Altitude ranges for which the S/N is at detectable levels for the Arecibo (panel a), PFISR (panel b) and MU (panel c) radars for the case of a meteoroid of mass 5 μg entering the atmosphere at 40° zenith angle with a velocity of 56 km s−1. The black line represents the altitude profile of the electron number density (m−1) predicted by CABMOD. The meteor will be detected by the radar only if it enters the radar beam at altitudes within the respective ranges. For this example, the Arecibo radar has a more extended range, which includes the ablation of alkalis such as Na and K (∼112–118 km) as well as the main constituents such as Si, Mg, and Fe; the other two radars can detect the meteor only during the ablation of the main constituents. Radar beam cross sections include the first sidelobes. Horizontal distances are estimated at 100 km altitude.