Relationship between Radar Cross Section and Optical Magnitude based on Radar and Optical Simultaneous Observations of Faint Meteors
Ryou Ohsawa, Akira Hirota, Kohei Morita, Shinsuke Abe, Daniel Kastinen, Johan Kero, Csilla Szasz, Yasunori Fujiwara, Takuji Nakamura, Koji Nishimura, Shigeyuki Sako, Jun-ichi Watanabe, Tsutomu Aoki, Noriaki Arima, Ko Arimatsu, Mamoru Doi, Makoto Ichiki, Shiro Ikeda, Yoshifusa Ita, Toshihiro Kasuga, Naoto Kobayashi, Mitsuru Kokubo, Masahiro Konishi, Hiroyuki Maehara, Takashi Miyata, Yuki Mori, Mikio Morii, Tomoki Morokuma, Kentaro Motohara, Yoshikazu Nakada, Shin-ichiro Okumura, Yuki Sarugaku, Mikiya Sato, Toshikazu Shigeyama, Takao Soyano, Hidenori Takahashi, Masaomi Tanaka, Ken'ichi Tarusawa, Nozomu Tominaga, Seitaro Urakawa, Fumihiko Usui, Takuya Yamashita, Makoto Yoshikawa
HHighlights
Relationship between Radar Cross Section and Optical Magnitude based on Radar and OpticalSimultaneous Observations of Faint Meteors
Ryou Ohsawa, Akira Hirota, Kohei Morita, Shinsuke Abe, Daniel Kastinen, Johan Kero, Csilla Szasz, Ya-sunori Fujiwara, Takuji Nakamura, Koji Nishimura, Shigeyuki Sako, Jun-ichi Watanabe, Tsutomu Aoki,Noriaki Arima, Ko Arimatsu, Mamoru Doi, Makoto Ichiki, Shiro Ikeda, Yoshifusa Ita, Toshihiro Kasuga,Naoto Kobayashi, Mitsuru Kokubo, Masahiro Konishi, Hiroyuki Maehara, Takashi Miyata, Yuki Mori,Mikio Morii, Tomoki Morokuma, Kentaro Motohara, Yoshikazu Nakada, Shin-ichiro Okumura, Yuki Saru-gaku, Mikiya Sato, Toshikazu Shigeyama, Takao Soyano, Hidenori Takahashi, Masaomi Tanaka, Ken’ichiTarusawa, Nozomu Tominaga, Seitaro Urakawa, Fumihiko Usui, Takuya Yamashita, Makoto Yoshikawa • In total, 331 meteors were detected simultaneously by radar and optically. • A correlation between the radar cross section and the optical magnitude is firmly confirmed. • The mass range of the meteor detected by MU radar is constrained to about 10 − –10 g. a r X i v : . [ a s t r o - ph . E P ] A ug elationship between Radar Cross Section and Optical Magnitude based onRadar and Optical Simultaneous Observations of Faint Meteors Ryou Ohsawa a,b , Akira Hirota c , Kohei Morita c , Shinsuke Abe c , Daniel Kastinen d , Johan Kero d , CsillaSzasz d , Yasunori Fujiwara e,n , Takuji Nakamura f , Koji Nishimura f , Shigeyuki Sako a , Jun-ichi Watanabe g ,Tsutomu Aoki b , Noriaki Arima a , Ko Arimatsu h , Mamoru Doi a,i , Makoto Ichiki a , Shiro Ikeda j , YoshifusaIta k , Toshihiro Kasuga l,g , Naoto Kobayashi a,b , Mitsuru Kokubo k , Masahiro Konishi a , Hiroyuki Maehara m ,Takashi Miyata a , Yuki Mori b , Mikio Morii j , Tomoki Morokuma a , Kentaro Motohara a , Yoshikazu Nakada a ,Shin-ichiro Okumura q , Yuki Sarugaku l , Mikiya Sato n , Toshikazu Shigeyama i , Takao Soyano b , HidenoriTakahashi a,b , Masaomi Tanaka k , Ken’ichi Tarusawa b , Nozomu Tominaga o,p , Seitaro Urakawa q , FumihikoUsui r , Takuya Yamashita g , Makoto Yoshikawa s a Institute of Astronomy, Graduate School of Science, The University of Tokyo, 2-21-1 Osawa, Mitaka, Tokyo 181-0015,Japan b Kiso Observatory, Institute of Astronomy, Graduate School of Science, The University of Tokyo 10762-30, Mitake,Kiso-machi, Kiso-gun, Nagano 397-0101, Japan c Department of Aerospace Engineering, College of Science & Technology, Nihon University, 7-24-1 Narashinodai, Funabashi,Chiba 274-8501, Japan d Swedish Institute of Space Physics, Box 812, SE-981 28 Kiruna, Sweden e SOKENDAI (The Graduate University for Advanced Studies), 10-3 Midoricho, Tachikawa, 190-8518 Tokyo, Japan f National Institute of Polar Research, 10-3, Midori-cho, Tachikawa-shi, Tokyo 190-8518, Japan g National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan h Astronomical Observatory, Graduate School of Science, Kyoto University, Kitashirakawa-oiwake-cho, Sakyo-ku, Kyoto606-8502, Japan i Research Center for the Early Universe, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku,Tokyo 113-0033, Japan j The Institute of Statistical Mathematics, 10-3 Midori-cho, Tachikawa, Tokyo 190-8562, Japan k Tohoku University, 6-3 Aramaki, Aoba, Aoba-ku, Sendai, Miyagi 980-8578, Japan l Department of Physics, Kyoto Sangyo University, Motoyama Kamigamo Kita-ku Kyoto 603-8555 Japan m Okayama Branch Office, Subaru Telescope, National Astronomical Observatory of Japan, NINS, Kamogata, Asakuchi,Okayama, Japan n The Nippon Meteor Society o Kavli Institute for the Physics and Mathematics of the Universe (WPI), The University of Tokyo, 5-1-5 Kashiwanoha,Kashiwa, Chiba 277-8583, Japan p Department of Physics, Faculty of Science and Engineering, Konan University, 8-9-1 Okamoto, Kobe, Hyogo 658-8501,Japan q Japan Spaceguard Association, Bisei Spaceguard Center, 1716-3 Okura, Bisei, Ibara, Okayama 714-1411, Japan r Center for Planetary Science, Graduate School of Science, Kobe University, 7-1-48 Minatojima- Minamimachi, Chuo-Ku,Kobe, Hyogo 650-0047, Japan s Japan Aerospace eXploration Agency, 3-1-1 Yoshinodai, Chuo-ku, Sagamihara, Kanagawa 252- 5210, Japan
Abstract
Radar and optical simultaneous observations of meteors are important to understand the size distribution ofthe interplanetary dust. However, faint meteors detected by high power large aperture radar observations,which are typically as faint as 10 mag. in optical, have not been detected until recently in optical observations,mainly due to insufficient sensitivity of the optical observations. In this paper, two radar and opticalsimultaneous observations were organized. The first observation was carried out in 2009–2010 using Middleand Upper Atmosphere Radar (MU radar) and an image-intensified CCD camera. The second observationwas carried out in 2018 using the MU radar and a mosaic CMOS camera, Tomo-e Gozen, mounted onthe 1.05-m Kiso Schmidt Telescope. In total, 331 simultaneous meteors were detected. The relationshipbetween radar cross sections and optical V -band magnitudes was well approximated by a linear function.A transformation function from the radar cross section to the V -band magnitude was derived for sporadicmeteors. The transformation function was applied to about 150,000 meteors detected by the MU radar in009–2015, large part of which are sporadic, and a luminosity function was derived in the magnitude rangeof − . . r = 3 . ± .
