ISBN 978-2-87355-024-4

Proceedings of theInternational Meteor Conference

La Palma, Canary Islands, Spain

20–23 September, 2012

Published by the International Meteor Organization 2013

Edited by Marc Gyssens and Paul Roggemans

Proceedings of the International Meteor ConferenceLa Palma, Canary Islands, Spain, 20–23 September, 2012International Meteor OrganizationISBN 978-2-87355-024-4

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Pro eedings of the IMC, La Palma, 2012 1Meteor head e ho observations with the MU radar andfuture possibilities with EISCAT_3DJohan KeroSwedish Institute of Spa e Physi s, 981 28 Kiruna, Swedenkero�irf.seEISCAT_3D is a three-dimensional imaging radar proje t for atmospheri and geospa e resear h.It will onsist of multiple phased arrays lo ated in northern Fenno-S andia. The multi-purposeexperiment and data analysis approa h will enable ontinuous meteor observations, unique in termsof overage and quality. The aim of this paper is to establish a hannel through whi h the EISCATand IMO ommunities an intera t. A presentation of the meteor head e ho observations using theShigaraki Middle and Upper atmosphere (MU) radar in Japan gives a �avor of some of the possibilitiesof EISCAT_3D.1 Introdu tionA radar is a dete tion system whi h transmits ele tro-magneti energy in the form of radio waves, and re- eives e hoes from obje ts enabling determination oftheir range, dire tion, velo ity, and other properties.The EISCAT (European In oherent S atter) S ienti� Asso iation is an international resear h organisation op-erating s ienti� radar systems in northern Fenno-S an-dia. The EISCAT_3D radar system, hereafter alledE3D, is a three-dimensional imaging radar proje t foratmospheri and geospa e resear h. It will onsist ofmultiple phased arrays of thousands of antennas.E3D is not in onstru tion yet, but in preparatory phasefrom 2010 through 2014. This means, in parti ular,that the radar performan e spe i� ation is a living do -ument. Any input and demands from the (potential)user ommunity during the preparatory phase an betaken into a ount in the hardware design. Additionalinput and demands regarding experiment design andsoftware will be of great use, also during onstru tion,and, later on, for the operation of the radar. The E3Dradar sites will be omplemented by a set of supportiveinstruments. Multi-station video and spe tral imagerswould allow simultaneous head e ho and opti al meteorobservations (Campbell-Brown et al., 2012).In oherent s atter radars are introdu ed in Se tion 2and Se tion 3 is a review of meteor head e hoes. Thepresent EISCAT radar systems, urrent operations andthe on eptual design of E3D are presented in Se tion 4.A brief overview of the 2009�2010 meteor head e hoobservation program arried out using the Middle andUpper Atmosphere (MU) radar in Japan is given in Se -tion 5. Sin e MU is a phased array, the MU observationprogram gives a �avor of some possibilities of E3D.It is of great pra ti al and theoreti al importan e tomeasure the masses of meteoroids, to identify meteoroidpopulations, to determine the mass indexes of thesepopulations, to onstrain models of Solar System for-mation, and to estimate the hazards meteoroids present

