Validation of the Service

The detection of SO₂ emissions, the selection criteria for the e-mail notification service will be validated against selected known volcano eruptions. Input for the validation is on the one hand the data from the NRT system and on the other hand information on volcano eruptions (from the VAACs, websites and newspapers).

Note that the Service is not aimed at deriving SO₂ data to high accuracy. This does, of course, not mean that we are not interested in accurate SO₂ columns, but the work on those aspects officially falls under other projects.

 

Extract from the "C5 Service Validation Protocol"
document of the GSE-PROMOTE project:

 
SACS is dedicated to the early detection and mapping of abrasive ashes and corrosive sulphur compounds emitted by volcanoes and transported by winds, that represent a major hazard to aviation. The service aims to provide in near-real-time data derived from satellite measurements regarding SO₂ and aerosol volcanic emissions and, in the event of an exceptional SO₂ concentration, to send an e-mail notification to interested parties, mainly official Volcanic Ash Advisory Centres (VAACs), pointing them to dedicated web pages.

In the event of an exceptional SO₂ concentration, the location of the SO₂ peak value will be used to start backward and foreward trajectories, images of which will be placed on the dedicated web page of the event. This feature will facilitate the interpretation of the satellite observations and by providing an indication of the location of the source of the SO₂ and of the height of the plume.

Validation of this two-faceted service should take into consideration the following two tasks: first, a validation of the service components and related geophysical data products, based on classical correlative analysis and information content studies; second, a validation of notification-related aspects. Quantitative validation of SO₂ and aerosol data products of volcanic origin is not straightforward, due to:

1. the difficulty to plan correlative measurement long-term programmes or even campaigns for - nearly - unpredictable eruptions;
2. safety and practical issues to get correlative measurements in the vicinity of an erupting volcano;
3. the current lack of suitable devices to perform accurate SO₂ column measurements from the ground.

A major experimental support is expected from the FP6-funded Network for Observation of Volcanic and Atmospheric Change (NOVAC), which will operate DOAS instruments at observatories of 15 volcanoes on five continents, including some of the most active and strongest degassing volcanoes in the world. The geographical development of plumes of volcanic ash can be confronted to images provided by satellite instruments like Envisat MERIS and EOSAqua MODIS. Aerosol lidars operated in the context of networks like the NDACC can provide correlative information on the vertical structure of the plume and on its temporal development (overpass of station at a given time).

In a first stage, the validation of the SACS will be its demonstration for a sufficient amount of past volcanic eruptions in long-term satellite data records. The study of notification-related aspects should address the following logical cases (if possible in terms of probability and of detection threshold):

• a potentially hazardous eruption occurs and SACS reports it;
• a potentially hazardous eruption occurs and SACS does not report it;
• a potentially hazardous eruption does not occur but SACS emits a notification.

More quantitative might be envisaged in a later stage, using ground- based SO₂ and aerosol measurements as well as satellite data. Suitable validation methods are still in their infancy and should be further developed.


Link to the "C6 Service Validation Report"
document of the GSE-PROMOTE project.

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