Monitoring the Calderone glacierets in Central Italy using Digital Elevation Models generated from COSMO-Skymed X band synthetic aperture radar
Authors: Alvan Romero Nancy , Palermo Gianluca , Raparelli Edoardo , Tuccella Paolo , D'Aquila Pino , Caira Tiziano , Pecci Massimo 
Published: February 2023

In recent decades, snowfalls, snow cover and duration over Central Italy have decreased and there have been some extreme snowfall events followed by extreme avalanche activities. In this regard, the Calderone Glacier (hereinafter Calderone) represents a geographical and geomorphological element of great interest and is defined as a sentinel of climate change in central Italy, as it is going through a strong phase of reduction: fragmented into 2 glacierets since the end of the last century, it is the only glacial area in the Apennines, and the southernmost in Europe, and for its position on the summit of the Italian Gran Sasso (2912 m asl), a mountain group located in the center of the Apennine belt in the Mediterranean area.The Italian Glaciological Committee (Comitato Glaciologico Italiano (CGI) every year with ad hoc in-situ inspections in early autumn monitor the Calderone mass balance. The mass balance of a glacier depends on the interplay between the mass gains and losses promoted by climate and those associated by the inherent flux; its monitoring is essential because it can contribute to the knowledge of the current ongoing evolution of glaciers.Continuation of the traditional type of monitoring, like the one performed by CGI, based on direct measurements of accumulation and ablation by means of a network of stakes, appears to be an unlikely prospect, because in-situ data gathering usually implies expensive field campaigns and with difficult access to the sites, resulting in limited spatial and temporal resolution. In contrast, techniques based on remotely sensed data, among several techniques, those relying on Synthetic Aperture Radar (SAR) demonstrated to be very effective due to the instrument&#8217;s capability of operating day and night independently of the weather conditions.Differential interferometry or DInSAR can be used to estimate displacements, but due the slow-changing nature of glacier masses and the consequent temporal distance necessary to appreciate changes between two dates, DInSAR technique, in such evaluation conditions, suffers from generally low coherence values, which generally prevent accurate estimates.&#160;For such a reason, in this work we propose to estimate the mass balance for the Calderone through the displacement maps obtained from the difference between two Digital Elevation Models (DEM) obtained from the processing of COSMO-Skymed X band data. Each DEM is obtained from adjacent dates (w.r.t. products availability), and their generation is less subject to the low-coherence problem. In this way two DEMs, whose temporal distance is about 12 months, can be subtracted to obtain displacement maps that are subsequently compared with CGI in-situ measurements for the winter periods from 2010 to 2022. The data used in this study consist of COSMO-SkyMed satellite X-band single-look complex images in slant geometry (level 1A), Stripmap Himage mode (HH polarization) at 3m of spatial resolution. Processing includes, in addition to a canonical DEM generation process, a specific part focused on obtaining the average values, active area and total area for the calculation of the mass balance.Preliminary results will be illustrated and discussed, pointing out potential developments and critical issues.