Review of Methods for Mapping Forest Disturbance and Degradation from Optical Earth Observation Data

This paper presents a review of the current state of the art in remote sensing based monitoring of forest disturbances and forest degradation from optical Earth Observation data. Part one comprises an overview and tabular description of currently available optical remote sensing sensors, which can be used for forest disturbance and degradation mapping. A section is devoted to currently existing mapping approaches, including both operational methods and recent developments. Part two reviews the two main categories of existing mapping approaches: first, classical image-to-image change detection and second, time series analysis. With the launch of the Sentinel-2a satellite and available Landsat imagery, time series analysis has become the most promising but also most demanding category of degradation mapping approaches. Hence, an emphasis is put on methods of time series analysis, among which four different classification methods are distinguished. The methods are explained and their benefits and drawbacks are discussed. A separate chapter presents a number of recent forest degradation mapping studies for two different ecosystems: The first ecosystem comprises the temperate forests with a geographical focus on Europe. The second ecosystem consists of the tropical forests with a geographical focus on Africa. Mapping examples from both ecosystems help to better illustrate the current state of the art.