Volcanic ash infrared signature: porous non-spherical ash particle shapes compared to homogeneous spherical ash particles
Journal article, 2014
The reverse absorption technique is often used to detect volcanic ash clouds from thermal infrared satellite measurements. From these measurements effective particle radius and mass loading may be estimated using radiative transfer modelling. The radiative transfer modelling usually assumes that the ash particles are spherical. We calculated thermal infrared optical properties of highly irregular and porous ash particles and compared these with mass-and volume-equivalent spherical models. Furthermore, brightness temperatures pertinent to satellite observing geometry were calculated for the different ash particle shapes. Non-spherical shapes and volume-equivalent spheres were found to produce a detectable ash signal for larger particle sizes than mass-equivalent spheres. The assumption of mass-equivalent spheres for ash mass loading estimates was found to underestimate mass loading compared to morphologically complex inhomogeneous ash particles. The underestimate increases with the mass loading. For an ash cloud recorded during the Eyjafjallajokull 2010 eruption, the mass-equivalent spheres underestimate the total mass of the ash cloud by approximately 30% compared to the morphologically complex inhomogeneous particles.
1988
GEOPHYSICAL RESEARCH LETTERS
RETRIEVAL
CLOUDS
ATA AJ
EXTINCTION SPECTRA
DISCRETE-DIPOLE APPROXIMATION
LIGHT-SCATTERING
1989
1973
LLACK JB
V19
APPLIED OPTICS
V16
SPACE
RADIATIVE-TRANSFER CALCULATIONS
P372
AEROSOLS
P1293
V27
GLASSES
ICARUS
AMNES K
P2502
Author
A. Kylling
Norwegian Institute for Air Research (NILU)
Michael Kahnert
Chalmers, Earth and Space Sciences, Global Environmental Measurements and Modelling
H. Lindqvist
University of Helsinki
T. Nousiainen
Finnish Meteorological Institute (FMI)
University of Helsinki
Atmospheric Measurement Techniques
1867-1381 (ISSN) 1867-8548 (eISSN)
Vol. 7 4 919-929Subject Categories
Meteorology and Atmospheric Sciences
DOI
10.5194/amt-7-919-2014