An FDTD model of scattering from meteor head plasma

Abstract

We have developed a three‐dimensional finite difference time domain (FDTD) model of scattering of radar waves from meteor head plasma. The model treats the meteor head plasma as a cold, collisional, and magnetized plasma, and solves Maxwell's equations and the Langevin equation simultaneously and self‐consistently in and around the plasma. We use this model to investigate scattering of radar waves from a meteor head (the “head echo”) under a range of plasma densities, meteor scale sizes, and wave frequencies. In this way we relate the radar cross section (RCS) to these variable parameters. We find that computed RCS disagrees with previous analytical theory at certain meteor sizes and densities, in some cases by over an order of magnitude. We find that the calculated meteor head RCS is monotonically related to the “overdense area” of the meteor, defined as the cross‐section area of the part of the meteor where the plasma frequency exceeds the wave frequency. These results provides a physical measure of the meteor size and density that can be inferred from measured RCS values from ground‐based radars. Meteoroid mass can then be inferred from the meteor plasma distribution using established methods.

Radar Detectability Studies of Slow and Small Zodiacal Dust Cloud Particles. III. The Role of Sodium and the Head Echo Size on the Probability of Detection

“…This comparison suggests that using the MFP or Jones radius does not change the results significantly. Furthermore, from Figure 7 of Marshall & Close (2015), it can be seen that the RCS derived from Close et al (2004) analytical model for a given radius is larger than the one derived by the FDTD simulations. This suggests that the Jones radius correction (0.023) derived by Close et al (2004) could be even smaller.…”

“…In this section we first examine how well this approximation fares with a recent and more comprehensive model of the meteor HE, and determine what improvements can be made to find reconciliation between radar observations and ZoDy. Specifically, we will compare our results to the model reported by Marshall & Close (2015), who have developed a threedimensional Finite-difference Time-domain (FDTD) model to investigate the scattering of radar waves from the meteor HE, treating it as a cold, collisional, magnetized plasma. Solving Maxwell's equations and the Langevin equation simultaneously and self-consistently in and around the plasma, the model explores the dependence of the meteor RCS with physical variables such as plasma densities, meteor HE scale sizes, and wave frequencies.…”

“…These results provide a physical measure of the meteor HE size and density that can be inferred from measured RCS values from ground-based radars. Figure 6 shows the absolute difference between the RCS calculated using the FDTD model developed by Marshall & Close (2015) and the coherent scattering model utilized thus far by our approach. It can be seen from this figure that the ensemble of electrons model is in reasonably good agreement with the FDTD simulations for the range of masses between 0.01 and 1000 micrograms, where at low velocities the RCS from the FDTD simulations is at most a factor of 0.1 smaller than that resulting from the coherent scattering approach.…”

“…For this case, the head plasma should emulate coherent scattering as the radar wave is able to penetrate the plasma and be seen by all of the head plasma electrons, which each scatter the radar wave independently and coherently. On the other hand, when the HE is overdense, the radar wave hits a "wall" where w w > p,max 0 , and the head plasma reflects the wave; only under those circumstances, Marshall & Close (2015) report an RCS p´r p 2 , where r p is the overdense radius. The calculated electron densities from CABMOD result in normalized plasma frequencies that are smaller than 3 and actually generally smaller than 1.…”

“…Difference between RCS values derived using the FDTD model developed by Marshall & Close (2015) and the ensamble of electrons proposed by Mathews et al (1997) and utilized in our detectability model, as a function micrometeoroid mass and velocity.…”