When the finite-difference time-domain (FDTD) method is applied to light scattering
computations, the far fields can be obtained by either a volume integration method,
or a surface integration method. In the first study, we investigate the errors associated
with the two near-to-far field transform methods. For a scatterer with a small
refractive index, the surface approach is more accurate than its volume counterpart
for computing the phase functions and extinction efficiencies; however, the volume
integral approach is more accurate for computing other scattering matrix elements. If
a large refractive index is involved, the results computed from the volume integration
method become less accurate, whereas the surface method still retains the same order
of accuracy as in the situation of a small refractive index.
In my second study, a fourth order symplectic FDTD method is applied to the
problem of light scattering by small particles. The total-field/ scattered-field (TF/SF)
technique is generalized for providing the incident wave source conditions in the symplectic
FDTD (SFDTD) scheme. Numerical examples demonstrate that the fourthorder
symplectic FDTD scheme substantially improves the precision of the near field
calculation. The major shortcoming of the fourth-order SFDTD scheme is that it
requires more computer CPU time than the conventional second-order FDTD scheme if the same grid size is used.
My third study is on multiple scattering theory. We develop a 3D Monte Carlo
code for the solving vector radiative transfer equation, which is the equation governing
the radiation field in a multiple scattering medium. The impulse-response relation for
a plane-parallel scattering medium is studied using our 3D Monte Carlo code. For a
collimated light beam source, the angular radiance distribution has a dark region as
the detector moves away from the incident point. The dark region is gradually filled
as multiple scattering increases. We have also studied the effects of the finite size of
clouds. Extending the finite size of clouds to infinite layers leads to underestimating
the reflected radiance in the multiple scattering region, especially for scattering angles
around 90 degrees. The results have important applications in the field of remote sensing.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/ETD-TAMU-1839 |
| Date | 02 June 2009 |
| Creators | Zhai, Pengwang |
| Contributors | Kattawar, George W., Yang, Ping |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | Book, Thesis, Electronic Dissertation, text |
| Format | electronic, application/pdf, born digital |
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