Monitoring the Calderone glacieret in Central Italy from COSMO-SkyMed synthetic aperture radar at X band

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, it is the only glacier 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 late spring and early autumn monitor the Calderone mass balance. The mass balance of a glacier depends on the interplay between the mass gains and losses associated with climate and those associated with 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's capability of operating day and night independently of the weather conditions.

Differential interferometry or DInSAR is a tool for accurate displacement measurements, and it is useful in identifying footprints of progressing movement. DInSAR is interferometry itself, the only difference is that topographical effects are compensated by using a Digital Elevation Model (DEM) of the area of interest, creating what is referred to as a differential interferogram.

In this work we propose the mass balance for the Calderone through the DInSAR results and its comparison with CGI in-situ measurements for the winter period 2018-2020. The data used in this study consist of COSMO-SkyMed satellite X-band single-look complex images in slant geometry (SCS, level 1A product),  Stripmap Himage mode (HH polarization) at 3 m per pixel of spatial resolution, and acquisition geometry Right Descending. The processing of this satellite data was applied over the entire area covered by the images and then refined to Calderone area, it includes a pre-processing first step that include: coregistration, interferogram formation, filtering and speckle; and a second part focused on obtaining the average values, active area and total area for the calculation of the mass balance.