A Systematic Study of Synthetic Aperture Radar Interferograms Produced From ALOS-2 Data for Large Global Earthquakes From 2014 to 2016

Many studies have used Advanced Land Observing Satellite 2 (ALOS-2) synthetic aperture radar (SAR) interferograms to make remarkable advances toward understanding and assessing seismic hazards. Next-generation satellites will make abundant L-band SAR data available in the near future, enabling even more progress in earthquake research and disaster response. Because a deep understanding of the performance capabilities and limitations of the only existing L-band satellite, ALOS-2, is crucial for planning future L-band SAR missions, this study produced SAR interferograms using ALOS-2 data for large global earthquakes that occurred between August 2014 and December 2016. All of the interferograms produced (49 from 30 seismic events) exhibited adequate coherence even in densely vegetated areas, where C-band interferograms tend to be unreliable because of severe decorrelation. Interferograms for 23 of the 30 seismic events successfully captured significant coseismic deformation signals. These results indicated that ALOS-2 can be leveraged to detect deformations with a high spatial resolution and a high precision unavailable from other instruments, particularly in tropical areas. In addition to the high coherence and high spatial resolution, ALOS-2 features such as left-looking and rapid emergency observations are also advantageous for earthquake research and disaster response. Although current baseline conditions are not always desirable for ALOS-2 interferograms because of limited observation resources, planned L-band missions (e.g., ALOS-4 and NASA-ISRO SAR), which will offer much wider coverage and higher observation frequency, are expected to improve this situation.