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explained by the overall higher wind speeds in all test areas during winter
time. Moreover, the northwestern Mediterranean Sea seemed to be the test
area with highest detected oil pollution, whereas the pollution seemed to
be lowest in the Baltic Sea. They concluded that this might be caused by
the difference in mean wind speed, which in turn causes a different visibil-
ity of oil pollution in SAR images. (However, it is of course also possible
that the northwestern Mediterranean Sea is simply the most polluted test
area.)
For our improved statistical analysis we included the mean local wind-
speed, as derived from interpolated values of the DWD model. As a first
step we calculated the distribution of the detected oil spills with wind
speed. As shown in the upper left panel of Figure 6 most oil spills were de-
tected at mean (modelled) wind speeds between 3 m s
-1
and 4 m s
-1
. The
upper right panel of Figure 6 shows the wind speed distribution of the
DWD model with a maximum between 5 m s
-1
and 6 m s
-1
. The lower
panel of Figure 6 shows the “normalised oil spill visibility” (NOSV) calcu-
lated as the (normalised) ratio of the two above.
Fig. 6. upper left:
histogram of the distribution of detected oil pollution as func-
tion of wind speed;
upper right:
distribution of the DWD model winds;
lower
left:
“normalised oil spill visibility” calculated as the ratio of the histograms for
oil spills and model winds
