Geo-referencing techniques of 3d models (SfM): Case study of mud volcano, Villaggio Santa Barbara (Caltanissetta)

In the last 2 years we have performed a topographic and geodetic monitoring on an active mud volcano located in central Sicily (Caltanissetta, Terra Pelata locality). The target was to understand how the volcano is evolving morphologically and kinematically. Topographic and geodetic surveys were performed periodically (every 3 months) by using a suite of doublefrequency GNSS receivers that where been setup to monitor the kinematics and to georeference cartographic products (DTM, DSM and orthophotos). Digital maps were realized through photogrammetry technics and 3D surface modelling by adopting Structure for Motion (SfM) algorithm. Following the aim, morphological variations due to active tectonics and/or ground movements which deform the area were achieved. The monitoring network has been deployed following a twofold target. The first one, is to observe the deformation and kinematics of the area surrounding the mud volcano. To do this, we fixed a stable benchmark by building a GNSS base and surveys were hence performed with a static DGNSS. This configuration allows us to obtain a subcentimetre precision in the point location. Other six points were also built and connected to the base. The second was to georeferencing, with highprecision, a series of ground control point (from now on GCPs) to positioning 3D surface model. Our data show that the combination of TST with GNSS provides a greater precision in georeferencing digital maps even if it requires a long acquisition time. The results, coming from the monitoring, allow us to quantify volumetric and altimetry changes of the mud volcano which are in the order of ± 1 dm during inflection or deflection phases. Our data suggest that the surface of mud volcano is experiencing a general trend of uplift in the order of one decimetre. The methods applied in this work to improve the positioning of objects in remote sensing techniques such as rock clusters, landslides, active structures and volcanic risk.