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31.
The Arecibo UHF radar is able to detect the head-echos of micron-sized meteoroids up to velocities of 75 km/s over a height
range of 80–140 km. Because of their small size there are many uncertainties involved in calculating their above atmosphere
properties as needed for orbit determination. An ab initio model of meteor ablation has been devised that should work over
the mass range 10−16 kg to 10−7 kg, but the faint end of this range cannot be observed by any other method and so direct verification is not possible. On
the other hand, the EISCAT UHF radar system detects micrometeors in the high mass part of this range and its observations
can be fit to a “standard” ablation model and calibrated to optical observations (Szasz et al. 2007). In this paper, we present a preliminary comparison of the two models, one observationally confirmable. Among the features
of the ab initio model that are different from the “standard” model are: (1) uses the experimentally based low pressure vaporization
theory of O’Hanlon (A users’s guide to vacuum technology, 2003) for ablation, (2) uses velocity dependent functions fit from
experimental data on heat transfer, luminosity and ionization efficiencies measured by Friichtenicht and Becker (NASA Special
Publication 319: 53, 1973) for micron sized particles, (3) assumes a density and temperature dependence of the micrometeoroids
and ablation product specific heats, (4) assumes a density and size dependent value for the thermal emissivity and (5) uses
a unified synthesis of experimental data for the most important meteoroid elements and their oxides through least square fits
(as functions of temperature, density, and/or melting point) of the tables of thermodynamic parameters given in Weast (CRC
Handbook of Physics and Chemistry, 1984), Gray (American Institute of Physics Handbook, 1972), and Cox (Allen’s Astrophysical
Quantities 2000). This utilization of mostly experimentally determined data is the main reason for calling this an ab initio
model and is made necessary by the fact that individual average meteoroid mass densities are now derivable from Arecibo observations. 相似文献
32.
对近20年来狮子座流星雨的预报工作,进行了系统的阐述和分析。1998年Tempel-Tuttle彗星的回归,再度带来了狮子座流星雨的观测热,也大大促进了对狮子座流星雨预报工作的研究与验证。有的研究在时间预报准确度方面已显示出其模型的优越性,有的在流星雨的强度方面显示出一定的准确度。指出了两大类不同的方法实际上是在三维空间强调了不同的方面。将不同方法的优势结合起来,可能会使流星雨的预报更加成熟。 相似文献
33.
Miloš Šimek 《Earth, Moon, and Planets》1995,68(1-3):545-553
Diurnal variations of the median echo durations of sporadic meteor echoes during August and December-January periods are discussed. It is shown that differences between seasonal distributions result from the superposition of simultaneous diurnal effects controlling the electron loss processes in the ionized meteor trail. 相似文献
34.
J. Zvolánková 《Earth, Moon, and Planets》1995,68(1-3):653-660
The activity of the Leonid shower in the years 1944–1953 was derived from visual records obtained at the Skalnaté Pleso Observatory, using the zenithal exponent = 1.47 in the reduction factor cos
z
R. 相似文献
35.
We have compiled and analyzed historical Korean meteor and meteor shower records in three Korean official history books, Samguksagi which covers the three Kingdoms period (57 B.C.-A.D. 935), Goryeosa of Goryeo dynasty (A.D. 918-1392), and Joseonwangjosillok of Joseon dynasty (A.D. 1392-1910). We have found 3861 meteor and 31 meteor shower records. We have confirmed the peaks of Perseids and an excess due to the mixture of Orionids, north-Taurids, or Leonids through the Monte Carlo test. The peaks persist from the period of Goryeo dynasty to that of Joseon dynasty, for almost one thousand years. Korean records show a decrease of Perseids activity and an increase of Orionids/north-Taurids/Leonids activity. We have also analyzed seasonal variation of sporadic meteors from Korean records. We confirm the seasonal variation of sporadic meteors from the records of Joseon dynasty with the maximum number of events being roughly 1.7 times the minimum. The Korean records are compared with Chinese and Japanese records for the same periods. Major features in Chinese meteor shower records are quite consistent with those of Korean records, particularly for the last millennium. Japanese records also show Perseids feature and Orionids/north-Taurids/Leonids feature, although they are less prominent compared to those of Korean or Chinese records. 相似文献
36.
