Sporadic Meteors Research Articles

Multi-station Meteor Monitoring (M3) System. II. System Upgrade and a Pathfinder Network

Meteors are important phenomena reflecting many properties of interplanetary dust particles. The study of their origin, mass distribution, and orbit evolution requires a large data volume, which can only be obtained using large meteor networks. After meteor networks in Europe and America, we present our designs and upgrades of a proposed network in China. The new designs are mainly aimed at facilitating the data gathering process. Each of the newly designed meteor stations can now support up to four cameras to cover the full sky. A newer version of the meteor station software now works as an integral system, which can streamline the process of detecting, measuring, and uploading meteors. We have built a meteor data platform to store, process, and display the meteor data automatically. The software and data platform are designed to be easy to learn and use, so they can attract more people to join and operate meteor stations. Four stations are installed as the first phase of the network, and during the operation, in 10 months, the network detected 8683 orbits; we find that half of the orbits can be related to established meteoroid streams. The statistical analysis of sporadic meteoroids shows a bimodal distribution of the velocities, which coincides with previous studies. The distribution of Tisserand parameters, T j , shows the two peaks at T j = 0 and 3, indicating the different orbits of parent bodies (isotropic and ecliptic), which are divided by T j = 2. The falling trajectory of a meteorite was also predicted using the observational data of the network. We are currently expanding the network, and in the future, we will carry out a detailed analysis of the key parameters of the distribution of the meteoroids.

The threshold at which a meteor shower becomes hazardous to spacecraft

Although the risk posed to spacecraft due to meteoroid impacts is dominated by sporadic meteoroids, meteor showers can raise this risk for short periods of time. NASA’s Meteoroid Environment Office issues meteor shower forecasts that describe these periods of elevated risk, primarily for the purpose of helping plan extravehicular activities. These forecasts are constructed using a list of meteor shower parameters that has evolved over time to include newly discovered showers and incorporate improved measurements of their characteristics. However, at this point in time, more than a thousand meteor showers have been reported by researchers, many of which are extremely minor, are unconfirmed, or lack measurements of critical parameters. Thus, a comprehensive approach is no longer feasible. In this report we present a quantitative criterion for a potentially hazardous meteor shower and apply this criterion to the list of established meteor showers in order to determine which showers should be included in our annual forecasts.

NELIOTA: New results and updated statistics after 6.5 years of lunar impact flashes monitoring

We present results of the Near-Earth objects Lunar Impacts and Optical TrAnsients (NELIOTA) campaign for lunar impact flashes observed with the 1.2 m Kryoneri telescope. From August 2019 to August 2023, we report 113 validated and 70 suspected flashes. For the validated flashes, we calculate the physical parameters (masses, radii) of the corresponding projectiles, the temperatures developed during the impacts, and the expected crater sizes. For the multiframe flashes, we present light curves and thermal evolution plots. Using the whole sample of NELIOTA that encompasses 192 validated flashes in total from 2017, the statistics of the physical parameters of the meteoroids, the peak temperatures of the impacts, and the expected crater sizes has been updated. Using this large sample, empirical relations correlating the luminous energies per photometric band were derived and used to roughly estimate the parameters of 92 suspected flashes of the NELIOTA archive. For a typical value of the luminous efficiency, we found that the majority (>75%) of the impacting meteoroids have masses between 1 and 200 g, radii between 0.5 and 3 cm and produced craters up to 3.5 m. 85% of the peak temperatures of the impacts range between 2000 and 4500 K. Statistics regarding the magnitude decline and the cooling rates of the multiframe flashes are also presented. The recalculation of the appearance frequency of meteoroids (lying within the aforementioned ranges of physical parameters) on the Moon yields that the total lunar surface is bombarded with 7.4 sporadic meteoroids per hour and up to 12.6 meteoroids per hour when the Earth-Moon system passes through a strong meteoroid stream. By extrapolating these rates on Earth, the respective rates for various distances from its surface are calculated and used to estimate the probability of an impact of a meteoroid with a hypothetical infrastructure on the Moon, or with a satellite orbiting Earth for various impact surfaces and duration times of the missions.

