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[Programme]
Session 6: "Classical Radar
Observations of Meteors"
Date: Wednesday
10.30-12.00
Features of the Enhanced AMOR: The Advanced
Meteor Orbit Radar
W.J. Baggaley (Department of Physics and
Astronomy, University of Canterbury, Christchurch,
New Zealand)
AMOR is a continuously operating radar facility
for measuring the heliocentric orbits and
atmospheric parameters of Earth-impacting grains
down to sizes of 40 micrometres. The facilty
provides a data base of the order of 10^6 orbits.
Recent extensions to the facility including
augmented antenna arrays and increased velocity
resolution are providing an enhanced system
capability. 6.1
Radar-meteor Velocity Determination
J. Jones, K. Ellis and M. Campbell.
(Department of Physics and Astronomy, University of
Western Ontario, London, ON, N6A 3K7 Canada)
Meteoroid velocities are essential for the
calculation of orbits. Most methods for measuring
radar-meteor velocities require high
signal-to-noise ratios and the question arises
whether the process of selecting those meteor
echoes suitable for velocity determination
introduces bias. For example, are fragmenting
meteors discriminated against because their Fresnel
oscillations are "washed out"? In this paper we
have examined the time-honored "rise-time" method
and tried to push it to its limit. Model
calculation indicated that an accuracy of 5% should
be attainable for signal-to-noise rations of 20 dB.
Simultaneous measurements using identical radars
operating at 29 MHz and 38 MHz yield an accuracy of
about 13% for echoes with signal-to-noise ratios
> 6dB. The method allows a velocity
determination for every echo. 6.2
Results of Foward-Scatter Radio
Observations
Masayoshi Ueda (Nippon Meteor Society)
and Kimio Maegawa (Fukui National College of
Technology)
Our radio meteor observation uses its own 50W
continuous wave beacon on 53.750MHz in 6m amateur
band with a broad directivity antenna. The location
of transmitter is Fukui, Japan (Longitude 136.18
degrees E, Lattitude +35.93 degrees N). The
location of receiver is Osaka, Japan (Longitude
135.64 degrees E, Lattitude +34.53 degrees N).
Though the distance between Fukui and Osaka is
about 200km, we could detect about 1,500 meteor
echoes in no shower day. We report the mean daily
variation of meteor rates and The mean annual
variation of meteor rates. PSB-1
Interferometric Radar Observations at Widely
Separated Locations
A.R. Webster, J. Jones, K.J. Ellis and M
Campbell (The University of Western Ontario,
London, Canada), M.A. Abdu, P Batista and B.
Clemesha (Instituto Nacional de Pesquisas Espaciais
Sao Paulo, Brazil)
Back-scatter radars have been operated
simultaneously and on a continuous basis at
Tavistock, near London Canada and near Sao Paulo,
Brazil. Each system consists of five separate
receiving antennas arranged as two orthogonal
3-element arrays that allows the unambiguous
determination of the direction in space of the
meteor echo relative to the station location. The
antennas used are two-element Yagi type with
horizontal elements and pointed vertically upwards
to give all round coverage. Aside from the
operating frequency, 29.3MHz in Canada and 35.2MHz
in Brazil, the systems are identical. Results from
these operations during the time of the 1999
Geminids are presented illustrating the
similarities and differences arising from the
significantly different site coordinates. 6.3
Observations of the Structure of Meteor
Trails at Radio Wavelengths Using Fresnel
Holography
W.G. Elford (Department of Physics and
Mathematical Physics, University of Adelaide,
Adelaide 5005, Australia)
Radar observations of a meteor trail are the
temporal variations in the amplitude and phase of
the scattered radio signal usually recorded at one
site. During the formation of the trail in the
radar beam the recorded received signal can be
considered as a one-dimensional diffraction pattern
produced by a moving source. This diffraction data
contains information on the structure of the trail
that can be revealed by an appropriate Fresnel
Transform. An analytical technique for carrying out
this transform of meteor radar data will be
described and examples given of the outcomes for a
range of typical diffraction data. Inherent in the
outcomes are refinements in the value of the speed
of the meteoroid, the presence of multiple sources
(presumed due to fragmentation) and a measure of
the lateral motion of the trail during formation
due to wind drift. 6.5
Effects of Meteoroid Fragmentation on Radar
Observations of Meteor Trails
W.G. Elford and L. Campbell (Department
of Physics and Mathematical Physics, University of
Adelaide, Adelaide 5005, Australia)
The majority of radar echoes from meteor trails
do not show the Fresnel diffraction oscillations
expected to occur just after the ablating meteoroid
passes the point on the trail where the orthogonal
from the radar station intersects the trail. For 50
years this has been attributed to fragmentation of
the meteoroid prior to or during the ablation
phase. However, direct evidence of fragmentation
from radar studies has been almost non-existent.
