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1.
R. L. Hawkes P. G. Brown N. R. Kaiser A. J. Faloon K. A. Hill L. A. Rogers 《Earth, Moon, and Planets》2004,95(1-4):587-593
A digital image intensified CCD camera with an electronically gated image intensifier was used to produce very short duration
images of meteors. The observational system employed a 0.40 m F/4.5 Newtonian telescope to obtain high spatial resolution.
A second intensified CCD camera was used to yield height information using parallax. At a typical meteor height one pixel
(for the vertically oriented system) corresponded to about 1.1 m. A sampling of 59 mainly sporadic meteors was analyzed. There
is clear variability from meteor to meteor, with many meteors (nearly 50%) showing only a small amount of wake, while some
meteors (approximately 20%) have the off segments completely filled in. 相似文献
2.
The recent development and data collection results of the Astrobiology Instrumentation for Meteor Imaging and Tracking (AIM-IT)
system, has demonstrated an ability to point narrow field-of-view instruments at transient events such as meteors. AIM-IT
uses the principle of tracking moving objects via a paired set of relay mirrors along with an integrated hardware/software
solution, to acquire and track meteors in real-time. Development of the instrument has progressed from a prototype rocker-box
system through more recent use of a fast response mirror system during several meteor shower campaigns. Several narrow field
of view instruments have been deployed using AIM-IT including high spatial resolution video, high frame rate video, and meteor
spectrographic equipment. Analysis of the imagery shows evidence for meteor fragmentation in as many as 20% of the meteors
tracked thus far. The success of the AIM-IT technology in tracking meteors during their luminous flight provides a new tool
in enhancing the capabilities and data volume that can be obtained with existing narrow field of view instruments. 相似文献
3.
We have carried out double-station TV meteor observations between 1990 and 1994. The orbits of 326 meteors have been determined from doubly observed meteors, and radiant distributions are studied. The mean magnitude of the observed meteors was as faint as +4.7, since I.I. (Image Intensifier) and Video cameras were used. Radiants were widely distributed over the celestial sphere. The velocity distribution showed some similarity with the distribution predicted by the theoretical radiant distribution from comets rather than that from asteroids. In all 13 showers including both major and minor meteor showers were detected from radiant distributions of the observed meteors; from the orbital elements and meteor velocities as well as from the radiant directions. 相似文献
4.
Meteoroids that orbit the Sun encounter the Earth with speeds between 11 and 74 km/sec. However, the distribution of the velocities of meteoroids between these limits is not well known. The uncertainty is caused by the difficulty in measuring the true flux of meteors at the extrema of the velocity distribution. Whilst the most comprehensive measurements of meteor flux are those obtained using radio techniques, meteors with speeds > 50 km/sec occur at heights where the effects of initial radius of the trail and diffusion significantly reduce the radio reflection from the trails; on the other hand the high dependence of the collisional ionization probability on velocity (to the power 3.5) significantly inhibits the detection of meteors with speeds < 20 km/sec. Recent developments in meteor radar systems are now making it possible to measure the velocity of meteors at the extrema of the distribution. For meteoroids ablating at heights between 100 and 120 km the speed of entry can be measured at 2 and 6 MHz using a radar with a 1 km diameter array located near Adelaide; these observations will commence early in 1995. In the meantime a 54 MHz MST radar is being operated at a pulse repetition frequency of 1024 Hz to search for the presence of interstellar (speed > 74 km/sec) meteors. Both these radars exploit the phase information available prior to the closest-approach (to) point. 相似文献
5.
