Chemistry Reference
In-Depth Information
equipped with a SLAR and all but one were using IR/UV sensors for the
near-range investigation.
The SLAR sends out X-band radar pulses to the left and right hand side
of the aircraft and receives their reflection from small gravity and capillary
waves up to a distance of typically 40 km, depending on wind conditions
and aircraft altitude. These small waves are suppressed when an oil-film is
on the surface (Figure 1). Yet a number of other conditions can lead to
false returns that are difficult to distinguish from that of oil on the water,
among them algae blooms, freshwater fronts, sand banks and wind shad-
ows. These natural sea slicks are discussed in detail within Hühnerfuss et
al. (1986), their potential discrimination by multi-frequency radar is dis-
cussed for example in Hühnerfuss et al. (1994) or Gade et al. (1998).
These possible false returns are also one reason why satellite observations
are not sufficient as a stand-alone tool and it is the task of the near range
sensors to identify the origin of the missing radar signal area.
Fig. 1.
Non-rectified SLAR image of a sea area showing an oil spill as well as the
corresponding polluter. The aircraft track is in the middle of the image
The basic near range sensors are the infrared and ultraviolet detectors,
often coming together as IR/UV-sensor, in most cases in a line-scanner
(LS) assembly. The IR/UV-LS is a passive bi-spectral remote sensor that is
sensitive in the thermal infrared (TIR) between 8 and 14 Pm and in the
near ultraviolet (NUV) between 0.32 and 0.38 Pm. At an aircraft altitude
of 300 m its swath width amounts to approximately 500 m. This sensor on
the one hand is used to measure the thermal emission of the sea surface in
the TIR and on the other hand serves for the detection of highly reflecting
