Chemistry Reference
In-Depth Information
The line scanning Microwave Radiometer (MWR) enables quantitative
assessments of detected oil spills by analysing the radiant emission from
the sea surface and oil spills at two or three frequencies (for example 18.7,
36.5 and 89 GHz, see also Figure 2). The microwave emissivity of the
oil/air interface is higher than that of the water/air interface and depends on
the microwave frequency, oil thickness, and sea state. The three-channel
information acquired by the MWR can be used to calculate a thickness es-
timate for very thick oil layers being of the order of millimetres in thick-
ness (between 50 µm and 5 mm, Grüner et al. 1991). This information is
absolutely necessary for clean up operations and the guiding of oil combat
vessels. Since microwaves can penetrate clouds, rain, fog and drizzle, the
MWR is an all-weather remote sensor with a high potential for multi-
mission reconnaissance and surveillance applications.
4 Thermal imaging
Since thermal imagers, also known as Forward Looking Infrared (FLIR)
devices, became commercially available, they are increasingly installed
into smaller and mid-size aircraft. In 2004 a StarSAFIRE thermal imaging
system with a newly developed covert action laser illuminator (CALI)
started operation as part of the second German surveillance aircraft, en-
abling the operator to read the ships name in the absence of daylight or in-
vestigate areas of specific interest. This thermal imaging capability brings
an important step towards night operation and polluter identification. The
FLIR is also a sensor with a wide range of application, like search-and-
rescue or border patrol, making it a perfect device for multi-role aircraft,
sometimes only equipped with basic maritime surveillance sensors.
The covert illuminator is a 2 Watt laser diode inside the FLIR turret, ra-
diating around 800 to 820 nm @ 25°C. Therefore the CALI is not illumi-
nating the thermal camera detector (which is using the 3-5 µm mid-IR re-
gion), but the NIR sensitivity of the inbuilt CCD camera. These cameras
normally use an IR-cut filter during daytime, blocking unwanted NIR ra-
diation from its detector. During nighttime and in combination with the
CALI, this NIR cut filter is removed and the laser illumination is available
up to a distance of 1500 m (Figure 5).
FLIR devices can be divided in two classes by their detecting waveband.
Mid-IR detectors, like the StarSAFIRE series mentioned above, are com-
monly used in humid environments since they show less signal depression
by water vapour. However the detection of oil spills shows variable results
and is not favourable as a stand-alone sensor for this purpose. Long-IR de-
tectors (8-14 µm, sometimes realised by QWIP detectors with smaller
