Mechanism of spot dancing

The mechanism of spot dancing is clarified by the application of wave theory in a random medium. The solution is based on the moment equation which prescribes the statistical properties of waves scattered successively in the forward direction. Spot dancing is described by the use of wave function; the relation between the spot dancing and the random medium becomes clear. Spot dancing is a limited phenomenon in wave motions. The distribution of arrival position is normal along the two-dimensional Cartesian coordinates, and the variance is uniquely determined by the correlation function of the medium and the propagation length of the wave. In addition, the Rice-Nakagami distribution of irradiance can be physically interpreted as the log-irradiance distribution in the spot dancing of a Gaussian wave beam.