SAR interferometry and permanent
Aperture Radar (SAR) combines signal-processing techniques with
satellite orbit information to produce a high-resolution radar image.
Both amplitude and phase information are stored from the returning
echoes. Interferogram is a phase difference image of two SAR-images
acquired at slightly different positions. When the two images are not
taken simultaneously the technique is called repeat-pass
interferometry. Interferogram can be converted to a digital elevation
model (DEM) with meter accuracy.
topography also surface movement can be derived from an interferogram.
In differential SAR interferometry (DINSAR) the goal is to separate
phase contributions due to topography and displacement in order to get
the deformation field. A digital elevation model or another SAR-image
pair is needed to get the topographic phase, which will be subtracted
from the deformation interferogram. In theory accuracy of a few
millimeters can be obtained for the deformation velocity. Nevertheless
atmospheric disturbances and orbital errors corrupt the signal and
accuracy is reduced. Theoretical accuracy can be achieved by forming
time series and averaging many images.
Previous studies made have shown that the problem of temporal
decorrelation (change of scatterers in process of time) with
repeat-pass interferometry can be solved by using permanent scatterers
technique. The procedure involves identifying and exploiting stable
natural reflectors (buildings, rocks etc.) called permanent scatterers
(PS) using long temporal series of interferometric SAR images. Only
PS-pixels are used for motion detection. In numerous previous studies
DINSAR and PS have been successfully applied to study earthquakes,
volcanoes, glaciers, urban subsidence and landslides (usually) in
sparsely vegetated areas.
of the project is to
verify whether DINSAR and PS techniques are feasible for land
uplift determination, and furthermore, to find anomalies in the uplift
verify is it possible to detect land subsidence in vegetated,
northern areas where subsidence areas are known to be small.
find new geodetic applications for INSAR and PS techniques
with Finnish Geodetic Institute.