Satellite and aircraft-based techniques to measure volcanic emissions and hazards - Volcanism and Global Environmental Change - page 139

Over its mission lifetime, ASTER has released several Global Digital Elevation
Models (GDEMs; http://asterweb.jpl.nasa.gov/gdem.asp ) covering the Earth

'

s land

surface at 8 - 12-m vertical resolution at 30-m postings.
ASTER data has been used for a wide variety of volcanological investigations
(e.g. Pieri and Abrams, 2005 ). A few examples of these include the seminal
work on the detection and measurement of passively emitting tropospheric SO 2
plumes (e.g. Realmuto et al ., 1994 ), the systematic time-series monitoring of
summit crater thermal emissions (e.g. Buongiorno et al ., 2013 ), the monitoring
of dynamic summit crater domes (e.g., Ramsey et al ., 2012 ), and the detection of
low-temperature thermal eruption precursors (Pieri and Abrams, 2005 ).

9.2.4 Ash- and gas-cloud detection
No other volcanic hazard has the regional (and even global) impact of drifting
volcanic clouds. Their impact on aviation, especially within Europe after the
2010 Icelandic eruptions, was profound, in icting an estimated $5 billion eco-

nomic damage globally (Oxford Economics, 2012 ). Thus there has been a recent
enhanced effort within Europe and the United States to improve our understanding
of the properties of such clouds, and to enlarge the collection of now scant in situ
data on volcanogenic gas and aerosols (especially ash), as well as their effect
on aircraft.
Data from synoptic weather satellites, the NASA Terra and Aqua orbital
platforms (e.g. the Moderate Resolution Imaging Spectroradiometer (MODIS))
and high spatial resolution data (e.g. ASTER) in the TIR have been utilized for
investigation of ash and gas clouds at a variety of local-to-regional spatial scales.
Typical approaches exploit the reverse absorption effect (Prata, 1989a ; 1989b )
of dry silicate ash within TIR bands. A negative radiance differential between 10.6
and 12 µm indicates

ne ash (1 - 12 µm effective radius; Rose et al ., 2000 ). When
ash clouds diffuse, their radiant emission drops beneath instrument sensitivity
thresholds in remote sensing data (e.g. Schneider et al ., 1995 ); however, these
limits have only tentatively been correlated between remote sensing and very
rare validating in situ data (Pieri et al ., 2002 ; Schumann et al ., 2010 ; e.g., particle
size-frequency, cloud height-thickness-extent, concentration variations with time;
see also Chapter 7 ).
Likewise, orbital image data from ASTER, MODIS, AIRS (Atmospheric Infra-
red Sounder; all in the infrared - observations in the troposphere and stratosphere,
day and night) and OMI (Ozone Montoring Instrument; ultraviolet - observations
primarily in the stratosphere, daytime only) are employed in SO 2 detection and
tracking. SO 2 and ash typically track together - the 2008 Kasatochi eruption is a
good recent example (Prata et al ., 2010 ; Krotkov et al ., 2010 ), although there are