InSAR Analysis Results

InSAR Analysis Results are the interferometric SAR (InSAR) products published by the Geospatial Information Authority of Japan (GSI), the national surveying and mapping agency. They show ground and crustal movement that ground surveys such as GNSS and levelling capture only at individual points: earthquake and volcanic deformation, land subsidence and slope movement.

GSI analyses L-band SAR data from JAXA's ALOS-2 (since 2014) and ALOS-4 (since 2024) satellites, with archived results from ALOS (2006-2011). It reduces atmospheric effects using Japan Meteorological Agency numerical weather data and its own GEONET GNSS network. The work runs in two streams. A nationwide routine analysis covers all of Japan at least six times a year. Emergency analyses follow earthquakes, volcanic unrest and some overseas events; for the July 2026 Kumamoto earthquake, GSI also trialled NISAR data for the first time. The results include interferograms, 2.5- and 3-dimensional displacement maps, and time-series analyses. The time series cover all of Japan and the land-based active volcanoes whose analysis is complete.

Users can view the results as layers in GSI Maps. Since fiscal 2024, GSI has issued the nationwide time-series displacement velocities as basic survey results. They can be downloaded free as GeoTIFF from the Satellite SAR Ground Deformation Survey download service, which also provides interferogram, unwrapped-phase, coherence and line-of-sight vector data, along with tile URLs and free processing programs. The data are updated once a year, at the end of March. GSI names two uses: managing survey results (checking control points and maps against the current ground, including monitoring subsidence from groundwater pumping) and disaster response. In 2015, for example, interferograms supported decisions on access restrictions during volcanic unrest at Hakone.