Persistent Scatterer Interferometry (PSI)
is a revolutionary new technique for measuring ground displacements
to a degree of accuracy and over time periods previously unachievable
using conventional interferometry methods.
Current and historic ground displacement
measurements from 1991 to the present.
Displacement readings every 2 months on average.
High density of measurement points, typically
100km² for urban areas.
Measures displacement rates as small as 1.5
mm/year.
Data available for the whole of the UK, most
of mainland Europe and much of the US and Japan.
This powerful technique involves the processing of 30+ satellite
radar scenes spanning up to 12 years to identify an array
of pre-existing ground features, such as buildings, against
which millimetric measurements of displacement are made from
the satellite data. The arrays typically consist of 100-200
measurement points per square kilometre in urban areas, and
a few tens of points per square kilometre in more rural environments.
PSI yields maps showing rates of motion, good
to a few millimetres per year, over long periods- up to 12
years. In addition and significantly, the process provides
the millimetre-accuracy motion history for each and every
reflector point across the entire time period analysed.
Displacement history chart for each measurement point
Each PSI study consists of a geographic database of precise
displacement measurements for each measurement point (typically
100/km² for urban areas). The points are overlaid on
reference data (map or satellite / aerial image). For each
point, a chart of displacements over the period of study is
accessible. These not only show the rate of subsidence experienced
by each point but also the temporal variation - highlighting
periods of low and high displacement rates.
Digital GIS Data
The PSI product is delivered in the Microimages
TNTmips GIS format by default but can be delivered in a customer
specified format, such as ArcView, at no extra charge. Included
in the product are:
A total displacement map interpolated from individual
measurement points.
A database of movements for each point.
Annual displacement rates for each point linked to a pop-up
chart window for each point selected*.
Multi date Reflectivity Image (the average intensity image
computed from all the scenes used).
*Depending on GIS software used (available in TNTmips).
