Volcanic Ash /Aerosol and Dust

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Volcanic Ash /Aerosol and Dust

• Dr. Bernadette Connell
• CIRA/CSU/RAMMT
• December 2003

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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.

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Introduction

• Detection of Volcanic Ash for aviation hazards -
  background
• 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

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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)

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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)

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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.

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How much detectable ash causes problems?

• Recent encounter (Feb. 2000) of a NASA DC-8-72
  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
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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
WHERE ARE THE VOLCANOES?
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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.

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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.

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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
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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
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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

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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

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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

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Lascar, Chile July 20, 2000 GOES-8 visible
imagery
ash cloud
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Lascar, Chile July 20, 2000 1639 UTC GOES-8
Infrared (10.7 um)
ash cloud
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Lascar, Chile July 20, 2000 1639 UTC Split
Window (12.0 10.7 um)
ice cloud negative differences
ash cloud positive differences
positive differences
negative differences
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IR4
TD5-4
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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) gt 0.0

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GOES-10 VISIBLE Imagery
?Blowing dust
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?Blowing dust
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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

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GOES-8 T(3.9um) T(10.7um) during the day
Lascar, Chile ?
? Volcanic ash
July 20, 2000 1639 UTC
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?Blowing dust
Reflectivity Product
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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

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GOES-8 12.7 um channel
18 N
7-hr Ash cloud
At night
Montserrat gt
cirrus
low cloud
15 N
66 W
convective cloud
GOES-8 IR2 (3.9 um)
63 W
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10.7 - 12.0 um Product
18 N
7-hr Ash cloud
T(3.9um)-T(10.7um)
Montserrat gt
cirrus
low cloud
15 N
convective cloud
66 W
63 W
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3.9/10.7/12.0 Product

• Experimental Volcanic Ash Product (Ellrod et al.
  2001)
• BC m T(12.0)-T(10.7)T(3.9)-T(10.7)
• B output brightness value
• Cconstant60 (determined empirically)
• Mscaling factor10 (determined
  empirically)
• T brightness temperature at (wavelength)

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Lascar, Chile July 20, 2000 1639 UTC Three
Band Product (3.9, 10.7, 12.0 um)
? Volcanic ash
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18 N
7-hr Ash cloud
3.9/10.7/12.0 product
Montserrat gt
cirrus
low cloud
15 N
convective cloud
66 W
63 W
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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.

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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 (lt-40 C), the instrument noise at
  3.9 um becomes very large
• Uncertainties with properties of
  reflectance/emittance/transmittance of the ash
  cloud.

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Challenge of GOES-1212.0 um replaced by 13.3 um
Picture and avi loop from G. Ellrod
NOAA/NESDIS/ORA
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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 -gt H2SO4 (sulfuric acid) The
resulting ash/acid mix is highly corrosive and
can cause damage to jet engines and external
parts of the aircraft.
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Absorption by SO2
Note MODIS channels
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SO2 detection

• Greater SO2 absorption at 7.3 um
• BT 7.3 um BT 6.7 um lt 0
• Less SO2 absorption at 8.5 um
• Ash absorption at 8.5 um
• BT 8.5 um BT 12.0 um lt 0

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MODIS imagery and products for Reventador Volcano
eruption
Ash and SO2 detection
SO2 detection
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Other uses of satellite imagery for volcano
monitoring

• Hot spot detection
• Determination of cloud height with VISIBLE shadow
  technique .

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lt Popocatepetl, Mexico
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Cloud height determined from cloud shadows
22 km
Guagua Pichincha, Ecuador
16 km
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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/w
  ashington.html