Ocean acoustic tomography is a method for remotely sensing deterministic and stochastic variations in the ocean sound speed field. The fundamental tomographic measurement is sound speed, and therefore tomography directly provides acoustic propagation models with this essential, first-order, environmental information. In one form or another the various sound propagation codes rely on sound speed data in either 2-, 3- or 4-dimensional form. Experiments have shown that both mean and range-varying sound speed data can be obtained using tomography, and that when appropriate assumptions are made about the known horizontal and vertical covariance structure of the ocean, these data are spatially continuous. Thus it is not necessary to choose an interpolation scheme for discrete profiles that may be mathematically sensible, but physically less meaningful. Further, since the tomographic measurement itself uses propagating acoustic waves, it affords an opportunity to obtain simultaneously selected sound propagation parameters. We discuss these and other aspects of tomographic remote sensing and its application to acoustic propagation.