Thte Advanced Meteor Orbit Radar Facility - Amor

A radar meteor facility in operation in the Southern Hemisphere has been constructed so as to provide routine measurements of the heliocentric orbits of Earth-intersecting meteoroids to a limiting size equivalent to the largest of the zodiacal dust particles (a few hundred mum). Such information pertaining to the orbital characteristics of the solar system small particle population is essential in providing a database for dynamical studies of this population, and of its origin and evolutionary processes. The features of this installation (Advanced Meteor Orbit Radar: AMOR) are compared with those of other techniques for orbit determination. The system uses a 26.2 MHZ, 20 kW pulse radar transmitter. AMOR's limiting sensitivity is equivalent to a visual meteor magnitude Of +13 corresponding to a particle radius of approximately 100 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-shaped antenna beam to constrain the echo azimuth of detected meteor trains, a 5lambda phase pair being used to determine their elevations. The velocity and radiant position are then obtained by measuring the time-lags between multiple receiver sites, these time differences being the result of the time-of-flight between points on the train at which specular reflections occur for each site. These multiple stations provide 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 provide independent velocity determinations through the Fresnel diffraction profile as the train forms, permitting the determination of meteoroid atmospheric decelerations in 5-10 per cent of cases. This is an important feature since an accurate calculation of the pre-atmospheric speed can then be made for many meteoroids and the deceleration modelled for those not displaying the Fresnel oscillations. The tasks of on-site recording of multiplexed signal channels, the data organization, and signal processing routines to extract suitable echoes in the presence 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 diffraction patterns in order to yield the meteor motion in topocentric coordinates, and thereafter the heliocentric orbit. The radar measurement uncertainties are also investigated in terms of the accuracy of the deduced orbits. Additionally, well-known streams which yield meteors of high 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 orbital 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 date; this is greater than the number determined in all previous meteoroid orbit surveys combined. Most of these orbits have been from radiants at declinations +5-degrees < delta < -30-degrees, but the transmitting antenna is now being modified so as to permit deep southern radiants to be surveyed more effectively.