Fusing Sentinel-2 Imagery and ALS Point Clouds for Defining LULC Changes on Reclaimed Areas by Afforestation

Abstract

The study was performed on two former sulphur mines located in Southeast Poland: Jeziórko, where 216.5 ha of afforested area was reclaimed after borehole exploitation and Machów, where 871.7 ha of dump area was reclaimed after open cast strip mining. The areas were characterized by its terrain structure and vegetation cover resulting from the reclamation process. The types of reclamation applied in these areas were forestry in Jeziórko and agroforestry in the Machów post-sulphur mine. The study investigates the possibility of applying the most recent Sentinel-2 (ESA) satellite imageries for land cover mapping, with a primary focus on detecting and monitoring afforested areas. Airborne laser scanning point clouds were used to derive precise information about the spatial (3D) characteristics of vegetation: the height (95th percentile), std. dev. of relative height, and canopy cover. The results of the study show an increase in afforested areas in the former sulphur mines. For the entire analyzed area of Jeziórko, forested areas made up 82.0% in the year 2000 (Landsat 7, NASA), 88.8% in 2009 (aerial orthophoto), and 95.5% in 2016 (Sentinel-2, ESA). For Machów, the corresponding results were 46.1% in 2000, 57.3% in 2009, and 60.7% in 2016. A dynamic increase of afforested area was observed, especially in the Jeziórko test site, with the presence of different stages of vegetation growth.

Reclaimed Area Land Cover Mapping Using Sentinel-2 Imagery and LiDAR Point Clouds

“…For the LULC classes of broad-leaved forest, coniferous forest, and transitional woodland shrub, we can observe a dynamic change in growth. In previous studies [11][12][13], these areas showed an increase of spatial range in forested areas from the year 2000 to 2016, using image classification of Landsat 7 (2000), on-screen vectorization orthophoto (2009), Landsat 8 (2013), and the image classification of Sentinel-2 (2016).…”

“…The results of the Sentinel-2 image classification (2016), the LULC classification for the analysed area, are presented in Figure 6. The assessment parameters have the following values: AA = 86.17%, AR = 87.73%, and OA = 90.54% (Table 2) [11,56,57]. The most dominant LULC classes for the Jeziórko area are forested areas.…”

“…The visualization, in the form of hillshade (Figure 7b), shows the effect of the reclamation works carried out at the Jeziórko sulfur mine, such as roads, drainage ditches, and slopes [60]. Detailed information about the spatial structure of the vegetation is presented in Figure 8 [11,60]. For the Jeziórko analysed area, we can observe the different stages of growth in the forested vegetation; for presentation, a different color scale than for Machow has been chosen to precisely show the differences in height vegetation.…”

“…The parameters, derived based on ALS point clouds, showed precise information about the structure (3D) of the vegetation. Detailed information about the spatial structure of the vegetation is presented in Figure 8 [11,60]. For the Jeziórko analysed area, we can observe the different stages of growth in the forested vegetation;…”

“…The process of land cover mapping, especially in terms of reclaimed areas, is the subject Sentinel-2 satellite imageries (European Space Agency; ESA) consist of two satellites: Sentinel-2A (launched in 2015) and Sentinel-2B (launched in 2017). The satellites are equipped with modern multi-spectral high-resolution scanners − 13 spectral channels with spatial resolution of 10, 20, and 60 m. Using Sentinel-2 (ESA) imageries opens up new possibilities in environmental studies [11,[31][32][33][34], mainly as a result of the good spatial and spectral resolution and short revisit time (five days for two satellites).…”