12. The present observation indicates that the MU radar has capability todetect interplanetary dust of 10 − –10 g in mass as meteors. Keywords: meteors, meteoroids, interplanetary medium
1. Introduction
Asteroids and comets are relatively active members in the solar system. They sometimes show cometaryactivities in the vicinity of the Sun and abruptly eject dust by collision or rapid rotation. The Earth issurrounded by small dust particles generated by such events, which are widely referred to as the interplan-etary dust. The mass and size distributions of the interplanetary dust provide important information tounderstand the origin and evolution of the solar system. The interplanetary dust grains are steadily collidingwith the Earth. The amount of the grains incoming to the Earth is estimated to be about 5–300 × kgper day (Plane, 2012), which largely consists of grains of 10 − –10 − g in mass (Flynn, 2002). The inter-planetary dust grains smaller than 10 − g have been intensively examined by direct dust detectors onboardspacecrafts (Gr¨un et al., 1985; Gruen et al., 1992; Gurnett et al., 1997; Szalay et al., 2013). A detectorwith a much larger collecting area is, however, required to investigate larger dust grains. Observing meteorsis a method to use the Earth’s atmosphere as a huge detector. Atoms and molecules in the atmosphereare ionized and excited by an interplanetary dust grain which enters the atmosphere. These processes areinterpreted by the theory of thermal ablation (Baldwin and Sheaffer, 1971; Ceplecha et al., 1998; Popova,2004). Part of the kinetic energy is converted into light. The fraction of the energy converted into light tothe lost kinetic energy is called the luminous efficiency , which is a key physical quantity to determine thebrightness of the meteor. Part of the kinetic energy is also used to ionize surrounding atmospheric molecules.The probability that an atmospheric atom is ionized on a deposition of a single atom from the meteoroidis called the ionization coefficient , which determines the electron density of the meteor. There are severalattempts to constrain these coefficients observationally (e.g., Verniani, 1965), experimentally (e.g., Boitnottand Savage, 1972; Friichtenicht and Becker, 1973; Thomas et al., 2016), and theoretically (e.g., Jones, 1997).Radar and optical observations are important to constrain these quantities. Radar meteors correspondingto extremely faint optical meteors have been detected in the meteor head echo observations with high powerand large aperture radar systems such as the European Incoherent Scatter (EISCAT) radars, AdvancedResearch Projects Agency Long-Range Tracking And Instrumentation Radar (ALTAIR), Middle-and-UpperAtmosphere radar (MU radar), the Middle Atmosphere ALOMAR Radar System (MAARSY), SouthernArgentine Agile MEteor Radar (SAAMER), and Poker Flat Incoherent Scatter Radar (PFISR) (Pellinen-Wannberg and Wannberg, 1994; Close et al., 2000; Sato et al., 2000; Kero et al., 2011; Schult et al., 2017;Fentzke et al., 2009; Sparks et al., 2009; Janches et al., 2014, 2015, 2019). Pellinen-Wannberg et al. (1998)estimated that EISCAT is able to detect meteors as faint as 10 mag based on the measurements of crosssections and event rates. Thanks to the advances of digital video cameras, such faint meteors have sincethen been detected optically. Meteors brighter than 4 mag are routinely collected by large meteor surveynetworks (Jenniskens, 2017), such as Cameras for All-sky Meteor Surveillance (CAMS; Jenniskens et al.,2011), European viDeo MeteOr Network Database (EDMOND; Kornos et al., 2013), and SonotaCo network(Kanamori, 2009). Recently, high-sensitive optical camera systems make it possible to observe meteors asfaint as ∼
10 mag in the optical regime (Nishimura et al., 2001; Weryk et al., 2013; Ohsawa et al., 2019). Sinceevery observation method is subject to biases and errors, simultaneous observations of the same meteorsusing different methods are important. Part of previous simultaneous observations are described here. Fu-jiwara et al. (1995) carried out simultaneous observations with the MU radar and three video cameras withimage intensifiers. In two observation runs, they detected 19 simultaneous meteors and suggested a log-linear
Email address: [email protected] (Ryou Ohsawa)
Preprint submitted to Planetary and Space Science August 21, 2020 elationship between the radar received power and the optical magnitude for Geminids. Nishimura et al.(2001) detected 35 simultaneous meteors during two nights using the MU radar and an image-intensifiedCCD video camera. They showed that the radar received power changed partly in synchronization with theoptical brightness. They also confirmed a log-linear relationship between the radar received power and theoptical magnitude for sporadic meteors. Michell (2010) detected seven meteors in optical out of 338 meteorsobserved with PFISR, and confirmed that a similar positive correlation between the optical brightness andthe back-scattered radar power. Using a combination of SAAMER and an EMCCD video camera, Michellet al. (2015) obtained 6 meteors simultaneously by radar and optically and showed that the meteoroidmasses independently estimated from the radar and optical observations were roughly consistent with eachother. Michell et al. (2019) carried out optical and dual-frequency radar observations with the Areciboradar and an EMCCD camera. In total, 19 meteor events were detected simultaneously in the three meth-ods. No apparent correlation between the optical mass and the radar signal-to-noise ratios was, however,confirmed. Since not a small fraction of the meteors were detected in side lobes, they presumed that theradar cross sections could be underestimated, resulting in a possible artificial bias. Campbell-Brown et al.(2012) carried out observations with EISCAT and two image-intensified CCD video cameras and detected4 meteors whose orbits were determined both by radar and optically. They confirmed that the photometricand ionization masses were consistent within estimated errors. Weryk and Brown (2013, 2012) used theCanadian Meteor Orbit Radar (CMOR) and multiple image-intensified CCD video cameras and detectedabout ∼
500 simultaneous meteors in the magnitude range of about 0–5 mag. They derived the relation-ship between the electron line density and the photon radiant power. The dependency of the ionizationcoefficient to the luminous efficiency ratio on the speed of meteors was observationally constrained. Theluminous efficiency they derived indicated that the meteoroid mass flux in the range 10 − –10 − g couldbe lower than previously estimated. Brown et al. (2017) carried out observations with MAARSY and twoimage-intensified video cameras. They detected more than 100 simultaneous meteors whose orbits wereconstrained both by radar and optically. The magnitudes of the detected meteors ranged from 0–7 mag.They found a clear trend where brighter meteors showed higher peak radar cross sections. More completeoverviews are found in Weryk and Brown (2012, 2013) and Brown et al. (2017). Although there have been anumber of radar and optical simultaneous observations in literature, meteors fainter than ∼ ∼
10 mag with a mosaic CMOS camera, Tomo-e PM, mounted on the 1.05-m Kiso Schmidt telescope. Acombination of a large and wide-field telescope and a mosaic CMOS camera is preferable to detect faintmeteors. Here, we report two simultaneous observations of faint sporadic meteors. The observations areintended to confirm the trends between the radar cross section in the meteor head echo observation and theoptical magnitude suggested in previous studies (Nishimura et al., 2002; Michell et al., 2015; Brown et al.,2017) with a large number of samples and a wide magnitude range. In the first observation run, observationswere carried out with the MU radar and an image-intensified CCD video camera in 2009–2010. The secondobservation run were carried out with the MU radar and Tomo-e Gozen, which is a successor of Tomo-ePM. The paper is organized as follows; Details of the observations are described in Section 2. Statisticalproperties of detected meteors are presented in Section 3. In Section 4, the relationship between the radarcross section and the optical brightness and the luminosity function of sporadic meteors are discussed, andthen Section 5 summarizes this paper.
2. Observations
The first observation run was carried out in 2009 and 2010 (hereafter, referred as to ICCD09). Spec-ifications of the observations are summarized in Table 1. We had several observations in 2009 and 2010.Radar observations were carried out with Middle and Upper Atmosphere Radar (hereafter, MU radar) in the3 able 1: Summary of Observations with the MU radar and ICCD camera in 2009–2010
Date Sep. 24–26, Oct. 19–21, Nov. 8, and Dec. 13–14 in 2009Mar. 11, Aug. 12, Sep. 13, and Dec. 14 in 2010Radar System Middle and Upper Atmosphere Radar (46.5 MHz)Optical System Canon 200 mm F/1.8 and Hamamatsu CCD camera (ORCA-05G)Video Frame Rate 29.97 HzField of View ∼ ◦ in diameter (radar), 9 . ◦ × . ◦ (optical) Table 2: Summary of Observations with the MU radar and Tomo-e Gozen in 2018
Date Apr. 18–22 in 2018 (11:00–20:00 UT, 36 hours in total)Radar System Middle and Upper Atmosphere Radar (46.5 MHz)Optical System 1.05-m Kiso Schmidt telescope and Tomo-e Gozen (Q1)Video Frame Rate 2.0 HzField of View ∼ ◦ in diameter (radar), 20 × . (cid:48) × . (cid:48) (optical) Shigaraki MU Observatory of Research Institute for Sustainable Humanosphere (RISH), Kyoto University.The MU radar was operated in the general head echo mode (Kero et al., 2011). Optical observations werecarried out with an image-intensified CCD camera made by Hamamatsu equipped with a Canon 200 mmF/1.8 lens. The optical camera system was set up in Shigaraki. The camera was pointed toward zenith andcontinuously monitored the sky at 29.97 Hz. GPS time stamps were imprinted in the video data. The radardata were reduced using a standard data reduction process of the MU radar (Kero et al., 2011, 2012a,b).The three dimensional trajectory and the radar cross section (RCS) along the trajectory of each meteor wereobtained. Meteors in the optical data were detected with a time shifted motion capture software, UFOCap-ture . The optical trajectories and the magnitudes of the meteors were derived with a post processing tool,UFOAnalyzer . The second observations were carried out in April, 2018 (hereafter, referred as to KISO18). Radarobservations were also carried out with the MU radar in the same setting as in ICCD09. Optical observationswere carried out with a mosaic CMOS camera, Tomo-e Gozen, mounted on the 1.05-m Schmidt Telescope inKiso Observatory of the Institute of Astronomy, the University of Tokyo. Specifications of the observationsare summarized in Table 2. Tomo-e Gozen is equipped with 84 CMOS image sensors of 2000 × . degree, and Tomo-e Gozen is able to monitorthe sky up to at 2 Hz (Sako et al., 2016, 2018; Kojima et al., 2018). The readout of the image sensor issynchronized with the GPS time and the time stamp of Tomo-e Gozen is as accurate as 0.2 ms (Sako et al.,2018). Observations are carried out in a clear filter and a nominal limiting magnitude for stars is about18 mag, which is corresponding to about 12 mag for meteors (Ohsawa et al., 2019). At the time of theobservations, only one quadrant of the camera was available and one sensor was not operating. Thus, theobservations were carried out with 20 CMOS sensors ( ∼ . . degree in total). The Kiso Schmidt telescopewas pointed toward the sky 100 km above the MU radar. Since the telescope tracked the sky, the direction ofthe telescope was adjusted every 3 minutes. Thus, the length of each video is 3 minutes. Kiso Observatory islocated about 173 km distant from the Shigaraki MU Observatory. The elevation angle of the telescope wasabout 30 ◦ and the distance between the telescope and the volume monitored by the MU radar was about200 km. The radar data were reduced in the same manner as in ICCD09. The three dimensional trajectory Shigaraki MU Observatory is located at +34 d m s . d m s .
