Interferometric meteor head echo observations using the Southern Argentina Agile Meteor Radar (original) (raw)
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Radar interferometric imaging studies of long‐duration meteor echoes observed at Jicamarca
Journal of Geophysical Research: Space Physics, 1994
A large number of long‐duration (≥15 s) meteor echoes were detected at the Jicamarca Radio Observatory on two nights in early August 1990 during an evening electrojet experiment. Using an interferometric imaging technique, we were able to measure a zonal velocity profile for each meteor trail. Our analysis procedure differs from conventional meteor wind methods in that it provides instantaneous profiles rather than long‐term average information. Significant altitudinal and temporal variabilities of the horizontal velocities were noted. Zonal speeds of up to 100 m s−1, large vertical shears of up to 20 m s−1/km, and rapid temporal variations of up to 50 m s−1 over an hour interval were observed. Spectral analysis indicates the presence and decay of asymmetrical high‐frequency signal components. Possible explanations for the observed high‐frequency components are discussed as are the angle of arrival of and the scattering mechanism responsible for the meteor echoes.
Scattering characteristics of high-resolution meteor head echoes detected at multiple frequencies
1] Meteor data collected at the Kwajalein Missile Range (KMR) during the peak of the 1998 Leonid storm comprise the only simultaneous observations of meteor head echoes and trails using seven frequencies (very high frequency (VHF), ultrahigh frequency (UHF), L-, S-, C-, Ka-, and W-band spanning 160 MHz to 95 GHz). The primary sensor was the ARPA Long-Range Tracking and Instrumentation Radar (ALTAIR) radar operating at 160 MHz with 30 m range resolution and 422 MHz with 7.5 m range resolution, including both interferometric and polarization capabilities. This paper presents an analysis of this high-resolution data set with the following results: First, these observations support the theory that head echo scattering arises from an ionized region with a density sufficiently high that its plasma frequency exceeds the radar frequency (overdense reflection). Second, radar cross section (RCS) decreases rapidly with decreasing wavelength because higher frequencies must penetrate further into the increasing density of the plasma surrounding the meteoroid to reach its reflection point. Third, head echo angle measurements indicate that most of the observed meteors are sporadics not originating from the Leonid radiant. Fourth, polarization ratios showed that head echo reflections result from plasmas with a circular cross section. Fifth, the highest RCS values are detected near 105 km altitude, where the meteoroid gives up the most kinetic energy during its decent. This paper presents the first analyses of a three-frequency head echo as well as the polarization ratios and RCS characteristics from numerous twofrequency head echoes, which will allow us to develop a better understanding of meteor physics.
D.: Determination of meteoroid physical properties from tristatic radar observations, Ann
2020
Abstract. In this work we give a review of the meteor head echo observations carried out with the tristatic 930 MHz EISCAT UHF radar system during four 24 h runs between 2002 and 2005 and compare these with earlier observations. A total number of 410 tristatic meteors were observed. We describe a method to determine the position of a compact radar target in the common volume monitored by the three receivers and demonstrate its applicability for meteor studies. The inferred positions of the meteor targets have been utilized to estimate their velocities, decelerations and directions of arrival as well as their radar cross sections with unprecedented accuracy. The velocity distribution of the meteoroids is bimodal with peaks at 35-40 km/s and 55-60 km/s, and ranges from 19-70 km/s. The estimated masses are between 10 −9 -10 −5.5 kg. There are very few detections below 30 km/s. The observations are clearly biased to high-velocity meteoroids, but not so biased against slow meteoroids as ...
Plasma and Electromagnetic Simulations of Meteor Head Echo Radar Reflections
Earth Moon and Planets, 2008
Recently, meteor head echo detections from high powered large aperture radars (HPLA) have brought new measurements to bear on the study of sporadic interplanetary meteors. These same observations have demonstrated an ability to observe smaller meteoroids without some of the geometrical restrictions of specular radar techniques. Yet incorporating data from various radar reflection types and from different radars into a single consistent model has proven challenging. We believe this arises due to poorly understood radio scattering characteristics of the meteor plasma, especially in light of recent work showing that plasma turbulence and instability greatly influences meteor trail properties at every stage of evolution. In order to overcome some of the unknown relationships between meteoroid characteristics (such as mass and velocity) and the resulting head echo radar cross-sections (RCS), we present our results on meteor plasma simulations of head echo plasmas using particle in cell (PIC) ions, which show that electric fields strongly influence early stage meteor plasma evolution, by accelerating ions away from the meteoroid body at speeds as large as several kilometers per second. We also present the results of finite difference time domain electromagnetic simulations (FDTD), which can calculate the radar cross-section of the simulated meteor plasma electron distributions. These simulations have shown that the radar cross-section depends in a complex manner on a number of parameters. In this paper we demonstrate that for a given head echo plasma the RCS as a function of radar frequency peaks at sqrt (2*peak plasma frequency) and then decays linearly on a dB scale with increasing radar frequency. We also demonstrate that for a fixed radar frequency, the RCS increases linearly on a dB scale with increasing head echo plasma frequency. These simulations and resulting characterization of the head echo radar cross-section will both help relate HPLA radar observations to meteoroid properties and aid in determining a particular radar facility’s ability to observe various meteoroid populations.