to spa e raft and manned spa e missions. The mass in-�ux of extraterrestrial material onto Earth is the sour eof the neutral and ion metal layers in the middle atmo-sphere and plays an important role in atmospheri dy-nami s and pro esses as the formation of high-altitude louds, possibly through oagulation of harged mete-ori smoke parti les a ting as ondensation nu lei forwater vapor.2 In oherent s atter and HPLA radarsAn in oherent s atter radar is a s ienti� instrumentdesigned to enable re eption and analysis of the veryweak signal s attered o� ele trons in the ionosphere,the ionized part of the atmosphere at about 85 to 600km altitude above ground (Nygrén, 1996). The peaktransmitter power has to be of the order of 1 MW andthe array or dish antenna aperture of at least around1000 m2. The large aperture means that the antennagain pattern is fo used into a narrow main beam with afull-width-at-half-maximum (FWHM) of the order of 1◦at their VHF and/or UHF operating frequen ies. VeryHigh Frequen y (VHF) is the frequen y interval 30�300 MHz, while Ultra High Frequen y (UHF) is in therange of 300 MHz�3 GHz. Corresponding wavelengthsare 10�1 m (VHF) and 1�0.1 m (UHF).In oherent signal pro essing allows measurements of theele tron density, ion and ele tron temperatures, ion ol-lision frequen y, ion omposition, and ion drift velo ity.The term �in oherent� is used to designate that the mo-tion of the ionospheri ele trons is random and la kswell-de�ned stru ture in ontrast to a ( oherent) me-teor trail plasma. However, the altitude region of thelower ionosphere overlaps with the meteor zone, and in- oherent radar systems an therefore advantageously beused to study radar e hoes from oherent meteor plasmastru tures, too.The high power density permits numerous head e hodete tions from very faint meteors. Sporadi meteorstherefore dominate the size regime. A meteor head e ho

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2 Pro eedings of the IMC, La Palma, 2012 omes from the ompa t region of plasma lose to andtraveling along with a meteoroid, and is therefore highlytransient and Doppler-shifted. Its hara teristi s arevery di�erent from those of a meteor trail e ho, whi his an e ho from the already slowed-down olumns ofplasma drifting with the lo al wind speed.Not all s ienti� High Power Larger Aperture (HPLA)radar systems are designed for in oherent s atter analy-sis. Some of them are optimized to study, e.g., oherente hoes from neutral wind stru tures in the middle andupper atmosphere. The MU radar, its sibling the Equa-torial Atmosphere Radar (EAR) in Indonesia, and theMiddle Atmosphere Alomar Radar System (MAARSY)in Norway are three su h examples. Some defense agen- ies also operate HPLA radars as part of their ballis-ti missile early warning defense systems. One su hradar su essfully used also for meteor s ien e purposesis ALTAIR�the Advan ed Resear h Proje ts Agen yLong-Range Tra king and Instrumentation Radar onthe Kwajalein missile range (Close et al., 2002).3 Meteor head e hoesA meteor head e ho is aused by radio waves s at-tered from the intense region of plasma surrounding and o-moving with a meteoroid during atmospheri �ight.The signal's Doppler shift and/or target's range rate an therefore be used to determine meteoroid velo ity.The �rst head e hoes were reported by Hey et al. (1947)from observations ondu ted in 1946 between O tober 7and 11, overing the anti ipated 1946 Dra onid meteoroutburst, using a 150 kW VHF radar system.Sin e the 1990s, head e ho observations have been madewith most HPLA radar fa ilities around the world (e.g.,Pellinen-Wannberg and Wannberg, 1994; Mathews etal., 1997; Close et al., 2000; Sato et al., 2000; Chau andWoodman, 2004; Mathews et al., 2007; Malhotra andMathews, 2011). However, few published observations on ern shower meteors (e.g., Chau and Galindo, 2008)before the 2009�2010 observation program with the MUradar des ribed in Se tion 5.Most in oherent s atter radar operating frequen ies donot permit spe ular meteor trail e ho dete tions. Thereason is destru tive interferen e of e hoes from dif-ferent parts of the trail be ause the wavelengths areshorter than typi al meteor trail plasma radii. Non-spe ular trail e hoes from �eld-aligned irregularities are,however, ommon if/when observations are arried outperpendi ular to the geomagneti �eld lines (Zhou etal., 2001). With the EISCAT radars, and E3D, su hobservations are di� ult to ondu t due to the verysteep magneti in lination (approximately 77�82◦) atthe high-latitude radar lo ations.4 Present EISCAT operationsEISCAT urrently operates the monostati 224 MHzVHF and 930 MHz UHF radars near Tromsø, Norway