Statistical equivalence of metrics for meteor dynamical association

Meteor showers, originating as a result of the activity of comets or the disruption of large objects, provide a unique window into the composition and dynamics of our Solar System. While modern meteor detection networks have amassed extensive data, distinguishing sporadic meteors from those belonging to specific meteor showers remains challenging. In this study, we statistically evaluate and compare four orbital similarity criteria within five-dimensional parameter space (DSH,DD,DH, and ϱ2) to study dynamical associations using the already classified meteors (manually by a human) in CAMS database as a benchmark. In addition, we assess various distance metrics typically used in Machine Learning with two different vectors: ORBIT, grounded in heliocentric orbital elements, and GEO, predicated on geocentric observational parameters. To estimate their degree of correlation and efficacy, the Kendall rank correlation coefficient and the Top-k accuracy are employed. The statistical equivalence of the Top-1 results is examined using the Kolmogorov–Smirnov test and the percentage of Top-1 agreement is calculated on an event-by-event basis. Additionally, we compute the optimal cut-offs for all methods for distinguishing sporadic background events. Our findings demonstrate the superior performance of the sEuclidean metric in conjunction with the GEO vector. Within the scope of D-criteria, DSH emerged as the preeminent metric, closely followed by ϱ2. The Bray-Curtis metric displayed an advantage compared to the other distance metrics when paired with the ORBIT vector for Top-k accuracy, however, the Cityblock metric is more effective when considering the sporadic background. ϱ2 stands out as the most equivalence to the distance metrics when utilizing the GEO vector and the most compatible with GEO and ORBIT simultaneously, whereas DD aligns more closely when using the ORBIT vector. The stark contrast in DD’s behavior compared to other D-criteria highlights potential inequivalence. Our results suggest that geocentric features provide a more robust basis than orbital elements for meteor dynamical association. Most distance metrics associated with the GEO vector surpass the D-criteria when differentiating the meteoroid background. Accuracy displayed a dependence on solar longitude with a pronounced decrease around 180° matching an apparent increase in the meteoroid background activity, tentatively associated with the transition from the Perseids to the Orionids. Considering lately identified meteor showers, ∼27% of meteors in CAMS would have different associations. This work unveils that Machine Learning distance metrics can rival or even exceed the performance of tailored orbital similarity criteria for meteor dynamical association.

Implementation and Application of a Regional Fireball Monitoring Network Based on All-sky Camera Networking

Fireball monitoring network is the main equipment for monitoring impact from small-size near-Earth objects (NEOs), and determining meteorite fall locations. In this paper, a monitoring system using a multi-station distributed all-sky video camera network is proposed, and a regional prototype system has been constructed in Jiangsu and surrounding areas. The main processes of fireball monitoring were implemented, including network control, video capture, data processing, trajectory determination, and orbit calculation. After running for 1 yr, the results show that the limiting apparent magnitude - 1.0 for meteors in the video, and the absolute magnitude exhaustive detection regime can reach around - 2.5. The flux of fireballs is found to be 2.68×10−7 km−2· h−1. The percentages of streams and sporadic meteors are 46% and 54%, respectively, and the fraction of cometary orbits equals 72.9%, while for asteroidal-type it is 27.1%. The statistical results are close to those of the international meteor monitoring networks, which verified the monitoring capability of the network system in practical operation.

Current Knowledge of Objects Approaching the Earth

Modern ideas about objects approaching the Earth are discussed. This population includes near-Earth asteroids (NEAs), including potentially hazardous asteroids, short-period comets, meteoroid streams, and large sporadic meteoroids. An overview is given of the currently available information on the dynamic and physical properties of NEAs and comets. Almost 5% of the currently known NEAs are extinct cometary nuclei or their fragments. Being outwardly similar with true asteroids, they differ markedly in their dynamic and physical properties. In order to distinguish between these groups of objects, it is necessary to study both their dynamic and physical parameters. Some of the known meteoroid streams are shown to contain, along with the countless small meteoroids, also large extinct fragments of cometary nuclei, which are classified as NEAs. A meteoroid stream and such bodies belonging to it form together an asteroid–meteoroid complex. Observational and theoretical data are presented to confirm the modern understanding of near-Earth objects.

