## 2 Remote Sensing in Peatland Research  
### Temporal and Spatial Pattern of Using RS in Peatland Studies  
The development of remote sensing methods and a greater accessibility, quantity and quality of remote sensing images made using these materials in the analyses of peatlands more common after 2000 [2; 30]. [PERSON] (2015) [14], based on studied works from 2002 to 2015, pointed out that the application of an object-based image analysis (OBIA) used for wetlands study has increased significantly since 2010. [PERSON] concluded that OBIA could be employed in tasks ranging from the detection, classification and delineation of wetland bodies to comprehensive analyses of within-wetland cover types and their changes [14; 31]. Similar to wetlands, the state and condition of peatlands depend on water resources (moisture); furthermore, this is related to an occurrence/succession of peat-forming plants. Both can be monitored using remote sensing tools [22; 32]. Methods for obtaining data through remote sensing can be categorised as follows:  
* Satellite remote sensing (long-range)--the detail level and data availability depend on the selected Earth observation system. In generally available systems, the spatial resolution varies between 10 and 100 m. Their cyclicality also distinguishes the most popular satellite remote sensing systems (Landsat and Sentinel) because every land area on the Earth's surface is monitored at regular intervals (3-16 days);
* Medium-range (Airborne) and close-range remote sensing (UAV-- unmanned aerial vehicle, such as a drone). The intensive development and accessibility of unmanned aerial vehicles (UAV) allows for their widespread use in monitoring the natural environment. These images feature a very high spatial resolution (1-10 cm) and enable a high repeatability;  
Due to the accessibility of data and the regularity of measurements, peatland research most often uses satellite images from passive multispectral remote sensing systems Landsat 5-8 and Sentinel-2 (Supplementary Material, Figure S1), and from the active (radar) remote sensing system Sentinel-1. There are two main approaches to assessing the condition of the peatland environment: evaluation of peatland vegetation and evaluation of surface water resources (moisture). Detailed information related to the studied papers is provided in Supplementary Material, Table S1. The 59 studied works analysed peatlands located in different climatic regions (Table 1); however, many of the works (17) concerned subtropical and tropical peatlands. Our analysis shows a noticeable increase in the use of remote sensing methods in the study of peatlands approximately 1-2 years after the open data became available (Figure 1, Supplementary Material Table S1). The rapid increase in the use of this data occurred after 2016, i.e., two years after the launch of the Sentinel-1A system and one year after the launch of the Sentinel-2A system (a detailed description of remote sensing data development is provided in Supplementary Materials). The development of the use of GIS data and remote sensing data in research on peatlands was also influenced by the rapid development and availability of applications that allowed the use of these data, such as QGIS (formerly Quantum GIS) and SAGA GIS (intensive development since 2008) as well as the remote sensing data analysis application provided by the European Space Agency--SNAP (Sentinel Application Platform)--from 2014.