Effect of Spherical Wavefront on VHF Lightning Interferometer Observations

Abstract:

VHF interferometer (INTF) observations of lightning typically assume the incident radiation to be a plane wave, based on the antenna baselines being relatively short (~100 m). However, for localized sources at close distances or with longer baselines, neglecting the spherical nature of the wavefront can produce noticeable errors in the 2-D arrival direction that affects comparing the radiation sources with other observations, such as a second INTF for obtaining 3-D observations. The errors can be significant even for sources within 5-10 km distance or more. In addition, the plane wave assumption is totally inappropriate for using a larger number of antennas with expanded baselines to obtain 3-D observations from a single INTF system. In this paper, we investigate the effect of the wavefront being spherical on conventional 2-D INTF azimuth-elevation observations, and techniques for obtaining 3-dimensional observations from expanded-baseline, multi-antenna INTF measurements.