Satellite Interferometry (InSAR) is particularly
useful for remote measurements of ground and structure
displacements (following CR installation, if required),
and may be particularly cost-effective for very remote,
inaccessible or very large areas for ground survey teams.
The measurements can be used to complement and extrapolate
sparse ground surveys, further confirm provisional findings
regarding ground movement, and to help establish spatial
limits around areas that are suspected to be moving over
time.
Measurement of ground motion can be realized
along pipelines, over oil & gas infrastructure in
relation to landslip, river crossings, tectonic hazard
zones, underground oil and gas storage facilities and
mining areas using state-of-the-art satellite radar interferometry
(InSAR) techniques.
The range of techniques offered within
PIPEMON include the new Persistent Scatterer Interferometry
(PSI; sub-millimetric precision in height), conventional
differential InSAR (centimetric precision) and the Corner
Reflector Interferometry (sub-centimetric precision).
The PIPEMON ground
and structure motion monitoring services have been applied
to some typical application areas for pipeline-related
ground motion monitoring as investigated within the PIPEMON
project. The following bullet points show how the requirements
of these applications are met with the most applicable
InSAR techniques:
For more details
on the individual InSAR techniques please go to the Resources
page.
Underground
Storage Areas
Natural gas underground storage areas
are frequently composed of leached salt domes or depleted
natural gas reservoirs where storage monitoring is governed
by mining law, which typically requires ongoing documentation
of any soil subsidence and upheaval. Typically, ground
movements of more than 1 cm above a closed, usually circular
area with a diameter of 500 m to 5 km need to be detected
and closely monitored over time.
A new satellite radar technique called
Persistent Scatterer Interferometry (PSI) can be applied
to measure ground movement over underground storage areas.
The technique measures the motion of individual structures
and ground features to millimetric precision over entire
regions in a single process. The power of PSI resides
in the archive of radar data that stretches back to 1992,
allowing for an up-to-date motion history for every measurement
point. The technique assumes the existence of buildings
or other man-made infrastructure overground, as these
will provide the measurement point locations. In Europe,
storage areas are usually below cultivated land so that
farmhouses, farm outbuildings and pipeline surface infrastructure
may all act as suitable measurement points. PSI can detect
slow ground movements that might be overlooked using conventional
ground-based methodologies.
For more details on the individual InSAR
techniques please go to the Resources
page.
Coal
Mining Activity Areas
In particular in parts of Europe, natural
gas pipelines may run through regions of current or former
coal mining activity that are affec-ted by considerable
differential subsidence. The conventional requirement
of pipeline operators and regulators in these areas is
that subsidence of more than 5 cm in usually single, but
not necessarily regularly shaped areas, sized 0.25 km²
to 100 km² must be detected and closely monitored
over time.
Conventional differential interferometry
(DifSAR) can be used to measure ground subsidence over
coal mining areas. Ground movements are typically very
fast during the removal of a mining panel (for example,
50 cm within two months). In contrast to PSI, which cannot
measure velocities of more than 10 cm per year, DifSAR
can measure faster movements after or during the mining
activity event. In summary, DifSAR can measure fast ground
movement over short intervals.
For more details on the individual InSAR
techniques please go to the Resources
page.
Landslides
For landslide areas, including local
landslip zones, instable locations associated with river
crossings or other features, or pipelines constructed
through regions characterized by inherently unstable terrain,
requirements for ground motion detection and ongoing monitoring
are typically similar to those as for coal mining activity.
Landslide areas have to be regularly checked to measure
possible drift or movement of buried or surface pipelines,
and to understand – over time – characteristics
and rates of movement, for example, predictable seasonal
patterns and extents of ground motion.
For landslide areas with slowly creeping
soil, PSI and DifSAR may be used under some circumstances,
or alternatively, artificial corner reflectors can be
employed in an array to precisely measure the sliding
ground at specific locations. Corner reflector interferometry
(CRInSAR) allows ground displacement measurements at centimetric
precision, carried out remotely.
For more details on the individual InSAR
techniques please go to the Resources
page.
