Chemistry Reference
In-Depth Information
offers a resolution similar to that of other systems. Likewise, marine radar
systems produce NRCS measurements of comparable quality with esti-
mated relative NRCS errors generally of the order of 0.6 dB. The extended
temporal coverage and flexible temporal resolution of the marine radar
contrast sharply with the poor coverage and measurement repetitivity dis-
played by airborne and satellite systems. Overall, the comparison of these
performances indicates that marine radar systems can provide reliable
high-resolution NRCS images of specific areas with any chosen interval
over extended periods of time. This type of information thus represents an
ideal complement to interpret the large-scale snapshots obtained with satel-
lite and airborne radars.
5 Controlled surfactant spill experiments
Results are presented for two controlled slicks carried out a few miles off
the Isle of Portland on the south coast of the UK. The marine radar system
was located on a cliff overlooking the sea to the west of the island at a
height of approximately 60 meters above mean sea level. The surfactant
deployed in these experiments consisted of a biodegradable chemical
known as Emkarox, specifically developed for the Defence and Evaluation
Research Agency (DERA), and designed to reproduce the visco-elastic
properties of monomolecular natural films. In both cases, some informa-
tion on the slicks' position, morphology and spreading was available
through visual observations from the cliff top and the boat used for slick
generation.
The first experiment took place in light wind and sea conditions (U
10
=
4.5 m s
-1
from the east; H
s
= 1m). A sequence of marine radar images ob-
tained during the deployment of the surfactant material is shown in Figure
2. The bright echoes in the middle of the images were produced by three
instrumented buoys providing
in-situ
measurements of wind, wave and
current conditions. The elongated bright echo seen in the upper part of the
first image indicates the boat from which the surfactant was poured slowly
and steadily while the boat travelled North. Some 20 minutes later, as the
surfactant had spread sufficiently to form a coherent linear slick, a narrow
line of reduced NRCS became visible to the east of the buoys. One hour
after deployment of the surfactant, the radar image correctly indicated that
the slick started to break up, presumably due to steady spreading and dis-
persion of the limited amount of surfactant deployed.
