An ambiguity‐function‐based method for analysis of Doppler decompressed radar signals applied to EISCAT measurements of oblique UHF‐VHF meteor echoes

Abstract

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 compressed signal is usually accomplished by matched filtering techniques. If the target has appreciable velocity, the resulting Doppler shift detunes the scattered signal relative to the filter, and the target response spreads over a large range interval. The paper describes the development of a new data analysis method, based on an ambiguity function description of radar total‐power measurements, which uses the characteristic Doppler decompression signatures to identify, extract, and analyze high‐velocity events from conventional Barker‐coded power profile 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 contain many events which are associated with individual meteors crossing the radar beams over a wide range of aspect angles, including a few near‐radial cases. Line‐of‐sight velocities and effective cross sections are derived for some of the best dual radar events. The cross sections are very small and increase with decreasing wavelength, something not observed before. It is suggested that this is indicative of a scattering mechanism different from the one operating at near‐normal incidence at VHF, and Rayleigh scatter from compact “balls” of plasma contained within the meteor coma is proposed as a possible candidate, in qualitative agreement with the observations. Finally, some signal‐processing related aspects of the method are discussed. It is shown that most IS radars should be able to apply it to their existing programs with 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.

Meteor fluxes and visual magnitudes from EISCAT radar event rates: a comparison with cross-section based magnitude estimates and optical data

“…However, as the Doppler shift increases, less and less of the signal power eventually falls within the ®lter. This e ect is described in detail in the Appendix of Wannberg et al (1996), and shown in their Fig. A2.…”

“…There are always spread over 25 gates, and they can by no means represent any physical ionization distributions in the ionosphere. In Wannberg et al (1996) we have shown that the forms are consequences of the Barker-coding of the radar pulses. The ambiguity function of the used 13 baud Barker code spreads over 2´13 A 1 = 25 gates.…”

“…This is most often also ful®lled for the EISCAT UHF radar, while the data from the VHF system are generally more noisy (see Fig. 10 in Wannberg et al, 1996). The event of Fig.…”

“…Many more events were observed at VHF than at UHF, but this is probably mostly due to the much wider ®eld of view of the VHF antenna. Even after accounting for this, it is di cult to estimate the normalized meteor rates, as there is also the scattering cross-section frequency dependence we have reported in Wannberg et al (1996) due to the scattering mechanism at these frequencies. The average hourly rates over all our measurements on the UHF radar are bout 8 and on the VHF radar about 65 meteor head echoes.…”

“…This ®eld of use of incoherent scatter radars then lay dormant for years, but has recently been revitalized. Since 1994, measurements have been performed at the Jicamarca, EISCAT and Arecibo incoherent scatter radars (ISR) and numerous papers have been published (Chapin and Kudeki, 1994;Wannberg, 1994, 1996;Zhou et al, 1995;Wannberg et al, 1996;Malnes et al, 1996;Mathews et al, 1997;Zhou and Kelley, 1997). Earlier studies comparing visual and in that case meteor radar observations on meteor head echoes have been done by Jones and Webster (1991).…”