Is geometry the only factor in specular scattering which determines

As was shown in Fig. 2.16, CMOR is capable of detecting meteor head echoes and off-specular echoes for the closest ranges. These events complicate radar time-of-flight measurements since the meteor trail is not confined to be in the interferometry plane. We find that echoes which show clean backscatter signatures cluster strongly (better than 1◦_{) around the specular point,} confirming geometry as the major factor in backscatter visibility, a result also found by McKin- ley and Millman (1949b).

recording the second station video data, and the two anonymous referees for reviewing this manuscript.

[1] Baggaley, W.J., (2002). Meteors in Earth’s atmosphere. Cambridge University Press. [2] Beech, M., Brown, P., Jones, J., Webster, A.R., (1997). The danger to satellites from

meteor storms. Adv. Space Res. 20. 1509–1512

[3] Blaauw, R.C., Campbell-Brown, M.D., Weryk, R.J., (2011). Mass distribution indices of sporadic meteors using radar data. Monthly Notices of the Royal Astronomical Society. 412. 2033–2039.

[4] Boroviˇcka, J., (1990). The comparison of two methods of determining meteor trajectories from photographs. Bulletin of the Astronomical Institute of Czechoslovakia. 41, 391–396. [5] Brosch, N., Polishook, D., Helled, R., Schijvarg, S., Rosenkrantz, M., (2004). Radar and

optical leonids. Atmos. Chem. Phys. 4. 1063–1069.

[6] Brown, P., Wong, D.K., Weryk, R.J., Wiegert, P., (2010). A meteoroid stream survey using the Canadian Meteor Orbit Radar. II: Identification of mintor showers using a 3D wavelet transform. Icarus. 207. 66–81.

[7] Campbell, M.D., (2002). Correcting Radar Meteor Observations for the Initial Radius Effect. Thesis, (Ph.D.) The University of Western Ontario.

[8] Campbell-Brown, M.D., (2008). High resolution radiant distribution and orbits of spo- radic radar meteoroids. Icarus 196, 144–163.

[9] Campbell-Brown, M., Jones, J., (2003). Determining the initial radius of meteor trains: fragementation. MNRAS 343. 775–780.

[10] Ceplecha, Z., Boroviˇcka, J., Elford, W., ReVelle, D., Hawkes, R.L., Porubˇcan, V., Simek, M., (1998). Meteor Phenomena and Bodies. Space Science Reviews 84. 327–421. [11] Cook., A.F., Forti, G., McCrosky, R.E., Posen, A., Southworth, R.B., Williams, J.T.,

(1972). Evolutionary and Physical Properties of Meteoroids, Proceedings of IAU Colloq. 13. NASA SP 319. 23–44.

[12] Fujiwara, Y., Ueda, M., Nakamura, T., Tsutsumi, M., (1995). Simultaneous Observations of Meteors with the Radar and TV Systems. EM&P 68. 277–282

[13] Grygar, J., Kohoutek, L., Plavcov´a, Z., (1968). Simultaneous Radar and Optical Obser- vatinof of Meteors at Ondrejov in 1962. IAUS 33. 63–69.

[16] Hill, K.A., Rogers, L.A., Hawkes, R.L., (2005). High geocentric velocity meteor ablation. A&A 444. 615–624.

[17] Hocking, W.K., (2000). Real-time meteor entrance speed determinations made with in- terferometric meteor radars. Radio Science 35. 1205–1220.

[18] Hocking, W.K., Fuller, B., Vandepeer, B., (2001). Real-time determination of meteor- related parameters utilizing modern digital technology. JASTP 63. 155–169.

[19] Holdsworth, D. A., Reid, I.M., (2004). Comparisons of full correlation analysis (FCA) and Imaging Dopper Interferometry (IDI) winds using the Buckland Park MF radar. An- nales Geophysicae 22. 3829–3842.

