2. Background
The GPRI-II is the second generation instrument of the Gamma Portable Radar Interferometer GPRI
[1,2]. The GPRI-1 was developed as a proof of concept and later used on numerous scientific and
commercial campaigns. The new second generation instrument GPRI-II has improved performance and
is hardened for field measurements.
The GPRI development at Gamma was initiated based on the perceived benefits of in-situ measurement
of deformation using differential radar interferometry. Our extensive experience with satellite
differential interferometry has demonstrated successful application of this technique for measuring
deformation due landslides, pumping of oil and water, mining, glaciers, and tectonic motion.
However, when the deformation between repeat observations exceeds wavelength/4 the usefulness and
interpretation of the data rapidly become difficult. A ground-based instrument can be rapidly deployed
and obtain data with both high spatial and temporal resolutions that are particularly well suited to
measuring rapid deformation.
Unlike orbital SAR systems, in-situ measurement permit flexibility in the selection of the observation
geometry. The geometry can be selected to give maximum sensitivity to deformation along the line of
sight. Observations from multiple aspect angles can be combined to resolve the deformation into
components along different look vectors.
Path delay variation due to tropospheric water vapor is the most significant cause of error in
deformation using differential interferometry. A stationary instrument has the ability to acquire multiple
observations for mitigation of path delay variations. Note that ground measurements have a shorter
path length through the atmosphere than orbital observations also leading to reduced error from this
source.
Multiple observations acquired over short time intervals have the advantage that decorrelation is
minimized by the shorter time intervals. Successive measurements can be processed to track non-linear
deformation within the scene.