Observational evidence of high-altitude meteor trail from radar interferometer
Whether radar meteor echoes occur at high altitudes (above ~130 km) in the Earth’s atmosphere is a long-standing question within the meteor radar community. Using observations from the Sanya VHF coherent radar interferometer during 11 July to 10 August 2013, we have found a new class of range-spread high-altitude meteor trail echoes (HAMEs), some of which appeared at ~170 km altitude lasting more than 10 s. A statistical analysis on the local time dependence of the identified HAME events shows a maximum around 00–04 LT. The results imply that there could be much more meteor mass input due to meteoroid sputtering at high altitudes in the Earth’s atmosphere than previously thought.
Annales Geophysicae, 2004
Meteor head echo altitude distributions have been derived from data collected with the EISCAT VHF (224 MHz) and UHF (930 MHz) high-power, large-aperture (HPLA) radars. At the high-altitude end, the distributions cut off abruptly in a manner reminiscent of the trail echo height ceiling effect observed with classical meteor radars. The target dimensions are shown to be much smaller than both the VHF and the UHF probing wavelengths, but the cutoff heights for the two systems are still clearly different, the VHF cutoff being located several km above the UHF one. A single-collision meteor-atmosphere interaction model is used to demonstrate that meteors in the (1.3-7.2) µg mass range will ionise such that critical electron density at 224 MHz is first reached at or around the VHF cutoff altitude and critical density at 930 MHz will be reached at the UHF cutoff altitude. The observed seasonal variation in the cutoff altitudes is shown to be a function of the seasonal variation of atmospheric density with altitude. Assuming that the electron density required for detection is in the order of the critical density, the abrupt altitude cutoffs can be explained as a consequence of the micrometeoroid joint size-speed distribution dropping off so fast at the large-mass, high-velocity end that above a certain altitude the number of detectable events becomes vanishingly small. Conversely, meteors at the lowmass end of the distribution will be gradually retarded such that the ionisation they generate never reaches critical density. These particles will remain unobservable. Key words. Radio science (instruments and techniques)-Interplatery physics (interplanetary dust)-General or miscellaneous (new fields)
The Astrophysical Journal, 2015
We present an initial survey in the southern sky of the sporadic meteoroid orbital environment obtained with the Southern Argentina Agile MEteor Radar (SAAMER) Orbital System (OS), in which over three-quarters of a million orbits of dust particles were determined from 2012 January through 2015 April. SAAMER-OS is located at the southernmost tip of Argentina and is currently the only operational radar with orbit determination capability providing continuous observations of the southern hemisphere. Distributions of the observed meteoroid speed, radiant, and heliocentric orbital parameters are presented, as well as those corrected by the observational biases associated with the SAAMER-OS operating parameters. The results are compared with those reported by three previous surveys performed with the Harvard Radio Meteor Project, the Advanced Meteor Orbit Radar, and the Canadian Meteor Orbit Radar, and they are in agreement with these previous studies. Weighted distributions for meteoroids above the thresholds for meteor trail electron line density, meteoroid mass, and meteoroid kinetic energyare also considered. Finally, the minimum line density and kinetic energy weighting factors are found to be very suitable for meteroid applications. The outcomes of this work show that, given SAAMER's location, the system is ideal for providing crucial data to continuously study the South Toroidal and South Apex sporadic meteoroid apparent sources.
Journal of Geophysical Research, 2010
1] The Southern Argentina Agile Meteor Radar (SAAMER) was installed at Rio Grande on Tierra del Fuego (53.8°S, 67.8°W) in May 2008 and has been operational for ∼24 months. This paper describes the motivations for the radar design and its placement at the southern tip of South America, its operating modes and capabilities, and observations of the mean winds, planetary waves, and tides during its first ∼20 months of operation. SAAMER was specifically designed to provide very high resolution of large-scale motions and hopefully enable direct measurements of the vertical momentum flux by gravity waves, which have only been possible previously with dual-or multiple-beam radars and lidars or in situ measurements. SAAMER was placed on Tierra del Fuego because it was a region devoid of similar measurements, the latitude was anticipated to provide high sensitivity to an expected large semidiurnal tide, and the region is now recognized to be a "hot spot" of small-scale gravity wave activity extending from the troposphere into the mesosphere and lower thermosphere, perhaps the most dynamically active location on Earth. SAAMER was also intended to permit simultaneous enhanced meteor studies, including "head echo" and "nonspecular" measurements, which were previously possible only with high-power largeaperture radars. Initial measurements have defined the mean circulation and structure, exhibited planetary waves at various periods, and revealed large semidiurnal tide amplitudes and variability, with maximum amplitudes at higher altitudes often exceeding 60 m s −1 and amplitude modulations at periods from a few to ∼30 days. Citation: Fritts, D. C., et al. (2010), Southern Argentina Agile Meteor Radar: System design and initial measurements of large-scale winds and tides,
Spatial domain interferometric VHF radar observations of spread meteor echoes
Journal of Atmospheric and Solar-terrestrial Physics - J ATMOS SOL-TERR PHYS, 2002
This paper is concerned with short lived (<2s) meteor trails which produced VHF radar echoes, spread in range >10km. The Doppler spectrum of these echoes in each range bin is very broad and asymmetric with many discrete peaks. Spatial domain Interferometer observations of Spread Meteor Echoes were made at the Indian National MST Radar Facility to locate the echoing regions on the trail producing the discrete peaks in the broad Doppler spectra of each range bin. We report that the mean direction of arrival was found to be similar for all Doppler frequencies in each range bin and varies for successive bins by much less than one degree. The echoing regions on the trail are located nearly parallel to the radar beam direction. Further, the directions of arrival were found to be not necessarily normal to the geomagnetic field. The observations are discussed in terms of ionization structures developed within the meteor trail.