Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
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 236 Recent Advances in Fluid Mechanics, Heat & Mass Transfer and Biology 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: 978-1-61804-065-7 237 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: 238 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 239 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: 978-1-61804-065-7 240