24 E (WGS84). UFOCaptrueV2 (ver 2.24) in http://sonotaco.com/soft/e_index.html UFOAnalyzerV2 (ver 2.44) in http://sonotaco.com/soft/e_index.html Kiso Observatory is located at +35 d m s . d m s . l e v a t i o n a t K i s o O b s e r v a t o r y ( d e g ) Azimuth at Kiso Observatory (deg)
MU radar Streak Tomo-e Gozen Streak100 km 110 km 120 km
24 26 28 30 32 34 230 232 234 236 238 240
24 26 28 30 32 34 230 232 234 236 238 240
24 26 28 30 32 34 230 232 234 236 238 240
24 26 28 30 32 34 230 232 234 236 238 240
Figure 1: The meteors detected in KISO18 are projected onto the sky from Kiso Observatory in the elevation and azimuthcoordinates. Each panel illustrates the meteors detected in a night. The orange segments indicate the meteors detected bythe MU radar; The filled and empty circles are, respectively, the first and last detection points. The gray dashed lines arethe extensions of the MU trajectories for reference. The gray rectangles are the fields-of-view of Tomo-e Gozen. The redsegments indicate the meteors detected by Tomo-e Gozen. The blue segments indicate the distances between the meteorsegments detected by the MU radar and Tomo-e Gozen. The violet, green, and navy circles respectively indicate the center ofthe field-of-view of the MU radar at 100, 110, and 120 km in altitude. able 3: The Number of Sporadic Meteor Events in MURMHED Year Jan. Feb. Mar. Apr. May Jun. Jul. Aug. Sep. Oct. Nov. Dec.2009 — — — — — 3819 5465 — 5419 9071 4925 46322010 3398 2788 2000 2205 2479 3064 3570 8520 4441 21467 4856 83142011 — — — — — — — — — 6087 — —2012 — — — — — — — — — 10930 — —2013 3298 2231 1708 — — — — — — — — 133322014 3300 — — — 136 — — — — — — 64772015 — — — 2148 — — — — — — — —total 9996 5019 3708 4353 2615 6883 9035 8520 9860 47555 9781 32755and the RCS of each meteor were obtained. The optical data were reduced in a standard astronomicaldata reduction procedure for imaging observations: a dark frame was subtracted and a flat frame correctionwas applied. Meteors in the optical video data were extracted with an algorithm based on the Houghtransformation (Ohsawa et al., 2016, 2019). The detected events are summarized in Figure 1. The meteorsdetected by the MU radar are shown by the orange segments, while those detected by Tomo-e Gozen areshown by the red segments. The gray rectangles indicate the fields-of-view of Tomo-e Gozen. A number ofrectangles appear in Figure 1 since the telescope was moved frequently. The violet, green, and navy circlesin Figure 1 indicate the center of the field-of-view of the MU radar at different altitudes for reference. Thisindicates that the fields-of-view of Tomo-e Gozen were, however, slightly displaced due to a miscalculation.
Meteors detected by the MU radar were retrieved from an archival data, in order to discuss the luminosityfunction of faint meteors. Part of data were already published in (Kero et al., 2012a, 2011) and availablein the MU Radar Head Echo Database (MURMHED). All the data were reduced along with Kero et al.(2012b). The observations were carried out during 2009–2015 and the total observing time was 845.8 hour.The archive contains 157043 meteor events in total. The contributions from meteor showers were removedbased on the D-criterion , which is a criterion to determine whether a meteor belongs to a stream or not(Southworth and Hawkins, 1963). The threshold of the D-criterion was set to 0.2. This threshold is relativelyweak compared to previous studies which identify meteor showers by the D-criterion (e.g., Jenniskens andN´enon, 2016), but reasonable to roughly estimate the contributions from meteor showers (Andrei´c et al.,2014; ˇSegon et al., 2014; Gural et al., 2014; Andrei´c et al., 2013). Some sporadic meteors may be wronglyremoved due to the weak threshold, but the result will not be affected. The removed meteors were mainlycomposed of Geminids (1034), Orionids (2049), and η Aquariids (1900). Finally, 150080 meteors wereextracted as sporadic meteors. The archive was complied with several campaign observations. The numberof events per month is listed in Table 3. The table indicate that the observations were biased toward meteorsobserved in October and December.
3. Results
We define “a simultaneous meteor” as a meteor observed both by radar and optically. In case of ICCD09,simultaneous meteors were identified based on the trajectories and timings of meteors. When meteors weredetected both by radar and optically and the time separation was within 0.5 s, the meteors were considered asidentical. Finally 145 meteors were identified as the simultaneous events. Some observations were scheduled The calculation was based on the orbital elements of the 112 established meteor showers issued in the IAU Meteor DataCenter on February 17, 2020. ε Geminids, 16 η Aquariids, 1 October Capricornids, and 1 November Orionids. Theremaining 103 meteors were considered to be sporadic. In the following sections, the 103 sporadic meteorswere investigated. The brightness of the ICCD09 meteors were calibrated against the V -band magnitudesin SKY2000 catalog version 4 (Myers et al., 2001) using UFOAnalyzer. The correction of the color term wasnot applied. Note that the derived magnitudes could be affected by an amount depending on the unknownspectral character of the meteors. The light curve of each meteor was derived. About 20% of the meteorsshowed light bursts with amplitudes of larger than 1 . , mag in their light curves, possibly attributed tofragmentation. Such sudden bursts are not necessarily accompanied by variations in the RCS (e.g., Brownet al., 2017). The meteors obtained in KISO18 were rarely affected by such bursts since they were observed ina narrow fields-of-view. To enable a fair comparison with the magnitude in KISO18, the magnitude averagedover the streak was adopted as the representative value of each meteor, instead of the peak magnitude, sincethe latter could be affected by fragmentation. Since the bursts were sufficiently short, the variability inthe brightness had little effect on the average brightness values. Finally, the observed magnitudes wereconverted into the meteor absolute magnitudes. To extract simultaneous meteors, we first sifted the optical meteors detected within ± ◦ and the separation angle of the two trajectories (the blue segmentin Figure 1) should be smaller than 0.25 ◦ . When the same meteor was detected in multiple detectors, thebrightest segment was adopted as the representative one. The total number of unique simultaneous meteorswas 485 in the four nights. As shown in Figure 1, the pointing of the telescope was displaced. The radar andoptical observations sometimes traced completely different portions of the trajectory. The magnitudes of suchmeteors could be erroneous. Thus, we removed about 250 simultaneous meteors whose optical trajectorieswere not completely covered by the radar observations. A possible contribution from meteor showers wereremoved based on the D-criterion. In total, 5 meteors were removed. Finally, the sample size was reducedto 228, which accounted for about 8% of the total number of the meteors whose radar trajectories crossedthe fields-of-view of Tomo-e Gozen. In the following sections, the 228 simultaneous sporadic meteors wereinvestigated. The meteors in KISO18 were observed at 2 Hz. Thus, the meteors were captured as streaks.We calculated the magnitudes of the meteors, following the method used in Iye et al. (2007), to derive thebrightness of the meteors from the detected streaks. The brightness of the meteor was estimated by I v v T ,where I v is the line intensity averaged along the streak, v is the angular velocity of the meteor, and T isthe exposure time of each video frame. In Iye et al. (2007), the meteor speeds v were uniformly assumed tobe 10 ◦ s − . The magnitudes of meteors were also derived based on the same assumption in Ohsawa et al.(2019). This assumption was a major source of the uncertainty in those studies. In the KISO18 observation,the projected motion of each meteor was directly derived from the MU radar observation. The magnitudesin the present research were little affected by the uncertainty in the meteor speed. The magnitudes of themeteors were first calibrated against the V -band magnitudes of the UCAC4 catalog (Zacharias et al., 2013).The color term correction was not applied. Note that the derived magnitudes could be affected by an amountdependeng on the unknown spectral character of the meteors. Then, the magnitudes were finally convertedinto the meteor absolute magnitudes using the distance between the telescope and the meteors. The distributions of the absolute magnitude is shown in Figure 2. The top panel shows the distributionof ICCD09, while the bottom panel does that of KISO18. The brightest meteor in ICCD09 was 1 . . .
0, 6 . F r e q u e n c y Absolute magnitude in the V-band
MU + Tomo-e (228 events)
Figure 2: Magnitude distributions of the meteors simultaneously detected by radar and optically. The top panel shows themagnitude distribution of the observations in 2009–2010 (ICCD09), while the bottom panel illustrates that of the observationsin 2018 (KISO18). . . . .
4, 8 .
1, and 8 . . see Figure4 in Ceplecha et al., 1998). The altitudes of the KISO18 meteors are generally lower than those of theICCD09 meteors. As shown in Figure 1, the pointing of the telescope in KISO18 was displaced downwardin elevation. The fields-of-view of Tomo-e Gozen were set below about 30 ◦ in elevation, corresponding toabout 100 km in altitude above the MU radar. Since the differences between the highest and lowest altitudesis typically about 10 km in Figure 3, the meteors below 110 km were selectively detected as simultaneousmeteors in KISO18. Thus, the difference in the altitude distributions is explained by the observation bias.Consequently, the present samples contained few meteors which were fainter than about 7 mag and whosealtitudes were higher than 100 km. The geocentric velocities are plotted against the optical magnitudes inthe bottom panel of Figure 3. No apparent trend is confirmed. The distribution of the geocentric velocityis bimodal. Figure 4 shows the distribution of the meteor radiants in the Hammer projection of the eclipticlatitude and Sun-centered ecliptic longitude coordinates. The meteors whose geocentric velocity is fasterthan 45 km s − are shown by the orange symbols. The distribution of the faster population is consistentwith the apex sources (e.g, Hawkins, 1956a), while the slower populations are possibly attributed to theantihelion and north toroidal sources (e.g., Hawkins, 1956a; ˇStohl, 1968). No significant concentration isfound in Figure 4, suggesting that possible contributions from meteor showers were successfully removed.Figure 5 shows the optical absolute magnitude against the RCS, which is the value at the maximumsignal-to-noise ratio (SNR) along the whole radar trajectory. On the other hand, the brightest magnitudeswere independently measured in the optical observations. Thus, the section where the RCS was measuredand the section where the optical brightness was measured could be different. A possible uncertainty dueto this time difference is discussed later. The data of ICCD09 and KISO18 seem to follow the same trend,where the optical magnitude became brighter as the RCS bacame larger. The trend was approximated by alinear regression line. Since there was large scatter in Figure 5, trial regression lines were calculated both interms of the RCS and the magnitude via a least-square method and then the line with the averaged slopewas adopted as the representative regression line: M V = − (0 . ± . × A + (4 . ± . , (1)where M V is the meteor absolute magnitude in the V -band and A is the radar cross section in units ofdBsm (decibel relative to 1 m ). The representative regression line is shown by the blue dashed line inFigure 5. The uncertainties were estimated by the bootstrapping method. It should be noted that, since thecolor-term correction was not applied, the present result could suffer from a systematic bias due to differentspectral responses of the cameras. Such a possible bias was not taken into account in the uncertainties inEquation (1).
