Science is built up with facts, as a house is with stones. But a collection of facts is no more a science than a heap of stones is a house.
— Henri Poincare (1854-1912)
The preceding chapters have explored frequency-dependent phenomena related to acquisition (vibroseis harmonics) and wave propagation (shallow-water waveguide, layer-induced anisotropy, and attenuation) that would be seen and dealt with on prestack data. Data processing ideally will remove or correct for those phenomena and will be unseen by the interpreter. However, dispersion (in our broad meaning) remains in the poststack realm of the final imaged data. In the sections below, we consider the frequency behavior of thin-bed response set up by two neighboring reflections, the more general interference from many reflections, and finally the special case of reflection from a gradational boundary.