J. F. Pawlowski T. J. Hebert R. L. Hawkes M. J. Matney E. G. Stansbery 《Meteoritics & planetary science》2001,36(11):1467-1477
Abstract— We have used a 3.0 m diameter liquid mirror telescope (LMT) coupled to a microchannel plate image‐intensified charge‐coupled device (CCD) detector to study the 1999 Leonid meteor shower. This is the largest aperture optical instrument ever utilized for meteor detection. While the observing system is sensitive down to stars of +18 astronomical magnitude under optimum conditions, when corrections for meteor motion are applied the majority of the meteors collected fall in the absolute magnitude range from +5 to +10, corresponding to photometric masses from about 10?7 to 10?9 kg. This is largely due to the fact that the field of view of the LMT was only 0.28°, so that only a small portion of the luminous meteor trail was recorded. While the flux of these small (1.4 times 10?9 kg) Leonid meteors is low (on the order of one Leonid meteor per hour per square kilometer perpendicular to the Leonid), we do have clear evidence that the Leonid stream contains particles in the mass range studied here. The data showed a possibly significant peak in Leonid flux (9.3 ± 3.5) for the 1 h period from 11:00 to 12:00 u.t. 1999 November 17 (solar longitude 234.653 to 234.695, epoch 2000.0), although the main trend of these results is a broad low‐level Leonid activity. There is evidence that small meteoroids are more widely distributed in the Leonid stream, as would be expected from cometary ejection stream models. As would be expected from an extrapolation of mass distribution indices for brighter meteors, the vast majority of meteors at this size are sporadic. The LMT is a powerful detector of sporadic meteors, with an average non‐Leonid detection rate of more than 140 meteor events per hour. 相似文献
6.
Abstract— We have used dual coaxial microchannel plate image-intensified monochrome charge-coupled device (CCD) detectors run at standard NTSC frame rates (30 frames per second, fps) to study the Leonid meteor shower on 1998 November 17 from an airborne platform at an altitude of ~13 km. These observations were part of NASA's 1998 Leonid multi-instrument aircraft campaign (MAC). The observing systems had fields of view (width) of 16.3° and 9.5°, and limiting stellar sensitivities of +8.3m and +8.9m. During 12 h of recording, 230 meteors were detected, of which 65 were Leonid meteors. Light curves are presented for 53 of these meteors. The magnitudes at peak brightness of the meteors investigated were generally in the range from +4.0m to +6.0m. The mass distribution indices for the two samples are 1.67 and 1.44, with the former being based on the wider field of view dataset. The light curves were skewed with the brightest point towards the beginning of the meteor trail. The F parameter for points one magnitude below maximum luminosity had a mean value of 0.47 for the wider field system and 0.37 for the more sensitive narrower field system. We provide leading and trailing edge light curve slopes for each meteor as another indication of light curve shape. There were few obvious flares on the light curves, indicating that in-flight fragmentation into a large number of grains is not common. There is variability in light curve shape from meteor to meteor. The light curves are inconsistent with single, compact body meteor theory, and we interpret the data as indicative of a two-component dustball model with metal or silicate grains bonded by a lower boiling point, possibly organic, substance. The variation in light curve shape may be indicative of differences in mass distribution of the constituent grains. We provide trail length vs. magnitude data. There is only a slight hint of a bend at +5m in the data, representing the difference between meteors that have broken into a cluster of grains prior to grain ablation, and those that continue to fragment during the grain ablation phase. Two specific meteors show interesting light curve features. One meteor is nebulous in appearance, with significant transverse width. The apparent light production region extends for 450 m from the center of the meteor path. Another meteor has several main fragments, and evidence of significant separated fragments. We offer several suggestions for improvements for the 1999 Leonid MAC light curve experiment. 相似文献
7.
We have carried out a simultaneous observation of radar and optical meteors with the MU radar (Middle and Upper Atmosphere Radar), Shigaraki and TV camera systems. We usually obtained about 20 meteors per an hour with 85 mm lens, but very small part of them are simultaneously observed by the MU radar (< 5%), suggesting the significance of rectangular scatterring. We have analyzed about 20 simultaneous meteors with magnitudes from 0 to +5.5, most of which are overdense meteors. For Geminid meteors, a linear relation between the logarithm of the echo duration and the absolute magnitude of the TV meteor, was deduced. 相似文献
8.
Pavlo Kozak 《Earth, Moon, and Planets》2008,102(1-4):277-283
Software named “Falling Star” has been developed for digital processing of double-station TV meteor observations. It was designed
for measurement and calculation of both kinematic and photometric parameters of faint meteors observed with any video system.
