Proceedings with Extended Abstracts (single PDF file) - Radio ...

on the decoded raw data profiles to decrease further the peak to side-lobe levels (from -22 dBto less than -32 dB) at the expense of spreading the side-lobe contamination into moreranges. This second filter is needed in order improve the discrimination between head andtrail echoes.Once the Doppler velocity for optimum decoding is found, the raw voltages for eachof the channels are decoded and signal statistics are recorded. Then we proceed by findingthe range where the power is highest for each profile. Working with the ``peak'' signalstatistics is much faster, allowing us to test and implement robust algorithms for meteorcharacterization. We have been able to measure directly, the initial range, the range coverage,signal-to-noise ratio, radial velocities (using three methods), and duration of the meteor,radial decelerations, and azimuth of meteor trajectory. In addition, we are able to derive theabsolute velocities and decelerations, and elevation angles.3. ResultsOur observations have been mainly conducted around Leonid meteor showers since1998. However we have recently started observations at different seasons. Statistically, weare observing similar characteristics during Leonid and non-Leonid events in velocity,deceleration and altitude distributions. In Figure 3, we show examples of where meteors arecoming from during a Leonid (left) and non-Leonid (right) event. The sky maps show theprojected Ecliptic plane (solid black curve), some constellations for reference, and theEarth’s Apex (thick star) for the given time. Each meteor observed around 0700 LT arerepresented with circles. The absolute velocity is color-coded and the size is proportional tothe signal-to-noise ratio (SNR).1364. Summary and ConclusionsAs it has been shown in previous sections, we have successfully implemented atechnique to observe and characterize meteor head echoes at equatorial latitudes. The use ofthe large power-aperture capabilities at Jicamarca has allowed us to observe a high rate ofmeteors (more than 3000 per hour) in the small volume subtended by the 1 o antenna-beam.Moreover, using interferometry, we have been able to characterize the three-dimensionalcomponents of meteor velocities in the Earth's frame of reference.Our results do not show any evidence of the Leonid meteor showers, in agreement toresult reported by other large power-aperture radars. We have shown that meteor parametersduring both Leonid and non-Leonid events are statistically similar (range of occurrence,velocity distribution, deceleration distribution, origin). Apparently, we detect only the verysmall sporadic meteors, which are much more abundant than the larger meteors associated tomajor meteor showers and which seldom cross the 1 o antenna beam.Besides providing meteor-head observations at a unique frequency (50 MHz) andlocation (equatorial latitudes), our results are particularly important for the 3Dcharacterization of meteor heads. We have shown, at different seasons that the velocitydistribution of meteors respect to the Earth's frame of reference is clustered around the EarthApex, within ±18 o transverse to the Ecliptic and narrow (±8.5 o ) in heliocentric longitude inthe Ecliptic plane. A change to a solar inertial frame of reference, roughly double the widthsof these distributions, since most of the meteors have a relative velocity which is about twicethe orbital velocity of the Earth. The velocity representation in heliocentric coordinatesincluding the gravitational attraction as well as its orbital distribution will be left for a futureeffort.So far, our observations have been concentrated around sunrise time when the EEJare expected to be weak. In the future, we plan to extend our observations to other times,