Recently, a breakthrough has occurred on two
fronts, (a) observations of amplitude oscillations
in down the beam meteor echoes, and (b) deduction
of the structure of meteor trails using radio
holography. In this paper plausible models to
explain the new observations will be presented and
applied to the question of the degree of
fragmentation required to explain the paucity of
Fresnel diffraction oscillations. Also, other new
evidence of fragmentation will be presented.
PSB-2
Radar Meteor Observations at 2 MHz
S. I. Grant and W.G. Elford (Department
of Physics and Mathematical Physics, University of
Adelaide, Adelaide 5005, Australia)
The Buckland Park MF radar ( 34 S, 138 N ),
located near Adelaide, Australia has been used for
night time meteor observations. Distributions of
meteor heights and incoming speeds have been
determined from observations over selected periods
during 1999 and 2000. Most radar meteor
observations are conducted using VHF radars, with
the wavelength-dependent meteor echo ceiling
limiting observation to heights below about 110 km.
In contrast MF radars have the potential to make
observations to heights exceeding 140 km, and hence
provide information on any high altitude component
that contributes to the meteor true height
distribution. A significant limiting factor
affecting such observations is the presence and
strength of the night time E-region. PSB-3
TV and Radar Observation of Meteors
Petr Pecina, Pavel Koten and Rosta Stork
(Petr Pridal Astronomical Institute, Academy of
Sciences, Ondrejov Observatory, 251 65 Ondrejov,
Czech Republic)
The identification of simultaneously observed TV
and radar meteors is usually based on time
coincidence of both events. The derivation of the
range the TV data yields for the radar one in case
when the radar station does not coincide with any
TV station, is presented. Since also the height of
meteor is important quantity we performed the
derivation of formulae providing us with the height
of the radar reflection point in case when only one
TV station observation accompanied by the radar one
was made. PSB-4
Relation between the Optical and Radar
Characteristics of Meteors
Petr Pecina, Pavel Koten, Rosta Stork
(Petr Pridal Astronomical Institute, Academy of
Sciences, Ondrejov Observatory 251 65 Ondrejov,
Czech Republic)
Some results on simultaneous TV double station
and radar observations of meteors performed in the
Czech Republic in 1998 and 1999 are presented. The
relation of the magnitude of each TV meteor, in the
height corresponding to the radar reflection point,
to the radar amplitude or the duration of the echo,
is studied. 6.4
The Detection of the Motion of Radio Meteor
Reflection Point of Geminids by HRO
Kouji Ohnishi (Nagano National College of
Technology,Japan), Toshiyuki Ishikawa, Shinobu
Hattori, Osamu Nishimura, Akiko Miyazawa, Masatoshi
Yanagisawa, Makoto Endo, Masaki Kawamura, Toshiyuki
Maruyama, Kai Hosayama, Mai Tokunaga, Yoshie Aoki,
Yukiko Iijima, Aya Kobayashi (Nagano National
College of Technology, Japan), Kimio Maegawa (Fukui
National College of Technology) and Shinsuke
Abe, The Institute of Space and Astronautical
Science, Japan
Ham-band Radio Observation (HRO) is one of the
observational techniques of the forward scatter
observation of meteors. We observe the meteor echo
with two-element loop antennas (F/B ratio is 10 dB)
at the Nagano National College of Technology
(Nagano, JAPAN) using the continuous transmission
of beacon signals for meteor observations at
53.750MHz, 50W from Fukui National College of
Technology (Sabae, Fukui, JAPAN). To prove that the
radio echo is really the echo due to meteor, we
construct the Directional Determination System
using the paired antennas that can detect the
direction roughly where the radio echo come from.
