Detecting logging roads and clearcuts with TerraSAR and RADARSAT data

Abstract:

In many parts of the world, tropical forest cover is declining at an alarmingly high rate (FAO, 2011b). This process is of global concern, as it is considered to be one of the main drivers of climate change. Radar remote sensing is useful to monitor forest cover since the presence of clouds often limits a continuous and periodic monitoring by optical sensors. This chapter presents an outcome of a research that was conducted in Youbi, Congo-Brazzaville. The overall objective of this research was to assess the potential of very high (1m – 3m) and medium (8m – 30m) resolution synthetic aperture radar imagery for identifying forest degradation signs. This was done with a view as to contribute to the development of alternative monitoring strategies in support of the monitoring, reporting, and verification (MRV) framework of UN-REDD+. Visual interpretation was the main approach adopted in this research. Logging roads were only visible on 1m TerraSAR-X SpotLight and 3m TerraSAR-X StripMap imagery. Both of these data sources and RADARSAT Multi-Look Fine images could detect clearcuts in dense to open canopy forest types. This research concludes that the detection of logging roads by SAR requires a spatial resolution below 5m, while clearcuts are detectable with a 10m resolution SAR image. It was also found that the viewing geometry of the SAR data acquisitions has a strong effect on the possibility to visually detect forest degradation signs. For monitoring purposes, repeated monitoring using the same satellite sensor and viewing geometry is therefore recommended. Given the reasonably low-price and good coverage, TerraSAR StripMap acquisitions, is further recommended for future studies towards monitoring options in the framework of REDD+.