Transcript Workshop poster

Monitoring volcanic activity from space: Retrieval of sulphur dioxide plumes
from ERS-2/GOME backscatter data
Atmospheric Science Conference
ESA-ESRIN, Frascati
th
th
8 – 12 May 2006
Why watching the
Etna with GOME ?
Etna from space
• GOME is designed for to measure the content of
atmospheric trace species, among them SO2
• SO2 forms sulphate aerosol in the stratosphere and is
responsible for the “acid rain” phenomenon in the troposphere
• Volcanoes are the major source of natural sulphur dioxide emissions
• The stratovolcano Etna is the most active volcano in Europe
• Especially, Etna is one of the major global sources
of SO2
• There were two severe eruptions of Etna in
Summer 2001 and Autumn 2002
ASTER: July 29th 2001
LANDSAT: July 21st 2001
Results
VCD  2 DU
Retrieval of sulphur dioxide
The problem: We measure the
slant column but we need the
vertical column
MODIS: July 24th 2001
Sun
ERS-2
GOME
Effective
Slant Column
Results July 2001 - trajectory analysis and GOME SO2 vertical columns
Vertical
Column
Density
Atmosphere
VCD  3 DU
Fractional Cloud Cover
Sea
Land
ATSR-2: July 24th 2001
ESC  f c  GVC  AMFcloud
VCD 
f c  AMFcloud  1  f c   AMFground
Validation
Average increase of the SO2
content from 31st Oct to
2nd Nov 2002 is about 3 DU
Air Mass factor
calculation
Results Oct/Nov 2002 - trajectory analysis and
GOME SO2 vertical columns
AMFs describe the enhancement of
absorption along slant paths in the atmosphere.
AMFs are pure radiative transfer simulations
and are a function of
• Viewing geometry (SZA, LOS, AZM)
• T-p- profiles, profile shape
• trace gas concentration profiles
profile shape
This is the amount
seen by GOME
Brewer Thessaloniki
Conclusion
GOME is able to measure volcanic SO2 but needs external
information about plume height and aerosol loading to do it with
reasonable accuracy of < 30%
  3 DU
31st- Oct
2nd- Nov
Athens Lidar
Impact of aerosol loading and plume height (profile shape)
• Aerosol loading and aerosol
optical properties
• Albedo and height of the
underlying reflecting surface
(ground or cloud-top)
Justification of simulated
aerosol loading by LIDAR
measurements – Fall 2002
Quality of SO2 retrieval depends strongly on the a priori knowledge about the SO2 profile and the aerosol loading (AOT, type)
More information in: Thomas et al., J. Atm. Chem., 50, pp. 295-320, 2005