Blitzortung (German for "lightning direction-finding", German pronunciation: [ˈblɪtsˌɔʁtʊŋ]) is an informal, non-commercial group of citizen scientists supported by professional scientists. Active since 2005,[1] station operators manage a worldwide network of ~1800 active VLF radio wave receiver stations in 83 countries.[2] These receivers are used to determine the location of lightning strikes based on time-of-flight detector measurements of the received signals.[3][4] The only compensation that station operators receive is free access to the raw data of all stations. The data is processed by various websites using geoinformatics methods and made available on the Internet as a map display.[5][6]