A new algorithm, which is the combination of the generalized singular value decomposition (GSVD) and the improved algebraic reconstruction technique (IART), is proposed to image ionospheric electron density （IED） distribution in this paper. In this new method, the GSVD is first used to resolve the ill-posed problem in computerized ionospheric tomography (CIT) system. Its estimate inverted from total electron content (TEC) measurements is then provided as the initial approximation required by the IART. The combined algorithm therefore offers a more reasonable approach to choose an initial approximation for the IART and improve the quality of the final reconstructed image. A numerical simulation experiment demonstrates that the combined algorithm is more accurate than the GSVD alone or the IART alone for the tomographic inversion of IED. The new method is then applied to perform the inversion of the IED during a magnetically disturbed period on 21 August 2003. Tomographic results show that the main ionospheric effects of this storm over China are as follows: the negative storm phase effect appears in F region, the positive storm phase effect occurs above F region, and meanwhile, some prominent features in the ionospheric structure can be revealed in the ionospheric images, such as the disturbance and mid-latitude trough. The reliability of the new method is also validated by the ionosonde data recorded at Wuhan station.
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