Observability of the scattering cross-section through phase decoherence

We derive the stochastic dynamics for scattering of a wavelike field from a large population of scatterers whose dynamics is arbitrary. This leads to a result concerning the observability of the scattering cross section in terms of the resultant phase fluctuations that is independent of the population dynamics. An emergent concept is a certain notion of an ideal filter. The diffusion based model of K-scattering arises as a special case. The experimental implications of the results in a variety of contexts are discussed.