LAUSR

Abstract The flux densities of meteoroids and asteroids in the intermediate size range (approx. 20 cm – 30 m) impacting the Earth’s Atmosphere still have large uncertainties. There are too few objects of these sizes to be detected with localized fireball networks. Two detection methods that provide a global coverage of fireballs and bolides in this size range are infrasound monitors and space-based satellite sensors. Results from these sensors have large uncertainties specifically what concerns the energy release of the impacting bodies. In this paper a detailed analysis of infrasound data is performed to better understand recorded signals and uncertainties. This will allow to put the analysis and interpretation of infrasound data from impacts on a more solid scientific basis. Atmospheric impacts from large meteoroids or sometimes even asteroids generate infrasound signals which can often propagate over large distances and be registered at infrasound stations. The world-wide network of infrasound stations from the IMS (International Monitoring System) which is operated by the CTBTO (Comprehensive Nuclear-Test-Ban Treaty Organisation, Vienna, Austria) monitors most of the Earth’s Atmosphere and can detect the energy released by meteoroids. Hence, fireball infrasound signals can be used as a very promising information source for fireball research. Nonetheless, the data analysis is very complex and a topic of current discussions and research. In this paper a detailed analysis of the infrasound signals of some fireballs is carried out to be adapted to systematically calculate location, speed, and size or energy of the impacting objects from the infrasound data. Comparisons of other observation methods are also used for this purpose. Moreover, particular attention is paid to uncertainties in the analysis of infrasound data. The infrasound data analysis is part of the NEMO (NEar real-time MOnitoring system) project which started in autumn 2017. It is an information system analysing and combining data from multiple sources ranging from Social Media to infrasound data to monitor the impacts of fireballs on a global scale and to maximize the available scientific information. The infrasound data of the well-studied Chelyabinsk superbolide that exploded over southern Russia in 2013 and the Sulawesi, Indonesia, fireball that was registered in 2009 are reprocessed and the results compared to previous studies. To demonstrate the capacities and advantages of infrasound for the gathering of scientific information two recent fireballs are analysed in detail. These occurred on 08 March 2018 over Washington State (WS), USA, and on 21 June 2018 over the Ozerki region, Russia, respectively. For both fireballs infrasound signals were recorded making it possible to determine the source energy. We derived energies of about E W S = 22 t TNT and E R u s s i a = 2.4 kt TNT using a published yield estimation relationship. Combining all available different data sources, which have information on these fireballs, ranging from rain radar to witness reports allowed us to derive a size (diameter) of the entering body in both cases, s W S = 0.8 m and. s R u s s i a = 3.8 m .