AN AMBIGUITY-FUNCTION-BASED METHOD FOR ANALYSIS OF DOPPLER DECOMPRESSED RADAR SIGNALS APPLIED TO EISCAT MEASUREMENTS OF OBLIQUE UHF-VHF METEOR ECHOES

Binary phase modulation using Barker codes as the modulating sequences is often used as a pulse compression technique in incoherent scatter radar measurements of the ionospheric E region. Demodulation of the co mpressed signal is usually accomplished by matched filtering technique s. If the target has appreciable velocity, the resulting Doppler shift detunes the scattered signal relative to the filter, and the target r esponse spreads over a large range interval. The paper describes the d evelopment of a new data analysis method, based on an ambiguity functi on description of radar total-power measurements, which uses the chara cteristic Doppler decompression signatures to identify, extract, and a nalyze high-velocity events from conventional Barker-coded power profi le type incoherent scatter (IS) measurements. Data sets recorded with the European Incoherent Scatter UHF (931 MHz) and VHF (224 MHz) radars during the 1990-1991 Geminid and 1993 Perseid showers are shown to co ntain many events which are associated with individual meteors crossin g the radar beams over a wide range of aspect angles, including a few near-radial cases. Line-of-sight velocities and effective cross sectio ns are derived for some of the best dual radar events. The cross secti ons are very small and increase with decreasing wavelength, something not observed before. It is suggested that this is indicative of a scat tering mechanism different from the one operating at near-normal incid ence at VHF, and Rayleigh scatter from compact ''balls'' of plasma con tained within the meteor coma is proposed as a possible candidate, in qualitative agreement with the observations. Finally, some signal-proc essing related aspects of the method are discussed. It is shown that m ost IS radars should be able to apply it to their existing programs wi th very little effort and without having to compromise the performance in normal E region applications. The method could therefore become a powerful tool for studies of meteor statistics at UHF frequencies.