GPRI: Gamma Portable Radar Interferometer

The GAMMA Portable Radar Interferometer (GPRI) is a ground-based real-aperture radar system with rotating antennas operating at Ku-band with 17.2 GHz.

The GPRI is ideally suited for millimeter-precision deformation measurements, long-term monitoring, and digital elevation model (DEM) generation. The system can be rapidly deployed (30 - 45 minutes until the first acquisition) and provides very high temporal resolution. Repeat rates intervals of 60 seconds are possible for full 360° scans. Smaller sectors can be scanned within a few tens of seconds. Pulse-to-pulse interferometry permits temporal baselines of a few milliseconds.

The high signal quality of the GPRI within up to 10 km radius is ensured by the high gain of the narrow-beam (0.39°) real-aperture antennas. The real-aperture antennas ensure coherent imaging of quickly decorrelating targets like vegetation or even water surfaces. The two receive antennas, separated by a vertical baseline, support topographic and volume measurements.

The standard GPRI equipped with one transmit and two receive antennas supports interferometric acquisitions in repeat-pass or single-pass mode (V-pol). Optionally, an extra H-polarized antenna can be provided for dual-pol acquisitions. The two receives antennas permit single-pass interferometric DEM generation and volume change measurements.

For advanced studies, GAMMA provides a full-polarimetric version of the GPRIs with 2 transmit (H + V) and 4 receive antennas (2 x H, 2 x V). A bistatic version with two synchronized GPRIs is also available. 

The GPRI permits a wide range of interferometric and change detection applications for monitoring of dynamic processes on time-scales of milliseconds to years. Observable processes are, e.g., flexure of bridges under load, vibration/oscillation of infrastructure, and the motion of water waves, snow avalanches, sea ice, landslides, glacier velocity, slope stability assessment, deformation of infrastructure and surfaces due to underground working or mining. DEM differencing can be used to detect mass movements.

At GAMMA we mainly use the GPRI to monitor unstable slopes and rocks.

First instruments were built in 2010, with a quad-polarimetric version in 2015. The bistatic version is available since 2016.

The instrument generates data in the RAW and range-focused SLC format. Interferometric processing, geocoding, etc., is supported by the GAMMA Software.

A list of publications describing specific instrument properties, modes or applications can be found here: Instrument-specific Publications.

An extended list of available applications where the GPRI was used or mentioned can be found here: Instrument Application Publications.