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
37.
We report results from two station, short-baseline (< 100 m) high resolution measurements of faint meteors (limiting meteor
magnitude +9) with the goal of measuring their optical trail widths. Meteors were observed using two 0.40 m Newtonian telescopes
(field of view ˜0.4 degrees) equipped with image intensifiers. Both telescopes were vertically oriented in a fixed mount and
pointed to the same field of view. One system used a gated image intensified camera allowing the transverse velocity component
to be measured. The widest trail captured, out of a total of 34 common events measured by both optical systems, had a full-width
to half-maximum of 1.37±0.71 m. The widest trail overall was captured by the gated system only, and was found to have a full-width
of ∼
∼10 m. The brightness variation across this trail was found to be best represented by a Lorentzian. Most trails were smaller
than our resolution limit and hence we could only place upper limits on their optical width. These were generally less than
1 m after correction for instrumental effects. Four meteors were found to have heights near 65 km and very low transverse
velocities. These may be indicative of a largely unreported high density asteroidal component at these faint meteor magnitudes. 相似文献
38.
J. D. Mathews S. J. Briczinski D. D. Meisel C. J. Heinselman 《Earth, Moon, and Planets》2008,102(1-4):365-372
Radio science and meteor physics issues regarding meteor “head-echo” observations with high power, large aperture (HPLA) radars,
include the frequency and latitude dependency of the observed meteor altitude, speed, and deceleration distributions. We address
these issues via the first ever use and analysis of meteor observations from the Poker Flat AMISR (PFISR: 449.3 MHz), Sondrestrom
(SRF: 1,290 MHz), and Arecibo (AO: 430 MHz) radars. The PFISR and SRF radars are located near the Arctic Circle while AO is
in the tropics. The meteors observed at each radar were detected and analyzed using the same automated FFT periodic micrometeor
searching algorithm. Meteor parameters (event altitude, velocity, and deceleration distributions) from all three facilities
are compared revealing a clearly defined altitude “ceiling effect” in the 1,290 MHz results relative to the 430/449.3 MHz
results. This effect is even more striking in that the Arecibo and PFISR distributions are similar even though the two radars
are over 2,000 times different in sensitivity and at very different latitudes, thus providing the first statistical evidence
that HPLA meteor radar observations are dominated by the incident wavelength, regardless of the other radar parameters. We
also offer insights into the meteoroid fragmentation and “terminal” process. 相似文献
39.
J. Tóth L. Kornoš Š. Gajdoš D. Kalmančok P. Zigo J. Világi M. Hajduková Jr. 《Earth, Moon, and Planets》2008,102(1-4):257-261
We present our experience and initial results of single-station observation using the new fish-eye TV system, as well as double
station TV observation of the Geminids 2006 shower. The fixed fish-eye TV system was developed for monitoring meteor activity
throughout the year. We discuss the astrometric precision of our observations using the UFOAnalyser software. 相似文献
40.
The November 18, 1999 Leonid storm was rich in meteors and well observed by airborne intensified video cameras aimed low in
the sky which enabled enhanced meteor counts over ground-based observations. The two- and three-dimensional distribution of
meteoroids was investigated for signs of clustering that could provide evidence of meteoroid fragmentation shortly after lift-off
from the parent comet 55P/Tempel-Tuttle, or much later due to space weathering. Analysis of the video tapes yields a refined
estimation of the mass ratio during the peak of s = 1.65 and spatial flux density of 0.5 particles/km2 greater than those causing visual magnitude +6.5 during the 5 min centered around the peak of the storm. Furthermore, the
projection of the individual trails into three-dimensional Heliocentric coordinates, shows non-homogeneity of the stream on
spatial scales from hundreds to thousands of kilometers. 相似文献