*2.2. Field Measurements*

The field studies were conducted in the summer of 2017. Compact polygons (in the shape of circles with a radius of 3 meters) of *Rubus* spp., *Solidago* spp., *Calamagrostis epigejos*, and other background plants were located within the research area with the help of the Leica CS20 GNSS device (Figure 2). The number of polygons was proportional to the prevalence of species in the research area and amounted to 50 polygons for blackberry and wood small-reed, 60 polygons for goldenrod, and 100 polygons for background plants.

**Figure 2.** Collection of reference plot locations—plot for *Calamagrostis epigejos* shown in above picture.

Then, the polygons were transferred to ArcMap 10.3, where photo interpretation techniques were used to create an additional 30 reference polygons for other types of land cover (i.e., trees, buildings, bare soil, and shaded areas). These additional classes were meant to indicate for the algorithm the spectral properties of objects that occurred in the research area and constituted non-forest vegetation. Finally, reference polygons were created for eight classes: *Calamagrostis epigejos*, *Solidago* spp., *Rubus* spp., other plants, trees, bare soils, buildings, and shadows (Figure 1).
