Meteor head echo polarization at 930 MHz studied with the EISCAT UHF HPLA radar

Abstract

Abstract. The polarization characteristics of 930-MHz meteor head echoes have been studied for the first time, using data obtained in a series of radar measurements carried out with the tristatic EISCAT UHF high power, large aperture (HPLA) radar system in October 2009. An analysis of 44 tri-static head echo events shows that the polarization of the echo signal recorded by the Kiruna receiver often fluctuates strongly on time scales of tens of microseconds, illustrating that the scattering process is essentially stochastic. On longer timescales (> milliseconds), more than 90 % of the recorded events show an average polarization signature that is independent of meteor direction of arrival and echo strength and equal to that of an incoherent-scatter return from underdense plasma filling the tristatic observation volume. This shows that the head echo plasma targets scatter isotropically, which in turn implies that they are much smaller than the 33-cm wavelength and close to spherically symmetric, in very good agreement with results from a previous EISCAT UHF study of the head echo RCS/meteor angle-of-incidence relationship.Significant polarization is present in only three events with unique target trajectories. These all show a larger effective target cross section transverse to the trajectory than parallel to it. We propose that the observed polarization may be a signature of a transverse charge separation plasma resonance in the region immediately behind the meteor head, similar to the resonance effects previously discussed in connection with meteor trail echoes by Herlofson, Billam and Browne, Jones and Jones and others.

Determining meteoroid bulk densities using a plasma scattering model with high-power large-aperture radar data

“…However, besides the obvious need to guess a density, this approach also assumes ''single-body theory'' whereby the meteoroid impacts air molecules through a series of independent collisions. It also does not include effects such as fragmentation and differential ablation (Janches et al, 2009), both of which are further obscured by poorly-understood plasma processes such as polarization-dependent scattering mechanisms Wannberg et al, 2011). An alternative method is to use the signal strength, or radar-cross-section (RCS) of the scattered plasma to determine meteor plasma density Dyrud and Janches, 2008;Szasz et al, 2008).…”

Even a Blind Chicken Sometimes Finds a Grain of Corn—In My Case in Space

“…The tristatic feature made orbit determinations as well as estimates of the visual magnitudes of the recorded meteors possible before interferometry was implemented on radars (Szasz et al, 2008a(Szasz et al, , 2008b. Polarization observations revealed a signature of a transverse charge-separation resonance in the plasma immediately behind the meteoroid (Wannberg et al, 2011). Soon, other incoherent scatter and large radars such as the Arecibo Observatory radar in Puerto Rico, the ALTAIR radar on Marshall Islands and the MU radar in Japan started to apply the method (Close et al, 2000;Mathews et al, 1997;Zhou et al, 2001).…”

Controlled time integration for the numerical simulation of meteor radar reflections

“…One reason for this is dierences in the characteristics of the radar systems, e.g., in terms of frequency and antenna geometry, see [29]. According to the observations reported by, e.g., [30] and [31], the head echo can be modeled as over-dense scatter from a plasma layer surrounding the meteoroid, with a specic density distribution. In these models, the plasmatic object is assumed to be a conducting spherical object, and the electromagnetic phenomenon can be presented by partial dierential equations coupling the electric and magnetic elds.…”