GNGTS 2019 - Atti del 38° Convegno Nazionale

710 GNGTS 2019 S essione 3.2 to study in detail the internal structure of a glacier, mainly because frozen materials are characterized by low overall electrical conductivity, which in turn allows the electromagnetic signal to reach penetration depths of even hundreds of meters in favourable conditions. In addition, GPR allows to monitor a glacier evolution through time, if data from multiple surveys are available (Del Gobbo et al., 2016). In 2004 the Marmolada Glacier, in the Eastern Alps (Italy), was chosen to perform a GPR survey using two different ground-coupled systems, equipped with a 35 MHz and a 100 MHz antenna pair, respectively. In 2015, the survey was repeated, using an helicopter-borne GPR system (100 MHz antenna). In this work, we provided a 10-year mass balance of the Marmolada Glacier within the 2004-2014 period by comparing the ground- and air-borne GPR datasets. Moreover, considerations about the morphology of the glacier and about physical state of the ice were given. Methods. Quality control based on the identification of the boundary between ice and bedrock on the first dataset, acquired in October 2004 with two ground-coupled GPR systems, allows to select about 16 km as the most informative profiles. During processing, the mean EM velocity was estimated by means of diffraction hyperbolas analysis, equals to 17 cm/ ns, the typical value for ice with negligible free water content. Then, the ice thickness was calculated along each profile and carefully checked at each crossing point. The second dataset was acquired in June 2015 using a GPR system, suspended below an helicopter. Airborne GPR surveys are considered an extremely valid solution because they allow to rapidly cover wide areas, acquiring data up to tens of km per hour, and to avoid rough terrain challenges. Although the survey was performed in June 2015, it allowed to infer the remaining ice thickness at the end of the 2014 glaciological year, and for this reason the comparison represents a 10 year-long evolution of the Marmolada Glacier. After the quality control, necessary to identify and correct the errors due to airborne acquisition, as described in detail in Forte et al., 2019, only 22 km Fig. 1 - Summary of the GPR interpretation process. a) Exemplary portion of 2015 interpreted GPR profile; b) 2D glacier bed TWT as interpreted on all the 2015 GPR profiles crossing the glacier; c) 3D view of the glacier bed interpolated surface, with three GPR profiles crossing each other. H1, H2 and H3 refer to the topographic surface, to the ice top and to the glacier bed, respectively.