36
H. Rott
Fig. 2.15. Geometry of a side-looking imaging radar. rr - slant range resolution,
rg - ground range resolution
BAR interferometry (InSAR) is a new technique of interest for a wide
range of applications in geoscience and environmental monitoring (Massonet
and Feigl, 1998). With spaceborne SAR an interferogram is calculated from
two images of repeat orbits which are slightly displaced in the across-track
direction. A condition for interferogram generation is the preservation of the
signal phase (coherence) between the two images. Coherence is affected by
temporal changes of back scattering (e.g. due to snowmelt or rain). The phase
shifts in a repeat pass interferogram result from topography and from differential motion. If there is no motion, a digital elevation model can be derived
from a single interferogram. In case of motion (vertical and/or horizontal) at
least two interferograms (calculated from three or four images) are needed
to separate the topographic and motion-related phase shifts. This technique,
called differential interferometry, is very sensitive. Displacements of the order of fractions of a wavelength between the acquisition times of two images
can be detected. Applications include measurements of glacier motion, monitoring of subsidence due to ground-water withdrawal or mining activities,
detection of volcanic inflation, and mapping of seismic deformation.
Colour plates 2.A and 2.B show an example of interferometric analysis
based on SIR-C data of the L-band channel (,X = 24.3 cm), acquired on 9
and 10 October 1994 over Moreno Glacier, Southern Patagonia, Argentina
(Rott et al., 1998). The coherence image shows a high degree of coherence
H. Rott
Fig. 2.15. Geometry of a side-looking imaging radar. rr - slant range resolution,
rg - ground range resolution
BAR interferometry (InSAR) is a new technique of interest for a wide
range of applications in geoscience and environmental monitoring (Massonet
and Feigl, 1998). With spaceborne SAR an interferogram is calculated from
two images of repeat orbits which are slightly displaced in the across-track
direction. A condition for interferogram generation is the preservation of the
signal phase (coherence) between the two images. Coherence is affected by
temporal changes of back scattering (e.g. due to snowmelt or rain). The phase
shifts in a repeat pass interferogram result from topography and from differential motion. If there is no motion, a digital elevation model can be derived
from a single interferogram. In case of motion (vertical and/or horizontal) at
least two interferograms (calculated from three or four images) are needed
to separate the topographic and motion-related phase shifts. This technique,
called differential interferometry, is very sensitive. Displacements of the order of fractions of a wavelength between the acquisition times of two images
can be detected. Applications include measurements of glacier motion, monitoring of subsidence due to ground-water withdrawal or mining activities,
detection of volcanic inflation, and mapping of seismic deformation.
Colour plates 2.A and 2.B show an example of interferometric analysis
based on SIR-C data of the L-band channel (,X = 24.3 cm), acquired on 9
and 10 October 1994 over Moreno Glacier, Southern Patagonia, Argentina
(Rott et al., 1998). The coherence image shows a high degree of coherence