SO2 data and alert service
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Notifications of SO2 events Introduction Archive of notifications per day Archive of notifications per region Subscription to email list

Introduction to the notification system The near-real time process system evaluates the satellite measurements in separate segments of an orbit. If the SO2 concentrations in such a segment satifies certain criteria then this segment is marked as showing an exceptional SO2 concentration, i.e. an "SO2 event". Based on this finding a notification is issued by email to users who have subscribed to this service. This page gives a brief introduction to this service: Segments of an orbit used for the notification The notification process Dedicated web page of an alert Archive of notifications Some further notes and remarks

 

Segments of an orbit used for the notification

SCIAMACHY and OMI data are received and processed as orbits, whereas the GOME-2 data arrives in the 3-minute segments.

SCIAMACHY measures alternatively in nadir and in limb mode along its orbit. The SO2 service can only use nadir measurements. This in a naturaly way implies that nadir states of SCIAMACHY -- which constitute about one minute of measurements -- are used as segments of orbits for the alert service.

For GOME-2 the data arrives in so-called PDU ("Product Dissemination Units") which consitute 3 minutes of observations. The processing evaluates each PDU separately, i.e. each PDU serves as a segment of an orbit for the alert service. NOTE: GOME-2 is not yet used for notifications.

OMI ... [to be specified]
 

The notification process

The near-real time process system evaluates the satellite measurements in the above described separate segments of an orbit. If the SO2 concentrations in such a segment satifies certain criteria then this segment is marked as showing an exceptional SO2 concentration, i.e. an "SO2 event".

The criteria for the alerts are based on the total (vertical) column SO2 density of a set of ground pixels around a ground pixel that shows a peak value. Details of the criteria are given in the product information.

A single process run can analyse one or more orbits of measurements, each with several segments. Per process run there can thus be one or more segments that merit a notification. A given segment can lie (partly) in one or more of the predefined geographic regions. And more than one segment can issue an alert in a given region. It is at this point not possible to automatically group together different segments that belong to the same SO2 emission event.

For a given process run, the segments that merit a notification are grouped together in one email message to the users. For each segment the message provided brief information on the location of the event and the total (vertical) column SO2 value, and it gives a link to a dedicated web page that shows an image of the SO2, and gives some more details of the event. Click here for an example of a notification message and some additional information on the data given in the notification.
 

Dedicated web page of an alert

The dedicated web page the notification message points to starts with some info on the segment that triggered the alert, such as the average location and the SO2 peak value -- see the page on the example of a notification for some details on this.

Then follow images of SO2 and cloud cover in a 30 by 30 degree region around the segment that issued the alert, plus a plot of the location of the volcanoes in that region (if any). The web page further provides links to the near-real time data pages for the pre-defined geographic regions the segment (partly) lies in. That part of the page is generated automatically by the near-real time process.

The SO2 and cloud cover maps show only the data from the orbit (for SCIAMACHY and OMI) or segment (GOME-2) that triggered the alert, not the data of adjacent orbits -- details to be confirmed

Below the images there is room for additional information, which is added by hand(!) and can, for example, combine different notifications of the same SO2 emission event (e.g. a volcanic eruption), provide other relevant images, and provide links to external web pages with more information regarding the event.
 

Archive of notifications

The menu on the left, both here and on the dedicated webpage showing the SO2 event images, gives access to an archive of the notifications sent out by the processing. The events can be accessed in the following ways:

• Archive of notifications per day
  This shows a list of notifications issued per day for a selected month and it comes in two variants:
  • Sorted by the date at which the data was processed
    For each time the process that issued one or more notifications, this gives access to the dedicated web pages with the images of the SO2 events, as well as the full text of the notification message. The most recent process is listed first. The process time given is the time of the start of the process.

  • Sorted by the date at which the measurements where taken
    For the different processes that issued a notification, this lists the date and time of the processing and gives access to the individual web pages with the images of the SO2 events.

• Archive of notifications per region
  This shows a list of notifications issued per region for a selected month, along with the date and time of processing and measurement.

These pages also provide links to the near-real time data pages for the regions within which the alert falls.
 

Some further notes and remarks

• Alerts based on the data of the different satellite instruments can results from the same "SO2 event". But since the data of the different instruments comes along different data streams, they are analysed in separate processes, and they can therefore not be linked automatically to the same event.

• No attempt is made to automatically identify the source of the SO2, as this would be very tricky -- it could easily lead to false identifications.

• The timeliness of the alerts depends mainly on the delay with which the data is received by the processing system. In most cases the alerts should be available around 3 hours after the satellite took the measurements.
  For part of the SCIAMACHY orbits, however, the delay is usually much more, depending on the ground station that receives the satellite data. As it happens, data from orbits early in the day (orbits starting earlier than, say, 06:00 UTC) may arrive after data from later orbits. And two or three orbits may arrive (and be processes) together.

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