Data from video recordings are first digitized as standard AVI files, and then converted into the software’s TVS (TV sequence)
format. Additional astronomical information like date, time of observations, geographic position of point of the observation
and horizontal coordinates of TV camera optical axis orientation are added to the files. These parameters allow the right
ascension and declination of the optical center of camera for the moment of meteor flight to be calculated. “Falling Star”
includes a range of automated procedures for the identification of frame stars with star catalogues, search of movable meteor-like
objects inside frame, calculation of equatorial coordinates and photometry. Finally, meteor trajectory parameters, orbital
elements and brightness curves are calculated. Errors of calculations are determined using Monte-Carlo method. 相似文献
9.
Štefan Gajdoš 《Earth, Moon, and Planets》2008,102(1-4):117-123
A new meteroid stream—October Ursa Majorids—was announced by Japanese observers on Oct. 14–16, 2006 (Uehara et al. 2006).
Its weak manifestation was detected among coincidental major meteor showers (N/S Taurids, Orionids), as its meteors radiated
from a higher placed radiant on the northern sky. We have tried to find out previous displays of the stream throughout available
meteor orbits databases, and among ancient celestial phenomena records. Although we got no obvious identification, there are
some indications that it could be a meteor shower of cometary origin with weak/irregular activity, mostly overlayed by regular
coincidental meteor showers. With a procedure based on D-criterion (Southworth and Hawkins 1963) we found a few records in IAU MDC database of meteor photographic orbits which fulfill
common similarity limits, for October Ursae Majorids. However, their real association cannot be established, yet. With respect
to the mean orbit of this stream, we suggest for its parent body a long-period comet. 相似文献
10.
We analyse data obtained by different ground-based video camera systems during the 1999 Leonid meteor storm. We observe similar
activity profiles at nearby observing sites, but significant differences over distances in the order of 4,000 km. The main
peak occured at 02:03 UT (λ⊙=235.286, J2000, corrected for the time of the topocentric stream encounter). At the Iberian peninsula quasi-periodic activity
fluctuations with a period of about 7 min were recorded. The camera in Jordan detected a broad plateau of activity at 01:39–01:53
UT, but no periodic variations. The Leonid brightness distribution derived from all cameras shows a lack of faint meteors
with a turning point close to +3m, which corresponds to meteoroids of approximately 10-3 g. We find a pin-point radiant at αalpha=153.65 ±0.1, δ=21.80 ±0. (λ⊙=235.290). The radiant positionis identical before and after the storm, and also during the storm no driftis observed.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
11.
We present detailed data on 8 bright meteors recorded simultaneously by different observational techniques. All meteors were
recorded by all-sky cameras at the Czech stations of the European Fireball Network and by image intensified TV cameras placed
at Ondrejov and Kunzak observatories. As well as direct photographic and LLLTV recordings, most of meteors were recorded also
by the spectral TV camera and some also by photographic spectral cameras. For 6 cases, lightcurves from radiometers with very
high time resolution (1200 s−1) are also available. From all these detections we found a significant difference between TV and photographic beginning heights.
TV beginnings are in average about 40 km higher than the photographic ones. We found that meteor brightness is up to 2 magnitudes
higher in the photographic system than in the TV system. This difference for high velocity meteors is mainly caused by the
presence of strong Ca+ lines in the blue part of the spectrum, where the image intensifier is only marginally sensitive. At heights above 110 km,
the Na line is usually brighter than the Mg line, while at lower heights both lines have comparable brightness. In one of
two captured spectra of short duration luminous trains, a small initial brightening of the Mg and Na lines caused by recombination
processes was observed. 相似文献
12.
V. Sidorov S. Kalabanov S. Sidorova I. Filin T. Filimonova 《Earth, Moon, and Planets》2004,95(1-4):165-179
The discrete quasitomographic method of the analysis of the interferometric data of meteor radar gives us the possibility
of measuring coordinates and velocities of very weak meteor showers with a 2 × 2 square degree resolution on the celestial
sphere. The minimal rate of the meteors in each microstream is five meteors per day. At such sensitivity, basic distinctions
between irregularities of the sporadic background and meteor streams vanish. More than 1000 of the detected microshowers per
month are associated with a combination of (a) the large known meteor showers, (b) the weaker known meteor showers and (c)
till now unknown associations of microshowers. All microshowers regardless of association have the identical velocities, limited
areas of radiation and near simultaneity of their acting dates. The results are compiled as maps of radiant distribution and
average velocities of microstreams for different months. From these it is possible to see how the microshower activity for
various discrete sites on the celestial sphere correlate with the behavior of the well-known meteor streams and thus to infer
the orbital properties of the different microstream configurations. 相似文献
13.
