The ten-instrument payload on Envisat includes an Advanced Synthetic Aperture Radar (ASAR) instrument designed to acquire radar images of the Earth's surface. Part of Envisat's assigned 'background mission' as it orbits the world every 100 minutes is to prioritise ASAR acquisitions over the seismic belts that cover 15% of the land surface.
"By the time Envisat completes its nominal five-year mission we should have a satisfactory amount of images across all the seismic belts," said Professor Barry Parsons of the Centre for the Observation and Modelling of Earthquakes and Tectonics at Oxford University.
"To detect the fine ground deformation we are interested in, we require repeated radar images of each site. We then combine pairs of images together using a technique called SAR interferometry, or InSAR for short, to show up any change between acquisitions." (For more information see link: How does interferometry work?)
To accurately measure the slow build up of strain as tectonic plates move against each other along Earth's seismic belts, multiple interferograms are combined, requiring many individual SAR images.
"The reason for this is to minimise any atmospheric interference, relative to the small crustal deformation signal we are interested in," added Parsons. "Using data from Envisat's predecessor ERS, our group has recently measured tectonic movement across western Tibet with an accuracy of a few millimetres per year. The results show that slip rates across the major faults in the region are much smaller than had been previously thought and that the Tibetan plateau deforms
Contact: Mariangela D'Acunto
European Space Agency