Mercury's Circumsolar Dust Ring as an Imprint of a Recent Impact

A circumsolar dust ring has been recently discovered close to the orbit of Mercury. There are currently no hypotheses for the origin of this ring in the literature, so we explore four different origin scenarios here: the dust originated from (1) the sporadic meteoroid complex that comprises the major portion of the Zodiacal Cloud, (2) recent asteroidal/cometary activity, (3) hypothetical dust-generating bodies locked in mean-motion resonances beyond Mercury, and (4) bodies co-orbiting with Mercury. We find that only scenario (4) reproduces the observed structure and location of Mercury’s dust ring. However, the lifetimes of Mercury’s co-orbitals (<20 Ma) preclude a primordial origin of the co-orbiting source population due to dynamical instabilities and meteoroid bombardment, demanding a recent event feeding the observed dust ring. We find that an impact on Mercury can eject debris into the co-orbital resonance. We estimate the ages of six candidate impacts that formed craters larger than 40 km in diameter using high-resolution spacecraft data from MESSENGER and find two craters with estimated surface ages younger than 50 Ma. We find that the amount of mass transported from Mercury’s surface into the co-orbital resonance from these two impacts is several orders of magnitude smaller than what is needed to explain the magnitude of Mercury’s ring inferred from remote sensing. Therefore we suggest that numerous younger, smaller impacts collectively contributed to the origin of the ring. We conclude that the recent impact hypothesis for the origin of Mercury’s dust ring is a viable scenario, whose validity can be constrained by future inner solar system missions.

TALES FROM INDIA. 1: METEOR SHOWERS IN CLASSICAL AND COLONIAL SOURCES

Meteor phenomena are always fascinating and capture popular attention. This paper reports results of a search for references to and records of meteor showers observed in the Indian region, until the close of the nineteenth century. The sources explored were the Indian classics and chronicles, institutional reports and accounts by individuals, including those published in professional journals. We found very few references to such events in the classical sources. The earliest datable references that we found were in Shuka's <italic>Rajatarangini</italic> (Perseids or Leonids, 1533), Abu'l Fazl's <italic>Akbarnama</italic> (Alpha Capricornids or Delta Aquarids, 1592) and in Krishnaji Sabhasad's account of the life of Chhatrapati Shivaji Maharaj (Leonids, 1680). The subsequent accounts belong to the nineteenth century. Some of these are about sporadic meteors, while others are about meteor showers. The earliest published report is of the November Leonid meteor shower of 1832. We also came across a strong meteor shower on 10 September 1841 reported in the 13 September issue of the <italic>Englishman</italic> newspaper. We believe this is the September Epsilon Perseids, a minor shower known to peak on 9/10 September. This 1841 observation is 37 years before the September Epsilon Perseids were first described by William Denning, in 1878. We believe that such records can be of great value in fine-tuning time-lines in Indian history and understanding the dynamics of meteoroid streams.

Sporadic micro-meteoroid source radiant distribution inferred from the Arecibo 430 MHz radar observations

ABSTRACT This work presents the result of sporadic meteor radiant density distribution using the Arecibo 430 MHz incoherent scatter radar (ISR) located in Puerto Rico for the first time. Although numerous meteor studies have been carried out using the Arecibo ISR, meteoroid radiant density distribution has remained a mystery as the Arecibo radar cannot measure vector velocity. A numerical orbital simulation algorithm using dynamic programming and stochastic gradient descent is designed to solve the sporadic meteoroid radiant density and the corresponding speed distributions of the meteors observed at Arecibo. The data set for the algorithm comprises over 250 000 meteors from Arecibo observations between 2009 and 2017. Five of the six recognized sporadic meteor sources can be identified from our result. There is no clearly identifiable South Apex source. Instead, there is a broad distribution between +/−30° ecliptic latitude, with the peak density located in the North Apex direction. Our results also indicate that the Arecibo radar is not sensitive to meteors travelling straight into or perpendicular to the antenna beam but is most sensitive to meteors with an arrival angle between 30° and 60°. Our analysis indicates that about 75 per cent of meteoroids observed by the Arecibo radar travel in prograde orbits when the impact probability is considered. Most of the retrograde meteoroids travel in inclined low-eccentricity orbits.

Comet-Asteroid Classification Among Orbits of Sporadic Meteoroids Observed by BRAMON Between 2014 and 2021

Abstract The Brazilian Meteor Observation Network (BRAMON) is a TV meteor detection network that has been implemented in Brazil since 2014. The BRAMON data made it possible to determine the high-quality orbits of 630 sporadic meteors observed between 2014 and 2021. Using criteria from Jopek &amp; Williams, we assign each of these meteors an asteroidal or cometary origin. Cometary type orbits correspond to slightly more than 60% of sporadic meteors of our sample, a similar percentage to that obtained from other meteor surveys when considering the same magnitude range.

