A comparison of TerraSAR-X, RADARSAT-2 and ALOS-PALSAR interferometry for monitoring permafrost environments, case study from Herschel Island, Canada

Interferometric synthetic aperture radar (InSAR) data sets from TerraSAR-X, RADARSAT-2 and ALOS-PALSAR are compared for their ability to detect ground movement over the continuous permafrost site of Herschel Island, Yukon Territory, Canada. All three sensors maintain good coherence within a summer season and can be used to create summer displacement products. Stacking is advantageous for the TerraSAR-X and RADARSAT-2 data sets, although mottling, possibly an interaction of the SAR with vegetation, or residual tropospheric noise, is visible, reducing the reliability of the results. RADARSAT-2 and ALOS-PALSAR provide the most promising results with the ability to form one year interval interferograms. PALSAR can also form two and three year interval interferograms. Long interval data sets spanning 2007 to 2010 identify a band of movement of 20 to 30 cm/year along the north-east coast, and a region of movement of up to 5 cm/year near the northern tip of the island. The ability to form long interval displacement products holds the most promise for permafrost monitoring, since long-term trends are of greater interest for permafrost stability than short-term seasonal changes. TerraSAR-X data have the disadvantage that year to year interferograms cannot be formed. InSAR is not the ideal monitoring technique for the large thaw slumps of Herschel Island. Although general areas of instability can be identified, specific slump detection is limited by radar look direction, and the large and abrupt slump movement, often accompanied by disintegration and collapse of slump sections, causes loss of coherence in the InSAR data. Thaw slumps may require a different interferometric approach, such as slump extent mapping from coherence loss, or the installation of corner reflectors and point target techniques. The frequent revisit and high spatial resolution of TerraSAR-X provide the best chance of maintaining coherence over thaw slumps. In general, InSAR is more successful at identifying broad areas of subtle subsidence in gentle relief, areas of terrain instability, possibly due to permafrost thaw or ground ice melt and the removal of water volume, and prior to significant slumping.

► TerraSAR-X, RADARSAT-2 and PALSAR all maintain good coherence through summer months. ► RADARSAT-2 and PALSAR one year interferograms are useful for permafrost monitoring. ► PALSAR two and three year interferograms can also form good displacement products. ► Band of movement of 20–30 cm/year detected along the north-east coast. ► Region of movement < 5 cm/year detected on northern tip of island.