Volcanic Ash /Aerosol and Dust

Dr. Bernadette Connell

CIRA/CSU/RAMMT

December 2003

They have similar composition.

They provide another perspective on characteristics of clouds which can be detected by image channel combinations.

What do Volcanic Ash and Dust have in common?

Introduction1) Detection of Volcanic Ash for aviation

hazards - background2) Techniques for ash/aerosol, and dust

detectionMulti-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) Examples4) Limitations5) 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-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

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?

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 GOES-8 Infrared (10.7 um)

ash cloud

Lascar, Chile July 20, 2000 1639 UTC Split Window (12.0 – 10.7 um)

positive differencesnegative differences

ash cloud – positive differences

ice cloud – negative 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

Lascar, Chile Volcanic

ash

July 20, 2000 16:39 UTC

Reflectivity Product

Blowing dust

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

GOES-8 IR2 (3.9 um)

15 N

18 N

63 W

66 W

7-hr Ash cloud

low cloud

convective cloud

cirrus

Montserrat >

At night

10.7 - 12.0 um Product

T(3.9um)-T(10.7um)7-hr Ash cloud

18 N

low cloud

convective cloud

cirrus

15 N

63 W66 W

Montserrat >

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

3.9/10.7/12.0 product7-hr Ash cloud

18 N

low cloud

convective cloud

cirrus

15 N

63 W66 W

Montserrat >

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

SO2 detectionAsh and SO2 detection

3.54.0

4.55.0

5.56.0

6.57.0

7.58.0

8.59.0

9.510.0

10.511.0

11.512.0

12.513.0

13.514.0

14.515.0

15.5

Wavelength (micrometers)

200

220

240

260

280

300

Brigh

tness

Tem

pe

ratu

re (

K)

AIRS Aqua data

Volcano Reventador: 4 November 2002Volcano Etna: 22 October 2002Volcano Etna: 22 October 2002

Other uses of satellite imagery for volcano monitoring

• Hot spot detection

• Determination of cloud height with VISIBLE shadow technique .

< Popocatepetl, Mexico

Guagua Pichincha, Ecuador

22 km

16 km

Cloud height determined from cloud shadows

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