Comet fragmentation as a source of the zodiacal cloud

ABSTRACT Models of the zodiacal cloud’s thermal emission and sporadic meteoroids suggest Jupiter-family comets (JFCs) as the dominant source of interplanetary dust. However, comet sublimation is insufficient to sustain the quantity of dust presently in the inner Solar system, suggesting that spontaneous disruptions of JFCs may supply the zodiacal cloud. We present a model for the dust produced in comet fragmentations and its evolution. Using results from dynamical simulations, the model follows individual comets drawn from a size distribution as they evolve and undergo recurrent splitting events. The resulting dust is followed with a kinetic model which accounts for the effects of collisional evolution, Poynting–Robertson drag, and radiation pressure. This allows to model the evolution of both the size distribution and radial profile of dust, and we demonstrate the importance of including collisions (both as a source and sink of dust) in zodiacal cloud models. With physically motivated free parameters this model provides a good fit to zodiacal cloud observables, supporting comet fragmentation as the plausibly dominant dust source. The model implies that dust in the present zodiacal cloud likely originated primarily from disruptions of ∼50-km comets, since larger comets are ejected before losing all their mass. Thus much of the dust seen today was likely deposited as larger grains ∼0.1 Myr in the past. The model also finds the dust level to vary stochastically; e.g. every ∼50 Myr large (&amp;gt;100 km) comets with long dynamical lifetimes inside Jupiter cause dust spikes with order of magnitude increases in zodiacal light brightness lasting ∼1 Myr. If exozodiacal dust is cometary in origin, our model suggests it should be similarly variable.

Meteorite hazard model for a space mission to Mars

Currently, for the world’s space agencies, the robotic exploration of Mars is one of the most important tasks. One of the necessary stages for the implementation of this mission is the development and addition of new information to the State standard “Meteoric substance, spatial distribution model”. Until now, the State Standard has been more detailed in comparison with the American analogue (developed by NASA) and the European one. The standard is a mandatory document in the design of spacecraft. It should be noted that modeling of meteor hazard at a distance from Earth to Mars is a complex problem, since the analysis of the meteor population in near-Earth space does not give a complete picture of the propagation of meteoroids along the Earth-Mars route. Moreover, the further the trajectory of the spacecraft from the Earth’s orbit is, the less the number of near-Earth meteorites becomes. That is, objects that have the same orbital parameters with small bodies crossing the Earth’s orbit. The only way to solve this problem is to build an interpolation regression model, which is based on measurements from the Earth’s surface and observations of space missions. For this purpose, the density of sporadic meteoroids was transformed from the space mission coordinate system to the ground one. This was done in order to analyze meteorite observations by the Mariner 4 and Pioneer 10 spacecrafts. The results of the work made it possible to obtain new data for the spatial distribution of meteoroids on the Earth-Mars path. According to a comparison of our data with the data on the density of space debris in the previous works the most safe for space flights are normalization conditions of distributions of the elements of the orbits of meteoric bodies P(Z, e, i) < 60.

Analysis of modern observations of meteor showers based on PTM methods

The work is focused on the analysis of modern observations of meteoroids included in the data bank formed by both professional researchers and amateur astronomers. Based on the modern physical theory of meteoroids (PTM), a new method for analyzing measurements developed, which provides the accuracy comparable with the results of radar observations. Due to the fact that the accuracy of the new method for analyzing meteoroids observations has increased significantly, it became possible to process observations of the Perseid and Leonid showers over a period of 120 years. The use of PTM made it possible for the first time to explain the distribution of meteor echo signals observed at an altitude of 2 MHz, at which the upper part of this distribution refers to an altitude of 140 km. In the process of work, a database of orbital characteristics of meteoroids was created. A method has been developed for modeling the probability of hitting a certain area of a meteor particle with a mass greater than a certain specified value and determining the density of a meteor shower from radio observations as well as a new “tomography” method for calculating the density distribution of sporadic meteors in the sky using radar observations of meteors at the same station with a goniometer. The method allows calculating the density of a meteor shower on the celestial sphere with an angular resolution of 2°. The use of these methods served as a proof that the distribution density of meteoroid showers on the celestial sphere has two planes of symmetry: the first coincides with the plane of the ecliptic, passing through the poles of the Earth, the other one is perpendicular to the plane of the ecliptic.

