**6. Conclusions**

An X-ray micro-tomographic (micro-CT) measurements coupled with digital volume correlation and microstructural study are performed to investigate the microstructure of dry natural snow. The three-dimensional (3D) reconstruction of snow microstructure is essential to understand its metamorphism, and physical and mechanical properties of a snowpack. This initial study allows for an observation of the changes in internal microstructure during compression tests. Moreover, displacement and strain fields of the snow volume and microstructural properties such as porosity, density and specific surface area (SSA) are determined. The porosity distribution of the whole snow volume decreases with an increase in level of compaction. In addition, the analysis of vertical heterogeneity in porosity distribution shows the characteristics of snow sample preparation and settling of snow. The observations in this study further showed that the majority of ice crystals in the investigated snow volume has a deep hollow core, irrespective of the shape and size of the crystal. The DVC analysis showed the displacement field in response to compaction, while the two-dimensional (2D) cross-cuts of the snow volume showed the grain re-arrangemen<sup>t</sup> and bond breakage due to compaction. The presented techniques may be useful to determine stress-strain response of snow for better understanding of the various snow layer transitions.

**Author Contributions:** Conceptualization, F.F. and J.C.; methodology, F.F.; software, F.F. and H.L.; validation, F.F., H.L. and L.E.; formal analysis, F.F. and L.E.; investigation, F.F. and L.E.; resources, F.F., H.L. and L.E.; data curation, F.F.; writing–original draft preparation, L.E. and F.F.; writing–review and editing, L.E. F.F., J.C., and H.L.; visualization, F.F. and L.E.; supervision, F.F. and J.C.; project administration, J.C.; funding acquisition, J.C.

**Funding:** This research was founded by European Regional Development Fund, Region Norrbotten and others, gran<sup>t</sup> number 20201424.

**Conflicts of Interest:** The authors declare no conflict of interest.
