R Klees, R F Hanssen, and F Amelung.

Geothermal field deformation monitoring using radar interferometry.

In General Assembly European Geophysical Society,
The Hague, The Netherlands, 19-23 April 1999, 1999.

Surface deformation due to the extraction of geothermal fluid and
steam typically occurs over long temporal periods. The deformation
depends on volumetric changes in the reservoir, and is closely related
to variation in production and injection rates. Monitoring of the
deformation signal is typically performed by levelling and GPS
measurements, capturing long wavelength deformation signal, depending
on the benchmark distribution.  Radar interferometry is a suitable
method for deformation measurement, as it yields a more wide-spread,
fine-resolution deformation signal.
Due to temporal changes in the scattering characteristics of the
terrain, areas with a coherent interferometric phase become isolated
amidst a decorellated background. Resolving the $2\pi$ phase ambiguity
between the coherent patches limits geophysical interpretation in terms of
uniqueness and reliability.
Here we show how, using a series of radar interferograms, short time
interval pairs can be combined to form a first-order deformation
model. This model can be used to impose constraints to the probability
density function to resolve phase ambiguities in a maximum likelihood