4. Discussion
Figure 5 indicates that the data follow a single and linear relationship. No apparent deviation fromthe regression line is confirmed. The dependence of the relationship on the meteor speed is investigated bysplitting the sample into the fast ( >
45 km s − ) and slow ( ≤
45 km s − ) members, but no significant differenceis confirmed. This suggests that sporadic meteors from the apex, antihelion, and north toroidal sourcesfollow the same relationship. The scatter in Figure 5 is much larger than the errors of the data. This mayin part be due to the fact that the sections where the RCS and the optical magnitude were measured wereclose but not exactly the same. Both the RCS and the optical brightness are variable along the trajectory9
80 90 100 110 120 M e t e o r A l t i t u d e ( k m ) MU + CCDMU + Tomo-e 0 10 20 30 40 50 60 70 80 1 2 3 4 5 6 7 8 9 10 11 G e o c e n t r i c V e l o c i t y ( k m s - ) Absolute Magnitude in the V-band
MU + CCDMU + Tomo-e
Figure 3: The altitude and the geocentric velocity are shown against the optical magnitude in the V -band. The data of ICCD09are shown by the black circle symbols, while those of KISO18 are shown by the red square symbols. The top panel illustratesthe observed heights in km. The empty and filled symbols are respectively the highest and lowest altitudes measured by theMU radar. The geocentric velocity in km s − is shown in the bottom panel. U + CCD (v<45km) MU + CCD (v>45km) MU + Tomo-e (v<45km) MU + Tomo-e (v>45km)Sun-Centered Ecliptic Longitude (deg) E c l i p t i c L a t i t u d e ( d e g )
60º 30º 0º 330º 300º 270º 240º 210º 180º 150º 120º-40º-20º0º 20º 40º 60º
Figure 4: The radiant distribution of the simultaneous meteors in the Sun-centered Ecliptic coordinates. The data of ICCD09are shown by the circle symbols, while those of KISO18 are shown by the square symbols. The meteors whose geocentricvelocities are faster than 45 km s − are shown in orange, while the meteors slower than 45 km s − are shown in green. A b s o l u t e M a g n i t u d e i n t h e V - b a n d RCS at the maximum SNR (dBsm)
MU + CCDMU + Tomo-eLinear Regression
Figure 5: The relationship between the radar cross section and the optical absolute magnitude in the V -band. The meteors ofICCD09 and KISO18 are shown by the black circle and red square symbols, respectively. The blue dashed line indicates thelinear regression line. see Figure 11 in Brown et al., 2017). The variation in the RCS and the optical brightness shouldcontribute to the scatter. Especially, fragmentation may cause a sudden increase in the RCS and opticalbrightness, but the impacts of the fragmentation on the RCS and the magnitude are not necessarily thesame (Campbell-Brown et al., 2013; Brown et al., 2017). Fragmentation may cause pulsations in head echoRCS curves due to interference from two or more scattering centers (Kero et al., 2008), while the luminosityproduced is assumed to be proportional to the total kinetic energy lost by the meteoroid (Campbell-Brownet al., 2013), thus proportional to the increased cross-sectional area to mass of the fragments. Weryk et al.(2013) reported that 17% of meteors detected by the CAMO system showed clear signs of fragmentation.Similarly, a significant fraction of the data in Figure 5 could be affected by fragmentation. This may partlyexplain the large scatter: ∼ ∼
10 dBsm in the RCS, which are roughlyconsistent with the changes caused by the fragmentation. Several studies have suggested that the ratio ofthe emission to ionization coefficients depends on the velocity (Saidov and Simek, 1989; Jones, 1997; Werykand Brown, 2013). This dependence may contribute to the scatter, but the difference in the distributionswas not confirmed in the present data. A variety of chemical compositions may contribute to the scatter.Spectroscopic observations are required to confirm it. Although the origin of the large scatter has not beenidentified, we tentatively conclude that the relationship between the RCS and the optical magnitude is wellapproximated by a linear function over a magnitude range of about 1–9 mag, but we do not exclude thepossibility that any deviations from the linear relationship are hidden within the scatter. The possibilitythat the relationship is variable or there are multiple relationships is not excluded as well. The scatter can beattributed to possible variations in the relationship. In such a case, the present relationship is considered tobe an averaged one over the current dataset. Note that the uncertainties in Equation (1) were derived withthe assumption that the relationship is unique among the dataset, where the variation in the relationship wasnot taken into account. A scattering model of a head echo plasma was developed by Close et al. (2004), whichprovided a method to estimate the meteoroid mass, referred as to scattering mass , from the head echo RCS(Close et al., 2005). Close et al. (2007) investigated the dependence of the head echo RCS on the electronline density ( q ), the scattering mass ( m s ), the velocity ( v ), and the mean-free-path ( l ). A multivariateregression provided a relationship q ∝ m . v . l − . and the head echo RCS ( A ) was approximated as A ∝ q . ∝ m . × . . Here, we simply assume that the brightness of the meteor approximately follows I ∝ m p , where m p is the photometric mass. By equating m s with m p , a relationship between the magnitude( M V ) and the head echo RCS is derived: M V = − . A + const. The slope of this relationship is similar tobut steeper than the present result. This may implicate that the dependence of the head echo RCS is largerthan suggested in Close et al. (2007), or that the dependence of the optical brightness on the meteoroidmass is smaller. Note that the comparison above is highly simplified. A model calculation which evaluatesthe head echo RCS and the optical brightness simultaneously is required. Nishimura et al. (2001) provided aconversion function from the optical magnitude to the radar received power in units of dB, where the opticalmagnitude decreased by about 0 . − .
3. Since their result was derived from 20 simultaneous meteors, the slope could be affected by aconsiderable uncertainty. We estimate the uncertainty of the slope in case that the sample size is limited to20 using a bootstrap sampling method: 20 meteors are randomly selected from the present 332 simultaneousmeteors and a slope is derived by a least-square method. This process is repeated 1,000 times. Then, theposterior probability distribution of the slope is approximated by the distribution of the derived slopes. The95% confidence interval is ( − . , − . see , Figure 9). While no regression line waspresented, the optical magnitude decreased roughly by 0 . .
