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complex problem. In particular, environmental and operational conditions
strongly affect the microwave propagation mechanisms at low-grazing an-
gles. These issues are outside the scope of this paper, but the reader is in-
vited to consult Gommenginger (1997; Chapter 7 and 8) for further details
on these problems.
Time-series of NRCS images were obtained and found able to provide
information on the position, size, shape and surfactant distribution of the
slicks as they evolved in time. Similarly, the sequence of images allowed
bathymetric features with similar radar signatures to be rightly identified in
view of their constant position in the images. It is expected that, in com-
mon with traditional radar systems, naturally occurring slicks would also
produce this type of radar signatures, which would then be difficult to dis-
tinguish from artificial slicks. However, wind conditions conducive to bio-
genic slick formation (< 5 m s
-1
) do not generally coincide with conditions
needed to warrant sufficient backscatter contrast at low-grazing angles.
Hence, biogenic slicks would be imaged only in exceptional circumstances
(e.g., transient wind regime) when they would not be expected to persist.
These results confirm that marine radar systems can provide useful and
reliable NRCS measurements in complex areas such as the coastal zone.
These cost effective instruments provide a robust and reliable tool for
long-term monitoring of sensitive coastal areas. The long-term monitoring
facility suggests that these data may also be useful to interpret larger scale
snapshots obtained from satellite or airborne radars.
Acknowledgements.
We would like to thank Dr John Scott and Peter
Dovey at DERA who provided access to the DERA cliff-top location on
the Isle of Portland and enabled us to take part in the surfactant experi-
ments. Many thanks also to Nicholas Ward for developing some of the ra-
dar image processing software used in this work.
7 References
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Attema EPW, Hoogeboom IP (1978) Microwave measurements over sea in the
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