The Moving Window FDTD model is based on the 2D finite-difference time-domain method. This model is used to simulated propagation of radio waves at UHF and VHF frequencies over irregular terrain. A vertical plane passing through the transmitter and receivers location defines the 2D geometry. Modeling propagation over terrain typically involves long distances. The amount of computer memory and time required to perform FDTD on the entire path is often prohibitive. Moving Window FDTD takes advantage of the fact that the radio pulse width is limited in spatial extent, and only creates computation grid wide enough to include the radio pulse. As the pulse propagates over the terrain, the computational mesh is also moved so that the pulse is always contained in the grid. This allows the method to only calculate field values in regions where the field is nonzero. Since this method solves Maxwell's equations directly, it is a full-wave model that includes all relevant physical processes associated with radio wave propagation in the 2D environment.