Ground Deformation in Afar Detected by ALOS-2 ScanSAR InSAR Time Series Analysis

The ground deformation associated with rifting and volcanic activities in Afar has been gradually revealed by geodetic measurements such as Global Navigation Satellite System (GNSS) and Interferometric Synthetic Aperture Radar (InSAR) time series analysis using Sentinel-1 data. However, decorrelation of the C-band InSAR data especially in vegetated areas is still a limiting factor to obtain the spatially complete deformation signals. Recently, all ScanSAR data from L-band Advanced Land Observing Satellite-2 (ALOS-2) have been released by Japan Aerospace Exploration Agency as open and free datasets. While ALOS-2 ScanSAR InSAR may be able to detect ground deformation with high coverage, there are some challenges to overcome. For example, ALOS-2 data are strongly affected by ionospheric turbulence compared to Sentinel-1 data because of its longer wavelength. Also, ALOS-2 has a longer repeat cycle (i.e., less observation frequency) than Sentinel-1, which increases the uncertainty in velocity estimation. We carefully reduced such noise by applying methods proposed in the previous studies in ALOS-2 ScanSAR InSAR time series analysis. Consequently, both tectonic and volcanic ground deformations were successfully obtained with comparable accuracy to Sentinel-1. The derived deformation using ALOS-2 ScanSAR data has better coverage than that from Sentinel-1 data and it will enable a more detailed interpretation of the ground deformation.