QC 351 A7 no. 19 / ABSTRACT The classical properties of an image formed by an optical system looking through a turbulent medium are scintillation, agitation, and blur. A simple but adequate statistical model is obtained describing the pupil function in the presence of random wavefront disturbances in both amplitude and phase. A measure of scintillation is then obtained in the form of a normalized, weighted integral in frequency space containing all the pertinent properties of the optical system. A similar measure of agitation is then developed, and finally a description of the blur is obtained in the form of an equivalent transfer function for the turbulent medium in which the contribution from amplitude variations and the contribution from phase variations are independent.