RADARSAT-2 D-InSAR for ground displacement in permafrost terrain, validation from Iqaluit Airport, Baffin Island, Canada

Abstract

The use of Differential Interferometric Synthetic Aperture Radar (D-InSAR) is rapidly gaining acceptance as a source of ground displacement information for permafrost regions. The accuracy of the information however, is still not well established. This paper uses a stack of RADARSAT-2 D-InSAR data to map seasonal ground displacement at the Iqaluit Airport, Baffin Island, Canada. The accuracy and information content of the D-InSAR products are evaluated with a variety of ground truth data. The D-InSAR derived seasonal ground displacement patterns align well with surficial geology units and reflect the thaw settlement characteristics of the sediments; they also identify localised displacement patterns in the vicinity of features such as ice wedges and frost cracks. Comparisons with ground settlement measurements from in-situ thaw tubes indicate sub-centimetre agreement in dry areas. In low lying wet areas however, subject to saturation and flooding, the D-InSAR stack significantly underestimates the true settlement, detecting only 3.7cm of the 8.5cm thaw tube measurement. The combination of high phase gradients and poor coherence over intermittently flooded surfaces makes it challenging to preserve reliable phase measurements in these areas. Information from electromagnetic surveys shows that some surface displacement is related to sub-surface conditions (<6m depth), possibly conditions related to the presence and movement of water in the active layer and to a lesser extent, unfrozen water content within the permafrost.