Mie scattering is the way spherical particles scatter radiation that bounces off of them. The formulas used to describe the scattering of the wave of radiation work best when the particles are similar in size to the length of the wave. Water droplets in the atmosphere and healthy animal cells will both scatter electromagnetic radiation in accordance with the principles of Mie scattering.
The formulas that describe Mie scattering can be used to determine a number of different things. The size and composition of the particle can be used to predict how much radiation will be scattered and in which directions the radiation will travel. Conversely, examining the behavior of an electromagnetic wave after it comes into contact with a particle can give scientists an idea of the size and composition of the spherical particle itself.
Particles of the sizes applicable to the formulas of Mie scattering scatter light in a predictable way. The radiation is scattered all around the particle, though more of it is scattered on the side of the particle that is facing away from the source of the electromagnetic radiation. Small amounts of radiation do, however, bounce back towards the source of the radiation, and at acute angles to it.
Meteorology and biological sciences use the information gathered from Mie scattering. In meteorology, the behavior of electromagnetic waves when they bounce off of particles can help determine how dense the particulate matter in the sky is. This particulate matter can include dust, water, and pollen, as well as common pollutants, which makes it possible to assess air quality through the application of Mie scattering equations. In biology, healthy cells scatter light according to the principles of Mie scattering. Cancerous cells scatter light in a different way, which makes Mie scattering useful in diagnosing cancers that are visually similar to healthy cells.
Mie scattering was developed in the 1900s by the German physicist Gustav Mie. He developed his formulas in order to better describe the behavior of electromagnetic waves around particles that were approximately the same size in diameter as one wavelength of the radiation. Particles that are much smaller than one wavelength can be described using a set of formulas that describe Rayleigh scattering. Particles that are much larger than the wavelength of the radiation scatter light in a way that is described well by the formulas for Rayleigh-Gans-Debye scattering.