Download Computational Visualization of Volcanic Ash Plume Concentrations

Recent Advances in Fluid Mechanics, Heat & Mass Transfer and Biology
Computational Visualization of Volcanic Ash Plume Concentrations
Measured by light Aircrafts over Germany and Iceland during the
Recent Eruptions of the Volcanoes Eyjafjallajökull and Grimsvötn
Weber, K., Reichardt, R. Vogel, A., Fischer, C., Moser, H.M.
Department of Mechanical and Process Engineering
University of Applied Sciences Düsseldorf
Josef-Gockeln-Str. 9, 40474 Düsseldorf
GERMANY
Eliasson, J.
University of Iceland, Faculty of Civil and Environmental Sciences VRII
Hjardarhagi 2-6, 107 Reykjavík,
ICELAND
[email protected] http://mv.fh-duesseldorf.de/d_pers/Weber_Konradin
Abstract: - A software tool has been developed at the Duesseldorf University of Applied Sciences in Germany
for the rapid visualization of the results of aircraft measurements in volcanic ash plumes. This became of high
importance during the recent eruptions of the Icelandic volcanoes Eyjafjallajökull and Grimsvötn. Due to the
eruption of the Eyjafjallajökull volcano in spring 2010 the airspace over most European countries was closed.
This caused the cancellation of a huge number of flights and had consequently a significant impact to economy.
The dispersion of the ash plume was calculated by a simulation model of the VAAC London. However, in
order to quantify the real concentration of ash particles in the plume over Germany the Duesseldorf University
of Applied Sciences performed 14 research flights with a light aircraft and optical particle counters over
Germany. The software tool, which was developed at the Duesseldorf University of Applied Sciences, was used
in this situation for preprocessing of the data and for the visualization of the flight tracks in combination with
the ash concentrations immediately after the flights. During the eruption of the Grimsvötn volcano in spring
2011 this software tool was again used by the Duesseldorf University of Applied Sciences for the rapid
visualization of the ash concentrations investigated by aircraft meaurements over Iceland and Germany. The
aircraft measurement results contributed significantly to the decision of the air navigation service provider
ISAVIA of re-opening of the international airport of Keflavik. This international airport had been closed before
because of high ash concentrations predicted by the London VAAC model.
Key-Words: data visualization, google earth, KML, XML, volcano, Eyjafjallajökull, Grimsvötn
visualization of the ash plume data userfriendly.
This visualization can be interpreted easily and can
therefore be helpful in situations, when it has to be
decided, if the air space should be closed or could
be kept open.
1 Introduction
During the airspace closures caused by the eruptions
of the volcanoes Eyjafjallajökull 2010 and
Grimsvötn 2011 it became clear, that real ash plume
measurements are necessary additional to the
predictions of the dispersion model of the London
VAAC (Volcanic Ash Advisory Center), as the
predictions often were overestimating the ash
concentrations and the model could not map the ash
plume in all details. In this situation aircraft
measurements became important to deliver more
detailed in-situ information about the ash plume. It
is necessary, that this information can be delivered
very fast to the authorities and decision makers.
Therefore the Duesseldorf University of Applied
Sciences developed a software, which enables a
ISBN: 978-1-61804-065-7
2 Measurement equipment
The measurements were performed in Germany
with an aircraft “Flight Design CT” and in Iceland
with a “Cessna 206”. Both aircrafts were equipped
with laser based instruments for the measurement of
ash particles (optical particel counters OPC: Grimm
EDM 107, Turnkey Dustmate). They are able to
measure ash concentrations in classes PM10, M2.5,
PM1 and TSP. The data were delivered at serial
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using its individual interface connection and its
proprietary data format. In general each
measurement is represented and separated by one
line in a text file. Every second a timestamp, explicit
the internal clock of the recording notebook, is
added to these lines with a precision of one second.
Afterwards, during parsing these lines this
timestamp is recognized and removed from the data
set. Hence, the original format is reconstructed.
Datasets which are delivered with checksum
information are rejected, if their checksum is wrong.
To keep this parser open for further measurement
devices, we implemented the parsers by object
oriented classes. The device is identified by its
original data format.
Never the less it could happen that more than one
single measurement of one device was received
within one second. Therefore they have the same
timestamp, but in subsequent lines. Because of that,
timestamps are linear interpolated afterwards
assuming that the measurements are delivered in
constant time steps but stored with a small random
delay caused by the receiving buffer.
All values are converted to SI units before
storing in the internal data structure.
output ports of the instruments. More details of the
measurements can be found e.g. in [1,2,3].
Figure 1: research aircraft “Flight Design CT” in
Germany
3 Preprocessing data
During the flights the output data of the different
devices were recorded in their individual proprietary
formats, added with a timestamp and separately
stored in files. The timestamp is the local and
probably wrong time of the internal clock of the
notebook which has been used to receive the values
of the connected devices. By adding this timestamp,
we destroyed the syntax of the original data format
of the devices, but this information is needed to
merge the different data sources.
Hence, preprocessing is necessary to convert the
different input data into an according output.
