The technique was formally introduced by Farley and co-workers in 1981 [ Farley et al., 1981 ] to study plasma turbulence in the ionosphere and was an extension of a method describe by Woodman  who showed that a radar interferometer could accurately determine the position of a highly localized scattering region. The cross spectrum of the backscattered signals received from approximately overhead on two antennas is formed, separated in the case of field aligned irregularities at Jicamarca along an east-west baseline, as well as the individual power spectra. From the phase of the cross spectrum at different Doppler frequencies it can be determined the individual positions of plasma wave packets propagating vertically with different velocities. By using the irregularity patches as tracers and following their east-west motion, we can obtain a vertical profile of drift velocity. This approach has proven to be useful in the study of E [e.g., Kudeki et al., 1982 , Hysell et al., 1997 ] and F [e.g., Kudeki et al., 1981 , Hysell and Burcham, 1998 ] region irregularities. Below is an example of F region zonal drifts obtained in this operational mode.