The Main Asteroid Belt: The Primary Source of Debris on Comet-like Orbits

Abstract Jupiter-family comets (JFCs) contribute a significant amount of debris to near-Earth space. However, telescopic observations of these objects seem to suggest that they have short physical lifetimes. If this is true, the material generated will also be short-lived, but fireball observation networks still detect material on cometary orbits. This study examines centimeter-to-meter-scale sporadic meteoroids detected by the Desert Fireball Network from 2014 to 2020 originating from JFC-like orbits. Analyzing each event’s dynamic history and physical characteristics, we confidently determined whether they originated from the main asteroid belt or the trans-Neptunian region. Our results indicate that &lt;4% of sporadic meteoroids on JFC-like orbits are genetically cometary. This observation is statistically significant and shows that cometary material is too friable to survive in near-Earth space. Even when considering shower contributions, meteoroids on JFC-like orbits are primarily from the main belt. Thus, the presence of genuine cometary meteorites in terrestrial collections is highly unlikely.

Formation of the Lunar Dust Ejecta Cloud

Abstract The Lunar Dust Experiment (LDEX) on board the Lunar Atmosphere and Dust Environment Explorer (LADEE) mission orbited the Moon from 2014 September to 2015 April and observed a dynamic, permanently present dust cloud produced by continual meteoroid bombardment. For the latitudes observed by LDEX, the sporadic background contribution to the impacting dust flux is dominated by helion (HE), apex (AP), and antihelion (AH) sources oscillating with lunar phase. Using improved impact ejecta distributions, a three-dimensional model was implemented to estimate the inner and outer ejecta cone angles from LDEX plume measurements. Expanding upon this single-plume model and the derived ejecta cone angles, we implemented a global lunar model fitted to LDEX measurements of the sporadic background to constrain the product of meteoroid impactor fluxes and ejecta mass yield per source. We use the observed asymmetry between sunward and antisunward impactor fluxes to discuss the possible contributions of β-meteoroids, in addition to the HE and AH sporadic meteoroid sources. We find that if β-meteoroids are responsible for the day/night asymmetry, they must have an impact ejecta yield of at least 103.

Long‐Term Observations and Physical Processes in the Moon's Extended Sodium Tail

AbstractThe lunar surface is constantly bombarded by the solar wind, photons, and meteoroids, which can liberate Na atoms from the regolith. These atoms are subsequently accelerated by solar photon pressure to form a long comet‐like tail opposite the sun. Near new moon, these atoms encounter the Earth's gravity and are “focused” into a beam of enhanced density. This beam appears as the ∼3° diameter Sodium Moon Spot (SMS). Data from the all sky imager at the El Leoncito Observatory have been analyzed for changes in the SMS shape and brightness. New geometry‐based relationships have been found that affect the SMS brightness. The SMS is brighter when the Moon is north of the ecliptic at new moon; the SMS is brighter when new moon occurs near perigee; and the SMS peaks in brightness ∼5 h after new moon. After removing these effects, the data were analyzed for long term and seasonal patterns that could be attributed to changes in source mechanisms. No correlation was found between the SMS brightness and the 11‐year solar‐cycle, the proton or the He++ flow pressure, the density, the speed or the plasma temperature of the solar wind, but an annual pattern was found. A ∼0.83 correlation (Pearson's “r”) was found between the SMS brightness and a 4‐year average of sporadic meteor rates at Earth, suggesting a cause‐and‐effect. The new insights gained from this long‐term study put new constraints on the variability of the potential sources of the Na atoms escaping from the Moon.

FRIPON: a worldwide network to track incoming meteoroids

Context.Until recently, camera networks designed for monitoring fireballs worldwide were not fully automated, implying that in case of a meteorite fall, the recovery campaign was rarely immediate. This was an important limiting factor as the most fragile – hence precious – meteorites must be recovered rapidly to avoid their alteration.Aims.The Fireball Recovery and InterPlanetary Observation Network (FRIPON) scientific project was designed to overcome this limitation. This network comprises a fully automated camera and radio network deployed over a significant fraction of western Europe and a small fraction of Canada. As of today, it consists of 150 cameras and 25 European radio receivers and covers an area of about 1.5 × 106km2.Methods.The FRIPON network, fully operational since 2018, has been monitoring meteoroid entries since 2016, thereby allowing the characterization of their dynamical and physical properties. In addition, the level of automation of the network makes it possible to trigger a meteorite recovery campaign only a few hours after it reaches the surface of the Earth. Recovery campaigns are only organized for meteorites with final masses estimated of at least 500 g, which is about one event per year in France. No recovery campaign is organized in the case of smaller final masses on the order of 50 to 100 g, which happens about three times a year; instead, the information is delivered to the local media so that it can reach the inhabitants living in the vicinity of the fall.Results.Nearly 4000 meteoroids have been detected so far and characterized by FRIPON. The distribution of their orbits appears to be bimodal, with a cometary population and a main belt population. Sporadic meteors amount to about 55% of all meteors. A first estimate of the absolute meteoroid flux (mag &lt; –5; meteoroid size ≥~1 cm) amounts to 1250/yr/106km2. This value is compatible with previous estimates. Finally, the first meteorite was recovered in Italy (Cavezzo, January 2020) thanks to the PRISMA network, a component of the FRIPON science project.

