Remote Sensing Applications - Marine Surface Films - page 273

The expression in dB is used as quantitative performance of the variability
of wind waves in slick or spill areas.
Figures 2-5 show the ERS-1 and Almaz-1 SAR sub-images around ob-
served oil spills and the NRCS sections through the spills. Note that thin
white arrows show length and direction of the sections while thick black
arrows indicate the wind direction. On the images of August 25 (Figure 4)
both spills can be delineated.
Fig. 2. ERS-1 and Almaz-1 SAR images of August 22 nd , 1991, at 10:48 and 16:41
UTC showing the first oil spill released on August 21 st (incidence angles 23q and
35q, wind speed 5-7 m s -1 and 2-3 m s -1 , spill age 16 hrs and 22 hrs respectively)
( left ). Variations of the radar backscatter along the scan lines are shown on the
ERS-1 and Almaz-1 SAR images by white thin arrows ( right ), flight/look direc-
tions by thin black arrows, and wind direction by a double black arrow (image
courtesy ESA and NPO Mashinostroenia)
The first pair of images was acquired on Aug. 22 nd , 1991, at 10:48
(ERS-1) and 16:41 (Almaz-1) (Figure 2). The damping ratio in the ERS-1
image is low (1.2 dB), while in the Almaz-1 image acquired 6 hours later
the damping ratio is 2.5 dB. In the latter image a wedge-shaped area of in-
creased NRSC can be observed upwind from the spill's upwind border. It
is located opposite to the wind direction and is ~1 dB brighter than the
background. It follows from Table 1 that at the time of the ERS-1 overpass
a south-westerly wind with 5-7 m s -1 speed and a westerly swell of 150 m