We have carried out multi-station TV observations since 1994 in order to determine the orbit of the Arietid daytime meteor
stream. In 1999, one possible Arietid meteor was recorded by our simultaneous observations and its orbit was determined. In
2003, two Arietid meteors were observed from two stations of our observing site, those orbits were determined precisely, the
orbital elements were in good agreement with each other. This is the first time that determination of the precise orbit of
the Arietids has been made from optical observations. The orbit of these Arietid meteors, and comparison with the orbit obtained
from radar observations are discussed. 相似文献
14.
Shinsuke Abe Noboru Ebizuka Hideyuki Murayama Katsuhito Ohtsuka Satoru Sugimoto Masa-yuki Yamamoto Hajime Yano Jun-ichi Watanabe Jiří Borovička 《Earth, Moon, and Planets》2004,95(1-4):265-277
Spectra of persistent meteor trains were observed at wavelength between 300 and 930 nm. Two obtained train spectra during
the 1998 and 2001 Leonid meteor showers are reported here. During the 1998 Leonids, one train was detected by a photographic
camera with a spectrograph covering 370–640 nm region. On the other hand, during the 2001 Leonids, video observations were
carried out using image intensified cameras in ultraviolet (UV), visible and near infrared (near-IR) wavelengths. Temperatures
in persistent trains have been measured by atmospheric O2 A(0,1) band at the wavelength near 864.5 nm. From a video spectrum obtained just 7 s after parent fireball’s flare, a rotational
temperature of 250 K at altitude of 88.0±0.5 km was estimated. We can say that the cooling time scale of train strongly depends
on the initial mass of its fireball at least for Leonids. Based on cooling constant calculated from our results, we estimated
a temperature of ∼
∼130 K as a final exothermic temperature at early stage of persistent trains. 相似文献
15.
The IAU Meteor Data Center in Lund has acted as a central depository for meteor orbits obtained by photographic, video and
radar techniques. The database of precisely reduced photographic meteors contains data on 4581 meteor orbits obtained by 17
different stations or groups in the period 1936–1996. The orbital and geophysical data are available in two separate files
as well as in an alternative file with the merged data. In various studies of meteoroid streams as well as in studies of the
sporadic meteor background, it is often necessary to utilize both the orbital and the geophysical data files. Since the database
is a compilation of partial, not perfectly compatible catalogues from many observing stations, the merging of parameters from
one data set to another may sometimes present problems. The present contribution is a note on some problems encountered in
the merging procedure. Moreover, it is evident that the database includes a small amount of erroneous data – either in the
observations or in the subsequent data reductions. The latter error is not surprising in view of the lack of modern computers
at several stations in the past. A final, corrected version of the IAU MDC Lund photographic meteor orbits (eq. 2000.0) can
now be requested through the homepage of the Astronomical Institute, Slovak Academy of Sciences (http://www.astro.sk/~ne/IAUMDC/Ph2003/database.html). 相似文献
16.
The 1998 Leonid meteor shower was observed at the Gaomeigu station of Yunnan Observatory during five successive days in November.
The visual records indicate that the number of meteors increased suddenly, from a ZHR of about 140 to over 400, in the early
morning of November 17th, Beijing time. But it decreased slowly in the following two days. During the maximum there was a
high proportion – about 10 percent – of very bright fireballs with enduring trains. The brightest one was about -10 magnitude
with a smoke train fading about three minutes after.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
17.
Joseph A. Nuth III John L. Lowrance George R. Carruthers 《Earth, Moon, and Planets》2008,102(1-4):495-504
The prime measurement objective of the Near Earth Object Chemical Analysis Mission (NEOCAM) is to obtain the ultraviolet spectra
of meteors entering the terrestrial atmosphere from ∼125 to 300 nm in meteor showers. All of the spectra will be collected
using a slitless ultraviolet spectrometer in Earth orbit. Analysis of these spectra will reveal the degree of chemical diversity
in the meteors, as observed in a single meteor shower. Such meteors are traceable to a specific parent body and we know exactly
when the meteoroids in a particular shower were released from that parent body (Asher, in: Arlt (ed.) Proc. International
Meteor Conference, 2000; Lyytinen and van Flandern, Earth Moon Planets 82–83:149–166, 2000). By observing multiple apparitions
of meteor showers we can therefore obtain quasi-stratigraphic information on an individual comet or asteroid. We might also
be able to measure systematic effects of chemical weathering in meteoroids from specific parent bodies by looking for correlations
in the depletions of the more volatile elements as a function of space exposure (Borovička et al., Icarus 174:15–30, 2005).
