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1.
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   

2.
The tristatic EISCAT 930-MHz UHF system is used to determine the absolute geocentric velocities of meteors detected with all three receivers simultaneously at 96 km, the height of the common radar volume. The data used in this study were taken between 2002 and 2005, during four 24-h runs at summer/winter solstice and vernal/autumnal equinox to observe the largest seasonal difference. The observed velocities of 410 tristatic meteors are integrated back through the Earth atmosphere to find their atmospheric entry velocities using an ablation model. Orbit calculations are performed by taking zenith attraction, Earth rotation as well as obliquity of the ecliptic into account. The results are presented in the form of different orbital characteristics. None of the observed meteors appears to be of extrasolar or asteroidal origin; comets, particularly short-period (<200 yr) ones, may be the dominant source for the particles observed. About 40 per cent of the radiants can be associated with the north apex sporadic meteor source and 58 per cent of the orbits are retrograde. There is evidence of resonance gaps at semimajor axis values corresponding to commensurabilities with Jupiter, which may be the first convincing evidence of Jupiter's gravitational influence on the population of small sporadic meteoroids surveyed by radar. The geocentric velocity distribution is bimodal with a prograde population centred around 38 km s−1 and a retrograde population peaking at 59 km s−1. The EISCAT radar system is located close to the Arctic Circle, which means that the North Ecliptic Pole (NEP) is near zenith once every 24 h, i.e. during each observational period. In this particular geometry, the local horizon coincides with the ecliptic plane. The meteoroid influx should therefore be directly comparable throughout the year.  相似文献   

3.
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   

4.
We present the first clear observations of meteor shower activity from meteor-head echoes detected by a high-power large-aperture radar (HPLAR). Such observations have been performed at the Jicamarca VHF radar using its interferometric capabilities allowing the discrimination of meteor shower echoes from the much more frequent sporadic meteors. Until now, HPLARs were unable to distinguish meteor shower from the much more common sporadic meteor ones. In this work we have been able to detect and characterize the η-Aquariids (ETA) as well as the Perseids (PER) showers. The shower activity is more conspicuous for the ETA than for the PER shower due to the more favorable geometry. Namely, PER meteors come from low elevation angles, experiencing more filtering due to the combined Earth-atmosphere-radar instrument. In both cases, there is an excellent agreement between the measured mean velocity of the shower echoes and their expected velocity, within a fraction of 1 km s−1. Besides the good agreement with expected visual results, HPLARs observe meteors with a variety of particles sizes and masses, not observed by any other technique. Taking into account the different viewing volumes, compare to optical observations Jicamarca observes more than 1000 times more ETA meteors. Our results indicate that Jicamarca and other HPLARs are able to detect the echoes from meteor showers, but without interferometric capabilities such populations are difficult to identify just from their velocity distributions, particularly if their velocity distributions are expected to be similar to the more dominant distributions of sporadic meteors.  相似文献   

5.
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.
We have developed an all-sky charge coupled devices (CCD) automatic system for detecting meteors and fireballs that will be operative in four stations in Spain during 2005. The cameras were developed following the BOOTES-1 prototype installed at the El Arenosillo Observatory in 2002, which is based on a CCD detector of 4096 × 4096 pixels with a fish-eye lens that provides an all-sky image with enough resolution to make accurate astrometric measurements. Since late 2004, a couple of cameras at two of the four stations operate for 30 s in alternate exposures, allowing 100% time coverage. The stellar limiting magnitude of the images is +10 in the zenith, and +8 below ~ 65° of zenithal angle. As a result, the images provide enough comparison stars to make astrometric measurements of faint meteors and fireballs with an accuracy of ~ 2°arcminutes. Using this prototype, four automatic all-sky CCD stations have been developed, two in Andalusia and two in the Valencian Community, to start full operation of the Spanish Fireball Network. In addition to all-sky coverage, we are developing a fireball spectroscopy program using medium field lenses with additional CCD cameras. Here we present the first images obtained from the El Arenosillo and La Mayora stations in Andalusia during their first months of activity. The detection of the Jan 27, 2003 superbolide of ± 17 ± 1 absolute magnitude that overflew Algeria and Morocco is an example of the detection capability of our prototype.  相似文献   

7.
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   

8.
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   

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   

10.
We deal with theoretical meteoroid streams the parent bodies of which are two Halley-type comets in orbits situated at a relatively large distance from the orbit of Earth: 126P/1996 P1 and 161P/2004 V2. For two perihelion passages of each comet in the far past, we model the theoretical stream and follow its dynamical evolution until the present. We predict the characteristics of potential meteor showers according to the dynamical properties of theoretical particles currently approaching the orbit of the Earth. Our dynamical study reveals that the comet 161P/2004 V2 could have an associated Earth-observable meteor shower, although no significant number of theoretical particles are identified with real, photographic, video, or radar meteors. However, the mean radiant of the shower is predicted on the southern sky (its declination is about −23°) where a relatively low number of real meteors has been detected and, therefore, recorded in the databases used. The shower of 161P has a compact radiant area and a relatively large geocentric velocity of ∼53 km s−1. A significant fraction of particles assumed to be released from comet 126P also cross the Earth’s orbit and, eventually, could be observed as meteors. However, their radiant area is largely dispersed (declination of radiants spans from about +60° to the south pole) and, therefore, mixed with the sporadic meteor background. An identification with real meteors is practically impossible.  相似文献   

