Interferometric Synthetic Aperture Radar versus Inclinometer Ground Surface Deformations at Active Landslide

Abstract

Rockfalls and landslides commonly occur in the Hawaiian islands. When these events occur along a thoroughfare, they can result in the loss of lives, cause significant damage to infrastructure, and force full or partial road closures, resulting in traffic congestion and commuting delays, sometimes for months. The Hawaii Department of Transportation (HDOT) is interested in historic slope movements along its roads and highways, as this history can guide in prioritizing spending on slope remediation. This has prompted HDOT to be interested in the use of interferometric synthetic aperture radar (InSAR) imagery for detecting historical slope movements and identifying areas that might pose concern for landslide or rockfall activity. To provide a proof of concept for the implementation of this technology in Hawaii, an InSAR case study of a landslide on the island of O’ahu was conducted to compare the results with available inclinometer data. Two-dimensional decomposition was implemented for opposing orbits of descending and ascending Sentinel-1 datasets. Overall, the results show that when both ascending and descending datasets are used to derive line-of-sight displacements that are resolved in a direction along the direction of movement (typically perpendicular to the slope contours), InSAR analysis can effectively capture inclinometer trends in areas experiencing relatively no or little displacement over time (<30 mm/year) but the accuracy diminishes in fast-moving slides (≥270 mm/year).