|dc.contributor.author||Clarke, Adrian Jonathan Miles||
|dc.description.abstract||A new 3D model of light scattering applicable to dielectric faceted objects is
presented. The model combines Geometric Optics with diffraction on individual
facets yet maintains the low computational expense of standard Geometric
Optics. The current implementation of the model is explained and then applied
to the problem of light scattering by ice crystals in cirrus clouds. Accurate
modelling of the scattering properties of such crystals is crucial to better understanding
of cirrus radiative properties and hence to climate modelling and
Calculations using the new model are compared to a separation of variables
method and the Improved Geometric Optics method with encouraging results.
The model shows significant improvements over standard Geometric Optics.
The size applicability of the new model is discussed.
The model is applied to a range of crystal geometries that have been observed
in cirrus including the hexagonal column, the hollow column, the droxtal and
the bullet rosette. For each geometry the phase function and degree of linear
polarization are presented and discussed.
Ice analogue crystals grown at the University of Hertfordshire have optical properties
very close to ice but are stable at room temperature. The geometries of
three ice analogue crystals are reconstructed and the single scattering properties
of the reconstructions are presented.
2D scattering patterns calculated using the model are compared to laboratory
photographs of scattering patterns on a screen created by an ice analogue hexagonal
column. The agreement is shown to be very good. By applying the model
to a range of geometries, it is shown that the results in the form of 2D scattering
patterns can potentially be used to aid particle characterization.
By combining the model with a Monte Carlo radiative transfer code, comparisons
are made with aircraft radiance measurements of cirrus provided by the
Met Office. The improvements over standard Geometric Optics are found to
persist following a radiative transfer treatment.||en_US
|dc.publisher||University of Hertfordshire||en_US
|dc.title||Modelling of light scattering by cirrus ice crystals using geometric optics combined with diffraction of facets||en_US