Correlation of thermal performance of ASTER with the hydrothermal alteration zones: the case of Nisyros volcano, Greece

Abstract

We aim to investigate the relation between advanced spaceborne thermal emission and reflection radiometer (ASTER) and thermal infrared (TIR) data with the hydrothermal alteration zones within the hydrothermal field of the caldera of Nisyros volcano in Greece. This is achieved by utilizing clustering on a dataset of five ASTER L1T TIR images spanning the period 2003 to 2007. Each one of these images is converted to temperature images, coregistered, and vegetation masked, creating a five-band ASTER temperature image. In the sequel, probabilistic clustering hypothesis is applied to the five-band vegetation masked ASTER temperature image, subset to the area of the hydrothermal field. The probabilistic clustering algorithm identifies three “thermal” clusters that exhibit a satisfactory degree of agreement with the active hydrothermal alteration field of Nisyros. Each cluster corresponds to a different degree of hydrothermal alteration zone. We show the existence of a middle temperature zone (cluster), which exhibits significant overlap with the middle hydrothermal alteration zone, along with a high-temperature zone and a low-temperature zone. This temperature transition from high-temperature cluster to the middle and gradually to low-temperature cluster for the time-spanning of the data is significant as the hydrothermal field of Nisyros was very active during this period. This finding coincides temporally and spatially with the continuous N–S trending (Lakki rupture).