Detection by HF radar of the Eta Aquarid meteor shower

Abstract Frequencies in the HF band below 15 MHz have in the past been little used for radar meteor research owing to the requirement for large antenna arrays and the confusion which may be presented by ionospheric echoes. However, radars employing such frequencies are potentially able to detect very many more underdense meteor echoes than are radars operating at the more conventional higher frequencies, above about 20 MHz. This occurs as a consequence of the greater limiting height for the detection of echoes at longer wavelengths which is set by the so-called underdense echo ceiling. The successful observation of the Eta Aquarid meteor shower reported below demonstrates the value of HF skywave radars operating at frequencies below 15 MHz for meteor detection. The results are consistent with the shower radiant having a diameter of about 6° centred on R.A. = 339°, Dec = 0°. If the cumulative distribution of meteoroidal particles exceeding a lower threshold mass m is described by a power law of the form N ( m ) ∼ m c , where the exponent c is assumed to equal −1.0 for sporadic meteors then, by comparison, the particles of the Eta Aquarid shower must belong to a flatter distribution with c in the range from −1.0 to −0.6.