The precursor theory of an electromagnetic wavetrain propagating through a dispersive medium is briefly reviewed. The few successful experimental determinations of these precursors, which have been reported in the literature, are limited to transients in waveguides. The determination of precursors in the optical frequency range appears to be achievable in the laboratory. However, in the geodetic context of long wavepaths through the troposphere the utilisation of precursors for measuring distances and directions free of atmospheric effects is judged as not feasible at the present time.
On precursors of electromagnetic wave propagation
