Investigation of Sentinel-1 capabilities to detect hydrothermal alteration based on multitemporal interferometric coherence: the case of Nisyros volcano (Greece)

Abstract This paper aims to investigate the capability of Sentinel-1 Synthetic Aperture Radar (SAR) data to detect hydrothermal alteration zones within the caldera of the Nisyros volcano in Greece through a multitemporal interferometric coherence analysis. For that purpose, seven ascending pass Sentinel-1B SAR Single Look Complex images were collected spanning October 2017 to January 2018. The local meteorological conditions, precipitation in particular, were taken into consideration as the humidity levels could affect the radar scattering properties. Six coherence images were calculated using as master image the 16th October 2017 acquisition and as slave images the other dates. The coherence products were then used for a multitemporal interferometric coherence analysis through the calculation of the average coherence map. The average coherence map showed that Sentinel-1 data seems to well delimitate the hydrothermal alteration area according to the geologic map of Nisyros. Comparing the hydrothermal alteration with the loose alluvial deposits within the caldera, the hydrothermal altered products showed high coherence values while the loose alluvial products low coherence values. The preliminary results show the potential of Sentinel-1 multitemporal interferometric coherence to differentiate hydrothermal alteration from volatile loose formations such as alluvial deposits.