Large meteoroids can be registered in infrasound recordings during their entry into the Earth’s atmosphere. A comprehensive study of 10 large fireball events of the years 2018 and 2019 highlights their detection and characterization using global infrasound arrays of the International Monitoring System (IMS) of the Comprehensive Nuclear-Test-Ban Treaty (CTBT). The study focuses on the observation and event analysis of the fireballs to estimate their respective location, yield, trajectory, and entry behavior. Signal characteristics are derived by applying the Progressive Multi-Channel Correlation method as an array technique. The comparison of the events with a NASA reference database as well as the application of atmospheric propagation modeling allows to draw conclusions about infrasound-based detection capability, localization accuracy, yield estimation, and source characterization. The infrasound technique provides a time- and location-independent remote monitoring opportunity of impacting near-Earth objects (NEOs), either independent or complementary to other fireball observation methods. Additionally, insights about the detection and localization capability of IMS infrasound stations can be gained from using large fireballs as reference events, being of importance for the continuous monitoring and verification of atmospheric explosions in a CTBT context.

Astronomy & Astrophysics (A&A) is an international journal which publishes papers on all aspects of astronomy and astrophysics

In meteor physics the luminous efficiency ${\tau}$ is used to convert the meteor's magnitude to the corresponding meteoroid's mass. However, lack of sufficiently accurate verification methods or adequate laboratory tests leave this parameter to be controversially discussed. In this work meteor/fireball data obtained by the Fireball Recovery and InterPlanetary Observation Network (FRIPON) was used to calculate the masses of the pre-atmospheric meteoroids which could in turn be compared to the meteor brightnesses to assess their luminous efficiencies. For that, deceleration-based formulas for the mass computation were used. We have found ${\tau}$-values, as well as the shape change coefficients, of 294 fireballs with determined masses in the range of $10^{-6}$ kg - $100$ kg. The derived ${\tau}$-values have a median of ${\tau}_{median}$ = 2.17 %. Most of them are on the order of 0.1 % - 10 %. We present how our values were obtained, compare them with data reported in the literature, and discuss several methods. A dependence of ${\tau}$ on the pre-atmospheric velocity of the meteor, $v_e$, is noticeable with a relation of ${\tau}=0.0023 \cdot v_e^{2.3}$. The higher luminous efficiency of fast meteors could be explained by the higher energy released. Fast meteoroids produce additional emission lines that radiate more efficiently in specific wavelengths due to the appearance of the so-called second component of higher temperature. Furthermore, a dependence of ${\tau}$ on the initial meteoroid mass, $M_e$, was found, with negative linear behaviour in log-log space: ${\tau}=0.48 \cdot M_e^{-0.47}$. This implies that the radiation of smaller meteoroids is more efficient.

Fireballs are very bright meteors with magnitudes of at least -4. They can spark a lot of public interest. Especially, if they can be seen during daytime over populous areas. Social Media allows us to be informed about almost everything, worldwide, and in all areas of life in real-time. In the age of intensive use of these media, information is freely available seconds after the sighting of a fireball.This is the basis of the alert system which is part of NEMO, the NEar real-time MOnitoring system, for bright fireballs. It uses Social Media, mainly Twitter, to be informed about a fireball event in near real-time. In addition, the system accesses various data sources to collect further information about the detected fireballs. The sources range from meteor networks, the data from weather satellites or lightning detectors to the infrasound data of the IMS (International Monitoring System) operated by the CTBTO (Comprehensive Nuclear-Test-Ban Treaty Organisation).Since large meteoroids or asteroids can be detected by these infrasound sensors when they enter the Earth's atmosphere, this network provides the possibility to detect fireballs worldwide and during day and night. From the infrasound data the energy of the object that caused the fireball can be determined and hence, its size and mass can be calculated. By combining all available information about the fireball from different data sources the amount of scientific knowledge about the event can be maximized.NEMO was under development for about 2.5 years. Since the beginning of the year the system is in operation at the European Space Agency, as part of its Space Safety Programme. In this presentation we will give an overview about NEMO, its working principle and its relation to the IMS.

Various meteor and fireball networks exist worldwide. Most data sets which include ground-based observational data of meteors are affected by biases. The larger and faster the entering meteoroid, the brighter is the produced meteor. Hence, small and slow objects often stay undetected. This bias of meteor observations towards faster meteoroids is a challenge if quantitative population and flux models are derived. In this work the velocity distribution of objects in space is analysed by using different data sets that are not affected by this velocity bias since they include only large objects, like the near-Earth object (NEO) risk list of ESA's (European Space Agency) SSA (Space Situational Awareness) near-Earth object Coordination Centre (NEOCC), and the fireballs in NASA's (National Aeronautics and Space Administration) CNEOS (Center for near-Earth object Studies) JPL (Jet Propulsion Laboratory) fireball database. Additionally, when only the largest objects recorded with the CILBO (Canary Island Long-Baseline Observatory) camera setup were analysed, a very similar distribution was shown. These velocity distributions are in good agreement with a widely used velocity distribution for smaller sporadic meteoroids in free space which was adopted as reference by the ECSS (European Cooperation for Space Standardisation) Space Environment Standard.