THE ADVANCED METEOR ORBIT RADAR FACILITY - AMOR

A radar meteor facility in operation in the Southern Hemisphere has be en constructed so as to provide routine measurements of the heliocentr ic orbits of Earth-intersecting meteoroids to a limiting size equivale nt to the largest of the zodiacal dust particles (a few hundred mum). Such information pertaining to the orbital characteristics of the sola r system small particle population is essential in providing a databas e for dynamical studies of this population, and of its origin and evol utionary processes. The features of this installation (Advanced Meteor Orbit Radar: AMOR) are compared with those of other techniques for or bit determination. The system uses a 26.2 MHZ, 20 kW pulse radar trans mitter. AMOR's limiting sensitivity is equivalent to a visual meteor m agnitude Of +13 corresponding to a particle radius of approximately 10 0 mum, or a mass of approximately 1 mug. In contrast to previous orbit radars the system employs a narrow (width 3.2-degrees to 3 dB) fan-sh aped antenna beam to constrain the echo azimuth of detected meteor tra ins, a 5lambda phase pair being used to determine their elevations. Th e velocity and radiant position are then obtained by measuring the tim e-lags between multiple receiver sites, these time differences being t he result of the time-of-flight between points on the train at which s pecular reflections occur for each site. These multiple stations provi de an 8 km baseline and are linked via FM telemetry. In addition, for a proportion of the meteors the echoes at one or more of the sites pro vide independent velocity determinations through the Fresnel diffracti on profile as the train forms, permitting the determination of meteoro id atmospheric decelerations in 5-10 per cent of cases. This is an imp ortant feature since an accurate calculation of the pre-atmospheric sp eed can then be made for many meteoroids and the deceleration modelled for those not displaying the Fresnel oscillations. The tasks of on-si te recording of multiplexed signal channels, the data organization, an d signal processing routines to extract suitable echoes in the presenc e of noise, are facilitated by the use of high-level software language operation on PCs. Data processing provides multiple echo analysis and the extraction of velocity and deceleration information from diffract ion patterns in order to yield the meteor motion in topocentric coordi nates, and thereafter the heliocentric orbit. The radar measurement un certainties are also investigated in terms of the accuracy of the dedu ced orbits. Additionally, well-known streams which yield meteors of hi gh atmospheric velocity provide a stringent astronomical test of AMOR' s overall performance. The data handling capacity of AMOR permits the recording, the orbit reduction and the efficient presentation of orbit al data using graphical packages to be carried out on a routine basis. The daily Yield is approximately 1500 with > 2 X 10(5) secured to dat e; this is greater than the number determined in all previous meteoroi d orbit surveys combined. Most of these orbits have been from radiants at declinations +5-degrees < delta < -30-degrees, but the transmittin g antenna is now being modified so as to permit deep southern radiants to be surveyed more effectively.