TOMOGRAPHIC IMAGING OF THE IONOSPHERE OVER JAPAN BY THE MODIFIED TRUNCATED SVD METHOD

A computerized tomography technique was applied to reconstruct two-dim ensional electron density distributions from measurements of total ele ctron content (TEC). We found that the modified truncated singular val ue decomposition (MTSVD) method, which is usually effective in ill-pos ed inversion problems, is effective in the ionospheric application. Fu rthermore, a main control parameter for a good reconstruction was exam ined by using several density distribution models, and the effects of noise in TEC and discretization error were also investigated. After th e simulation study, the MTSVD method was applied to actual TEC data in a magnetically disturbed period. Total electron contents were observe d, at four receiving stations covering a latitudinal range of 9.7 degr ees with a longitudinal range of 2.2 degrees over Japan, by using sign als transmitted from a Navy Navigational Satellite System (NNSS) satel lite. The tomographic reconstruction revealed a large-scale structure of electron density in the disturbed ionosphere.