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|Title:||An automated approach for segmenting and classifying a large sample of multi-date Landsat imagery for pan-tropical forest monitoring|
|Authors:||RASI Rastislav; BODART Catherine; STIBIG Hans-Jurgen; EVA Hugh; BEUCHLE Rene'; ACHARD Frederic; CARBONI Silvia; SIMONETTI Dario|
|Citation:||REMOTE SENSING OF ENVIRONMENT vol. 115 no. 12 p. 3659-3669|
|Publisher:||ELSEVIER SCIENCE INC|
|Type:||Articles in periodicals and books|
|Abstract:||The TREES-3 project of the Joint Research Centre aims at assessing tropical forest cover changes for the periods 1990-2000 and 2000-2010 using a sample-based approach. This paper refers to the 1990-2000 assessment. Extracts of Landsat satellite imagery (20 km × 20 km) are analyzed for these reference dates for more than 4,000 sample sites distributed systematically across the tropical belt. For the processing and analysis of such a large amount of satellite imagery a robust methodological approach for forest mapping and change detection has been developed. This approach comprises two automated steps of multi-date image segmentation and object-based land cover classification (based on a supervised spectral library), followed by an intense phase of visual control and expert refinement. Image segmentation is done at two spatial scales, introducing the concept of a minimum mapping unit via the automated selection of a site-specific scale parameter. The automated segmentation of land cover polygons and the pre-classification of land cover types mainly aim at avoiding manual delineation and at reducing the efforts of visual interpretation of land cover to a reasonable level, making the analysis of 4,000 sample sites feasible. The importance of visual control and correction can be perceived when comparing to the initial automatic classification result: about 20% of the polygon labels were changed through expert knowledge by visual interpretation. The component of visual refinement of the mapping results had also a notable impact on forest area and change estimates: for a set of sample sites in Southeast Asia (~90% of all sites of SE Asia) the rate of change in tree cover (deforestation) was assessed at 0.9% and 1.6% before and after visual control, respectively.|
|JRC Directorate:||Sustainable Resources|
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