and the 500 MHz EISCAT Svalbard Radar (ESR) nearLongyearbyen on Svalbard. Previous meteor head e hoobservations have been ondu ted using the now non-operational passive 930 MHz UHF re eivers in Kiruna,Sweden, and Sodankylä, Finland, in onjun tion withthe UHF monostati transmitter/re eiver (Kero, 2008;Szasz, 2008). Several supporting instruments are in-stalled at the radar sites, the most prominent of whi his an ionospheri heater at the Tromsø site.The present EISCAT Asso iates in lude Norway, Swe-den, Finland, Japan, China and the United Kingdom.Germany (until 2011) and Fran e (until 2005) are ear-lier EISCAT Asso iates. The onstru tion of E3D willprobably lead to additional ountries joining (and re-joining).EISCAT radar operations are divided into CommonProgramme (CP) and Spe ial Programme (SP) experi-ments and totals about 1000 hours per year and radarsystem. CP is run by EISCAT sta� a ording to a pre-arranged s hedule and the data is available to any s i-entist from an Asso iate ountry. SP time is appor-tioned to ea h Asso iate ountry a ording to the sizeof its �nan ial ontribution to EISCAT. Ea h ountryde ides how its time is utilized, and time is usually ap-plied for by parti ular individuals. A ess to SP data islimited to these individuals for one year after the dataare taken. Then the same rules apply as for the CP.EISCAT also invites appli ations for observing time ontheir fa ilities by individual s ientists, resear h groups,and onsortia throughout the world on equal basis. In2012, 200 hours of experiment time was open for su hinternational peer-reviewed ompetition.Real-time graphs of ionospheri parameters from allEISCAT experiments are freely available on the web.Meteor analysis, on the other hand, has been ondu tedin a post-pro essing manner on subsets of ar hived rawdata, primarily through SP experiments.Virtanen et al. (2008) present a multi-purpose exper-iment and data analysis approa h to be used as thestandard, ontinuous, observational mode at E3D. Thisapproa h will enable meteor observations to be run inparallel to in oherent s atter data analysis, wheneverthe radar is running. Our aim is to provide real-timegraphs of meteor data on the web and an open sour e li-brary of analysis routines, similar to what already existfor ionospheri data.A ording to the EISCAT S ienti� Asso iation, thePreparatory Phase will ensure that the E3D proje trea hes a su� ient level of maturity with respe t tote hni al, legal and �nan ial issues, so that the on-stru tion of E3D an begin immediately after the on- lusion of the phase. The E3D Preparatory Phase isfunded by the European Commission until September2014. Further information is available on the website ofthe E3D proje t11http://www.eis at3d.se/.

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Pro eedings of the IMC, La Palma, 2012 35 MU radar and EISCAT_3DKero et al. (2012 ) have developed an automated anal-ysis s heme for meteor head e ho observations using the1 MW, 46.5MHz, interferometri , Shigaraki Middle andUpper atmosphere (MU) radar in Japan (λ = 34 .◦85 N,ϕ = 136 .◦10 E). An aerial view of the radar is given inFigure 1. The analysis te hnique an be adapted to real-time meteor �ux monitoring with E3D and extended toin orporate the E3D's superior sensitivity, higher reso-lution, and multiple re eiver sites.The analysis s heme has made it possible at MU to de-termine meteoroid velo ities and radiants of faint mete-ors with unpre edented a ura y and pre ision. Thus,the a tivity and �ux of meteor showers an now be stud-ied also with the head e ho observation te hnique (Keroet al., 2011; 2012a). An extensive set of data (more than500 hours of observing and over 100 000 meteors) was olle ted with the MU radar between June 2009 andDe ember 2010 (Kero et al., 2012b). The predominantpart of the mass distribution dete ted with MU is esti-mated to be in the range 10

−9 to 10−6 kg.Figure 2, adapted from Kero et al. (2011), shows anexample in the form of a radiant plot of MU data ol-le ted between 2009 O tober 19, 14

h UT, to O tober 21,9h UT. Most numerous in the data are sporadi meteors.However, more than 600 of about 10 000 head e hoeswere asso iated with the Orionid meteor shower. Thesemeteors onstitute a very lear enhan ement of me-teor radiants with an atmospheri entry velo ity around67 km/s. The radiant density distribution is as ompa tas the distribution of all pre isely redu ed Orionids (66photographi and 19 video meteors) of the IAU Me-teor Data Center presented by Lindblad and Porub£an(1999). This indi ates that the radar method providespre ision and a ura y omparable to photographi re-du tion of mu h brighter meteors with longer dete tabletraje tories.The Orionid a tivity within the MU radar beam rea hedabout 50 per hour during radiant ulmination. The �uxof sporadi meteors in the MU radar data peaked atabout 700 per hour. Also, several minor meteor show-

Figure 1 � Aerial view of the MU radar.