The direction of one of this paired antennas was
West toward Sabae and the other was East which has
proved to be the most sensitive for this research.
Using this system, we detected the change of the
direction of reflection point of meteor radio
signal of Geminids in 2000; from the westward to
eastward before and after the culmination of the
radiant which is consistent the formula of
reflection point of meteors. At the same time, we
detected the change of a trend of the Doppler shift
of meteor echos. This result is consistent of the
meteor wind data of MU Rader of Radio Science
Center for Space & Atmosphere (RASC), Kyoto
University. PSB-5
The Earth Rotation and Revolution Effect of
the Daily and Annual Variation of Sporadic Meteor
Echo by HRO
Kouji Ohnishi (Nagano National College of
Technology ,Japan), Shinobu Hattori, Osamu
Nishimura, Toshiyuki Ishikawa, Akiko Miyazawa,
Masatoshi Yanagisawa, Makoto Endo, Masaki Kawamura,
Toshiyuki Maruyama, Kai Hosayama, Mai Tokunaga,
Yoshie Aoki, Yukiko Iijima, Aya Kobayashi (Nagano
National College of Technology, Japan), Kimio
Maegawa (Fukui National College of Technology,
Japan) and Shinsuke Abe (The Institute of
Space and Astronautical Science, Japan)
Ham-band Radio Observation (HRO) is one of the
observational techniques of the forward scatter
observation of meteors. We started the observation
of the daily and annual variation of sporadic
meteor echo with paired two-element loop antennas
(F/B ratio is 10 dB) at the Nagano National College
of Technology (Nagano, JAPAN) using the beacon
signals at 53.750MHz, 50W
>from Fukui National College of Technology
(Sabae, Fukui, JAPAN) from Aug.2000. The direction
of one of this paired antenna was West toward Sabae
and the other was East. This system could be
roughly detected the direction of the radio echos.
Using this system, we observe the daily variation
of sporadic meteor echos; the echo rose from
midnight with the peak coming at about 6 a.m. and
decreasing to the noon, the peak echos were
observed from the West antennas at 4 a.m. and the
peak from East antenna was at 10 a.m. This daily
variation is interpreted as the effect of the Earth
rotation and revolution around the sun. At the
conference, we will also discuss the annual
variation of sporadic meteor echos. PSB-6
The New Meteorite Radar of the Sodankylä
Geophysical Observatory
Thomas Ulich (1), Markku Lehtinen (1),
Antero Väänänen (1),
JuhaPirttilä 2), Markku Markkanen (1) and
Jyrki Rahkola(2)
1) Sodankylä Geophysical Observatory,
Sodankylä, Finland; 2) Invers Ltd.,
Sodankylä, Finland
At the Sodankylä Geophysical Observatory
(67° 22' N, 26° 38' E) a new meteorite
radar was built during the winter 2000/01. The
radar employs a new antenna geometry minimising the
directional ambiguities of the received echos.
Furthermore, the 8-channel radar does not only
sample the received signals but also the
transmitted pulses in order to get an accurate
picture of their shapes. The transmitted pulses are
sampled with all 8 channels allowing for
calibration of the receivers on a pulse-to-pulse
basis. In June 2001 test operations began. Here we
present the new instrument and some first results.
PSB-7
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