Chemistry Reference
In-Depth Information
mum coverage is limited to a 180 degrees sweep in azimuth with an 8 km
interval in range. These parameters are, however, specific to this board and
may easily be extended. The system also enables the acquisition of time-
series of images in specific areas separated by 2.4, 4.8 or 9.6 seconds. This
facility allows 2D maps of the backscatter's statistical moments to be de-
rived with later processing.
Table 1.
Typical spatial and temporal resolutions for marine radar and airborne/
satellite systems
Marine radar
system
Airborne/satellite
systems
Spatial resolution in range
10 - 130 m
10 to 100 m
Spatial resolution in azimuth
1 degree
10 to 100 m
Spatial coverage
8 km
10 - 150 km
Temporal resolution
2.4 seconds to
minutes/hours/days
Airborne: hour to
days
Satellite: days
Temporal coverage
2.4 seconds to
minutes/hours/days
-
3 Radiometric performance
The typical radiometric performance of marine radar systems was deter-
mined with an end-to-end calibration of the marine radar system described
above. The object of this work was to use the performance of this particu-
lar low-cost technology to assess the applicability to the detection of slicks
at sea.
Based on the classical Radar Equation, a normalising relationship be-
tween the pixel intensity, X, in the images and the Normalised Radar Cross
Section (NRCS), V
0
, of the sea surface was established as:
(1)
V
0
(
dB
)
f
(
X
)
10
log
R
4
10
log
Ar
K
p
10
10
p
where
R
is the range of the pixel,
Ar
is the dimension of the antenna foot-
print at that range,
f
p
is the marine radar system transfer function relating
the received backscatter power to the image intensity, and
K
p
is a constant
representative of the system antenna properties. The accurate de-
termination of
f
p
and
K
p
is presented in detail in Gommenginger et al.
(1999). This calibration procedure also identified the system's noise floor
and saturation level. The system's dynamic range thereby defined is pre-
sented in terms on NRCS in Figure 1 as a function of distance from the ra-
dar.
