# Towards a Digital Twin Prototype of Alpine Glaciers: Proposal for a Possible Theoretical Framework
## 4 Discussions  
The availability of a tool continuously fed with a vast, multi-temporal, multi-scale, and multi-platform dataset related to glacier spatial dynamics and health status could be a significant advancement in glacier modelling and in the understanding of the future evolution of glaciers in the Italian Alps. This could provide valuable insights about the impacts of climate change on glaciers at both local and regional levels, as well as support decisions and address behaviour from policymakers and stakeholders. The open and free data from the Copernicus program have greatly enhanced the ability to monitor glacier extension with frequent updates. Nevertheless, especially for Alpine glaciers that are frequently small/medium in size, the medium spatial resolution of Sentinel data can sometimes appear not suitable for properly supporting their modelling and mapping. This situation is going to be worse and worse, since global warming is expected to increase the fragmentation of glaciers (more glaciers of smaller size). Therefore, higher-spatial-resolution data (both optical and SAR) became highly desirable [83; 84; 85] for accurately monitoring small to medium size glaciers, particularly in regions where such glaciers are predominant. This is particularly true over the southern/eastern flank of the Alps, where small size glaciers are predominant [86; 87]. Additionally, these data can only produce flat representation of glaciers, completely losing the third dimension related to their thickness and volume. Data providing height information are, instead, highly desirable, enabling 3D measuring capabilities able to guarantee vertical accuracy consistent with the occurring glacier volume changes. Detailed height data are essential to generate proper 3D models useful to model glacier changes/dynamics. Stereo, LiDAR and SAR acquisitions can play an important role, and efforts should be made by space agencies to properly support such actions. Revisit times of satellites over the same area is another limiting factor, also considering the strong climatic variability typical of mountainous areas. As a result, monitoring instances at proper geometric resolutions, related to the continued acquisition of new data, is hardly achievable. SAR missions can certainly help to improve frequency of acquisitions, but especially in mountain regions, they strongly suffer from geometric distortion and limitations that weaken their effectiveness. Foreshortening, layover and shadows are the main responsible factors that limits the use of SAR data for continued monitoring. Moreover, data processing is difficult and the meaning of spectral, polarimetric and interferometric information is too complicated to be explicitly referred to a glaciological meaning. Nevertheless, great opportunities appear to rely on SAR technology, especially if operated at high geometric resolution (see COSMO-Skymed, Tandem-X, TerraSAR-X missions) over glaciers. In this context, great potential improvement is expected, especially for the Alps, from the upcoming Italian IRIDE Earth Observation program. It will be based on a new low-orbit (500 km height) satellite constellation and will be developed by the Italian Government. Economical resources from the Next Generation EU program (PNRR in Italy) will finance IRIDE together with other complementary national founds. It is expected to be operational in 2026 under the guide of the Italian Space Agency (ASI) and the management of the ESA. IRIDE is thought to be like a \"constellation of constellations\", able to enable high acquisitions capabilities. It is intended as an end-to-end system having the following segments: (i) an upstream one made of a set of sub-constellations of Low Earth Orbiting--LEO satellites; (ii) a downstream one made of an operational ground infrastructure; and (iii) some services intended for supporting the Italian Public Administration. Satellites of IRIDE constellations will host a variety of both SAR and optical sensors exploring different geometric, spectra and temporal resolutions.