Chemistry Reference
In-Depth Information
features of the sea surface in the NUV. In general, the oil/air interface ex-
hibits a lower integral emissivity in the TIR than the water/air interface.
For this reason those areas of an oil spill, being in thermal equilibrium
with the underlying water surface and slightly exceeding a specific limit of
detection, appear colder in the TIR than the surrounding sea surface. How-
ever, very thick oil layers may be heated by the sun and thus appear as hot
spots in TIR images. The infrared line-scanner can be used during both day
and night time. By the way of contrast, the usability of the ultraviolet sen-
sor requires daylight conditions because it measures the global NUV radia-
tion reflected by the sea surface. The detection of oil spills in the NUV is
based on the fact that the oil/air interface shows a higher integral NUV re-
flectivity than the water/air interface. The lower TIR and NUV detection
limits of oil on water differ substantially. While in the NUV the minimum
detectable oil thickness lies in the sub-micron range, the corresponding
thickness threshold in the TIR amounts to a few tens of microns. For this
reason the IR/UV-LS is used to map the total extent of the oil spill and
those portions that are of intermediate or large oil thickness (Figure 2). The
IR/UV-LS is probably the most important near-range remote sensor for the
oil spill operator since it provides high-resolution imagery information on
relative oil thickness.
3 Advanced sensors
In addition to the above described standard there are more sophisticated
sensors like the laser fluorosensor (LFS) or the microwave radiometer
(MWR) that allow an advanced analysis of oil spills concerning the remote
identification of oil species and the quantification of film thickness. The
two German maritime surveillance aircrafts are examples of operationally
used pollution control systems incorporating the above-mentioned wide
range of remote sensors (Figure 3). Other nations operate comparable sys-
tems or are at the step of defining new airborne systems, incorporating
these advanced sensors for the second generation of maritime surveillance
aircraft.