Subsequently, this output is used as an input file for
the visualization in time and space using Google
Earth.
3.2 Merging
After the parsing step the values of the different
devices have to be merged. This is an important step
to assign time space coordinates from the GPS to
the aerosol measurements.
The matching is done by the datasets timestamp
of the different measurement. Because the devices
are not always operational at the same time, e.g. the
GPS device is switched on at ground, but the aerosol
measurement starts later in the air, some datasets do
not match because of the missing time stamp at their
counterparts datasets.
Furthermore the different devices do deliver their
datasets in different time intervals, e.g. GPS signal
are received once per second, whereas other datasets
are received every 6 seconds. Because of that the
datasets are stored in a tree data structure ordered be
the timestamp. As a result several GPS signals are
assigned to one aerosol dataset.
At least all timestamps, representing the local
and probably wrong time of the recording notebook,
are adjusted. The offset is calculated using the
reliable time received within the GPS information.
The preprocessing requires the following tasks:
 Parsing each of the input files
 Storing the important values in a data
structure.
 Merging of the measurement of the different
devices
 Detecting measurement errors and calculate
uncertainties
 Basic statistical analysis, e.g. to adjust the
color coding
 Generating and exporting the “Keyhole
Markup Language” file for Google Earth
This procedure was implemented in Java to be
platform independent.
3.4 Detecting GPS measurement errors
Obviously, some of the GPS datasets are incorrect,
e.g. the airplane “jumps” in space. The tolerance of
the position information is known for every dataset,
3.1 Parsing
Each single device sends the measured values
immediate after the measurement to the notebook
ISBN: 978-1-61804-065-7
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Recent Advances in Fluid Mechanics, Heat & Mass Transfer and Biology
depending on the number involved satellites during
the measurement.
The flight path of the airplane is analyzed to
calculate velocities and acceleration. In order to
detect incorrect positions, thresholds for unrealistic
accelerations are needed. These 3D-thresholds are
represented by the 98% quantile of all acceleration.
Thus, different thresholds per dimension are
received. This takes into account that the maximal
acceleration of the airplane differs in longitudinal
and lateral direction.
After that the flight path is recursively
interpolated by b-splines considering the tolerance
of the position information and the threshold for the
acceleration. Positions which are identified as
measurement errors are replaced by an interpolation.
The result of this procedure is a polygonal chain
in space. Each vertex has additional information
about the velocity, acceleration and its confidence
interval. Hence, now the flight path could be
understood as a curved tube in space. Its radius is
the confidence information and the true position of
the airplane in somewhere within the hollow tube.
Several aerosol concentration classes are
measured during the flight, but it is confusing to
display all of them at once. Thus, we used different
folders for the hierarchically arrangement of the
different classes and optional information. Each
measurement is equipped with the complete
datasheet of all the measurements at this coordinate.
The visibility of measurements within a certain
interval is configurable, e.g. to show high
concentrations, only.
Finally, we enabled an optional animated flight
from the viewpoint of the pilot along the recorded
flight path.
4 Measurement
results
and
application of the software – examples
from the recent Eyjafjallajökull and
Grimvötn eruptions
4.1 Example of the visualization of a research
flight on 18 May 2010 in the Eyjafjallajökull
ash plume over Germany
3.4 Color coding
Within the Eyjafjallajökull eruption period of
April/May 2010 the Duesseldorf University of
Applied Sciences performed 14 research flights
over North Germany in situations with and without
ash plumes. A typical ash plume situation was on 18
May 2010, when the London VAAC predicted an
ash concentration zone (red) over Germany, that
means a zone where ash could be encountered by
aircrafts (see Fig. 2)
The flight track is visualized by a colored belt,
constructed by planes orthogonal to the earth
surface (see fig. 3). The height of the belt represents
the altitude of the airplane. The face color of the
planes is color coded in dependence of the aerosol
concentration the mutual position of the flight track.
Optionally we used color coded spheres. The
position of the sphere (vertex) represents the
location of the measurement and the color
represents the ash concentration.
The color depends on the underlying user defined
color map. It turned out that the automatic
assignment of values to a color is a difficult task.
Therefore the assignment is a just suggestion for the
user and can be changed manually. This is also
useful to compare two different measurement flights
by using the same color coding.
3.5 Exporting
The datasets are exported using the Keyhole
Markup Language (KML) which is an XML
notation for expressing geographic visualization
within three-dimensional browsers like Google
Earth [4]. Because we are additionally generating
bitmaps for the color bars and legends, several files
are needed collectively. The distribution of one
small single file is easier than handling several files,
and therefore we combined the files to the
compressed version of the file format (KMZ).
ISBN: 978-1-61804-065-7
Figure 2: Ash concentration prediction by the
London VAAC for 18 May 2010, caused by the
Eyjafjallajökull eruption
Therefore the German Weather service stipulated
research flights for that day by the Duesseldorf
University of Applied Sciences. The results are
visualized by the software tool in Figure 3:
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Recent Advances in Fluid Mechanics, Heat & Mass Transfer and Biology
that day. Because the London VAAC model
predicted significant high ash concentrations for the
whole Island, the international airport Keflavik was
closed several times during the eruption period and
this caused the cancellation of several flights.
