## 5 Conclusions  
In this study, the development and application of a new method for automated coastline extraction from VHR multispectral imagery and DSMs was conducted. The Coastal Extraction Tool (CET) was developed as a straightforward and simple-to-use tool that is applicable for accurate automated detection and extraction of coastlines. CET is recognized as a highly accurate tool that successfully overcomes spectral-induced errors (e.g., shadows or spectral reflections) that were present in coastlines extracted by other existing tested tools. Considering its accuracy and ease of use, we suggest that CET should be applied for automated coastline extraction in other large and indented coastal areas. Additionally, we suggest that it could be potentially applied for various purposes, e.g., the detection and mapping of multi-temporal changes in coastline position (1), detection of very small and fast-moving objects (e.g., fishing boats, aircrafts, etc.) (2), and mapping the coastal infrastructure and fish farms (3), etc. In this study, we managed to determine the total number of islands, islets, rocks, and rocks awash within the Iz-Rava island group, significantly rising the total area and insular coastline length. As a result of the analysis, two small rocks (Sika and Garofulin) were detected within the study area, which due to their small size have not been mapped within earlier mapping efforts. Thus, this research managed to raise the official total number of islands, islets, rocks, and rocks awash in Croatia from 1246 to 1248. It is to be expected that the application of the same method in all Croatian coastal regions would further increase the number of Croatian rocks and rocks awash. The application of the developed CET within the Iz-Rava island group has demonstrated that WV imagery has great potential for large-scale extraction of coastlines, from local to regional scale. Given the very high temporal and spatial resolution of the WV imagery, the application of CET on WV-derived models can significantly facilitate mapping efforts and provide effective management over very large coastal areas. Although the accuracy of such coastline extraction still lags behind \"field-based\" remote sensing methods (e.g., UAV photogrammetric survey), the accuracy achieved within the whole study area is very satisfactory. Therefore, within future research, WV imagery and developed CET should be used for detailed mapping of the whole Croatian coastline. The following are available online at [[https://www.mdpi.com/article/10](https://www.mdpi.com/article/10)]([https://www.mdpi.com/article/10](https://www.mdpi.com/article/10)) 3390/app11209482/s1, Figure SI: Scheme of Coastal Extraction Tool (CET) created in ModelBuilder. Conceptualization, F.D., A.S., and J.F. ; Formal analysis, F.D. ; Funding acquisition, A.S. and J.F. ; Investigation, F.D., A.S., and I.M. ; Methodology, F.D., A.S., I.M., J.F., E.V., and LP. ; Project administration, F.D., A.S., and J.F. ; Resources, F.D. and A.S.; Software, F.D., A.S., and E.V. ; Supervision, A.S.; Validation, F.D., A.S., I.M., J.F., and E.V. ; Visualization, F.D., I.M., E.V., and L.P.; Writing--original draft, F.D., I.M., and L.P.; Writing--review and editing, F.D., I.M., J.F., and L.P. All authors have read and agreed to the published version of the manuscript. This research was funded by the Italy-Croatia cross-border cooperation program 2014-2020 as part of the STREAM (Strategic development of flood management) project. This research was performed within the project UIP-2017-05-2694, which was financially supported by the Croatian Science Foundation. The authors would like to thank Croatian Science Foundation for providing necessary research funds. Not applicable. The data presented in this study are available on request from the corresponding author. This publication was produced as part of the STREAM (Strategic development of flood management) project, funded by the Italy-Croatia cross-border cooperation program 2014-2020.