Lava flow identification and ageing by means of LiDAR intensity: the Mt. Etna case

Abstract

An application of LiDAR (Light Detection and Ranging) intensity for the identification and mapping of different lava flows from the Mt. Etna (Italy) active volcano is described. In September 2004 an airborne LiDAR survey was flown over summit sectors of Mt. Etna. The information derived from LiDAR intensity values was used to compare the lava flows with respect to their age of emplacement. Analysed lava flows vary in age between those dating prior to AD 1610 and those active during the survey (2004-2005 eruptions). The target-emitter distance, as well as surface roughness and texture at the LiDAR footprint scale, are the main parameter controlling the intensity response of lava flows. Variations in the roughness and texture of surfaces at a meter scale result from two main processes, initial lava cooling and subsequent surface weathering; both lead to variations in the original surface roughness of the flow. In summary: i) initially, from the time of emplacement, the LiDAR intensity of lava flow surfaces decreases; ii) about 6 years after emplacement the LiDAR intensity of lava surfaces starts to increase with the age of flows. LiDAR capability in terms of geometric (accuracy of ~ 1 m in plan position and less than 1 m in elevation) and spectral (LiDAR intensity depends on surface reflection at λ= 1.064 μm) information can thus be effectively used to map lava flows and define a relative chronology of lava emplacement.