The effect of atmospheric and topographic correction on pixel-based image composites: Improved forest cover detection in mountain environments

• Systematic evaluation of four different scenarios in which 2 components alter.
• Increased accuracy by topographic correction after pixel-based compositing.
• Highest accuracies with corrected Support Vector Machine classification.
• Selection of classifier has stronger impact on accuracy then topographic correction.
• Steady greening of the Romanian Carpathian Ecoregion between 1985 and 2010.

Quantification of forest cover is essential as a tool to stimulate forest management and conservation. Image compositing techniques that sample the most suited pixel from multi-temporal image acquisitions, provide an important tool for forest cover detection as they provide alternatives for missing data due to cloud cover and data discontinuities. At present, however, it is not clear to which extent forest cover detection based on compositing can be improved if the source imagery is firstly corrected for topographic distortions on a pixel-basis. In this study, the results of a pixel compositing algorithm with and without preprocessing topographic correction are compared for a study area covering 9 Landsat footprints in the Romanian Carpathians based on two different classifiers: Maximum Likelihood (ML) and Support Vector Machine (SVM). Results show that classifier selection has a stronger impact on the classification accuracy than topographic correction. Finally, application of the optimal method (SVM classifier with topographic correction) on the Romanian Carpathian Ecoregion between 1985, 1995 and 2010 shows a steady greening due to more afforestation than deforestation.