[20] Jones, J., Brown, P., Ellis, K.J., Webster, A.R., Campbell-Brown, M., Krzemenski, Z., Weryk, R.J., (2005). The Canadian Meteor Orbit Radar: System overview and prelimi- nary results. Planetary and Space Science 53. 413–421.

[21] Jones, J., Webster, A.R., Hocking, W.K., (1998). An improved interferometer design for use with meteor radars. Radio Science 33. 55–65.

[22] Jones, W., (1997). Theoretical and observational determinations of the ionization coeffi- cient of meteors. Monthly Notices of the Royal Astronomical Society. 288. 995–1003. [23] Kikwaya, J.B., Campbell-Brown, M., Brown, P.G., Hawkes, R.L., Weryk, R.J., (2009).

Physical characteristics of very small meteoroids. A&A 497. 851–867.

[24] Kohoutek, L., Grygar, J., Plavcova, Z., Kvizova, J., (1970). Comparison of radar and optical meteor observations. Results of the meteor expedition Ondˇrejov 1962. BAICz 21. 18–28.

[25] Koschny, D., Chilson, P.B., Schmidt, G., (1997). A setup for parallel observations be- tween an intensified meteor camera and backscatter radar. pimo.conf. 115–121.

[26] McKinley, D.W.R., Millman, P.M., (1949), Proc. of the I.R.E. 37. 364–375.

[27] McKinley, D.W.R., Millman, P.M., (1949), A phenomenological theory of radar echos from meteors. Publications of the Dominion Observatory Ottawa. 11, 327–340.

[28] Michell, R.G., (2010). Simultaneous optical and radar measurements of meteors using the Poker Flat Incoherent Scatter Radar. JASTP 72. 1212–1220.

[29] Myers, J.R., Sande, C.B., Miller, A.C., Warren Jr., W.H., Tracewell, D.A., (2002). SKY2000 Master Catalog, Version 4. Goddard Space Flight Center, Flight Dynamics Division, V/109.

[30] Nishimura, K., Sato, T., Nakamura, T. Ueda, M., (2001). High Sensitivity Radar-Optical Observations of Faint Meteors. IEICE Trans. Commun. 12. 1877–1884.

[31] Olsson-Steel, D., Elford, W.G., (1987). The height distribution of radio meteors - Obser- vations at 2 MHz. JATP 49, 243-258.

[32] Pecina, P., Koten, P., Stork, R., Pridal, P., Novakova, D., (2001). Simultaneous optical and radar observations of meteors: another criterion of commonness. ESASP 495. 399–403.

[33] LMR-400 Flexible Communcations Coax. Online, accessed Aug 22, 2011.

”http://timesmicrowave.com/products/lmr/downloads/22-25.pdf”

[34] Thayaparan, T., (1996). Large and medium-scale dynamics in the mesosphere and lower thermosphere measured by MF and meteor VHF radars. Thesis, (Ph.D.). The University of Western Ontario.

[35] Verniani, F., (1973). An Analysis of the Physical Parameters of 5759 Faint Radio Meteors. JGR 78, 8429–8462.

[36] Webster, A.R., Brown, P.G., Jones, J., Ellis, K.J., Campbell-Brown, M., (2004). Canadian Meteor Orbit Radar (CMOR). ACP 4. 679–684.

[37] Weryk, R.J., Brown, P.G., (2004). A search for interstellar meteoroids using the Canadian Meteor Orbit Radar (CMOR). EM&P 95, 221–227.

[38] Weryk, R.J., Brown, P.G., Domokos, A., Edwards, W.N., Krzeminski, Z., Nudds, S.H., Welch, D.L., (2008). The Southern Ontario All-sky Meteor Camera Network. EM&P 102, 241–246.

[39] Weryk, R.J., (2010). The effects of video compression on photometry and astrometry. Meteoroids 2010, Breckenridge, USA.

Weryk, Robert J.; Brown, Peter G. (2012).

Simultaneous radar and video meteors – II: Photometry and Ionisation. Planetary and Space Science, submitted June 22, 2012.

