Ice/Water Coatings: Rabaul Caldera Example
This is an example of an atypical volcanic cloud in which the spectral
signiture is dominated by ice, instead of silicates.
Additonal information on the eruption can be found on the
Michigan Tech Volcanoes Page.
For more information of the satellite observations of this eruption:
Rose, W. I., D. J. Delene, D. J. Schneider, G. J. S. Bluth, A.
J. Krueger, I. Sprod, C. McKee, H. L. Davies and G. G. J. Ernst,
1995, Ice in the 1994 Rabaul eruption cloud: implications for
volcano hazard and atmospheric effects, Nature, 375: 477-479.
The images below (left and middle) are photographs from Space
Shuttle Mission STS064, of the Rabaul eruption cloud. Notice that the
cloud is bright white, which is not a typical for a cloud dominated by
volcanic ash. Compare those images with the one below (right). A typical ash cloud from the October, 1994
eruption of Klyuchevskoi, Russia.
September 19, 1994 at 0900 Z
The band 4 image shows a spectacular cloud from the eruption of Rabaul
Caldera, spreading for hundreds of kilometers to the west of the active
vents. This cloud is unique in our experience, in that it does not have the
characteristic negitive band 4-5 values associated with volcanic clouds. The
band 4-5 image shows the inverse in fact, a cloud marked by large positive
values.
AVHRR Band 4 image (left) and Band 4-5 image (right).
Radiannet Plot
Since the volcano erupted from a vent that was very near the ocean,
it was thought that perhaps the cloud had incorporated large amounts of water
which encased the silicates, thereby masking their signature. This was
tested using Radiannet, by substituting the refractive index of ice, for that
of silcate. Due to the fact that the cloud could not be discriminated via
its spectral signature, the outline of the cloud was digitized and the values
for the cloud extracted. The image below shows the Radius-Optical depth
plot for the image shown above. The red dots are the actual AVHRR pixel values
for the cloud, the solid lines are theoretical effective radius values and
the dashed lines are theoretical optical depth values.
Input parameters and output values
Execution Date . . . . . . Fri Mar 24 15:45:45 EST 1995
Input Data File Name . . . n12.94262.0859.ascii
Plot Title . . . . . . . . Rabaul Volcanic Cloud
Plot Sub Title . . . . . . NOAA-12 9/19/1994 0900 UTC
Theoretical Particle Size Distribution . . . . Lognormal
The Scale of the Mass Retrieval . . . . . . . . Frame Scale Retrieval
Reflective Index Material . . . . . . . . . . . Ice
Minimum Effective Radius (um) . . . . . . . . . . . . . 3.00000
Maximum Effective Radius (um) . . . . . . . . . . . . . 30.00000
Cloud-Top Temperature (k) . . . . . . . . . . . . . . . 192.00000
Cloud-Base Temperature (k) . . . . . . . . . . . . . . 297.00000
X Image Dimension . . . . . . . . . . . . . . . . . . . 23143.00000
Y Image Dimension . . . . . . . . . . . . . . . . . . . 1.00000
Pixel Area (km^2) . . . . . . . . . . . . . . . . . . . 16.00000
Delta X . . . . . . . . . . . . . . . . . . . . . . . . 0.10000
Band4 - Band5 Cutoff Value . . . . . . . . . . . . . . 100.00000
Number of Horizontal Lines . . . . . . . . . . . . . . 30.00000
Number of Radii Lines . . . . . . . . . . . . . . . . 55.00000
Total Pixel Units . . . . . . . . . . . . . . . . . . . 23143.00000
Mean Effective Radius (um) . . . . . . . . . . . . . . 15.36620
Mean Optical Depth . . . . . . . . . . . . . . . . . . 0.68000
Mean Pixel Mass (MT) . . . . . . . . . . . . . . . . . 126.09600
Total Cloud Mass (MT) . . . . . . . . . . . . . . . . . 2918240.00000
Map of Ice Mass Retrieval
The following image is a map of the ice mass retrieval using the parameters
shown above.
This page maintained by Dave Schneider (djschnei@mtu.edu)
