Simultaneous Optical and Meteor Head Echo measurements using the Middle Atmosphere Alomar Radar System (MAARSY): Data collection and preliminary analysis

TL;DR

This study presents initial findings from a two-year campaign combining optical and radar observations of meteors, revealing detailed correlations between radar cross-section, brightness, and speed, and highlighting the advantages of simultaneous multi-instrument measurements.

Contribution

It introduces a novel simultaneous optical-radar measurement approach for meteors, providing new insights into meteoroid detection thresholds, RCS behavior, and fragmentation effects.

Findings

MAARSY detects over 98% of head echoes not seen optically.

Radar cross-section (RCS) correlates with meteor brightness and speed.

RCS varies with height and shows a weaker dependence on velocity than expected.

Abstract

The initial results of a two year simultaneous optical-radar meteor campaign are described. Analysis of 105 double-station optical meteors having plane of sky intersection angles greater than 5 degrees and trail lengths in excess of 2 km also detected by the Middle Atmosphere Alomar Radar System (MAARSY) as head echoes was performed. These events show a median deviation in radiants between radar and optical determinations of 1.5 degrees, with 1/3 of events having radiant agreement to less than one degree. MAARSY tends to record average speeds roughly 0.5 km/s and 1.3 km higher than optical records, in part due to the higher sensitivity of MAARSY as compared to the optical instruments. More than 98% of all head echoes are not detected with the optical system. Using this non-detection ratio and the known limiting sensitivity of the cameras, we estimate that the limiting meteoroid detection mass of MAARSY is in the 10-9 kg to 10-10 kg (astronomical limiting meteor magnitudes of +11 to +12) appropriate to speeds from 30-60 km/s. There is a clear trend of higher peak RCS for brighter meteors between 35 and -30 dBsm. For meteors with similar magnitudes, the MAARSY head echo radar cross-section is larger at higher speeds. Brighter meteors at fixed heights and similar speeds have consistently, on average, larger RCS values, in accordance with established scattering theory. However, our data show RCS ~ v/2, much weaker than the normally assumed RCS ~ v^3, a consequence of our requiring head echoes to also be detectable optically. Most events show a smooth variation of RCS with height broadly following the light production behavior. A significant minority of meteors show large variations in RCS relative to the optical light curve over common height intervals, reflecting fragmentation or possibly differential ablation.