Detection and analysis of forest cover dynamics with Landsat satellite imagery, application in the Romanian Carpathian Ecoregion

Forest cover changes have essential implications on a variety of landscape functions and their associated ecosystem services. Globally, contrasting forest trends are present: some countries are greening, while others are still in a deforestation phase. The detection and mapping of forest dynamics is rather challenging since landscapes in the transition phase typically consist of patchy structures and often occur in inaccessible areas such as highlands, which impedes mapping approaches based on fieldwork. Furthermore, forest cover changes in the turnover phase are characterized by subtle up- and downward trends. Remote sensing techniques seem to be adequate tools for the analysis of forest cover changes in mountain areas. Over the past half century, remote sensing imagery has been acquired by a range of multispectral and hyperspectral sensors. Many regional long-term vegetation (change) maps have been derived from medium to low resolution imagery such as the Landsat sensor with a spatial resolution of 30m. Despite recent developments, remote sensing methods for the detection and analysis of forest cover dynamics at regional scale still suffer from methodological challenges: (1) recorded reflectance values are disturbed by atmospheric effects, (2) differences between illuminated and shadowed slopes occur in mountain areas, and (3) regional scale analyses require that multiple images are mosaicked to construct homogeneous image composites. During the last decades, a range of simple empirical and more advanced physically-based preprocessing techniques has been developed to solve these problems. At present, however, it is not clear what the added value of these techniques is for the detection of regional scale forest cover change. The main objective of this PhD research was to evaluate, compare and improve the methods for regional scale detection and analysis of forest cover dynamics. The Romanian Carpathians Mountains, which are characterized by significant forest cover dynamics related to a land decollectivization process were selected as the study area. In order to address the main objective of this thesis, the following specific research questions were formulated: 1. To what extent do available atmospheric and topographic correction techniques improve the land surface reflectance values derived from medium resolution imagery in mountain areas? Do complex physically-based methods perform better than simplified empirical approaches? 2. Does image preprocessin