# A MODIS-Based Robust Satellite Technique (RST) for Timely Detection of Oil Spilled Areas
## 3 Results and Discussion
### RST Implementation
By implementing a recursive buffer around these areas, indeed, the full structure of the oil slick can be identified by both indices. In detail, starting from the pixel with the highest anomalous value (H), an ad hoc implemented tool detects as anomalous all those pixels showing a S/N value within the \"H-5\" range in a 5 \(\times\) 5 mobile window. Focusing on the area where the oil spill was detected, several different ranges of confidence levels were identified. The lowest range (in green) corresponds to pixels  
Figure 5: R\({}_{\mathrm{rc}}\) images of (**a**) channel 1 and (**b**) channel 2 of the MODIS-Aqua image of 18 June 2007 at 10:50 a.m. GMT. The grey bars show the sea surface R\({}_{\mathrm{rc}}\) range of variation for each of the image; land is masked in black. (**c**) Variation of R\({}_{\mathrm{rc}}\) signal along the Z-Z’ blue transect in (**a,b**). where the oil is less present or thinner, while, with the increase of the confidence levels, the oil presence and thickness should grow. Figure 6: Application of \(\otimes_{\mathrm{ch1}}\) index (**a**) and \(\otimes_{\mathrm{ch2}}\) (**b**) to the MODIS image of 18 June 2007 at 10:50 a.m. GMT. In the background, the corresponding \(\mathrm{R_{rc}}\) images already shown in Figure 5a,b; land is masked in black. The two red insets highlight the few pixels detected as anomalous at the S/N levels reported in the legends. To better summarize the achieved results, Table 1 reports the number of the pixels identified as anomalous at each of the confidence levels for the two channels. Considering the 250 m spatial resolution of the used data, an area of at least 63 km\({}^{2}\) was recognized as anomalous, which, speculating an average oil thickness of 1 \(\upmu\)m [5], corresponds to about 63 m\({}^{3}\) of oil. \begin{table}
\begin{tabular}{c c c c} \hline \hline \multicolumn{3}{c}{**MODIS-Aqua Image of 18/06/2007 10:50 a.m. GMT**} \\ \hline \hline \(\mathbf{X=\otimes_{ch1}\) (Figure 7a)} & **Number Pixels** & \(\mathbf{X=\otimes_{ch2}\) (Figure 7b)} & **Number Pixels** \\ \hline \(14<\mathrm{x}\leq 16\) & 783 & \(22<\mathrm{x}\leq 27\) & 784 \\ \(16<\mathrm{x}\leq 18\) & 273 & \(27<\mathrm{x}\leq 32\) & 157 \\ \(18<\mathrm{x}\leq 20\) & 101 & \(32<\mathrm{x}\leq 37\) & 53 \\ \(20<\mathrm{x}\leq 22\) & 39 & \(37<\mathrm{x}\leq 42\) & 11 \\ \(22<\mathrm{x}\leq 24\) & 15 & \(42<\mathrm{x}\leq 47\) & 7 \\ \(24<\mathrm{x}\leq 26\) & 8 & \(47<\mathrm{x}\leq 49\) & 1 \\ \(\mathrm{x}>26\) & 4 & \(\mathrm{x}>49\) & 1 \\
**TOT** & **1223** & **TOT** & **1014** \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Number of pixels identified as anomalous at each of the \(\otimes_{chx}\) confidence levels used in Figure 7.  
Figure 7: Oil slick mapping during the event on 18 June 2007 at 10:50 a.m. GMT using (**a**) \(\otimes_{ch1}\) index and (**b**) \(\otimes_{ch2}\). The images on the right side highlight results achieved for the areas outlined in red in the left panels. The corresponding background \(\mathrm{R_{rc}}\) images are in greyscale. The same analysis was performed for the MODIS image acquired the following day (not shown) without finding any anomalous pixels. Weathering effects, as well as the presence of clouds, limited the capability to further detect the presence of the oil spill.