5. THE SOFTWARE TOOL “REviSED” 
The interface tool to link remote sensing data and oil 
drift model is REviSED (REmote SEnsing interface for 
Drift modelling). This core element of the processing 
chain was developed at BfG within the project using 
Interactive Data Language (IDL). It generates all 
necessary drift model input files using either aircraft or 
satellite data. In the following section, the program 
workflow is described in detail: 
When started, REviSED searches for input files and 
accesses the data. If a polygon file exists, the tool will 
create the model input files for Level-II processing. 
Otherwise, only the basis file with centre coordinates 
for Level-1 processing will be generated. 
For Level-II processing, spill information like date and 
time of observation are taken directly from the remote 
sensing data (no specification file required). Further 
parameters are either read from the specification file - 
as far as provided - or from the default file. 
The oil amount is an important input parameter for 
predicting the oil distribution. It can not be directly 
determined from radar data. If the oil amount is 
estimated during an aircraft mission, the assumed value 
can be written to the specification file by the user. 
Otherwise, either the default value (e.g. 10 tons) may be 
used or the volume can be estimated using an area- 
volume-relationship based on Fay’s equations ([15], 
[12]) by setting the keyword FAY as parameter in the 
basis file for the oil amount. Fay [15] assumes, that 
when the spreading process stops the polluted area 
reaches a maximum extent A max : 
5 3/4 
¡ - 1<>- i - (1) 
Using this relationship for calculating the oil volume 
(V) from the area of a pollution (taken as A niax ), implies 
that the spreading process lias already reached its end 
and thus the area of the spill lias reached its maximum 
at the time a radar image is taken. Though this will not 
be tme in many cases, this approach provides a 
conservative estimate of the volume, that means the real 
volume can only be the same or higher than the estimate 
(assumed undisturbed spreading and if the correct oil 
type is applied). The explanation is, that if the spreading 
process continues the oil thickness decreases and if it 
stops, it reaches a minimum. Thus, if there are two 
(theoretical) slicks with the same surface area, there will 
be more oil per area if the spreading is ongoing, than if 
it lias stopped. 
For Level-II processing, the approach that is used to 
generate the particle cloud is to equally distribute a 
number of maximum 1000 particles over the area 
enclosed by a polygon (Fig. 7). For this, the existing 
IDL’s polyfill v algorithm to raster the vector data is 
enhanced to come as close as possible to a number of 
1000 particles and to include all edges. Nevertheless, 
there are - depending on the polygon - sometimes a few 
more particles generated. In this case, the excess 
particles are deleted by random selection (Fig. 8, orange 
symbol in zoom). After the particle cloud is generated, 
the distribution’s centre of mass is calculated and builds 
the first point of the drift path. As a last step, REviSED 
creates all drift model input files. 
Figure 7. Example of drift model run: Level-II 
processing. 1000 particles are distributed over a 
shapefde using REviSED algorithm (zoom). The new 
center coordinate is also calculated (red star) and the 
dri ft path is shown. 
6. CASE STUDY 
In the selected case study, there is one pair of 
observations: one observation by satellite and one - 
with a certain time delay - by aircraft. The latter 
confirmed the possible pollution detected with help of 
the satellite service as a real mineral oil spill. 
Starting with the satellite sliapefile, REviSED and the 
oil drift model were nm assuming the standard 
parameter for oil age of 3 hours. All figures concerning 
oil spills and drift model outputs shown in this paper 
refer to this same oil slick. E.g. Fig. 3. shows the SAR 
and SLAR images and Fig. 8 shows the generated 
particle cloud and the computed drift path. 
Within the project, such pairs of observations are used 
to validate the model results. Fig. 8 shows the location 
of the oil spill at time to when detected by the CSN- 
service and the aircraft observation at time ti three hours 
later.