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It is well known that the entry of bright bolides is usually associated with sound effects. During the past century it was discovered that a large part of the acoustic energy is radiated in the non-audible, low frequency part of the acoustic spectrum, or infrasound, known for its unusual propagation. Already in connection with the giant Tunguska Meteor in 1908, it was discovered that the low-frequency signal generated by the event travelled more than once around the Earth and was detected by barographs around the world. The presence of infrasound emissions from meteoroid entries was furthermore confirmed when infrasound became a common tool for detection of explosions. Several infrasonic observations of meteoroid entries are found in the literature. A pioneering work on the understanding of infrasound generation by meteoroid entry was done by Douglas ReVelle of Los Alamos National Laboratory.
When searching for meteoroid signatures, the original time series recorded by the infrasonic array is needed. Therefore, a systematic search for meteoroid signatures in the data from the Swedish Infrasound Network, SIN, could be started after 1994, when complete time series from the arrays were stored in a database. This book contains a summary of the work, performed by the author, on infrasonic detection of meteoroid entries above and around northern Scandinavia. Two major events occurred in northern Sweden during the past few years. These triggered the author's interest in documenting the events that have occurred there during the past century. The author is indebted to Mr. Per-Gunnar Jonsson, Skellefteå, for supplying all his collected materials about meteor events in Västerbotten during the past century and to Mr. Anders Persson, Sävar, for all information concerning the Hökmark-event, which constitutes the major part of Chapter 1.
The research described in this book was to a greater part made possible by the support from the European Space Agency, ESA, through the ESA Contract No. 19076/05/NL/PG. The author is indebted to Dr. Håkan Svedhem and Dr. Gerhard Drolshagen of ESA for their support and interest in this project.
The author is grateful to the ESRANGE Space Center for providing accurate position data for analyzed rocket launchings. The author is also indebted to Dr Esko Kyro, Finnish Meteorological Institute for supplying the radiosonde data from Sodankylä. The study presented in this book would not have been possible without the help of my co- workers: Pär-Ola Nilsson, Jan Karlsson and Fredrik Rutqvist, who developed the software used in the operation of infrasonic arrays.
IRF Scientific Report 295
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