Automated UHF radar observations of meteors with aeronomic applications.

摘要

The micrometeor observations performed using the 430 MHz Arecibo Observatory radar have been crucial for the understanding of meteoric effects on the aeronomy of the upper atmosphere. Previous techniques using the Arecibo radar required manual confirmation of each event, followed by direct measurements of the parameters (i.e. altitudes, velocities and decelerations). A new periodic FFT searching algorithm, the meteor return signal detector (MRSD) has been developed and implemented, replacing previous (labor-intensive) visual verification. The MRSD shows an improvement over traditional searching routines by increasing the event detection rate by as much as 30% as well as significantly reducing the required analysis time. The new technique used to detect meteors as well as the measured parameters obtained from this method are presented.; The meteor parameters obtained from the MRSD are presented. Mass distributions are obtained from momentum considerations. Previous mass distributions have assumed a constant meteoroid mass density of 3 gm/cm3. Using statistical interpretations of the parameters obtained from the MRSD, the meteoroid mass density has been revised to a constant mass density of 1 gm/cm 3. This new mass result represents the first analysis and revision of the meteoroid mass since large aperture radars began observing meteors in the early 1990s.; In some cases meteors are observed that appear to catastrophically destruct within the beam. These meteors appear to undergo minor ablation of their volatile components before annihilation---the terminal event---that occurs in under 1 ms. As with essentially all observed meteoroids, the meteoroids that disappear in a terminal event appear to experience linear decelerations before their abrupt disappearance. This non-ablative mass deposition process may play an important role in the composition of the upper atmosphere as it apparently produces sub-micron-sized particles. The first statistical analyses of the terminal events relative to the overall meteor population are presented. Consideration is given to the terminal event destruction of meteoroids and resultant mass deposition as an important factor in the aeronomy of the meteor zone.; To better understand the process behind head-echo scattering, meteor observations at the Sondrestrom 1290 MHz incoherent scatter radar were conducted in July and August 2005, totaling approximately 30 hours of additional meteor data. The Sondrestrom radar was run in two modes to observe sporadic meteors. In the first mode, the radar beam was pointed at zenith to mimic conditions at Arecibo. In the second mode, the radar beam was pointed due east at a 60 degrees zenith angle. The second configuration was chosen as an attempt to maximize the meteor flux rate and was an observation condition not possible using the Arecibo radar. The MRSD was run on data sets from both radars. Sporadic meteor parameters from both facilities are compared, using a data set from Arecibo obtained in August 2004, while considering the resultant insights into the head-echo scattering process at 430 MHz versus 1290 MHz. A preliminary scattering model is proposed, along with its implication on meteor research at varying frequencies and latitudes. (Abstract shortened by UMI.)