Long-term TIR imagery processing for spatiotemporal monitoring of surface thermal features in volcanic environment: A case study in the Campi Flegrei (Southern Italy)

Different procedures were used to analyze a comprehensive time series of nighttime thermal
infrared images acquired from October 2006 to June 2013 by a permanent station at Pisciarelli (Campi
Flegrei, Italy). The methodologies were aimed at the detection and quantification of possible spatiotemporal
changes in the ground-surface thermal features of an area affected by diffuse degassing. Long-term infrared
time series images were processed without taking into account atmospheric conditions and emissivity
estimations. The data obtained were compared with the trends of independent geophysical and geochemical
parameters, which suggested that long-term temporal variations of the surface maximum temperatures were
governed by the dynamics of the deeper hydrothermal system. Analogously, the dynamics of the shallow
hydrothermal system are likely to control the short-period thermal oscillations that overlie the long-term
thermal signals. The map of the yearly rates of temperature change shows temperature increases clustered
in the thermal anomalous area of the infrared images, without evidence of modifications to the extension of
the anomaly or of growth of new areas with significant thermal emission. This suggests that in the present state,
the heat transfer is mainly due to hot gas emission through preexisting fractures and vents. Our data indicate
that the comprehensive picture of the spatiotemporal evolution of the thermal features of the hydrothermal
sites obtained by long-term infrared monitoring can provide useful information toward refining physical
and conceptual models, as well as improving surveillance of active volcanoes.

The TIR monitoring system was partially funded by the 2000–2006 National Operating
Programme and by the Italian Civil Protection Department in the framework of the 2004–2006 agreement with the Istituto Nazionale di Geofisica e Vulcanologia.

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