11.
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   

12.
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   

13.
Abstract— Two‐station electro‐optical observations of the 1998 Leonid shower are presented. Precise heights and light curves were obtained for 79 Leonid meteors that ranged in brightness (at maximum luminosity) from +0.3 to +6.1 astronomical magnitude. The mean photometric mass of the data sample was 1.4 × 10?6 kg. The dependence of astronomical magnitude at peak luminosity on photometric mass and zenith angle was consistent with earlier studies of faint sporadic meteors. For example, a Leonid meteoroid with a photometric mass of ～1.0 × 10‐7 kg corresponds to a peak meteor luminosity of about +4.5 astronomical magnitudes. The mean beginning height of the Leonid meteors in this sample was 112.6 km and the mean ending height was 95.3 km. The highest beginning height observed was 144.3 km. There is relatively little dependence of either the first or last heights on mass, which is indicative of meteoroids that have clustered into constituent grains prior to the onset of intensive grain ablation. The height distribution, combined with numerical modelling of the ablation of the meteoroids, suggests that silicate‐like materials are not the principal component of Leonid meteoroids and hints at the presence of a more volatile component. Light curves of many Leonid meteors were examined for evidence of the physical structure of the associated meteoroids: similar to the 1997 Leonid meteors, the narrow, nearly symmetric curves imply that the meteoroids are not solid objects. The light curves are consistent with a dustball structure.  相似文献   

14.
Li  Guangyu  Xu  Pinxin  Zhao  Haibin  He  Youwen 《Earth, Moon, and Planets》2000,88(1):11-26
On the basis of the radar observational data of the Leonids obtained in China in November of 1998, we found that the characteristics of the meteor population index γ during the main peak could not be explained well with a one-component magnitude distribution. Moreover, according the visual observational data obtained in China and other districts of Asia, γ also presents the property of non-uniformity. In this paper, we set forth a mathematical model of mixed particle streams. From this, the observed phenomenon of rarity of visual meteors and abundance of radar meteors during the main peak is interpreted. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

15.
The Advanced Research Project Agency (ARPA) Long Range Tracking and Instrumentation Radar has recorded thousands of head echoes from small meteoroids, which include detailed trajectory information as well as ionization measurements. In total, 25 complete ionization curves have been matched using a detailed model of meteoroid ablation, though the solutions are not necessarily unique. While measurements of the spread along the trajectory of the echoes indicate that most meteors in this size range do not have large separations among fragments, the ionization curves are consistent with fragmenting bodies in the most cases. Very precise radar measurements of meteors can be a valuable source of data on the chemical and physical properties of small meteoroids.  相似文献   

16.
We have developed an automated network of all-sky CCD video systems to detect medium–large meteoroids ablating over Southern Ontario, Canada. The system currently consists of five stations with the largest baseline being 180 km. Each site runs a video rate recorder with sufficient resolution to determine meteoroid trajectories with a typical precision of about 300 m but no worse than 1 km. The sensitivity of the camera is close to a stellar visual magnitude of +1 which allows for astrometric calibrations using field stars. Photometric procedures have also been developed and tested. The system has a limiting magnitude for meteors of about −2 with the current detection algorithm.  相似文献   

17.
The results of observations of the Orionid meteor shower are given in the period from 2006 to 2008. Observations were carried out using a highly sensitive camera FAVOR (FAst Variability Optical Registrator) a limiting magnitude of above +11.0m (for stars) and a field of view of 18° × 20°. Over the period of the shower from October 2 to November 7, 2006–2008, there were 3713 meteors. 449 of these meteors were associated with the Orionid meteor shower. The distributions of Orionid meteors by the stellar magnitude is presented. It turned out that most of meteors (65%) of this shower have a brightness of +5.0m-+7.0m. On each night of observation the index of meteor activity was calculated for Orionids.  相似文献   

18.
The hyperbolic meteor orbits among the 4,581 photographic and 62,906 radar meteors of the IAU MDC have been analysed using statistical methods. It was shown that the vast majority of hyperbolic orbits has been caused by the dispersion of determined velocities. The large proportion of hyperbolic orbits among the known meteor showers strongly suggests the hyperbolicity of the meteors is not real. The number of apparent hyperbolic orbits increases inversely proportional to the difference between the mean heliocentric velocity of meteor shower and the parabolic velocity limit. The number of hyperbolic meteors in the investigated catalogues does not, in any case, represent the number of interstellar meteors in observational data. The apparent hyperbolicity of these orbits is caused by a high spread in velocity determination, shifting a part of the data through the parabolic limit.  相似文献   

19.
S. Close  M. Oppenheim  A. Coster 《Icarus》2004,168(1):43-52
Large-aperture radars detect the high-density plasma that forms in the vicinity of a meteoroid and moves approximately at its velocity; reflections from these plasmas are called head echoes. To determine the head plasma density and configuration, we model the interaction of a radar wave with the plasma without using assumptions about plasma density. This paper presents a scattering method that enables us to convert measurements of radar cross-section (RCS) from a head echo into plasma density by applying a spherical scattering model. We use three methods to validate our model. First, we compare the maximum plasma densities determined from the spherical solution using 30 head echoes detected simultaneously at VHF and UHF. Second, we use a head echo detected simultaneously at VHF, UHF and L-band to compare plasma densities at all frequencies. Finally, we apply our spherical solution to 723 VHF head echoes and calculate plasma density, line density and meteoroid mass in order to compare these values with those obtained from a meteoroid ablation and ionization model. In all three comparisons, our results show that the spherical solution produces consistent results across a wide frequency range and agrees well with the single-body ablation model.  相似文献   

20.
We present a method to calculate the radiation pressure force to gravity ratio on meteoroids from their atmospheric flight. Radiation pressure corrections to meteor orbits are negligible for fireballs; of the order of or less than the measurement errors (≈ 1%) for photographic meteors; of the order of and in some cases substantially larger than the measurement errors (≈ 10%) for radar meteors.  相似文献   

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