2.2 Data acquisition and preparation
This study considers both spatial and non spatial data and they have been acquired from a variety of sources (Table 1). Satellite data includes Sentinel 2A, RapidEye, World View 2, multi date UAV and a digital elevation model from Shuttle Radar Topographic Missing (SRTM). Sentinel images represent winter season and pre and post influx of Rohingya situations. Vector data includes administrative boundary and location of camps, obtained from Survey of Bangladesh (SoB), BFD and UNHCR. In addition, human trails are derived from the UAVs and Google Earth imageries and population data of each camp was obtained from FCN UNHCR and NPM IOM. In addition, a field survey was conducted in February 2018 to understand state of the environmental condition. Observational technique along with photographic method was accepted, during the field works, to support satellite based evaluation of forest function loss in the study area.
Sentinel 2A imageries are first geometrically corrected and a root mean square error (RMSE) of <1 pixel is accepted. Atmospheric correction is then carried out with SEN2COR toolkit to convert Top of Atmosphere (TOA) value to surface reflectance (Cleverset et al., 2017; Quintano et al., 2018). A Universal Transverse Mercator (UTM) system with 46N is used to project spatial datasets and then clipped to the study area boundary.