Volcanic Ash /Aerosol and Dust
Dr. Bernadette Connell
CIRA/CSU/RAMMT
December 2003
What do Volcanic Ash and Dust
have in common?
They have similar composition.
They provide another perspective on
characteristics of clouds which can be
detected by image channel combinations.
Introduction
1) Detection of Volcanic Ash for aviation
hazards - background
2) Techniques for ash/aerosol, and dust
detection
Multi-channel image combinations are used to
distinguish reflective/emissive/transmissive
properties of each constituent. In order to
identify the ash/aerosol, and dust, we need to
know how water and ice cloud particles
appear in the same image combinations.
3) Examples
4) Limitations
5) Selected References
Volcanic Ash
“Ash clouds are not an everyday issue and
they do not provide frequent hazard. But if
encountered, volcanic ash can spoil your
entire day.”
(Engen, 1994)
Why?
• Between 1975 and 1994, more than 80 jet
airplanes were damaged due to unplanned
encounters with drifting clouds of volcanic ash.
• Seven of these encounters caused in-flight loss
of jet engine power, .. Putting at severe risk
more than 1,500 passengers.
• The repair and replacement costs associated
with with airplane-ash cloud encounters are
high and have exceeded $200 million.
(Casadevall, 1994)
More background
• The primary cause of in-flight engine loss
was the accumulation of melted and
resolidified ash on interior engine vents
which reduced the effective flow of air
through the engine, causing it to stall.
• Volcanic ash is abrasive, mildly corrosive,
and conductive. Airframes and engine
components can be destroyed. Windshields
are especially vulnerable to abrasion and
crazing.
How much detectable ash causes problems?
Recent encounter (Feb. 2000) of a NASA DC-872 research airplane with a diffuse volcanic ash
cloud from Mt Hekla volcano
– Ash detected with sensitive research instruments
– In-flight performance checks and post-flight visual
inspections revealed no damage
– Subsequent detailed examination of engines revealed
clogged turbine cooling air passages and required that
all 4 engines be replaced.
http://www.dfrc.nasa.gov/DTRS/2003/PDF/H-2511.pdf
WHERE ARE THE VOLCANOES?
Global volcano distribution. Open triangles represent volcanoes believed to
have erupted within the last 10,000 years, and filled triangles indicate those that
have erupted within the 20th century.
Figure from Simkin, 1994
Important Aviation Considerations
• The height that columns can reach and then
disperse their load of ash into the prevailing
winds.
• The column rise rate.
• The content of fine ash that may be
suspended or falling in the atmosphere for
considerable distances or periods.
• The duration of the ash clouds.
Importance of Remote Sensing
• Global coverage
• Allows for tracking of the plume both
during the day and at night.
– Provides information in remote locations
– Can be used in conjunction with
soundings to determine plume height and
probable plume movement.
Three possible modes of behavior of eruption columns - intensity of eruption increases from
left to right. Wind is from the left in each case. At side of each diagram are shown
normalized velocity (v) profiles versus height (h) for these columns. Left, weak isolated
thermals, which are influenced by the wind. Center, a higher intensity buoyant column,
influenced by wind only at the top. Right, a high intensity, superbuoyant column with a
pronounced umbrella region.
From Self and Walker, 1994
Schematic diagram
showing the
distribution of
hazards to aircraft
around explosive
eruption columns of
three selected
frequencies. Upper
diagram is sectional
view; lower diagram
is plan view.
Vertical and
horizontal scales are
equal.
Self and Walker, 1994
How is the ash/aerosol plume, or dust
distinguished on satellite imagery?
Use of multi-channel imagery:
• 10.7 um - 12.0 um temperature difference
• 8.5 um - 10.7 um temperature difference
• 3.9 um - 10.7 um radiance/temperature
difference
• 3.9/10.7/12.0 um combined product
10.7 um – 12.0 um temperature difference
• Volcanic ash clouds with a high
concentration of silicate particles exhibit
optical properties in the infrared (8-13
um) that can be used to discriminate
them from normal water/ice clouds.
• Emissivity of silicate particles is lower at
10.7 um than at 12.0 um
• Emissivity of water/ice particles is higher
at 10.7 um than at 12.0 um
…… therefore
Ash/Dust in the 10.7 – 12.0 um range
Silicates appear warmer at 10.7 um than at
12.0 um
Water/ice particles appear warmer at 12.0 um
than at 10.7 um
BT12.0um-BT10.7um = positive for ash/dust
BT12.0um-BT10.7um = negative for ice/water cloud
Lascar, Chile July 20, 2000
GOES-8 visible imagery
ash cloud
Lascar, Chile July 20, 2000 1639 UTC
ash cloud
GOES-8 Infrared (10.7 um)
Lascar, Chile July 20, 2000 1639 UTC
Split Window (12.0 – 10.7 um)
ice cloud – negative differences
ash cloud
– positive differences
negative differences
positive differences
IR4
TD5-4
Dust
• Detection of “dust” is similar to ash.
