1. Remote Sensing of Volcanic Ash
Royce Bohnert

2. Why is sensing of volcanic ash important?
The primary motivation is aircraft safety
Volcanic ash wreaks havoc on jet engines
The rock and glass particles are highly abrasive
High heat and pressure within the engine can melt the glass particles which then coat the surfaces inside the engine
There have been several close calls over the years. The most famous is the British Airways Flight 9 in 1982.
Nine Volcanic Ash Advisory Centers have been formed around the world to monitor volcanic Ash plumes.[1]

3. Engine damage from volcanic ash
Images from NASA

4. Dielectric properties of solid ash
One study measured the permittivity of ash from several different volcanoes in Japan. The relative permittivity was found to be fairly consistent among the samples.

5. Volcanic ash clouds on weather radar
Ash clouds are easily seen on WSR-88D weather radar when in range of one.
Image from Reference [7]

6. Common method for detecting volcanic ash
Large scale detection of volcanic ash is performed using IR satellite imagery.
The method known as “split-window”, “reverse absorption”, or BTD became the standard method for detecting volcanic ash starting in the late 1980s [3]
This method is based on the fact that the main constituents of volcanic ash (pumice, quartz) will have a higher absorption (emission) at around 11um vs 12um. Whereas, the ice and water will have the opposite behavior. This holds true for the typical particle sizes found in volcanic ash clouds. [4]

7. Image from Reference [4]
Volcanic ash clouds have high concentrations of particles in the 0.5um to 5.0um range [4].
Image from Reference [4]

8. Image from Reference [2]

9. More advanced methods of detection
The basic BTD technique has some shortcomings [3].
More advanced multi-spectral techniques have been developed which use more than 2 IR bands.
The GOES-16 satellite uses 5 different bands (7.4, 8.5, 11.2, 12.3, ad 13.3 um) to estimate ash loading, particle size, and ash cloud height.

10. Small errors in physical input parameters can have a large impact on the accuracy of ash loading estimates [9].

11. References https://www.ssd.noaa.gov/VAAC/vaac.html
A. J. Prata, I. J. Barton, R. W. Johnson, K. Kamo, & J. Kingwell. (1991). Hazard from volcanic ash. Nature, 354(6348), 25.
Prata, Fred. (1989). Radiative transfer calculations for volcanic ash clouds. Geophysical Research Letters - GEOPHYS RES LETT /GL016i011p01293.
T. Oguchi, M. Udagawa, N. Nanba, M. Maki and Y. Ishimine, "Measurements of Dielectric Constant of Volcanic Ash Erupted From Five Volcanoes in Japan," in IEEE Transactions on Geoscience and Remote Sensing, vol. 47, no. 4, pp , April 2009.
T. Steensen and P. Webley, "Qualitative analysis of input parameters for satellite-based quantification of airborne volcanic ash," 2012 IEEE International Geoscience and Remote Sensing Symposium, Munich, 2012, pp

12. Questions?