3D underground ice evolution in caves of the Canin massif, Eastern European Alps
Edited by Andrea Securo and Renato R. Colucci
A recent paper published in the international scientific journal Progress in Physical Geography by two members of the Alpine-Adriatic Meteorological Society redefines the methodology underlying the study of the evolution of the high-altitude underground cryosphere. The application of a photogrammetric approach will make it possible to monitor ice deposits variations over time with very high spatial accuracy.
Visual summary of the methodologies involved in this new approach. Structure from Motion Multi View Stereo (SfM-MVS) (derived from photogrammetry) was used for the 3D reconstruction of the scenes. Ground Penetrating Radar was used to calculate ice volumes and thickness. The comparison of different SfM-MVS products allowed the calculation of volume changes over time
Permanent Cave ice deposits, part of the underground cryosphere, are experiencing significant volume losses worldwide. The increasing melting rates threaten the preservation of these often underestimated sources of paleoclimatic information.
Although the entire scientific community agrees on this, what is missing so far is a proper methodological approach to correctly quantify how much such ice masses are effectively reducing, especially in terms of volume.
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This is where the paper Long-term mass-balance monitoring and evolution of ice in caves through structure from motion–multi-view stereo and ground-penetrating radar techniques, recently published in the scientific journal Progress in Physical Geography, tries to act. Among the authors of the work there are Renato R. Colucci and Andrea Securo, both members of the Alpine-Adriatic Meteorological Society, which is partner of this research project.
The work aims to redefine the methodology for studying the evolution of permanent ice deposits in caves, using a multidisciplinary approach. Structure from Motion (SfM) is used for 3D reconstruction and mass balance calculations while Ground Penetrating Radar (GPR) is used to measure ice volumes and thickness.
3D reconstruction (textured mesh) of one of the selected cavities.
Until now, changes in ice thickness of the underground cryosphere were almost always made by discrete punctual measurements. Instead, this approach introduces a solid full 3D calculation based on point clouds. Structure From Motion allows sub-centimetre resolution to be achieved using lightweight, portable and cost-effective instrumentation, perfect for surveying extreme environments such as alpine caves.
The 14 acquisitions performed between 2017 and 2020 in two caves of the Canin Massif (Julian Alps, SE-Alps), combined with previous GPR surveys (2012), allowed the precise calculation of volume variations observed within the caves and the estimation of total volumes. Structure from Motion and Ground Penetrating Radar proved to be a valid combination to obtain a complete and precise imaging of permanent ice deposits in caves and monitor their evolution in medium-long periods.
Example of seasonal comparison (July-October) between the acquired point clouds. The ceiling and walls of the cavity are taken as a reference and are not present in this figure. In addition to the total volume variations it is also possible to obtain the spatial distribution of the variations within the permanent ice deposit.
The potential and future applications of this methodology will be further studied and investigated at several sites in Friuli-Venezia Giulia region through a research project recently started.
Research activities in the underground cryosphere of high altitude karst areas of Friuli Venezia Giulia region will be carried out as part of the CryoKarstFVG Project (Cryosphere in the Karstic environments of Friuli Venezia Giulia), thanks to an operational agreement between the Institute of Polar Sciences (CNR-ISP) and the Geological Service of the Autonomous Region of Friuli Venezia Giulia.
Interior of one of the selected caves reconstructed in 3D (textured mesh). Note the presence of some Ground Control Points (yellow) used to scale the model to real-world size.
Among CryokarstFVG primary objectives there are the development of surveying techniques suitable for complex underground glacial environments, the implementation of the regional speleological database, the drafting of different surveying protocols, the organisation of training events, the monitoring and study of climate-cryosphere interactions in the underground environments of the Monte Canin massif (climate, paleoclimate, geomorphology and permafrost evolution).
Andrea Securo, first author of the paper, is a research fellow at the Institute of Polar Sciences of the National Research Council (ISP-CNR) and works at the CNR headquarters in Trieste, Area Science Park in Basovizza, under the guidance of Renato R. Colucci, scientist at the ISP-CNR and scientific leader of the CryoKrast project.
Both are members of the Alpine-Adriatic Meteorological Society, while Colucci is an affiliated to the Commmissione Grotte E. Boegan, Società Alpina delle Giulie, Sezione di Trieste del CAI.
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