4.1 Data visualization and metadata structure

4.1.1 GOME-2 SO₂ data

SO₂ column data is provided in form of GEOTIFF images (select “GOME-2 SO₂ column densities” under WP2 in add layer menu). The GIS system provides the option to display the SO₂ column amount of each individual pixel by using the info button (select the “info tool” and click on the pixel of interest).

Further information is provided in form of a text message. This message contains the total number of measurements within the selected area. It provides information on the maximum SO₂ amount detected together with its location and the time of measurement. Also certain threshold values are defined, in this case 1 DU and 1.5 DU, are defined and the number of measurements for the specified region that exceed these thresholds are reported. These threshold values also trigger a special SO₂ alert, to draw the user’s attention to exceptionally high SO₂ values that require further inspection. Alert level 0 indicates that all detected SO₂ values are below 1 DU, for values > 1 DU but < 1.5 DU the alert level is set to 1 and for values > 1.5 DU the alert level is set to 2.

The main metadata structure (written to an XML file) is as follows:

- <GOME2 volcano_id="0101-06=" project_id="ExuperyTest">

+ <range_upperleft>

+ <range_upperleft>

+ <range_lowerright>

+ <start_datetime>

+ <end_datetime>

+ <files>

+ <author>

+ <SO2 >

Within the <range_upperleft> and <range_lowerright> tags the coordinates (longitude and latitude) of the corners are written. Similar case is for <start_datetime> and <end_datetime> tags.

The tags <files> and <author> contain information about the produced files, their original location and who created them.

Information on the SO₂ observation is written into the <SO2> tag. It contains the number of measurements, the maximum SO₂ value measured, with location and time of measurement. It also provides information on the number of measurements exceeding certain threshold values (see above) and the alert level.

4.1.2 MODIS true colour images

As described in the Section “Purpose of the VFRS-component” the MODIS true color images reveal atmospheric features as a human eye would see them and therefore enable amongst others the detection of volcanic ash under clear sky conditions.

The MODIS true colour images of AQUA and TERRA respectively are downloaded as GEOTIFF files from http://rapidfire.sci.gsfc.nasa.gov/ for the subset „Azores“ and “Italy” and visualized in the Web GIS (select “MODIS Aqua imagery” or “MODIS Terra imagery” respectively under WP2 in add layer menu). Further information on the appropriate swath data is provided in form of a text message. The corresponding XML files are structures as follows:

-<Modis volcano_id="0101-06=" project_id="ExuperyTest">

+<files>

+<author>

+<mail_address>

+<time_of_creation>

+<start_datetime>

+<end_datetime>

+<range_upperleft>

+<range_lowerright>

+<swath >

The tags <files>, <author> and <mail_address> contain information about the produced files regarding the filename, size and their original location and the name and email address of the creator.

Within the <range_upperleft> and <range_lowerright> tags the coordinates (longitude and latitude) of the region corners are written. Similar to this the start and end times of the observations is documented in the <start_datetime> and <end_datetime> tags. The time of the XML file creation is written into the <time_of_creation> tag.

Information on the appropriate swaths used for the creation of the images is into the <swath> tag.

4.1.3 Trajectory and dispersion maps

Hypothetical volcanic trajectories

The stochastic trajectory analysis technique is used to automatically calculate hypothetical forward trajectories at different height levels for Agua de Pau (Portugal) and Etna (Italy) volcano. The forecasts are based on meteorological data of NCEP/GFS and allow forecasting the probable transport of volcanic emissions depending on the emission height in case of an eruption (select “Hypothetical volcanic trajectories” under WP2 in add layer menu). The geolocation and height information of each trajectory is written to the corresponding XML file and visualized in the Exupéry Web GIS. The altitude of each trajectory depending on time can be displayed using the corresponding legend or in more detail the “Information” button (select the “info tool” and click on the pixel of interest). Additionally the XML file contains information about the software, the starting points of the forward trajectories as well as the number of calculated trajectories (see below).

Plume dispersion probability

By applying the same method as used for identifying the emission source by means of coherent backward trajectory ensembles (see section “Purpose of the VFRS-component”), trajectory density maps are generated by coherent hypothetical forward trajectories. They indicate the most probable direction of volcanic ash and gas transport in case of an eruption (select “Plume dispersion probability” under WP2 in add layer menu. The GIS system provides the option to display the probability value at each individual location by corresponding legend or in more detail the “Information” button (select the “info tool” and click on the pixel of interest). In combination with the results of the hypothetical volcanic trajectory calculations a complete image of the dispersion characteristics of volcanic SO₂ and ash regarding the direction, time and the dependency on the emission height in case of an eruption is generated.

The XML file contains additional information about the software, the starting points of the forward trajectories as well as the number of trajectories used for the creation of the probability map.

Metadata structure

The combined XML files for the “Hypothetical volcanic trajectories” and the “Plume dispersion probabilities” is structured as follows:

- <Trajectories volcano_id="0101-06=" project_id="ExuperyTest">

+<files>

+<author>

+<mail_address>

+<time_of_creation>

+<software>

+<latitude>

+<longitude>

+<range_upperleft>

+<range_lowerright>

+<start_datetime>

+<end_datetime>

+<number_of_trajectories>

+<data>

The tags <files>, <author> and <mail_address> contain information about the produced files regarding the filename, size and their original location and the name and email address of the creator.

Within the <range_upperleft> and <range_lowerright> tags the coordinates (longitude and latitude) of the region corners are written. The time of the XML file creation is written into the <time_of_creation> tag.

More information on the initialisation and the results of the model calculations are written to the <latitude>, <longitude>, <start_datetime>, <end_datetime>, <number_of_trajectories> and <data> tags. <latitude> and <longitude> contain the coordinates of the starting point of the trajectories (here: the coordinates of the volcano).

The start and end times of the calculations is documented in the <start_datetime> and <end_datetime> tags. <number_of_trajectories> shows the total number of trajectories calculated and used for the creation of the dispersion probability maps. The location (longitude and latitude) and height information of the appropriate trajectories are also written to the XML file and can be found in the <data> tag. The <software> tag provides the name of the model.