Incoherent scattering is a type of scattering phenomenon in physics. The term is most commonly used when referring to the scattering of an electromagnetic wave (usually light or radio frequency) by random fluctuations in a gas of particles (most often electrons).
The most well known practical application is known as incoherent scatter radar theory, a ground-based technique for studying the Earth's ionosphere first proposed by Professor Bill Gordon in 1958. A radar beam scattering off electrons in the ionospheric plasma creates an incoherent scatter return. The distribution function of the ionospheric electrons is modified by the much slower and more massive positive ions — electron density fluctuations relate to ion temperature, mass distribution, and motion. The incoherent scatter signal allows measurement of electron density, ion temperature and electron temperatures, ion composition and plasma velocity.