Mapping expansive soils from space

This paper describes a new approach to detecting motion related to soil expansivity from ground motion time series data. Interferometric Synthetic Aperture Radar (InSAR) is a remote sensing technique used to detect and monitor ground and surface infrastructure motion with millimetric precision using SAR satellite imagery.

A total of 74 high resolution TerraSAR-X SAR images were used to produce ground motion time series covering a large urban area (450 km2) in Auckland NZ between August 2019 and May 2022. Sixense’s Atlas InSAR processing chain produced 7.6 million ground motion time series. Data science techniques were used to locate motion related to expansive clays swelling mechanisms.

Climate data from NIWA weather stations and soil data layers from Landcare Research NZ have been included to complement the analysis. 450k building footprints from Land Information New Zealand (LINZ) have been used to map those buildings potentially affected by expansive clay seasonal movements. Finally, ground instrumentation data from the Mount Eden City Rail Link (CRL) station construction site is used to validate the observed motion precision of Sixense’s Atlas InSAR.

The end goal of this study is to provide the Auckland city council cost effective added value information in the context of climate change adaptation, where erratic weather patterns pose a serious risk to building foundations.