Environmental Engineering Reference
In-Depth Information
Figure 7.2 Backscattered electron image of volcanic ash from Eyjafjallajökull
volcano from May 2010 showing the range of different components ash can
be made up of. The greyscale level represents differing densities, with brighter
shades indicating higher density (high atomic weight), and darker shades repre-
senting lower density (low atomic weight).
sensing in the IR the most salient feature is the per cent composition of SiO
2
,
since this molecule exhibits characteristic absorption features through the range
7
m. Shape does affect the radiative transfer of light interacting with particles.
The error caused by assuming spherical particles, rather than more realistic ragged,
agglomerates with asperities, is mostly seen in the retrieval of the mass loading.
The optical regime governing how radiation interacts with a particle depends on
both the wavelength (
-
12
μ
) and particle size (
r
). Models of light scattering can be
divided into different optical regimes depending on the size of the particle relative
to the wavelength of light. To incorporate this, we describe particle size in terms
of a dimensionless number known as the size parameter (
X
).
λ
2
πr
λ
X
¼
,
ð
7
:
1
Þ
