THE CORRECTION FOR THE SATELLITE-RECEIVER LONGITUDE DIFFERENCE IN IONOSPHERIC TOMOGRAPHY

The technique of ionospheric tomography involves the inversion of a nu mber of total electron content measurements to provide a two-dimension al image of electron density. In an experimental situation the initial data are oriented in an approximate plane between a longitudinal chai n of ground-based receivers and the trajectory of a polar-orbiting sat ellite. The effect of the longitude difference between the polar-orbit ing satellite and the receiver chain on the tomographic image is inves tigated in both an ionospheric-model and the experimental environment. Tomographic measurements recorded during an experimental campaign hel d in May 1995, together with independent electron density information from the EISCAT incoherent scatter radar, are used in the studies. Ele ctron-density comparisons between a number of tomographic images and c orresponding incoherent-scatter measurements allow an optimal longitud inal correction to be verified in an experimental situation. The resul ts indicate that the longitudinal corrections can be made to high accu racy, provided that a reliable estimate of the mean ionospheric height is obtained. A preliminary result from the experimental campaign, sho wing the early-evening east-west electron-density gradient, demonstrat es that ionospheric tomography has the potential to produce three-dime nsional images from a number of receiver chains displaced in longitude . (C) 1997 Elsevier Science Ltd.