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Figure 2 � The radiant distribution of about 10 000 meteorsdete ted with the MU radar during a 33 h observation in theperiod 2009 O tober 19�21, plotted in Sun- entered e lipti oordinates.ers, as the Southern Taurids and the Leonis Minorids,were observed.E3D will have far greater sensitivity than MU and en-able investigation of a broader part of the in�ux asfun tion of meteoroid mass. It will have several inter-ferometri re eiver stations providing meteoroid orbitswith unpre edented a ura y down to very faint andsub-visual meteors. The ontinuous mode of observa-tions will lead to a large database made available, e.g.,through the IAU Meteor Data Center (MDC) at the As-tronomi al Institute of the Slovak A ademy of S ien es,under the auspi es of Division III of the InternationalAstronomi al Union (IAU).A ru ial advantage of meteor head e ho observations ompared to meteor trail e ho observations is the ab-sen e of a strong e ho height eiling e�e t. This allowsdete tion of low-mass, high-geo entri velo ity mete-oroids, whi h ablate at altitudes above the e ho height eiling of the meteor trail radar systems, and are there-fore largely undete table with these systems (Elford,1993). E3D will enable investigation and orre tion ofthis dominant, and in meteor trail observations missing,part of the meteoroid in�ux.6 Con lusionE3D is a three-dimensional imaging radar proje t foratmospheri and geospa e resear h. It will onsist ofmultiple phased arrays in northern Fenno-S andia, ea harray having a very large antenna gain-power produ t.E3D has the potential to be ome the most advan ed in-strument on Earth for meteor studies. It should be om-bined with multi-station video and spe tral imagers.The IMO ommunity is ordially invited to share ex-perien es from visual, radar, and multi-station videoobservations, and take an a tive part in the realizationof the E3D meteor observation program.

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4 Pro eedings of the IMC, La Palma, 2012A knowledgementsThe MU radar study was supported by the Japan So- iety for Promotion of S ien e (JSPS) grants-in-aid 20-08730, 20-08731, and 21340141 and JSPS postdo toralfellowships for foreign resear hers, P08730 (Johan Kero)and P08731 (Csilla Szasz). The MU radar belongs to,and is operated by, the Resear h Institute of Sustain-able Humanosphere (RISH), Kyoto University, Kyoto,Japan. EISCAT is an international asso iation presentlysupported by resear h organisations in Norway (NFR),Sweden (VR), Finland (SA), Japan (NIPR and STEL),China (CRIPR), and the United Kingdom (STFC).Referen esCampbell-Brown M. D., Kero J., Szasz C., Pellinen-Wannberg A., and Weryk R. J. (2012). �Photo-metri and ionization masses of meteors with si-multaneous EISCAT UHF radar and intensi�edvideo observations�. J. Geophys. Res.: Spa e Phys.,117:A9.Chau J. L. and Galindo F. (2008). �First de�nitive ob-servations of meteor shower parti les using a high-power large-aperture radar�. I arus, 194, 23�29.Chau J. L. and Woodman R. F. (2004). �Observa-tions of meteor-head e hoes using the Ji amar a50 MHz radar in interferometer mode�. Atmos.Chem. Phys., 4, 511�521.Close S., Hunt S. M., M Keen F. M., and MinardiM. J. (2002). �Chara terization of Leonid me-teor head e ho data olle ted using the VHF-UHFAdvan ed Resear h Proje ts Agen y Long-RangeTra king and Instrumentation Radar (ALTAIR)�.Radio S i., 37:1, 9-1�9-9.Close S., Hunt S. M., Minardi M. J., and M Keen F. M.(2000). �Analysis of Perseid meteor head e ho data olle ted using the Advan ed Resear h Proje tsAgen y Long-Range Tra king and InstrumentationRadar (ALTAIR)�. Radio S i., 35, 1233�1240.Elford G. W. (1993). �Radar observations of meteors(Invited)�. In �tohl J. and Williams I. P., editors,Meteoroids and their Parent Bodies, pages 235�244.Hey J. S., Parsons S. J., and Stewart G. S. (1947).�Radar observations of the Gia obinids meteorshower, 1946�. MNRAS, 107, 176�183.Kero J. (2008). High-resolution meteor exploration withtristati radar methods. Ph. D. thesis, Swedish In-stitute of Spa e Physi s, Kiruna, Sweden.Kero J., Fujiwara Y., Abo M., Szasz C., and NakamuraT. (2012a). �MU radar head e ho observations ofthe 2011 O tober Dra onids�. MNRAS, 424, 1799�1806.

