Environmental Engineering Reference
In-Depth Information
7
Remote sensing of volcanic ash and sulfur dioxide
fred prata and gemma prata
7.1 Introduction
In 1979, the National Oceanic and Atmospheric Administration (NOAA) launched
the TIROS-N satellite carrying an Earth-observing instrument designed principally
for studying the atmosphere and oceans. The Advanced Very High Resolution
Radiometer (AVHRR) was a four-channel visible and infrared (IR) imaging device
that provided global images of the Earth
'
s atmosphere and surface at a spatial scale
of about 1
1km
2
. The data were essentially free: once a simple receiving dish
and some decoding electronics were installed, digital imagery could be received
twice per day (or more at polar latitudes) giving users access to real-time data over
a geographically large region (2,400 km
10,000 km). The data were also
radiometrically calibrated and could be used quantitatively to measure sea-surface
temperatures and the health of vegetation, apart from monitoring weather systems,
storms and many other meteorological phenomena. It was immediately apparent
that these data could be used for hazard monitoring and in particular to monitor
volcanoes and volcanic activity. The same satellite also carried an instrument for
measuring solar backscattered ultraviolet (SBUV) radiation in order to measure
ozone. In a landmark paper, Krueger (
1983
) reported the sighting of SO
2
clouds
from El Chichón using TOMS (Total Ozone Mapping Spectrometer) retrievals,
based on the same principles as the SBUV, by noting that bands at 312.5 and 317.5
nm were affected by SO
2
absorption. The same year Robock and Matson (
1983
)
showed the spread of the ash cloud from El Chichón using data from the NOAA
AVHRR instruments. One of the
first TOMS measurements of SO
2
emissions was
from Cerro Azul volcano on the Galápagos islands, acquired in February, 1979.
When TOMS was launched it was not anticipated that it would be able to monitor
volcanic activity. Exploitation of geostationary meteorological data for monitoring
