# The Survey of Lava Tube Distribution in Jeju Island by Multi-Source Data Fusion
## 6 Conclusions  
The geological importance of lava tubes in Jeju Island has been noted with the discovery of extraterrestrial lava tubes and their habitable environments. Since the risk caused by such a geological environment is not regularly monitored, both the known and the undisclosed lava tube networks in Jeju Island should be investigated. Moreover, with the construction of the second international airport in western Jeju, significant concern has been raised regarding the risk imposed by the instability of the hidden lava tube network. To address this issue, the present study conducted an InSAR campaign and subsequent machine learning applications, together with spatial analyses of geological clues. By employing a data fusion approach of InSAR and machine learning, we detected a number of potential LTDPs, demonstrating a plausible distribution of what would be classified as instabilities of the undiscovered lava tube networks, based on their peculiar patterns confined in thin corridors and on their deformation behaviors. In particular, the LTDP groups on the eastern coast showed the best-fit observation of the existence of unknown cave networks, a finding that was supported by the results of the geophysical surveys. However, some false/pseudo-LTDPs remained due to instabilities from other artificial structures and regional condensations.  
This study yielded two main lessons. First, the study elucidates a procedure to spot shallow lava tube networks and identify their risks by integrating various data sources. However, the outcomes also demonstrated the need to fuse groundworks such as GPS and corner reflector over suspected deformations to clarify InSAR results. Future InSAR missions with better penetration will be useful, as they will be able to detect subsurface deformation signals. Combining structural analyses to classify InSAR signals using estimated instability is a highly useful approach and will be the aim of future iterations of this study. Second, adding to the existing methods of discovering terrestrial/extraterrestrial lava tubes, we proved that an InSAR survey is an effective tool for detecting lava tube networks. Considering proposed planetary InSAR missions, this tool may potentially be applied to lava tubes on planetary surfaces.  
Conceptualization, [PERSON]-R.K.; methodology, [PERSON] and [PERSON]; processing, [PERSON] and [PERSON]; validation, [PERSON]-[PERSON], [PERSON] and [PERSON]-[PERSON]; analyses, [PERSON] and [PERSON]; writing, [PERSON], [PERSON] and [PERSON]; writing--review and editing, [PERSON] and [PERSON]-[PERSON]; visualization, [PERSON]-[PERSON]. All authors have read and agreed to the published version of the manuscript.  
The second author was supported by the Ministry of Science and Technology, Taiwan (Grant number: MOST 106-2420-H-004-015-MY3 and MOST 109-2625-M-004-002).  
Data Availability StatementData underlying the results presented in this paper are not publicly available at this time but may be obtained from the authors upon reasonable request.  
The authors would like to thank anonymous reviewers and editor for their useful comments on this paper.  
The authors declare that they have no conflict of interest.