## 2 Remote Sensing in Peatland Research
### RS Analytical Methods Used in Peatland Research
This indicator is currently used and modified in studies of peatlands (e.g., floating water band index (fWBI)) [80; 81]. Multispectral images are also used for analysing soil moisture, including the surface zone of peatlands. Here, the normalised difference water index (NDWI) [87] is most often used to monitor a peatland's surface water content. Currently, a number of indices were designed and improved for performing analyses of soil moisture levels [88; 89; 90]; compared with NDVI, all of them have a higher spectral resolution, usually in the short-wave infrared range (SWIR 1400-2400 nm). This method is ineffective in peatland studies because the areas in question tend to be covered with dense vegetation. Soil moisture in peatlands and their surrounding environments are also measured using a synthetic aperture radar (SAR, e.g., Sentinel-1) in the C band at a 5.6 cm wavelength, which partly penetrates through the vegetation and soil but is reflected off the water surface [26; 35; 39; 58; 65; 91]. Primarily, multispectral sensors can recognise treetops and land cover spectral features, while SAR microwaves are sensitive to vegetation structure, surface roughness, and moisture content. In addition, SAR can partially pass through the treetops depending on the crown's wavelength and characteristics. This ability is important in wetlands where stagnant water often occurs beneath the vegetation cover. As backscattered microwave radiation is sensitive to the dielectric permeability of the first centimetres of the soil, radar data constitute a promising tool for acquiring spatial information on soil moisture and groundwater table depths (WTD) [35; 38; 39; 58; 65; 92; 93; 94]. [PERSON] et al. (2019) [58] used data from a Sentinel-1 synthetic aperture radar to determine a temporal Spearman correlation coefficient between WTD and backscatter (\(\sigma^{0}\)\({}_{0}\) (VV) constant, all orbits), which was calculated as 0.45 (\(\pm\)0.17). The authors observed a significantly decreased correlation between groundwater table depths and backscatter during increased vegetation activity in summer and decreases due to haymaking and grazing [58]. In addition to satellite data, peatland studies certainly benefit from the development and availability of close-range remote sensing technologies (drone, UAV) [33; 34; 46; 95]. UAV technology allows for creating Digital Elevation Models (DEM), which are widely used in monitoring the environment, including peatlands [96; 2]. Digital elevation models can be created from overlapping aerial photographs taken at different viewing angles by an unmanned aerial vehicle (UAV) at a low altitude [97]. [PERSON] et al. (2013) [96] used UAV measurements to analyse the effects of fire on 5.2 hectares of peatland in Indonesia. A point cloud from UAV images for DTM (Digital Terrain Model) before and after the fire allowed the changes in the elevation of the peatland's surface and the thickness of the burnt layer of peat to be determined  
[PERSON] et al. (2017) [98] concluded that a photogrammetric UAV data-enabled accurate estimation of terrain elevation (in the range of 14-42 cm, which was related to the image resolution), depending on the plant cover and terrain complexity. Close-range photogrammetric methods could also be used to obtain very detailed orthophoto maps, which proved useful in delimitating and monitoring peatland habitats [30; 99; 100]. [PERSON] et al. (2019) [101] indicated that integration of environmental knowledge with remote sensing applications holds an immense potential to improve final mapping accuracy but is also likely to contribute to the knowledge of peatlands ecosystem functioning.