Mapping Tropical Rainforest Canopy Disturbances in 3D by COSMO-SkyMed Spotlight InSAR-Stereo Data to Detect Areas of Forest Degradation

Janik Deutscher,Mathias Schardt,Karlheinz Gutjahr,Roland Perko,Manuela Hirschmugl

doi:10.3390/rs5020648

Abstract

Assessment of forest degradation has been emphasized as an important issue for emission calculations, but remote sensing based detecting of forest degradation is still in an early phase of development. The use of optical imagery for degradation assessment in the tropics is limited due to frequent cloud cover. Recent studies based on radar data often focus on classification approaches of 2D backscatter. In this study, we describe a method to detect areas affected by forest degradation from digital surface models derived from COSMO-SkyMed X-band Spotlight InSAR-Stereo Data. Two test sites with recent logging activities were chosen in Cameroon and in the Republic of Congo. Using the full resolution COSMO-SkyMed digital surface model and a 90-m resolution Shuttle Radar Topography Mission model or a mean filtered digital surface model we calculate difference models to detect canopy disturbances. The extracted disturbance gaps are aggregated to potential degradation areas and then evaluated with respect to reference areas extracted from RapidEye and Quickbird optical imagery. Results show overall accuracies above 75% for assessing degradation areas with the presented methods.

Highlights

The need to conduct research on tropical forest degradation emerged in the 1990s, as the spatial extent of selective logging and fire damage was found not to be accounted for in deforestation studies.Later, in the frame of the Kyoto protocol, reducing emissions from deforestation and degradation in developing countries (REDD) was adopted as a mechanism for the post-Kyoto reporting and parties agreed to an evaluation process by initiating REDD pilot projects
Many definitions of forest degradation exist in the literature; a selection of definitions is provided on the FAO website [1]
For Cameroon, only the SRTM Difference Approach was applied in the hilly Pallisco area, as the Height Variance Approach only works in flat terrain

Summary

Introduction

In the frame of the Kyoto protocol, reducing emissions from deforestation and degradation in developing countries (REDD) was adopted as a mechanism for the post-Kyoto reporting and parties agreed to an evaluation process by initiating REDD pilot projects. The need to address and monitor degradation along with deforestation has been emphasized on numerous occasions, such as at the COP meeting in Bali, 2007 (FCCC/CP/2007/6), where the parties “acknowledge that forest degradation leads to emissions, and needs to be addressed when reducing emissions from deforestation”. In the Congo basin, degradation is considered more important than for example in Latin America or Asia, the ‘COMIFAC position on the international issue on REDD’ calls for “factoring of degradation as much as deforestation in emission calculations”. Since no common definition has been yet agreed upon within the REDD+

Methods

Results

Conclusion