Interferometry plays an important role in revealing fine-scale structures of ionospheric irregularity.By placing an additional receiving array of four 5-element Yagi antennas in the north of the main East-West array of the Sanya VHF radar,multiple interferometry baselines with components parallel and perpendicular to the magnetic meridian are formed.These baselines allow us to study the three-dimensional(3D)behavior of low-latitude ionospheric field-aligned irregularity(FAI)over Sanya.Using multiple non-collinear receiving baselines,an experiment for which the Sanya VHF radar operated as an interferometer was performed on 10 July 2013.Ionospheric E-region FAI echoes with periods of several minutes were observed during 0745-0915 UT;mean Doppler velocity was around -30 m/s with spectral widths of about 50 m/s.The interferometry results show fine-scale structures of E-region FAI with a zonal scale size of 15 km or less.In addition,we found that the periodic variations of echo intensity shown in radar range-time-intensity(RTI)maps were produced by spatially separated E-region irregularity patches.The patches drifted westward with a velocity of about 40-60 m/s and could be associated with propagating gravity waves.These results provide a clearer picture of the characteristics of FAI and thus help to investigate the generation and dynamics of low-latitude ionospheric irregularities in the Chinese sector.
