Tracing the evolution of 2010 Merapi volcanic deposits (Indonesia) based on object-oriented classification and analysis of multi-temporal, very high resolution images

摘要

We compare identification, delineation and recording of freshly erupted deposits around active volcanoes from very high resolution optical images with that done by traditional geologic mapping. Object-oriented classification (OOC) and normalized difference spectral indices of vegetation, moisture and soil redness (NDVI, NDWI and NDRSI) have been applied to sub-metric GeoEye-1 and Pleiades images to identify and map pyroclastic and lahar deposits and trace their spatio-temporal evolution over two years, following the 2010 eruption of Merapi Volcano, Indonesia. We could identify several categories of pyroclastic depositional areas, and also map the damaged forest and destroyed cultivated terraces and settlements in the Gendol and Opak River basins on the south flank of the volcano. More than 75% of erupted deposits were delineated semi-automatically unlike the ground geological map based on photo-interpretation of the 2010 GeoEye image and field observations. A temporal image analysis, using bivariate scatter diagrams of the three spectral indices between 2010 and 2012 and a combination of NDWI and NDVI, separated areas affected by surges from unscathed vegetation. Use of NDRSI and NDWI allowed us to differentiate overbank Pyroclastic Density Current deposits from wet lahar deposits. NDRSI values close to 0 refer to scoria-rich pyrodastic deposits.