16 mag when the RCS increased by 1 dB. Theslope seems smaller than that of the present result. The optical magnitudes ranged over roughly 0–6 mag inBrown et al. (2017), while only a handful of meteors were detected in this magnitude range in the presentwork. The possibility that the relationship changes around 5 mag is not excluded. The data of ICCD09and KISO18 were obtained using different systems and on different days. Equation (1) could suffer fromsystematic errors, such as the difference in spectral response and the annual variations. Further observationsare required to evaluate the uncertainty of Equation (1). The data of KISO18 were obtained in only fournights. This suggests that the combination of the MU radar and Tomo-e Gozen is promising to investigate12 -6 -5 -4 -3 -2 -1 (a) C u m u l a t i v e N u m b e r F l u x ( h - k m - ) RCS with constant collecting areaRCS with collecting area correction 10 -6 -5 -4 -3 -2 -1 -40-2002040 (b) A r e a ( k m ) RCS at the maximum SNR (dBsm) -40-2002040 -7 -6 -5 -4 -3 -2 -1 -2 0 2 4 6 8 10 12 (c) C u m u l a t i v e N u m b e r F l u x ( h - k m - ) Absolute Magnitude in the V-band
Luminosity Function of Sporadic MeteorsPower-law regression curve (r = 3.52) 10 -7 -6 -5 -4 -3 -2 -1 -2 0 2 4 6 8 10 12 Figure 6: The luminosity function of sporadic meteors. Panel (a) shows the cumulative number flux against the RCS. The blackdashed line indicates the number flux assuming that the meteor collecting area does not depend on the RCS. The number fluxshown by the red line properly takes into account the dependency. The shaded regions indicate 1 σ - and 3 σ -level uncertainties.The dependency of the meteor collecting area on the RCS is illustrated in Panel (b) in the red line. The black dashed line isthe constant collecting area for reference. Panel (c) shows the luminosity function of sporadic meteors. The uncertainties arethe same as in Panel (a). A regression curve is shown by the blue dashed line. the annual and diurnal variations in the relationship between the RCS and the optical magnitude. A luminosity function of visible meteors has been widely approximated by a power-law function (Hawkinsand Upton, 1958): log N ( 100 km ) isderived for each meteor by interpolating or extrapolating the trajectory. The area of πR is calculated.The data are divided into groups in the RCS and the median of the area among each group is adopted asthe collecting area as a function of the RCS. The derived collecting area against the RCS is shown in Panel(b) of Figure 6. The cumulative number flux calculated based on the derived collecting area is shown bythe red line with the 1 σ - and 3 σ -uncertainty regions in Figure 6. The cumulative number flux larger than25 dBsm is highly uncertain. The cumulative number flux peaks out around − 25 dBsm simply due to thedetection limit. In a range from − 20 to 20 dBsm, the cumulative number flux seems well approximated by13 able 4: The population indexes in literature Reference r -index s -index CommentHawkins and Upton (1958) ∼ . ∼ . − . . − . ± . 04 30000 HF radar echoesClifton (1973) ∼ . ∼ . 252 7–11 mag, TV observationHughes (1974) 3 . ± . 07 2 . ± . − . ± . 04 3–7 mag, TV observationˇStohl (1976) 3 . 70 — 12867 visual meteorsCook et al. (1980) 3 . 41 2 . 335 7–12 mag, phototubesRendtel (2004) 2 . ± . 06 2 . ± . 03 301499 visual meteors, IMO VMDBOhsawa et al. (2019) 3 . ± . . ± . 12 2 . ± . 09 0–9 mag, MURMHEDa linear function. The cumulative number flux against the RCS is converted into the luminosity function byapplying Equation (1). Panel (c) of Figure 6 illustrates the luminosity function in the red line with the 1 σ -and 3 σ -uncertainty regions. The luminosity function basically follows an exponential law, which is consistentwith previous works (e.g., Hawkins and Upton, 1958; Hawkes and Jones, 1975b; Cook et al., 1980; Ohsawaet al., 2019). The detection limit corresponds to about 10 mag, which is roughly consistent with the detec-tion limit for EISCAT in Pellinen-Wannberg et al. (1998). The population index is derived as r = 3 . ± . − . . -3 -2 -1 -2 0 2 4 6 8 10 12 (a-1) N o r m a l i z e d C u m u l a t i v e N u m b e r F l u x Absolute Magnitude in the V-band January (3.37)February (3.35)March (3.43)April (3.45)May (3.41)June (3.51)July (3.60)August (3.38)September (3.59)October (3.60)November (3.71)December (3.45) 10 -3 -2 -1 -2 0 2 4 6 8 10 12 (a-2) r - i n d e x Month -3 -2 -1 -2 0 2 4 6 8 10 12 (b-1) N o r m a l i z e d C u m u l a t i v e N u m b e r F l u x Absolute Magnitude in the V-band ⎯ ⎯ ⎯ ⎯ ⎯ ⎯ ⎯ ⎯ ⎯ ⎯ ⎯ ⎯ -3 -2 -1 -2 0 2 4 6 8 10 12 (b-2) r - i n d e x Local Time (hour) Figure 7: Panel (a-1) shows the month-by-month variation in the luminosity functions, while the diurnal variation in theluminosity functions is shown in Panel (b-1). All the luminosity functions are normalized around 5 mag. The numbers in thelegends of each panel indicate the population indexes. The annual and diurnal variations in the population index are shownin Panels (a-2) and (b-2), respectively. The times are based on the detection time stamps in the local time (Japan StandardTime). north toroidal sources. The meteors from these sources are typically slower than those from the apex sources,which are dominant in the radar observation (Kero et al., 2012a). Thus, the meteors which were used toderive Equation (1) could be biased toward a larger part of the meteor population. Part of the diurnalvariation can be attributable to such an observational bias. More systematic observations are required toexamine the validity of the present results. The optical magnitude is converted into mass using the ablationequations (e.g., Hawkes and Jones, 1975a; Ceplecha et al., 1998). When a meteoroid enters the atmosphere,it is decelerated and heated through interactions with atmospheric constitutions. The meteoroid loses itskinetic energy by decreasing bot its mass and velocity. Part of the lost energy is converted into light andobserved in optical. The fraction of the meteoroid’s kinetic energy which is converted into light is calledthe luminous efficiency. The thermal ablation of a meteoroid is calculated following the procedure givenby Hill et al. (2005). The parameters in the ablation equations are adopted from Hill et al. (2005). Atypical molecular mass and bulk density are respectively set to 50 amu and 3300 kg m − . The calculationends when the meteoroid loses 99.999% of the initial mass. The brightest magnitudes are calculated usingthe normal luminous equation for different meteoroid masses (10 , , . . . , − g), radiant zenith angles(0 , ◦ , ◦ , ◦ , and 90 ◦ ), and initial velocities (10 , , . . . , 70 km / s). The luminous efficiency is takenfrom Hill et al. (2005), but scaled by 0.081 as described in Weryk and Brown (2013). Then, a relationshipto calculate the meteoroid mass from the magnitude, velocity, and radiant zenith angle is approximated bythe following function: log m = 2 . − . M V − . 31 log V ∞ − . 07 log cos z, (3)where m is the mass in units of g, M V is the optical magnitude, V ∞ is the incident velocity in units of km s − ,and z is the zenith angle of the radiant point. V ∞ and z are calculated from the trajectories measured bythe MU radar. The deviation from Equation (3) is typically up to about 0 . The scaling factor in Weryk and Brown (2013) is 0 . × . 28, which was optimized to the observation in the R -band. It isfurther multiplied by 0.638, which is the band width ration of V -band to the R -band. -6 -5 -4 -3 -2 -1 -6 -5 -4 -3 -2 -1 C u m u l a t i v e N u m b e r F l u x ( h - k m - ) Meteoroid Mass (g) Mass Function (Hill+ 2005)Power-law regression (s = 2.46) 10 -6 -5 -4 -3 -2 -1 -6 -5 -4 -3 -2 -1 Figure 8: The mass function of sporadic meteors is shown by the red line. The 1 σ - and 3 σ -level uncertainties are shown by theshaded regions. The blue dashed line indicates the regression curve. on the selection of a luminous coefficient. While the current calculation uses the scaled luminous coefficientof Hill et al. (2005), larger luminous coefficients were reported by Ceplecha and Revelle (2005) and Werykand Brown (2013). If we adopt those luminous coefficients, the derived mass could be smaller by about anorder of magnitude. The cumulative mass distribution, or the mass function, is illustrated in Figure 8. Themass function peaks out around 10 − g, which is attributed to the mass detection limit. The mass functionis expected to follow a power-law function:log N ( >m ) = log N − ( s − 1) log m, (4)where m is the meteoroid mass in units of g , N ( >m ) and N are the event rates of meteors larger than m and 1 g, respectively, and s defines the slope of the mass function, referred as to the mass index . Thederived regression curve is shown by the blue line. Some mass indexes in literature are listed in Table 4.The mass function deviates from the regression curve around 10 − g. This deviation is likely not a realfeature, but could be attributed to the observational bias: the detection limit is given by the RCS ratherthan the meteoroid mass. The derived mass index is 2 . ± . 