vary when it comes to particular volcanoes. In the case of the Icelandic volcano that erupted in 2010, disrupting air traffic for many days, changes had been detected since 1994, even more evidently in 1999. This was particularly remarkable considering that the previous eruption was four centuries before. Not surprisingly, this alerted local scientists who suggested more careful monitoring of the volcano should be implemented.
It’s a stretch
In a similar fashion, leading up to earthquakes, the ground is slowly straining. With regular SAR data acquisitions over longer period, the team can pick strains of a few millimetres per year over distances of more than 100 km. While they cannot predict earthquakes, they can identify areas with significant strains and can improve maps of earthquake hazards.
Past the noise
Using radar means there is a lot of noise in the data. Hooper is currently working on boosting the signal-to-noise ratio using time series. It is easier to spot areas with good signals and areas with too much noise if you look at 50+ images of the same area.
“The original satellites we were using could have 35 days in between passes if you were lucky. But now, you can get satellite passes every day if you integrate many different satellites, so we can see with much more details things that are happening on the time scales of days or weeks. You can see the changes and evolutions on volcanoes.”
As the number of radar satellites increases, the Centre will continue to improve their monitoring and hopefully be able to detect even more over time.
Learn more about the power of SAR.