Meteors, comets and meteoric ionization

Lovell, A. C. B.; Prentice, Jonah; Porter, J. G.; Pearse, R. W. B.; Herlofson, N.

doi:10.1088/0034-4885/11/1/313

Cited by 9 publications

(6 citation statements)

References 106 publications

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“…Underdense meteor trails, with linear electron densities of less than 2.4 × 10 14 electrons m −1 (McKinley, 1961), produce radar echoes that decay at an exponential rate governed by the local ambipolar diffusion coefficient D (Lovell et al, 1947). The time, τ , for an underdense meteor trail's radar echo to decay to a factor of e −1 of the initial maximum is given by…”

Section: Meteor Echo Decay Timesmentioning

confidence: 99%

Meteor radar observations of polar mesospheric summer echoes over Svalbard

Younger¹,

Adami²,

Hall³

et al. 2021

Preprint

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Abstract. A 31 MHz meteor radar located in Svalbard has been used to observe polar mesospheric echoes (PMSE) during summer 2020. Data from 19 July was selected for detailed analysis, with a focus on extracting additional information to characterize the atmosphere in the PMSE region. The use of an all-sky meteor radar adds an additional use to data collected for meteor observations and enables the detection of PMSE layers across a wide field of view. Comparison with data from a 53.5 MHz narrow-beam MST radar shows good agreement in the morphology of the layer as detected between the two systems. Doppler spectra of PMSE layers reveal fine structure, including regions of enhanced return that move across the radar's field of view. The relationship between range and Doppler shift of off-zenith portions of the layer enable the estimation of wind speeds with high temporal resolution during PMSE conditions. Trials demonstrate good agreement between wind speeds obtained from PMSE Doppler spectra and those calculated from specular meteor trail radial velocities. Combined with the antenna polar diagram of the radar, this same relationship was used to infer the aspect sensitivity of observed PMSE backscatter, yielding a mean backscatter angular width of 6.6 ± 2.8°. A comparison of underdense meteor radar echo decay times during and outside of PMSE conditions did not demonstrate a strong correlation between the presence of PMSE and shortened underdense meteor radar echo durations.

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Section: Meteor Echo Decay Timesmentioning

confidence: 99%

Meteor radar observations of polar mesospheric summer echoes over Svalbard

Younger¹,

Adami²,

Hall³

et al. 2021

Preprint

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show abstract

“…Both of these plasmas reflect radio waves (Lovell et al, 1947). When measured with a radar, they cause so-called meteor head and meteor trail echoes (McKinley, 1961). To determine the position of these radar targets, interferometric or multi-static radar systems must be used.…”

Section: Introductionmentioning

confidence: 99%

Resolving the ambiguous direction of arrival of weak meteor radar trail echoes

Kastinen

Kero

Kozlovsky³

et al. 2021

Atmos. Meas. Tech.

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Abstract. Meteor phenomena cause ionized plasmas that can be roughly divided into two distinctly different regimes: a dense and transient plasma region co-moving with the ablating meteoroid and a trail of diffusing plasma left in the atmosphere and moving with the neutral wind. Interferometric radar systems are used to observe the meteor trails and determine their positions and drift velocities. Depending on the spatial configuration of the receiving antennas and their individual gain patterns, the voltage response can be the same for several different plane wave directions of arrival (DOAs), thereby making it impossible to determine the correct direction. A low signal-to-noise ratio (SNR) can create the same effect probabilistically even if the system contains no theoretical ambiguities. Such is the case for the standard meteor trail echo data products of the Sodankylä Geophysical Observatory SKiYMET all-sky interferometric meteor radar. Meteor trails drift slowly enough in the atmosphere and allow for temporal integration, while meteor head echo targets move too fast. Temporal integration is a common method to increase the SNR of radar signals. For meteor head echoes, we instead propose to use direct Monte Carlo (DMC) simulations to validate DOA measurements. We have implemented two separate temporal integration methods and applied them to 2222 events measured by the Sodankylä meteor radar to simultaneously test the usefulness of such DMC simulations on cases where temporal integration is possible, validate the temporal integration methods, and resolve the ambiguous SKiYMET data products. The two methods are the temporal integration of the signal spatial correlations and matched-filter integration of the individual radar channel signals. The results are compared to Bayesian inference using the DMC simulations and the standard SkiYMET data products. In the examined data set, ∼ 13 % of the events were indicated as ambiguous. Out of these, ∼ 13 % contained anomalous signals. In ∼ 95 % of all ambiguous cases with a nominal signal, the three methods found one and the same output DOA, which was also listed as one of the ambiguous possibilities in the SkiYMET analysis. In all unambiguous cases, the results from all methods concurred.

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“…The main categories of meteor radio scattering phenomena are known to be specular scattering from the enhanced electron density left suspended in the atmosphere behind the burning meteoroid (Pierce, 1938;Herlofson, 1947;Manning, 1948), non-specular trail echoes caused by Bragg scattering from ionospheric irregularities that form in the wake of the ablating meteoroid (Oppenheim et al, 2000;Dyrud et al, 2002;Chau et al, 2014), and finally meteor head echoes that originate from the area around the ablating meteor that has an electron density higher than the plasma frequency of the scattering radio wave (Hey et al, 1947;Evans, 1966;PellinenWannberg and Wannberg, 1994).…”

Section: Introductionmentioning

confidence: 99%

Coded continuous wave meteor radar

et al. 2016

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Abstract. The concept of a coded continuous wave specular meteor radar (SMR) is described. The radar uses a continuously transmitted pseudorandom phase-modulated waveform, which has several advantages compared to conventional pulsed SMRs. The coding avoids range and Doppler aliasing, which are in some cases problematic with pulsed radars. Continuous transmissions maximize pulse compression gain, allowing operation at lower peak power than a pulsed system. With continuous coding, the temporal and spectral resolution are not dependent on the transmit waveform and they can be fairly flexibly changed after performing a measurement. The low signal-to-noise ratio before pulse compression, combined with independent pseudorandom transmit waveforms, allows multiple geographically separated transmitters to be used in the same frequency band simultaneously without significantly interfering with each other. Because the same frequency band can be used by multiple transmitters, the same interferometric receiver antennas can be used to receive multiple transmitters at the same time. The principles of the signal processing are discussed, in addition to discussion of several practical ways to increase computation speed, and how to optimally detect meteor echoes. Measurements from a campaign performed with a coded continuous wave SMR are shown and compared with two standard pulsed SMR measurements. The type of meteor radar described in this paper would be suited for use in a large-scale multi-static network of meteor radar transmitters and receivers. Such a system would be useful for increasing the number of meteor detections to obtain improved meteor radar data products.

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Meteors, comets and meteoric ionization

Abstract: Normal hourly rate 30 to 40 7 ,, 10 40 ,, 60 10

Cited by 9 publications

References 106 publications

Meteor radar observations of polar mesospheric summer echoes over Svalbard

Meteor radar observations of polar mesospheric summer echoes over Svalbard

Resolving the ambiguous direction of arrival of weak meteor radar trail echoes

Coded continuous wave meteor radar

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