09. This value is similar to that in Hughes(1974) and Cook et al. (1980). The mass flux to the Earth in the mass range of 10 − –10 g is about3 × kg day − . Ceplecha (1992) provided an incremental mass flux of interplanetary bodies by compilingseveral observational researches. By integrating it from 10 − to 10 g, the mass flux was 1 × kg day − ,which is roughly coincident with our estimation. Love and Brownlee (1993), however, estimated the massflux in the similar mass range to be about 1 × kg day − from the examinations of impact craters on theLong Duration Exposure Facility satellite. The current estimate is more than an order smaller than theirestimate. Note that the estimated mass flux depends on the selection of the luminous efficiency. The massflux will be smaller if the luminous efficiencies of Ceplecha and Revelle (2005) and Weryk and Brown (2013)are applied. 16 . Conclusion We report the results of the two radar-and-optical simultaneous observations of faint meteors. The firstobservation run was in 2009–2010, using Middle and Upper Atmosphere Radar (MU radar) and an image-intensified CCD video camera equipped with a Canon 200 mm F/1.8 lens. In total, 103 simultaneous sporadicmeteors were detected and a typical magnitude was about 6 . . > 45 km s − ) and slow ( ≤ 45 km s − ) populations are attributed to theapex sources and the antihelion or north-toroidal sources, respectively. The optical magnitude calibrated tothe V -band linearly decreased with increasing radar cross section (RCS) at the peak signal-to-noise ratio.The linear regression line was derived as: M V = ( − . ± . × A + (4 . ± . M V is the V -bandmagnitude and A is the RCS in units of dBsm. The slope of the regression line was marginally consistentwith that in Nishimura et al. (2001). The slope in Brown et al. (2017), which was obtained in a magnituderange of 0–6 mag, was smaller than the present result. Further observations are required to investigate thedifference in the slopes. Although there is large scatter around the regression line, we confidently obtaineda conversion function from the RCS to the optical magnitude. By applying the derived conversion functionto more than 150,000 meteors collected from the MU Radar Meteor Head Echo Database (MURMHED), wecompile a luminosity function of faint sporadic meteors in units of hour − km − . The luminosity function iswell approximated by an exponential function in a magnitude range of − . . r is constrained to be 3 . ± . 12 by fitting the exponential function. The luminosity function peaks outaround 10 mag, corresponding to the detection limit of the MU radar. The annual and diurnal variationsin the luminosity function are investigated. The present result shows the opposite trend to the trendsin literature (ˇStohl, 1976; Rendtel, 2004). This is possibly explained by assuming the trend changes in atimescale of decades or that the trend depends on the optical magnitude. The present diurnal variationis consistent with previous works, suggesting that the diurnal variation is less dependent on the opticalmagnitude. The optical magnitude was converted into the mass of the meteoroid based on the thermalablation theory and the luminous efficiency in Hill et al. (2005) but scaled by 0.081 as described in Werykand Brown (2013). The size index s is constrained to be 2 . ± . 09 by fitting a power-law function. Themass function peaks out around 10 − g. We conclude that the MU radar is able to detect interplanetaryparticles of 10 − –10 g in mass as meteors. The mass flux to the Earth in this mass range is estimated to be afew 10 kg day − , but this amount could suffer from the uncertainty in the luminous efficiency. The presentresults are based on the relationship between the RCS and the optical magnitude. This is derived fromthe two observation runs, which were conducted with the different observing systems and in the differentseasons. The derived relationship is possibly affected by systematic errors which are not taken into accountin the current analysis. Further systematic observations are required to validate the present results. Thecombination of the MU radar and Tomo-e Gozen seems promising to conduct such observations and toinvestigate statistical characteristics of faint meteors. Acknowledgments This research has been partly supported by Japan Society for the Promotion of Science (JSPS) Grants-in-Aid for Scientific Research (KAKENHI) Grant Numbers 26287106, 16H02158, 16H06341, 18H01272,18H01261, 18H04575, and 18K13599. This research is also supported in part by the Japan Science andTechnology (JST) Agency’s Precursory Research for Embryonic Science and Technology (PRESTO), theResearch Center for the Early Universe (RESCEU), of the School of Science at the University of Tokyo, andthe Optical and Near-infrared Astronomy Inter-University Cooperation Program. The meteor head echodata (MURMHED) used in this study have been created by T. Nakamura (NIPR, Japan), J. Kero (IRF,Sweden) and members of the radar meteor head echo database group under the support by JSPS Grant-in-Aid for Publication of Scientific Research Results (KAKENHI Databases) Grant Number 258033. The17U radar belongs to and is operated by RISH (Research Institute of Sustainable Humanosphere), KyotoUniversity. References Andrei´c, ˇZ., Gural, P., ˇSegon, D., Skoki´c, I., Korlevi´c, K., Vida, D., Novoselnik, F., Gostinski, D., 2014. Results of CMN2013 search for new showers across CMN and SonotaCo databases I-0.5mm. WGN, Journal of the International MeteorOrganization 42, 90–97.URL http://adsabs.harvard.edu/abs/2014JIMO...42...90A Andrei´c, ˇZ., ˇSegon, D., Korlevi´c, K., Novoselnik, F., Vida, D., Skoki´c, I., 2013. Ten possible new showers from the CroatianMeteor Network and SonotaCo datasets. WGN, Journal of the International Meteor Organization 41, 103–108.URL http://adsabs.harvard.edu/abs/2013JIMO...41..103A Baldwin, B., Sheaffer, Y., 1971. Ablation and breakup of large meteoroids during atmospheric entry. Journal of GeophysicalResearch 76, 4653.URL https://ui.adsabs.harvard.edu/abs/1971JGR....76.4653B/abstract Boitnott, C. A., Savage, H. F., 1972. Light-Emission Measurements of Iron at Simulated Meteor Conditions. The AstrophysicalJournal 174, 201.URL http://adsabs.harvard.edu/abs/1972ApJ...174..201B Brown, P., Stober, G., Schult, C., Krzeminski, Z., Cooke, W., Chau, J. L., 2017. Simultaneous optical and meteor head echomeasurements using the Middle Atmosphere Alomar Radar System (MAARSY): Data collection and preliminary analysis.Planetary and Space Science 141, 25–34.URL https://ui.adsabs.harvard.edu/abs/2017P%26SS..141...25B/abstract Campbell-Brown, M. D., Boroviˇcka, J., Brown, P. G., Stokan, E., 2013. High-resolution modelling of meteoroid ablation.Astronomy and Astrophysics 557, A41.URL http://adsabs.harvard.edu/abs/2013A%26A...557A..41C Campbell-Brown, M. D., Kero, J., Szasz, C., Pellinen-Wannberg, A., Weryk, R. J., 2012. Photometric and ionization masses ofmeteors with simultaneous EISCAT UHF radar and intensified video observations. Journal of Geophysical Research (SpacePhysics) 117 (A9), A09323.URL https://ui.adsabs.harvard.edu/abs/2012JGRA..117.9323C/abstract Ceplecha, Z., 1992. Influx of interplanetary bodies onto earth. Astronomy and Astrophysics 263, 361–366.URL http://adsabs.harvard.edu/abs/1992A%26A...263..361C Ceplecha, Z., Boroviˇcka, J., Elford, W. G., Revelle, D. O., Hawkes, R. L., Porubˇcan, V., ˇSimek, M., 1998. Meteor Phenomenaand Bodies. Space Science Reviews 84, 327–471.URL https://ui.adsabs.harvard.edu/abs/1998SSRv...84..327C/abstract Ceplecha, Z., Revelle, D. O., 2005. Fragmentation model of meteoroid motion, mass loss, and radiation in the atmosphere.Meteoritics and Planetary Science 40 (1), 35.URL http://adsabs.harvard.edu/abs/2005M%26PS...40...35C Clifton, K. S., 1973. Television studies of faint meteors. Journal of Geophysical Research 78, 6511.URL https://ui.adsabs.harvard.edu/abs/1973JGR....78.6511C/abstract Close, S., Brown, P., Campbell-Brown, M., Oppenheim, M., Colestock, P., 2007. Meteor head echo radar data: Mass-velocityselection effects. Icarus 186, 547–556.URL https://ui.adsabs.harvard.edu/abs/2007Icar..186..547C/abstract Close, S., Hunt, S. M., Minardi, M. J., McKeen, F. M., 2000. Analysis of Perseid meteor head echo data collected using theAdvanced Research Projects Agency Long-Range Tracking and Instrumentation Radar (ALTAIR). Radio Science 35, 1233.URL https://ui.adsabs.harvard.edu/abs/2000RaSc...35.1233C/abstract Close, S., Oppenheim, M., Durand, D., Dyrud, L., 2005. A new method for determining meteoroid mass from head echo data.Journal of Geophysical Research (Space Physics) 110, A09308.URL http://adsabs.harvard.edu/abs/2005JGRA..110.9308C Close, S., Oppenheim, M., Hunt, S., Coster, A., 2004. A technique for calculating meteor plasma density and meteoroid massfrom radar