Kero J., Szasz C., Nakamura T., Meisel D. D., UedaM., Fujiwara Y., Terasawa T., Miyamoto H., andNishimura K. (2011). �First results from the 2009-2010 MU radar head e ho observation programmefor sporadi and shower meteors: the Orionids2009�. MNRAS, 416, 2550�2559.Kero J., Szasz C., Nakamura T., Meisel D. D., UedaM., Fujiwara Y., Terasawa T., Nishimura K., andWatanabe J. (2012b). �The 2009-2010 MU radarhead e ho observation programme for sporadi and shower meteors: radiant densities and diurnalrates�. MNRAS, 425, 135�146.Kero J., Szasz C., Nakamura T., Terasawa T.,Miyamoto H., and Nishimura K. (2012 ). �A me-teor head e ho analysis algorithm for the lowerVHF band�. Ann. Geophys., 30, 639�659.Lindblad B. A. and Porub£an V. (1999). �Orionid Me-teor Stream�. Contrib. Astron. Obs. Skalnaté Pleso,29, 77�88.Malhotra A. and Mathews J. D. (2011). �A statisti alstudy of meteoroid fragmentation and di�erentialablation using the Resolute Bay In oherent S atterRadar�. J. Geophys. Res.: Spa e Phys., 116:A4.Mathews J. D., Bri zinski S. J., Meisel D. D., and Hein-selman C. J. (2008). �Radio and meteor s ien eout omes from omparisons of meteor radar obser-vations at AMISR Poker Flat, Sondrestrom andAre ibo�. Earth, Moon, and Planets, 102, 365�372.Mathews J. D., Meisel D. D., Hunter K. P., GetmanV. S., and Zhou Q. (1997). �Very high resolutionstudies of mi rometeors using the Are ibo 430 MHzradar�. I arus, 126, 157�169.Nygrén T. (1996). Introdu tion to in oherent s attermeasurements. Invers Oy, 1st edition.Pellinen-Wannberg A. and Wannberg G. (1994). �Me-teor observations with the European In oherentS atter UHF radar�. J. Geophys. Res.: Spa ePhys., 99:A6, 11379�11390.Sato T., Nakamura T., and Nishimura K. (2000). �Or-bit determination of meteors using the MU radar�.IEICE Trans. Commun., E83-B:9, 1990�1995.Szasz C. (2008). Radio meteors above the Ar ti Cir le:radiants, orbits and estimated magnitudes. Ph. D.thesis, Swedish Institute of Spa e Physi s, Kiruna,Sweden.Virtanen I. I., Lehtinen M. S., and Vierinen J. (2008).�Towards multi-purpose IS radar experiments�.Ann. Geophys., 26, 2281�2289.Zhou Q. H., Mathews J. D., and Nakamura T. (2001).�Impli ations of meteor observations by the MURadar�. Geophys. Res. Letters, 28, 1399�1402.