By observing the relation between meteor entry characteristics (such as the rate of deceleration or breakup) and chemistry
we can determine if our meteorite collection is deficient in the most volatile-rich samples. Finally, we can obtain a direct
measurement of metal deposition into the terrestrial stratosphere that may act to catalyze atmospheric chemical reactions. 相似文献
18.
W. G. Elford 《Earth, Moon, and Planets》1995,71(3):245-253
Particles of mass less than about 1 gm are a minor fraction of the total matter impinging on the Earth averaged over millennia time scales. However, these particles dominate during a single particular year and produce the most obvious evidence of incoming extra-terrestrial matter in the form of ablation trails in the atmosphere which are visible at night as meteors.Observations of meteors give astronomical information on the composition, structure, and cometary associations of the particles. The composition is deduced from optical spectra of meteors, whilst telescopic studies of the trails during formation give information on the physical structure of the particles. Any cometary associations are deduced from measurement of meteor orbits determined photographically, using television, or by radar.Meteors occur in the atmosphere at heights from about 70 to 120 km. Optical observations are restricted to night-time and usually under conditions of low moonlight. A typical television based detector can record +8M meteors with a sporadic rate of 15–20 per hour and velocities accurate to about 3%. The luminosity of the trail is strongly dependent on the velocity of the meteoroid (to about the third power).Radar observations of meteors are unrestricted by weather or time of day, and can readily detect meteors at least two orders of magnitude smaller in mass than those detectable optically. Again the observations are heavily biased toward the higher velocities as the electron line density varies approximately asV
3.5. However, the higher the velocity of the meteoroid the greater the height of the meteor trail, and the reduced probability of radar detection due to rapid diffusion of the trail. Thus radar observations tend to select meteors in the intermediate velocity range 30–40 km s–1. 相似文献
19.
O. I. Evdokimov T. K. Filimonova V. V. Sidorov Rasim Amer Ali 《Earth, Moon, and Planets》1995,68(1-3):267-275
This article contains the tomographic problem's solution of the radiants distribution study by the meteor radar data. It was received the distribution of meteors velocities for the parts of celestial sphere with angular dimensions 10° × 10° and 1° × 1°. Was shown that the angular dimensions of most of radiants are equal 1° – 3° and larger part of the sporadic background looks like a totality of microstreams. 相似文献
20.
J. Oberst J. Flohrer T. Maue R. Schrödter M. Buhl A. Christou 《Planetary and Space Science》2011,59(1):1-9
We have developed a camera dedicated to imaging faint transient noctilucent phenomena, such as aurorae, electric discharges, meteors or impact flashes, on dark planetary hemispheres. The Smart Panoramic Optical Sensor Head (SPOSH) is equipped with a back-illuminated 1024×1024 CCD chip E2V 47-20 with up to 90% quantum efficiency and has a custom-made optical system of high light-gathering power with a wide field of view of 120°×120°. Images can be obtained over extended periods at high rate to make monitoring for transient events possible. To reduce the data transmission rate, only those images (or relevant portions thereof) that contain events are returned to the user. The camera has a sophisticated processing unit prepared to interface with a spacecraft system, for image processing and event detection at rates of up to 3 images per second at full resolution. While software optimized for detection of any noctilucent phenomenon can be implemented, the software is currently optimized for the detection of meteors. Over the past years, we have routinely carried out outdoor tests with 4 camera breadboard units that demonstrate that the camera has excellent radiometric performance and geometric resolution at low light levels over its large field of view. The camera has been demonstrated to capture meteors of magnitudes as faint as +6m moving at angular speeds of 5°/s. The camera opens up new science opportunities for planetary missions. 相似文献