OIL POLLUTION IN INDONESIAN WATERS: COMBINING STATISTICAL ANALYSES OF ENVISAT ASAR AND SENTINEL-1A C-SAR DATA WITH NUMERICAL TRACER MODELLING

Abstract. This Pilot Study aimed at improving the information on the state of the Indonesian marine environment that is gained from satellite data. More than 2000 historical and actual synthetic aperture radar (SAR) data from ENVISAT ASAR and Sentinel-1A/B C-SAR, respectively, were used to produce oil pollution density maps of two regions of interest (ROI) in Indonesian waters. The normalized spill number and the normalized mean polluted area were calculated, and our findings indicate that in general, the marine oil pollution in both ROI is of different origin: while ship traffic appears to be the main source in the Java Sea, oil production industry causes the highest pollution rates in the Strait of Makassar. In most cases hot spots of marine oil pollution were found in the open sea, and the largest number of oil spills in the Java Sea was found from March to May and from September to December, i.e., during the transition from the north-west monsoon to the south-east monsoon, and vice versa. This is when the overall wind and current patterns change, thereby making oil pollution detection with SAR sensors easier. In support of our SAR image analyses high-resolution numerical forward and backward tracer experiments were performed. Using the previously gained information we identify strongly affected coastal areas (with most oil pollution being driven onshore), but also sensitive parts of major ship traffic lanes (where any oil pollution is likely to be driven into marine protected areas). Our results demonstrate the feasibility of our approach, to combine numerical tracer modelling with (visual) SAR image analyses for an assessment of the marine environment in Indonesian waters, and they help in better understanding the observed seasonality.