Teoria De Mie

Introduction to Mie scattering
Single wavelength (monochromatic light)
The Mie algorithm models all of the "traditional" scattering processes caused by a spherical drop of water, such as externalreflection, multiple internal reflections, transmission and surface waves.
The MiePlot program can produce graphs of the intensity of scattered light as a function of scattering angle, where 0°implies forward-scattering (i.e. in the original direction) and 180° implies back-scattering (i.e. back towards the source of the light).
 
|[pic]|
|Fig. 1    MiePlot calculation of intensity for unpolarised red light (wavelength = 0.65 µm, refractive index = |
|1.33257) for waterdrops of radius 0.1, 1, 10, 100 and 1000 µm |


Classical geometrical optics (as described by Descartes and Newton) show that the primary rainbow isdue to light which has been reflected once within a raindrop, whereas the secondary rainbow is due to light suffering two internal reflections.  Geometrical optics indicates that these rainbow anglesare defined solely by the refractive index of water. For a wavelength of 0.65 µm, the refractive index of water is 1.33257 which implies rainbow angles of 137.8° and 129.4°.  However, Fig. 1 showsthat the appearance of rainbows depends on the size of the raindrop and that the rainbow angles are not well defined for small drops.
The maxima between 170° and 180° for r = 10 µm produce the glory orcircular rings around the anti-solar point (i.e. around the shadow of your head - or more frequently around the shadow of an aircraft as shown here).  Similarly, the individual maxima at angles below10° produce circular rings (corona) often seen around a cloud-covered moon.
Although scattering of light by an homogeneous sphere may seem to be a simple process, the graphs of Mie scattering are...