Environmental Engineering Reference
In-Depth Information
exceptions (e.g. El Chichon 1982 eruption; Schneider
et al
.,
1999
). Still, SO
2
has a
low (4
-
5 parts per billion by volume (ppbv) global ambient background, and thus
is often viewed as a proxy for volcanic ash (e.g. Kreuger
et al
.,
2009
). Better
knowledge of how solid aerosols (e.g. ash) and SO
2
are related and the conditions
under which they are, or are not, spatially correlated, is central to understanding
volcanogenic cloud chemistry (e.g. Rose
et al
.,
2000
). UAV-based
in situ
obser-
vations for calibration and validation of orbital remote sensing data hold out
important promise for improving our speci
c knowledge of such parameters, and
for illuminating these problems generally.
Typically, hazard responders rely on volcanic ash transport and dispersion
(VATD) models (Stunder
et al
.,
2007
), used for research and past event analyses
(D
Amours
et al
.,
2010
; Webley
et al
.,
2010
). Two current Lagrangian trajectory
models, one for ash trajectory tracking developed at the University of Alaska,
Fairbanks (Searcy
et al
.,
1998
), called PUFF, and the other, a NOAA-sponsored
Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model
(Stunder
et al
.,
2007
) are in common use. HYSPLIT is a successor to the well-
known Volcanic Ash Forecast Transport and Dispersion (VAFTAD) model,
pioneered by NOAA (Hefter and Stunder,
1993
). Initial boundary conditions at the
source vent, e.g. total erupted mass and eruption rate, solid aerosol size-frequency
distributions, plume-top altitudes, SO
2
'
flux, amount of ambient air ingested, and
the vertical distribution of ash within an eruption column, exert crucial in
uence
on model outcomes.
9.3 Airborne observations
9.3.1 Manned aircraft
Manned airborne observations employ sophisticated state-of-the-art optical, micro-
wave, and electro-magnetic instrumentation (e.g.
Table 9.2
), particularly effective
when correlated with seismic, ground-based geodetic and surface radiometric
observations. They have been useful for mapping volcanic deposits and features,
capturing dynamic in
ation events, and for elucidating faults
and fractures in three dimensions. Capturing eruption activity, including
in situ
sampling of aerosol and gas emissions, particularly for large explosive events,
is somewhat more problematic for manned aircraft. While comprehensive obser-
vations of volcanic plumes have been made by manned aircraft, these have
mainly been from above (where possible) or from stand-off positions (e.g. recent
observations of an arti
ation and de
cial ash plume with the Airborne Volcanic Object Imaging
Detector (AVOID); see also
Chapter 7
). Potential airborne ash ingestion into
aircraft engines, while deemed a marginally acceptable risk by European authorities,
