| InSAR stands for Interferometric Synthetic Aperture
Radar. This is thus a remote sensing technique that uses radar satellite
images. Those radar satellite (ERS1, ERS2, JERS, IRS or Radarsat)
shoot constantly beams of radar waves towards the earth and record
them after they bounced back off the Earth's surface.
Two information compose the images. One contains how much of the
wave bounced back off to the satellite (signal intensity). That
depends on how much of the wave has been absorbed on the way and
how much has been reflected in the direction of the satellite.
The second information is the 'phase' of the wave. When a wave
travels through space, we can think of it as a hand on a clock.
It starts on 12 when the wave leaves the satellite. The 'hand' (phase)
keeps running round and round the clock until the wave reaches the
ground. When the wave hits the ground, the hand stops and indicating
a certain 'time' or 'phase'. When the wave comes back to the satellite,
it tells the satellite on what value the hand/phase got stopped.
Every point in a satellite image (pixel) is carrying those two
information: the intensity and and the phase. The intensity can
be used to characterize the material in which the surface the wave
bounced off is made of and what orientation it has. Oil leaks on
the sea, for instance, can be spotted in that way. They look much
smoother than the water surrounding.
The phase is used in another way. When the radar satellite revisists
the exact same portion of the Earth, the phase image should be identical.
If it is not the case, then something has been going on. And by
combining those two images, we can measure how much and where the
ground has moved.
Our research focuses on tectonic
and volcanic
ground deformations. And sometimes, very unexpectedly, we find that
human impact is much more important than we would have thought before. |
