AURORAL EMISSION PROFILES EXTRACTED FROM 3-DIMENSIONALLY RECONSTRUCTED ARCS

The mathematics of emission-computed tomography is applied to the anal ysis of stereoscopic observations of auroral arcs. The incomplete data problem for three-dimensional computerized tomography, due to the ver y limited angular range and the small number of observers, is solved b y an iterative least squares method. A theoretical example with the pr ojection of two auroral arcs can be reconstructed with projection root -mean-square errors of the order of 1%. Application of noise deteriora tes the quality of reconstruction, but with suitable low-pass filterin g, root-mean-square errors of less than 5% can be obtained. The agreem ent between observed and calculated projections, as well as between th e original and the reconstructed volume emission distribution, is quan titatively discussed for different observation geometries. With only t wo observation sites the range of acceptable observation geometries is Limited to distances of 25 to 50 km between the observers but depends on the actual location and the morphology of the aurora. Sources of d istortion of real auroral observations with intensified CCD cameras ar e discussed and correction procedures proposed. The complete procedure is applied to a real stereoscopic auroral observation. The correspond ence of original pictures and projections of the reconstructed volume is discussed, and emission profiles along magnetic field lines are ext racted from the three-dimensionally reconstructed are.