head echo scattering. Icarus 168, 43–52.URL http://adsabs.harvard.edu/abs/2004Icar..168...43C Cook, A. F., Weekes, T. C., Williams, J. T., Omongain, E., 1980. Flux of optical meteors down to MPG = +12. MonthlyNotices of the Royal Astronomical Society 193, 645–666.URL https://ui.adsabs.harvard.edu/abs/1980MNRAS.193..645C/abstract Fentzke, J. T., Janches, D., Sparks, J. J., 2009. Latitudinal and seasonal variability of the micrometeor input function: A studyusing model predictions and observations from Arecibo and PFISR. Journal of Atmospheric and Solar-Terrestrial Physics71, 653–661.URL https://ui.adsabs.harvard.edu/abs/2009JASTP..71..653F/abstract Flynn, G. J., 2002. Extraterrestrial Dust in the Near-Earth Environment. In: Meteors in the Earth’s Atmosphere. p. 77.URL https://ui.adsabs.harvard.edu/abs/2002mea..book...77F/abstract Friichtenicht, J. F., Becker, D. G., 1973. Determination of Meteor Parameters Using Laboratory Simulation Techniques. NASASpecial Publication 319, 53.URL http://adsabs.harvard.edu/abs/1973NASSP.319...53F ujiwara, Y., Ueda, M., Nakamura, T., Tsutsumi, M., 1995. Simultaneous Observations of Meteors with the Radar and TVSystems. Earth Moon and Planets 68, 277–282.URL https://ui.adsabs.harvard.edu/abs/1995EM%26P...68..277F/abstract Gruen, E., Fechtig, H., Kissel, J., Linkert, D., Maas, D., McDonnell, J. A. M., Morfill, G. E., Schwehm, G., Zook, H. A., Giese,R. H., 1992. The ULYSSES dust experiment. Astronomy and Astrophysics Supplement Series 92, 411–423.URL https://ui.adsabs.harvard.edu/abs/1992A%26AS...92..411G/abstract Gr¨un, E., Zook, H. A., Fechtig, H., Giese, R. H., 1985. Collisional balance of the meteoritic complex. Icarus 62, 244–272.URL https://ui.adsabs.harvard.edu/abs/1985Icar...62..244G/abstract Gural, P., ˇSegon, D., Andrei´c, ˇZ., Skoki´c, I., Korlevi´c, K., Vida, D., Novoselnik, F., Gostinski, D., 2014. Results of CMN 2013search for new showers across CMN and SonotaCo databases II. WGN, Journal of the International Meteor Organization42, 132–138.URL http://adsabs.harvard.edu/abs/2014JIMO...42..132G Gurnett, D. A., Ansher, J. A., Kurth, W. S., Granroth, L. J., 1997. Micron-sized dust particles detected in the outer solarsystem by the Voyager 1 and 2 plasma wave instruments. Geophysical Research Letters 24, 3125–3128.URL https://ui.adsabs.harvard.edu/abs/1997GeoRL..24.3125G/abstract Hawkes, R. L., Jones, J., 1975a. A quantitative model for the ablation of dustball meteors. Monthly Notices of the RoyalAstronomical Society 173, 339–356.URL https://ui.adsabs.harvard.edu/abs/1975MNRAS.173..339H/abstract Hawkes, R. L., Jones, J., 1975b. Television observations of faint meteors. I - Mass distribution and diurnal rate variation.Monthly Notices of the Royal Astronomical Society 170, 363–377.URL https://ui.adsabs.harvard.edu/abs/1975MNRAS.170..363H/abstract Hawkins, G. S., 1956a. A radio echo survey of sporadic meteor radiants. Monthly Notices of the Royal Astronomical Society116, 92.URL https://ui.adsabs.harvard.edu/1956MNRAS.116...92H/abstract Hawkins, G. S., 1956b. Variation in the occurrence rate of meteors. The Astronomical Journal 61, 386.URL https://ui.adsabs.harvard.edu/abs/1956AJ.....61..386H/abstract Hawkins, G. S., Upton, E. K. L., 1958. The Influx Rate of Meteors in the Earth’s Atmosphere. The Astrophysical Journal 128,727.URL https://ui.adsabs.harvard.edu/abs/1958ApJ...128..727H/abstract Hill, K. A., Rogers, L. A., Hawkes, R. L., 2005. High geocentric velocity meteor ablation. Astronomy and Astrophysics 444,615–624.URL http://adsabs.harvard.edu/abs/2005A%26A...444..615H Hughes, D. W., 1974. The influx of visual sporadic meteors. Monthly Notices of the Royal Astronomical Society 166, 339.URL https://ui.adsabs.harvard.edu/1974MNRAS.166..339H/abstract Hughes, D. W., Stephenson, D. G., 1972. The diurnal variation in the massdistribution of sporadic meteors. Monthly Noticesof the Royal Astronomical Society 155, 403.URL https://ui.adsabs.harvard.edu/1972MNRAS.155..403H/abstract Iye, M., Tanaka, M., Yanagisawa, M., Ebizuka, N., Ohnishi, K., Hirose, C., Asami, N., Komiyama, Y., Furusawa, H., 2007.SuprimeCam Observation of Sporadic Meteors during Perseids 2004. Publications of the Astronomical Society of Japan 59,841–855.URL https://ui.adsabs.harvard.edu/abs/2007PASJ...59..841I/abstract Janches, D., Brunini, C., Hormaechea, J. L., 2019. A Decade of Sporadic Meteoroid Mass Distribution Indices in the SouthernHemisphere Derived from SAAMERs Meteor Observations. The Astronomical Journal 157 (6), 240.URL http://adsabs.harvard.edu/abs/2019AJ....157..240J Janches, D., Close, S., Hormaechea, J. L., Swarnalingam, N., Murphy, A., O’Connor, D., Vandepeer, B., Fuller, B., Fritts,D. C., Brunini, C., 2015. The Southern Argentina Agile MEteor Radar Orbital System (SAAMER-OS): An Initial SporadicMeteoroid Orbital Survey in the Southern Sky. The Astrophysical Journal 809, 36.URL https://ui.adsabs.harvard.edu/abs/2015ApJ...809...36J/abstract Janches, D., Hocking, W., Pifko, S., Hormaechea, J. L., Fritts, D. C., Brunini, C., Michell, R., Samara, M., 2014. Interferometricmeteor head echo observations using the Southern Argentina Agile Meteor Radar. Journal of Geophysical Research (SpacePhysics) 119, 2269–2287.URL http://adsabs.harvard.edu/abs/2014JGRA..119.2269J Jenniskens, P., 2017. Meteor showers in review. Planetary and Space Science 143, 116–124.URL Jenniskens, P., Gural, P. S., Dynneson, L., Grigsby, B. J., Newman, K. E., Borden, M., Koop, M., Holman, D., 2011. CAMS:Cameras for Allsky Meteor Surveillance to establish minor meteor showers. Icarus 216, 40.URL https://ui.adsabs.harvard.edu/2011Icar..216...40J/abstract Jenniskens, P., N´enon, Q., 2016. CAMS verification of single-linked high-threshold D-criterion detected meteor showers. Icarus266, 371–383.URL https://ui.adsabs.harvard.edu/abs/2016Icar..266..371J/abstract Jones, W., 1997. Theoretical and observational determinations of the ionization coefficient of meteors. Monthly Notices of theRoyal Astronomical Society 288, 995.URL https://ui.adsabs.harvard.edu/1997MNRAS.288..995J/abstract Kanamori, T., 2009. A meteor shower catalog based on video observations in 2007-2008. WGN, Journal of the InternationalMeteor Organization 37, 55. RL https://ui.adsabs.harvard.edu/2009JIMO...37...55S/abstract Kero, J., Szasz, C., Nakamura, T., Meisel, D. D., Ueda, M., Fujiwara, Y., Terasawa, T., Miyamoto, H., Nishimura, K., 2011.First results from the 2009-2010 MU radar head echo observation programme for sporadic and shower meteors: the Orionids2009. Monthly Notices of the Royal Astronomical Society 416, 2550–2559.URL https://ui.adsabs.harvard.edu/abs/2011MNRAS.416.2550K/abstract Kero, J., Szasz, C., Nakamura, T., Meisel, D. D., Ueda, M., Fujiwara, Y., Terasawa, T., Nishimura, K., Watanabe, J., 2012a.The 2009-2010 MU radar head echo observation programme for sporadic and shower meteors: radiant densities and diurnalrates. Monthly Notices of the Royal Astronomical Society 425 (1), 135–146.URL https://ui.adsabs.harvard.edu/abs/2012MNRAS.425..135K/abstract Kero, J., Szasz, C., Nakamura, T., Terasawa, T., Miyamoto, H., Nishimura, K., 2012b. A meteor head echo analysis algorithmfor the lower VHF band. Annales Geophysicae 30 (4), 639.URL https://ui.adsabs.harvard.edu/abs/2012AnGeo..30..639K/abstract Kero, J., Szasz, C., Pellinen-Wannberg, A., Wannberg, G., Westman, A., Meisel, D. D., 2008. Three-dimensional radar obser-vation of a submillimeter meteoroid fragmentation. Geophysical Research Letters 35, L04101.URL http://adsabs.harvard.edu/abs/2008GeoRL..35.4101K Kojima, Y., Sako, S., Ohsawa, R., Takahashi, H., Doi, M., Kobayashi, N., Aoki, T., Arima, N., Arimatsu, K., Ichiki, M., Ikeda,S., Inooka, K., Ita, Y., Kasuga, T., Kokubo, M., Konishi, M., Maehara, H., Matsunaga, N., Mitsuda, K., Miyata, T., Mori,Y., Morii, M., Morokuma, T., Motohara, K., Nakada, Y., Okumura, S.