3.1

Introduction

3.1.1

Motivation

Radar and optical measurements have historically been the two primary instrumental tech- niques for documenting the ablation behaviour of meteoroids in the Earth’s atmosphere. Op- tical techniques consist of visual, photographic, and video methods, each having benefits de- pending on the scientific questions being addressed.

Chapter 2 in this study made metric comparisons between radar and video meteor obser- vations to better understand the accuracy of radar interferometry measurements. Using the Canadian Meteor Orbit Radar (CMOR) and several Gen-III image intensified CCD video cam- eras, our radar interferometric measurements were found to be accurate to∼0.8◦_{. It was also} determined that the majority of our radar detections occur near the end of their corresponding optical trails detected by video: an important result, as assuming the radar detections occur at the peak of their corresponding ionisation curves can lead to systematic errors in mass esti- mates. Our previous work did not consider photometric and ionisation comparisons, which are

the focus of the present study.

Due to the nature of specular scattering in meteor trails, simultaneous radar-video detec- tions are rare. In our first paper, we showed (using a simple model) that 2%− 5% of video events should be detected by radar based purely on geometry. Because the simultaneous rate was∼7%, this implied that simultaneous meteor observations are biased towards larger single- body meteoroids.

Relating an observed meteor to the physical properties of its associated meteoroid is com- plicated by uncertain conversion efficiencies between the number and type of ablated meteoric atoms, and the number of electrons and photons produced during the ablation process. Ar- guably the most important physical property to be inferred from meteor observations is mass. This can be determined by summing either all the light emitted during a meteor’s passage (pho- tometric mass) or all the electrons generated during ablation (ionisation mass), but only if the efficiency of generating electrons and photons by each unit of ablated mass is known. This leads to the concepts of the ionisation coefficient, β, defined as the average number of elec- trons produced per meteoric atom, and the luminous efficiency, τI, defined as the percentage

of kinetic energy loss transformed into light. Values for β and τI have been determined by

many theoretical and lab-based measurement programs, but their true values and dependence on meteor speed remain poorly known. As no lab data set covers the full meteor speed range, relatingβandτI using simultaneous observations (eg. Saidov and ˇSimek, 1989) can help con-

strain their numerical values. Unfortunately, β andτI are not directly measurable as separate

quantities without knowing the composition, initial mass, and height interval of each observed meteor, but the ratioβ/τIcan be determined with only a few assumptions.

There are also complications in measuring the total light or ionisation production. For intensified video systems, the field-of-view (FOV) covers only a small portion of the visible sky, which limits the number of meteors having their entire trail visible. For single station backscatter radar systems, assumptions about the ionisation distribution as a function of height must be made in order to estimate the total electron count. This distribution is not directly

is to determine meteor electron line densities and compare these against photon production in the same trail segment, which will explicitly link the two quantitiesβandτIthrough their ratio β/τI. This allows for a relative radar-video mass scale to be better defined, and can confirm

either of our adoptedβorτI, assuming the other is correct. For direct comparisons ofqagainst I, we do not need to know the total meteoroid mass.

If an accurate value ofβcan be determined, it would refine ionisation-based meteoroid mass estimates, and would significantly improve meteoroid flux measurements, refine aeronomy models of electron/ion deposition in the atmosphere (Plane, 2002, and the references therein), and validate scattering models for radar head echo measurements (Close et al., 2004).

In this work, we wish to specifically address the following questions:

1. What are the detection limits of our radar and video instruments?

2. What is the relation betweenqandIfor both underdense and overdense echoes?

3. What assumptions dominate the uncertainty in determiningqandI, and therefore, mass estimates for radar and video meteors?

4. What is the ratio ofβ/τI, the ionisation coefficient to luminous efficiency? How does it

depend on speed?

5. How do different literature estimates ofτIaffect our video mass estimates? How do they

compare to our derivedτI?

Answers to these questions will help improve measurement interpretations of the meteoroid population detectable by either radar or video systems.