Therefore the University of Iceland in cooperation
with the Dussseldorf University of Applied Sciences
started research flights on Iceland for ash plume
observations on 22 May – 26 May. A Cessna 206
served as a platform for the optical particle counters,
which were used for the ash particle measurements.
The research flights on 22 May and 23 May were on
behalf of both Universities, the flights on 24 May to
26 May were stipulated by the Icelandic air
navigation service provider ISAVIA. Most of the
flights were performed in the region of the airports
Reykjavik and Keflavik in order to investigate, if
the airspace there showed high or low ash
concentrations. Figure 4 shows the tracks of the
flights over western Iceland.
Figure 3: Visualization of the track of flight of the
research aircraft over northern Germany combined
with ash concentrations and flight altitude
The flight started in the Rhein-Ruhr area, headed
along the Dutch border to the North Sea, from there
in direction of Hamburg and further on via
Recklinghausen back to the Rhein-Ruhr area. The
software was able to visualize very clearly the ash
concentrations (in figure 3: PM10) and the flight
altitude in one diagram. High measured ash
concentrations are visualized in red (above 100
µg/m3), low measured ash concentrations are
visualized in green. The height of the flight belt
visualizes the altitude of the aircraft at that point.
So it could clearly be demonstrated by the software
immediately after the research flight, that higher ash
concentrations could be observed at the Dutch
border and at some spots at the North Sea. Moreover
it can be seen clearly in figure 3, that the ash plume
was not homogeneously distributed over Germany.
4.2 Example of the visualization of a research
flight on 22 May 2011 on Iceland because of
the Grimsvötn eruption
In spring 2011 the Grimsvötn volcano erupted on
Iceland. The eruption started on 21 May and
stopped on 25 May 2011. During the period of the
eruption the south of Iceland was severely affected
by the ash plume. The London VAAC provided to
the air traffic authorities ash dispersion charts with
the predictions of the spread of the ash plume for
ISBN: 978-1-61804-065-7
Figure 4: Tracks of research flights on Iceland
during the Grimsvötn eruption 2011
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Recent Advances in Fluid Mechanics, Heat & Mass Transfer and Biology
Fig. 5: Visualization of Iceland research flight on 22
May 2011
of the flight track, the flight altitude and the
measured concentrations over a geographical map.
This software became important for the
visualization of the results of the aircraft
measurements in the volcanic plumes of
Eyjafjallajökull and Grimsvötns immediately after
the flights. In the future this software will be further
improved in a way, that online results are available
during the flights. These shall be visualized in the
cockpit of the research aircraft as a tool for
optimizing the flight track according to the
measured ash concentrations. Moreover, these
visualizations of ash concentrations are important
for decision makers in volcanic ash plume crisis
situations.
The research flights revealed generally significant
lower concentrations of ash over west Iceland
(region Keflavik and Reyjkjavik) than predicted by
the London VACC. The results of the measurements
were reported immediately after the flights to the air
navigation service provider ISAVIA. The reports of
low ash concentrations in the regions of Keflavik
and Reykjavik contributed to the decision of
ISAVIA, to re-open the airport of Keflavik, despite
higher predicted ash concentrations by the London
VAAC.
Figure 5 shows as one example of the 11 research
flights on Iceland the visualization by the software
of the flight track, measured ash concentration and
the flight altitude on 22 May 2011. In this
visualization an option of the software was chosen,
where the ash concentration values are represented
as small colored dots on top of the belt of the flight
track. As a further option, the diameter of the dots,
representing the concentration, can be varied
depending on the concentration. This is especially of
interest, if the visualization is not in colors but in
black and white. In this example of ash research
flight on 22 May 2011 it can be clearly seen, that the
concentrations were low in the region of Keflavik
and Reykjavik. The only higher concentrations
(indicated by red dots) could be found in the region
of Selfoss in a distance from the airports.
6 Acknowledgement
This work was partly funded by the German
Ministry of Transport, Building and Urban
Development, the German Weather Service and
Airbus.
References:
[1] Weber, K., A.Vogel, et.al.,,Airborne Measurements of the Eyjafjallajökull volcanic ash
plume with a light aircraft and an optical
particle counters. Atmospheric Remote Sensing
VI. SPIE Vol. 7832, 78320, 2011, P - 1-15
[2] Weber,K., et. al.,Airborne in-situ investigations
of the Eyjafjallajökull volcanic ash plume on
Iceland and over North-Western Germany,
Atmospheric Environment, 2011, in press
[3] Eliasson, J., Palsson, A., Weber, K, Monitoring
ash clouds for aviation. Nature Vol. 475, 2011,
Page455,DOI:10.1038/475455b.http://code.goo
gle.com/intl/de-DE/aps/kml/documentation
5 Conclusions
A software tool for the visualization of aircraft
measurements in volcanic ash plumes has been
developed. It allows the simultaneous visualization
ISBN: 978-1-61804-065-7
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