• Emissivity of many soil particles at 10.7 um
is less than that at 12.0 um:
T(12.0um) – T(10.7um) > 0.0
GOES-10 VISIBLE Imagery
Blowing dust
Blowing dust
3.9 – 10.7 um reflective/temperature differences
• The 3.9 um channel has both a strong
reflected component during the day, as well
as an emitted terrestrial component.
• DAY: higher reflectance for ash/dust clouds
and water droplets; lower reflectance for
ice particles
GOES-8 T(3.9um) – T(10.7um) during the day
July 20, 2000 16:39 UTC
 Volcanic ash
Lascar, Chile 
Blowing dust
Reflectivity Product
3.9 – 10.7 um reflective/temperature differences
• At night, there is no reflected component
– only the emitted (and transmitted)
components.
• NIGHT: BT3.0-BT10.7 = positive for thin
ash/dust clouds
= positive for ice cloud
= negative for water cloud
GOES-8 12.7 um channel
18 N
7-hr Ash cloud
At night
Montserrat >
cirrus
low cloud
15 N
66 W
GOES-8 IR2 (3.9 um)
63 W
convective cloud
10.7 - 12.0 um Product
18 N
7-hr Ash cloud
T(3.9um)-T(10.7um)
Montserrat >
cirrus
low cloud
15 N
66 W
63 W
convective cloud
3.9/10.7/12.0 Product
Experimental Volcanic Ash Product (Ellrod et al.
2001)
B=C + m [T(12.0)-T(10.7)]+[T(3.9)-T(10.7)]
B= output brightness value
C=constant=60
(determined empirically)
M=scaling factor=10
(determined empirically)
T= brightness temperature at (wavelength)
Lascar, Chile July 20, 2000 1639 UTC
Three Band Product (3.9, 10.7, 12.0 um)
 Volcanic ash
18 N
7-hr Ash cloud
3.9/10.7/12.0 product
Montserrat >
cirrus
low cloud
15 N
66 W
63 W
convective cloud
Challenges to using the 10.7-12.0 um
difference product
• For optically thick plumes, when water and
ice are mixed with the volcanic debris, the
‘ash’ signal may be confused.
• Low ash concentrations can be difficult to
detect.
Challenges to using the 3.9 – 10.7 um
difference product
• Limitations to measurements for cold
scenes at 3.9 um:
– The steep slope of the Plank function at cold
temperatures (<-40 C), the instrument noise at
3.9 um becomes very large
• Uncertainties with properties of
reflectance/emittance/transmittance of the
ash cloud.
Challenge of GOES-12:
12.0 um replaced by 13.3 um
Picture and avi loop from G. Ellrod NOAA/NESDIS/ORA
Volcanic gases/aerosols
Gases: water vapor, sulfur dioxide (SO2),
chlorine, hydrogen sulfide, nitrogen
oxides and more.
One of many processes: oxidation and hydration
of SO2 -> H2SO4 (sulfuric acid)
The resulting ash/acid mix is highly corrosive
and can cause damage to jet engines and
external parts of the aircraft.
Absorption by SO2
Note MODIS channels
SO2 detection
Greater SO2 absorption at 7.3 um
BT 7.3 um – BT 6.7 um < 0
Less SO2 absorption at 8.5 um
Ash absorption at 8.5 um
BT 8.5 um – BT 12.0 um < 0
MODIS imagery and products for Reventador Volcano eruption
Ash and SO2 detection
SO2 detection
AIRS Aqua data
Brightness Temperature (K)
300
280
260
240
220
Volcano Reventador: 4 November 2002
Volcano Etna: 22 October 2002
Volcano Etna: 22 October 2002
200
3.5
4.5
4.0
5.5
5.0
6.5
6.0
7.5
7.0
8.5
8.0
9.0
9.5
10.5 11.5 12.5 13.5 14.5 15.5
10.0 11.0 12.0 13.0 14.0 15.0
Wavelength (micrometers)
Other uses of satellite imagery
for volcano monitoring
• Hot spot detection
• Determination of cloud height with
VISIBLE shadow technique .
< Popocatepetl, Mexico
Cloud height determined
from cloud shadows
22 km
Guagua Pichincha, Ecuador
16 km
Selected References
Prata, A. J. 1989: Observations of volcanic ash clouds in the 10-12 um window using
AVHRR/2 data. Int. J. Remote Sensing, 10 (4 and 5), 751-761.
Engen; Cassadevall; Simkin; Self and Walker; Prata and Barton, Schneider and Rose,
and other articles can be found in: Casadevall, T. J., 1994: Volcanic Ash and
Aviation Safety: Proceedings of the First International Symposium on Volcanic Ash
and Aviation Safety. U.S. Geological Survey Bulletin 2047.
Ellrod, G. P., B. H. Connell, and D. W. Hillger, 2001: Improved detection of airborne
volcanic ash using multispectral infrared satellite data. J. Geophys. Res., 108
(D12), 6-1 to 6-13
Satellite Services Division – Washington Volcano Ash Advisory Center
http://www.ssd.noaa.gov/VAAC/washington.html