Slant stacking is used to transform an observed record section Φ(x,t) into its plane wave decomposition Ψ(p,τ). The invertible transformation untangles travel time triplications and removes focusing and defocusing effects, yielding signals with the plane wave amplitudes and phases. The principal arrival, composed of refraction and wide angle reflections, appears in these coordinates as a display of the intercept time function τ(p), which may be inverted by any of several currently popular methods. The transformation into the (p,τ) domain; is an objective procedure which removes many of the interpreter's difficulties by casting the picking process into much simpler variables. Moreover, the decomposition into plane waves directly yields the transient reflectivity matrix of the (one dimensional) medium. Several lines of argument lead us to conclude that the comparison of data and synthetic data should be done in the (p,τ) domain. The use of these techniques requires that the wave field be sampled with sufficient spatial density of receivers to avoid wave number aliasing. We show examples of plane wave decomposition for shallow data from the COCORP deep crustal reflection pr