Very-low-frequency (VLF, 3-30 kHz) electromagnetic waves are prevalent in near-Earth space, and are produced by a variety of space-based and ground-based sources. Lightning and VLF transmitters launch powerful waves that propagate through the Earth's ionosphere and into the magnetosphere. Within the magnetosphere, naturally occurring and locally generated waves include chorus, hiss, and electromagnetic ion-cyclotron (EMIC) waves. Each of these whistler-mode waves propagating in the magnetospheric plasma can induce pitch-angle scattering and precipitation of trapped energetic particles (e.g. Inan & Carpenter, 1987;Imhof et al., 1983). For example, Abel and Thorne (1998) concluded that VLF waves radiated from both lightning and ground-based VLF transmitters play a significant role in maintaining the slot region of depleted fluxes between the inner and outer radiation belts. Each of these waves occurs in different regions of space, and with different amplitudes and frequencies, and therefore each affect somewhat different populations of energetic particles.The propagation of these VLF waves within the magnetosphere, as well as from the ground through the ionosphere, is complex and difficult to experimentally assess. Chorus and hiss waves, for example, are regularly measured by spacecraft such as the Van Allen Probes, but without knowledge of the source region of these waves, the propagation characteristics are difficult to characterize. Propagation characteristics such as the propagation direction, amplitude decay and/or growth, and reflections within the magnetosphere, are critical to understanding the quantitative effect these waves have on energetic particles.