ON THE UNDERWATER ACOUSTIC FIELD OF A MOVING POINT-SOURCE .2. RANGE-DEPENDENT ENVIRONMENT

In a companion paper, the theory for the evaluation of the acoustic fi eld of a moving source in range-independent environments was developed [P. H. Lim and J. M. Ozard, J. Acoust. Soc. Am. 94, 131-137 (1993)]. In the present paper, the problem of extending the calculations to sou rces moving in weakly range-dependent environments is examined. The ca lculations in both papers are valid for sources whose velocity is smal l and horizontal but otherwise arbitrary. The formalism is initially d eveloped in the context of adiabatic mode theory without mode coupling . The corresponding equations for one-dimensional range dependence are further developed and the paper concentrates on solutions in this cas e. First, the acoustic field is obtained for a point source moving in an isospeed wedge-shaped ocean. This solution reduces exactly to previ ously found fields for the special cases of a uniform waveguide and of a stationary source in the wedge ocean. In the case that both source and receiver are distant from the shore, a new solution exhibiting ref lections off the sloping ocean floor is presented. The acoustic field is valid for arbitrary but small horizontal source motions and the pre sence of reflected waves may give rise to new and interesting features in matched-field processing problems. The remainder of the paper deve lops the field of a point source moving with arbitrary velocity in an ocean that is a perturbation of a uniform waveguide. The ensuing solut ion is then a perturbation of the solution presented in the companion paper. This field is developed explicitly for a specific bathymetry. A s in the companion paper, the fields are naturally expressed in terms of retarded times. For a specific type of source motion, the acoustic field can always be recast in terms of contemporary time, and the resu lting field is then in a convenient form for implementation.