**3.7 Delineation of mine area**

Following the identification of mine areas, isolation of these areas is the next step. Since some areas outside mines share the same mean NDVI values with mines,

**Figure 5.** *Mean NDVI value of segments.*

further processing of the vector layer is required. A dataset with rough boundaries of mine areas forms an auxiliary layer that can help to remove non-mine areas. In specific, Corine Land Cover (CLC) 2018 polygon of mine class was employed. A buffer area was computed using a fixed distance of 500 m for two main reasons. Minimum mapping unit of CLC datasets is 25 hectares, thus it is not appropriate for the scale of the analysis of this study and cannot be used unchanged. In addition, the reference year of satellite data used for the production of the latest CLC status layer is 2018, while the reference year of the imagery used in this paper is 2020. Several changes regarding mine boundaries occurred during this timeframe. CLC 2018 mine polygon and 500 m buffered polygon are presented in **Figure 6**.

A segment, in order to be characterized as mine area has to satisfy two conditions. It has to intersect with CLC 2018 buffered boundaries and its mean NDVI value has to be in the range of 0.00 to 0.25. Through this approach, segments were filtered and non-mine areas (polygons outside buffer zone) were erased. Furthermore, a manual more precise removal of non-mine areas was carried out to the remaining segments. The final step includes the implementation of dissolve algorithm in order to dissolve adjacent segments that share a common boundary.

**Figure 7.** *Mine area in crosshatch pattern.*

In this way, several segments were converted to a single meaningful image object (the mine area), that is demonstrated in **Figure 7**.
