Simultaneous meteor echo observations by large-aperture VHF and UHF radars

We report simultaneous meteor echo observations using the Arecibo 430-MHz and 46.8-MHz radars. Using identical data-taking and meteor selection criteria, 1868 and 367 meteors were found in the 430-MHz and 46.8-MHz beams, respectively, while 145 were found in both beams during the 7 hours of observation. Of the 367 VHF echoes, there were only 10 trail echoes, while the rest were head echoes, which was quite contrary to expectation. The smaller number of meteors detected by the VHF system and its wider beam width show that UHF meteors are far smaller than the VHF meteors. We estimate that VHF head echoes have a typical effective scattering cross section of the order of 10^-3 m², while the accompanying UHF echoes have an effective scattering cross section of the order of 10^-6 m². The paucity of VHF trail echoes observed leads us to suggest that the ratio of head echo power to the trail echo power increases with decreasing meteor size. When a meteor is too small, a radar can observe the head echo but not the trail echo. Of the 145 meteors observed by both radars, the powers received by the two systems were not correlated. Although antenna beam pattern contributes to the lack of correlation, it is also possible that UHF and VHF echoes may be enhanced by different scattering mechanisms.