-I., Sarugaku, Y., Sato, M., Shigeyama, T., Soyano,T., Tanaka, M., Tarusawa, K., Tominaga, N., Totani, T., Urakawa, S., Usui, F., Watanabe, J., Yamashita, T., Yoshikawa,M., 2018. Evaluation of large pixel CMOS image sensors for the Tomo-e Gozen wide field camera. In: Proc. SPIE. Vol.10709. International Society for Optics and Photonics, p. 107091T.URL https://doi.org/10.1117/12.2311301 Kornos, L., Koukal, J., Piffl, R., Toth, J., 2013. Database of meteoroid orbits from several European video networks. In:Proceedings of the 31st International Meteor Conference. The International Meteor Organization, pp. 21–25.URL https://ui.adsabs.harvard.edu/abs/2013pimo.conf...21K/abstract Kres´akov´a, M., 1966. The Magnitude Distribution of Meteors in Meteor Streams. Contributions of the Astronomical ObservatorySkalnate Pleso 3, 75.URL https://ui.adsabs.harvard.edu/abs/1966CoSka...3...75K/abstract Love, S. G., Brownlee, D. E., 1993. A Direct Measurement of the Terrestrial Mass Accretion Rate of Cosmic Dust. Science 262,550–553.URL http://adsabs.harvard.edu/abs/1993Sci...262..550L Michell, R. G., 2010. Simultaneous optical and radar measurements of meteors using the Poker Flat Incoherent Scatter Radar.Journal of Atmospheric and Solar-Terrestrial Physics 72 (16), 1212–1220.URL https://ui.adsabs.harvard.edu/abs/2010JASTP..72.1212M/abstract Michell, R. G., DeLuca, M., Janches, D., Chen, R., Samara, M., 2019. Simultaneous optical and dual-frequency radar observa-tions of small mass meteors at Arecibo. Planetary and Space Science 166, 1–8.URL http://adsabs.harvard.edu/abs/2019P%26SS..166....1M Michell, R. G., Janches, D., Samara, M., Hormaechea, J. L., Brunini, C., Bibbo, I., 2015. Simultaneous optical and radarobservations of meteor head-echoes utilizing SAAMER. Planetary and Space Science 118, 95–101.URL https://ui.adsabs.harvard.edu/abs/2015P%26SS..118...95M/abstract Myers, J. R., Sande, C. B., Miller, A. C., Warren, W. H., Tracewell, D. A., 2001. VizieR Online Data Catalog: SKY2000Catalog, Version 4 (Myers+ 2002). VizieR Online Data Catalog, V/109.URL https://ui.adsabs.harvard.edu/abs/2001yCat.5109....0M/abstract Nishimura, K., Sato, T., Nakamura, T., Ueda, M., 2001. High sensitivity radar-optical observations of faint meteors. IEICETransactions on Electronics E84-C (12), 1877–1884.Nishimura, S., Ohnishi, K., Dobashi, K., Watanabe, J.-I., Miyata, T., Nakada, Y., 2002. Optical Imaging of the Radiant Pointsof Leonids during the 2001 Storm with the 105cm Kiso Schmidt Telescope. Publications of the Astronomical Society ofJapan 54, L83–L88.URL https://ui.adsabs.harvard.edu/abs/2002PASJ...54L..83N/abstract Ohsawa, R., Sako, S., Sarugaku, Y., Usui, F., Ootsubo, T., Fujiwara, Y., Sato, M., Kasuga, T., Arimatsu, K., Watanabe,J.-i., Doi, M., Kobayashi, N., Takahashi, H., Motohara, K., Morokuma, T., Konishi, M., Aoki, T., Soyano, T., Tarusawa,K., Mori, Y., Nakada, Y., Ichiki, M., Arima, N., Kojima, Y., Morita, M., Shigeyama, T., Ita, Y., Kokubo, M., Mitsuda,K., Maehara, H., Tominaga, N., Yamashita, T., Ikeda, S., Morii, M., Urakawa, S., Okumura, S.-i., Yoshikawa, M., 2019.Luminosity function of faint sporadic meteors measured with a wide-field CMOS mosaic camera Tomo-e PM. Planetary andSpace Science 165, 281–292.URL https://ui.adsabs.harvard.edu/abs/2019P%26SS..165..281O/abstract Ohsawa, R., Sako, S., Takahashi, H., Kikuchi, Y., Doi, M., Kobayashi, N., Aoki, T., Arimatsu, K., Ichiki, M., Ikeda, S., Ita, Y.,Kasuga, T., Kawakita, H., Kokubo, M., Maehara, H., Matsunaga, N., Mito, H., Mitsuda, K., Miyata, T., Mori, K., Mori,Y., Morii, M., Morokuma, T., Motohara, K., Nakada, Y., Okumura, S.-i., Onozato, H., Osawa, K., Sarugaku, Y., Sato, M.,Shigeyama, T., Soyano, T., Tanaka, M., Taniguchi, Y., Tanikawa, A., Tarusawa, K., Tominaga, N., Totani, T., Urakawa,S., Usui, F., Watanabe, J., Yamaguchi, J., Yoshikawa, M., 2016. Development of a real-time data processing system for aprototype of the Tomo-e Gozen wide field CMOS camera. In: Proc. SPIE. Vol. 9913. International Society for Optics andPhotonics, p. 991339.URL http://proceedings.spiedigitallibrary.org/proceeding.aspx?articleid=2543636 Pellinen-Wannberg, A., Wannberg, G., 1994. Meteor observations with the European incoherent scatter UHF radar. Journal f Geophysical Research 99, 11379.URL https://ui.adsabs.harvard.edu/1994JGR....9911379P/abstract Pellinen-Wannberg, A., Westman, A., Wannberg, G., Kaila, K., 1998. Meteor fluxes and visual magnitudes from EISCAT radarevent rates: a comparison with cross-section based magnitude estimates and optical data. Annales Geophysicae 16 (11), 1475–1485.URL Plane, J. M. C., 2012. Cosmic dust in the earth’s atmosphere. Chemical Society Reviews, Vol. 41, p. 6507-6518, 2012 41,6507–6518.URL https://ui.adsabs.harvard.edu/abs/2012ChSRv..41.6507P/abstract Popova, O., 2004. Meteoroid ablation models. Earth Moon and Planets 95, 303–319.URL https://ui.adsabs.harvard.edu/abs/2004EM%26P...95..303P/abstract Rendtel, J., 2004. The population index of sporadic meteors. In: Proceedings of the 22nd International Meteor Conference.Vol. 22. Bollmannsruh, Germany, pp. 114–122.URL https://ui.adsabs.harvard.edu/abs/2004pimo.conf..114R/abstract Saidov, K. H., Simek, M., 1989. Luminous Efficiency Coefficient from Simultaneous Meteor Observations. Bulletin of theAstronomical Institutes of Czechoslovakia 40, 330.URL https://ui.adsabs.harvard.edu/1989BAICz..40..330S/abstract Sako, S., Ohsawa, R., Takahashi, H., Kikuchi, Y., Doi, M., Kobayashi, N., Aoki, T., Arimatsu, K., Ichiki, M., Ikeda, S., Ita, Y.,Kasuga, T., Kawakita, H., Kokubo, M., Maehara, H., Matsunaga, N., Mito, H., Mitsuda, K., Miyata, T., Mori, K., Mori,Y., Morii, M., Morokuma, T., Motohara, K., Nakada, Y., Osawa, K., Okumura, S.-i., Onozato, H., Sarugaku, Y., Sato, M.,Shigeyama, T., Soyano, T., Tanaka, M., Taniguchi, Y., Tanikawa, A., Tarusawa, K., Tominaga, N., Totani, T., Urakawa, S.,Usui, F., Watanabe, J., Yamaguchi, J., Yoshikawa, M., 2016. Development of a prototype of the Tomo-e Gozen wide-fieldCMOS camera. In: Proc. SPIE. Vol. 9908. International Society for Optics and Photonics, p. 99083P.URL http://proceedings.spiedigitallibrary.org/proceeding.aspx?articleid=2544194 Sako, S., Ohsawa, R., Takahashi, H., Kojima, Y., Doi, M., Kobayashi, N., Aoki, T., Arima, N., Arimatsu, K., Ichiki, M.,Ikeda, S., Inooka, K., Ita, Y., Kasuga, T., Kokubo, M., Konishi, M., Maehara, H., Matsunaga, N., Mitsuda, K., Miyata,T., Mori, Y., Morii, M., Morokuma, T., Motohara, K., Nakada, Y., Okumura, S.-I., Sarugaku, Y., Sato, M., Shigeyama,T., Soyano, T., Tanaka, M., Tarusawa, K., Tominaga, N., Totani, T., Urakawa, S., Usui, F., Watanabe, J., Yamashita, T.,Yoshikawa, M., 2018. The Tomo-e Gozen wide field CMOS camera for the Kiso Schmidt telescope. In: Proc. SPIE. Vol.10702. International Society for Optics and Photonics, p. 107020J.URL https://doi.org/10.1117/12.2310049 Sato, T., Nakamura, T., Nishimura, K., 2000. Orbit Determination of Meteors Using the MU Radar. IEICE TRANSACTIONSon Communications E83-B (9), 1990–1995.URL http://search.ieice.org/bin/summary.php?id=e83-b_9_1990&category=B&year=2000&lang=E&abst= Schult, C., Stober, G., Janches, D., Chau, J. L., 2017. Results of the first continuous meteor head echo survey at polar latitudes.Icarus 297, 1–13.URL http://adsabs.harvard.edu/abs/2017Icar..297....1S ˇSegon, D., Andrei´c, ˇZ., Gural, P., Skoki´c, I., Korlevi´c, K., Vida, D., Novoselnik, F., Gostinski, D., 2014. Results of CMN 2013search for new showers across CMN and SonotaCo databases III. WGN, Journal of the International Meteor Organization42, 227–233.URL http://adsabs.harvard.edu/abs/2014JIMO...42..227S Southworth, R. B., Hawkins, G. S., 1963. Statistics of meteor streams. Smithsonian Contributions to Astrophysics 7, 261.URL https://ui.adsabs.harvard.edu/1963SCoA....7..261S/abstract Sparks, J. J., Janches, D., Nicolls, M. J., Heinselman, C. J., 2009. Seasonal and diurnal variability of the meteor flux at highlatitudes observed using PFISR. Journal of Atmospheric and Solar-Terrestrial Physics 71, 644–652.URL http://adsabs.harvard.edu/abs/2009JASTP..71..644S ˇStohl, J., 1968. Seasonal Variation in the Radiant Distribution of Meteors. Physics and Dynamics of Meteors 33, 298.URL https://ui.adsabs.harvard.edu/abs/1968IAUS...33..298S/abstract ˇStohl, J., 1976. The magnitude distribution of sporadic meteors and its variations. Contributions of the Astronomical Obser-vatory Skalnate Pleso 7, 7.URL https://ui.adsabs.harvard.edu/abs/1976CoSka...7....7S/abstract Szalay, J. R., Piquette, M., Hor´anyi, M., 2013. The Student Dust Counter: Status report at 23 AU. Earth, Planets, and Space65, 1145–1149.URL https://ui.adsabs.harvard.edu/abs/2013EP%26S...65.1145S/abstract Thomas, E., Hor´anyi, M., Janches, D., Munsat, T., Simolka, J., Sternovsky, Z., 2016. Measurements of the ionization coefficientof simulated iron micrometeoroids. Geophysical Research Letters 43, 3645–3652.URL http://adsabs.harvard.edu/abs/2016GeoRL..43.3645T Verniani, F., 1965. On the Luminous Efficiency of Meteors. Smithsonian Contributions to Astrophysics 8, 141.URL http://adsabs.harvard.edu/abs/1965SCoA....8..141V Weryk, R. J., Brown, P. G., 2012. Simultaneous radar and video meteors — I: Metric comparisons. Planetary and Space Science62 (1), 132.URL https://ui.adsabs.harvard.edu/abs/2012P%26SS...62..132W/abstract Weryk, R. J., Brown, P. G., 2013. Simultaneous radar and video meteors — II: Photometry and ionisation. Planetary andSpace Science 81, 32.URL https://ui.adsabs.harvard.edu/abs/2013P%26SS...81...32W/abstract eryk, R. J., Campbell-Brown, M. D., Wiegert, P. A., Brown, P. G., Krzeminski, Z., Musci, R., 2013. The Canadian AutomatedMeteor Observatory (CAMO): System overview. Icarus 225 (1), 614–622.URL http://adsabs.harvard.edu/abs/2013Icar..225..614W Zacharias, N., Finch, C. T., Girard, T. M., Henden, A., Bartlett, J. L., Monet, D. G., Zacharias, M. I., 2013. The Fourth USNaval Observatory CCD Astrograph Catalog (UCAC4). The Astronomical Journal 145, 44.URL https://ui.adsabs.harvard.edu/2013AJ....145...44Z/abstracthttps://ui.adsabs.harvard.edu/2013AJ....145...44Z/abstract