Chemistry Reference
In-Depth Information
The NRCS reductions caused by (a) and (c) are better quantified in Fig-
ure 4 with transects taken across these features in the third radar image in
the sequence. The transects AB across (a) and BC across (c) show NRCS
reductions of similar magnitude (~ 3 dB) for both features with respect to
the control transect (dashed line) taken in “clean” water immediately south
of (a). The NRCS signature alone does thus not allow to differentiate (c)
from an artificial slick, and only the time-sequence enables us to identify
(c) with a stationary, bathymetry-related, process. The NRCS reduction
across (a) is comparable to the damping ratios observed, for example, for
biogenic slicks in SIR-C/X-SAR images (2 to 6 dB; see Gade et al. 1996).
We note that the NRCS profile across (a) indicates a gradual NRCS de-
crease within the slick in the A to B direction, with maximum damping oc-
curring at the eastern edge of the slick. This is consistent with a redistribu-
tion of the surfactant material within the slick under the action of the
westerly wind.
NRCS (dB)
Fig. 4.
NRCS transects taken across feature (a) and (c) as seen in the third radar
image of the sequence shown in Figure 3. Transect AB (solid line) across the arti-
ficial slick (a) and transect BC (dotted line) across the underwater dip (c) show a
similar NRCS reduction in excess of 3 dB, with respect to the transect across
“clean” water (dashed line)
6 Discussion and conclusion
Results were presented of two surfactant slick detection experiments using
a shore-based marine radar system. In both instances the slick was success-
fully detected and tracked at grazing angles less than 2 degrees in wind
conditions ranging from light to moderate. Defining further the range of
conditions favourable to slick detection with marine radar systems is a
