Specificity of our multi-sensor notification system

Example of GOME-2 notification on 16^th of June 2011

 

Satellites equatorial overpass solar local time

Illustration of the satellites equatorial overpass solar local time.

 

Data availability for each instrument and Characteristics of SACS products

 

The notification criteria

The criteria for the notifications are based on the SO₂ total (vertical) density (for UV-visible instruments) and on brightness temperature difference (for IR instruments) of a set of ground pixels.

Details of the criteria are given in the following table:

A threshold radius is only required for UV-visible instruments. Considering the surrounding pixels allows to avoid false notification due to noise of the UV-visible measurements.

- SCIAMACHY and GOME-2 measurements are also sensitive to the South Atlantic Anomaly. To avoid false notification, strict threshold values are considered for this region.

- For UV-visible instruments which are sensitive to SO₂ in the low troposphere (between 0 and 5 km), false notifications due to pollution in China, Russia, or South Africa are avoided by considering strict threshold values over these regions.

- The OMI instrument suffers from the so-called raw anomaly. To avoid false notifications from this instrument, the data affected by stripes (see for example the SO₂ OMI image) are not considered in our notification system.

- AIRS instruments is occasionally subject to data anomalies ('line anomaly'). To avoid false notification, a filter is applied.

- IR instruments are particularly attractive for the notification system thanks to day and night overpassess and almost no false notifications. However IASI and AIRS are only sensitive to SO₂ above around 5 km. This may be a limitation for some users (e. -g., interested by the monitoring of degassing volcanoes).
 

Dedicated web page of a notification

A SACS notification is sent by email to subscribers.The title of the email contains the name of the instrument, the date and time of measurement and the region concerned. This message starts with some information about the date and time of SACS processing. A link to the notification web page is given, then the message provides basic information about the notification, such as the average location, the SO₂ peak value, the time and the solar zenith angle of this measurement -- see the page on this link:

Example of GOME-2 notification on 16^th of June 2011

Images of SO₂ data (vertical column density in DU for UV-visible instruments, or brightness temperature difference for infrared instruments) and Ash indicators (Aerosol Abosorbing index or ash index). Others plots are shown: Cloud Cover Fraction (CCF) plot if available, SO₂ interpolated plot, and a Google Earth file (.KMZ). A plot of the volcanoes in this region and a link to a list and details about on these volcanoes is shown, as well as a link to the near real-time service.

During the next 12 hours which follows a notification, confirmations of notification are automatically updated on the notification web page.
 

Archive of notifications

World maps showing the 2011 notifications detected by the SACS multi-sensor approach (please click on the notification points to view the corresponding SO₂ images).

multi-sensor notifications 2011

An update of the SACS archives for all SO₂ data is in progress.