Coordinated observation of transient Luminous events by FORMOSAT-2 Satellite and Taiwan Sprites Campaign

The Imager of Sprites and Upper Atmospheric Lightning (ISUAL), which was on board the FORMOSAT-2 satellite launched in 2004, is the first instrument primarily dedicated to transient luminous events (TLEs) surveys from space. The geolocation accuracy and the detecting efficiency of ISUAL TLEs are validated in this paper through two coordinated observation events using ISUAL and the Taiwan TLE ground campaign, which is also the first coordinated observation from space and ground. Due to the long distances between TLEs and observation stations, the triangulation needs to take the earth's curvature into account by means of spherical trigonometry. After a series of systematic procedures on triangulation, the results indicate that the geolocation accuracy for the coordinated observation of ISUAL and the ground station is less than 7 km. Moreover, three columniform sprites were recorded at multiple sites during the ground campaign. The triangulation of individual elements is achieved from the accurate triangulation, showing that the map projection of columniform sprites is nearly circular, parallel and fan shaped. The aforementioned events demonstrate that the distribution patterns of columniform sprites are diverse. The average base altitude of columns is 72.4 ± 2.4 km, and the average terminal altitude is 82.3 ± 1.8 km. The width of sprite columns is estimated to be <0.5 km.