Coherent Radio Beacon Experiment (CRABEX) for tomographic imaging of the equatorial ionosphere in the Indian longitudes – Preliminary results

To investigate the equatorial ionospheric processes like the equatorial ionization anomaly (EIA), equatorial spread F (ESF) and their inter relationships, a network of ground based stations receiving the 150 and 400 MHz transmissions from the low earth orbiting satellites (LEOS) is set up along the 77–78°E longitudes covering the equatorial and low-latitude region. The receivers at these stations measure the relative phase of the 150 MHz beacon with respect to that at 400 MHz, which is proportional to the slant total electron content (TEC) along the line of sight. These simultaneously measured TECs are used to obtain the latitude-altitude distribution of electron densities (tomograms) in the meridional plane. The tomograms are generated using the Algebraic reconstruction technique (ART), a standard inversion algorithm. In this paper, the first tomographic images of the equatorial ionosphere along the 77–78°E meridian are presented, signalling the addition of a new dimension to the investigation of equatorial ionosphere. The images indicate the temporal evolution of the equatorial ionosphere and EIA, as well as the variability in the strength of EIA at various local times.