GROUPS OF METEORITE-PRODUCING METEOROIDS AND METEORITES IN ASTEROIDAL ORBITS AND THEIR SOURCES

This paper presents the results of theanalysis of possible existence of nine near-Earthmeteorite-producing groups in asteroidal orbits, consistingof sporadic fireballs from the IAU MDC 2007 database,sporadic meteors from the SonotaCo database, meteorites– namely, L5, L6 and H4-H6 ordinary chondrites and anureilite, for which atmospheric and orbital parameters areknown from instrumental observations – and theirplausible parent bodies, that is, near-Earth asteroids(NEAs). Orbits of the selected members of meteorite-producing groups were classified as asteroidal accordingto the Tisserand parameter T J &gt; 3.1.In order to test the link between meteorite-producinggroups in asteroidal orbits and their plausible parentbodies, we carried out an investigation into the possibleexistence of some known NEAs that move in similarorbits. Based on the orbital similarity, determined usingthe Drummond (D D ) and Southworth &amp; Hawkins (D SH )orbital similarity criteria, some associations between theidentified NEAs, known meteorites in asteroidal orbitsand small, as well as meteorite-dropping, meteoroids havebeen suggested. As a result, several meteorite-droppingsporadic fireballs and small meteors, whose orbits arecurrently similar to the orbits of known meteorites, havebeen detected and reckoned as possible members of thegroups in asteroidal orbits; their plausible source regionshave also been considered.

Meteors with extreme beginning heights from observations with high-sensitivity super-isocon TV systems

ABSTRACT Meteors with extremely high altitudes are considered. Parameters of seven meteors having anomalous beginning heights recorded with highly sensitive super-Isocon TV systems are presented. One 1993 Perseid meteor, one 2001 sporadic meteor and five meteors from the 2002 Leonid storm had beginning heights in the range 135–145 km. The sporadic meteor is used to demonstrate the methods of data processing and observation precision results. The original TV meteor images, photometric calibration curves and meteor light curve are shown. Light curves are shown for the Leonid shower meteors as well. Based on the sporadic meteor and the 2002 Leonid shower meteor data, mass-loss curves were calculated as functions of height and time: the maximum rates of mass loss were 0.14 and 0.20 g s−1, respectively. Using the classic equation for partially isothermal stone particle heating, the detected beginning heights of most meteors considered (136–135 km) are shown to possibly be related to blowing the molten layer off from a meteoroid surface and most segments of the light curves (below 124 km) show intensive evaporation. For some Leonid meteors, appearing higher than 145–140 km, energy exchange of atmosphere molecules and atoms with the ‘cold’ meteoroid surface can also be assumed. Another possible explanation lies in the low melting temperature of 1500–1600 K for Leonid meteors.

Relationship between radar cross section and optical magnitude based on radar and optical simultaneous observations of faint meteors

Radar and optical simultaneous observations of meteors are important to understand the size distribution of the 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 optical simultaneous observations were organized. The first observation was carried out in 2009–2010 using Middle and Upper Atmosphere Radar (MU radar) and an image-intensified CCD camera. The second observation was carried out in 2018 using the MU radar and a mosaic CMOS camera, Tomo-e Gozen, mounted on the 1.05-m Kiso Schmidt Telescope. In total, 331 simultaneous meteors were detected. The relationship between 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 sporadic meteors. The transformation function was applied to about 150,000 meteors detected by the MU radar in 2009–2015, large part of which are sporadic, and a luminosity function was derived in the magnitude range of −1.5–9.5 mag. The luminosity function was well approximated by a single power-law function with the population index of r=3.52±0.12. The present observation indicates that the MU radar has capability to detect interplanetary dust of 10−5–100g in mass as meteors.