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Publisher: München : European Geopyhsical Union × Subject: meteor ×

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Now showing 1 - 3 of 3
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    VHF antenna pattern characterization by the observation of meteor head echoes
    (München : European Geopyhsical Union, 2017) Renkwitz, Toralf; Schult, Carsten; Latteck, Ralph
    The Middle Atmosphere Alomar Radar System (MAARSY) with its active phased array antenna is designed and used for studies of phenomena in the mesosphere and lower atmosphere. The flexible beam forming and steering combined with a large aperture array allows for observations with a high temporal and angular resolution. For both the analysis of the radar data and the configuration of experiments, the actual radiation pattern needs to be known. For that purpose, various simulations as well as passive and active experiments have been conducted. Here, results of meteor head echo observations are presented, which allow us to derive detailed information of the actual radiation pattern for different beam-pointing positions and the current health status of the entire radar. For MAARSY, the described method offers robust beam pointing and width estimations for a minimum of a few days of observations.
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    All-sky interferometric meteor radar meteoroid speed estimation using the Fresnel transform
    (München : European Geopyhsical Union, 2007) Holdsworth, D.A.; Elford, W.G.; Vincent, R.A.; Reid, I.M.; Murphy, D.J.; Singer, W.
    Fresnel transform meteor speed estimation is investigated. A spectral based technique is developed allowing the transform to be applied at low temporal sampling rates. Simulations are used to compare meteoroid speeds determined using the Fresnel transform and alternative techniques, confirming that the Fresnel transform produces the most accurate meteoroid speed estimates for high effective pulse repetition frequencies (PRFs). The Fresnel transform is applied to high effective PRF data collected during Leonid meteor showers, producing speed estimates in good agreement with the theoretical pre-atmospheric speed of the 71 kms−1. Further simulations for the standard low effective PRF sampling parameters used for Buckland Park meteor radar (BPMR) observations suggests that the Fresnel transform can successfully estimate meteor speeds up to 80 kms−1. Fresnel transform speed estimation is applied using the BPMR, producing speed distributions similar to those obtained in previous studies. The technique is also applied to data collected using the BPMR sampling parameters during Southern delta-Aquarid and Geminid meteor showers, producing speeds in very good agreement with the theoretical pre-atmospheric speeds of these showers (41 kms−1 and 35 kms−1, respectively). However, application of the Fresnel transform to high speed showers suggests that the practical upper limit for accurate speed estimation using the BPMR sampling parameters is around 50 kms−1. This limit allows speed accurate estimates to be made for about 70% of known meteor showers, and around 70% of sporadic echoes.
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    Small scale density variations of electrons and charged particles in the vicinity of polar mesosphere summer echoes
    (München : European Geopyhsical Union, 2003) Rapp, M.; Lübken, F.-J.; Blix, T.A.
    We present small scale variations of electron number densities and particle charge number densities measured in situ in the presence of polar mesosphere summer echoes. It turns out that the small scale fluctuations of electrons and negatively charged particles show a strong anticorrelation down to the smallest scales observed. Comparing these small scale structures with the simultaneously measured radar signal to noise profile, we find that the radar profile is well described by the power spectral density of both electrons and charged particles at the radar half wavelength (=the Bragg scale). Finally, we consider the shape of the power spectra of the observed plasma fluctuations and find that both charged particles and electrons show spectra that can be explained in terms of either neutral air turbulence acting on the distribution of a low diffusivity tracer or the fossil remnants of a formerly active turbulent region. All these results are consistent with the theoretical ideas by Rapp and Lübken (2003) suggesting that PMSE can be explained by a combination of active and fossil neutral air turbulence acting on the large and heavy charged aerosol particles which are subsequently mirrored in the electron number density distribution that becomes visible to a VHF radar when small scale fluctuations are present.