Regional ionospheric Total Electron Content (TEC) models are most significant to investigate the variability of ionosphere during allweather conditions. Since the ground -based TEC measurements are not available in oceanic and polar regions, space -based observations are incorporated to increase the positional accuracy and reliability of Global Ionospheric TEC Maps (GIMs). Therefore, data fusion techniques are necessary to enhance the prediction capability of regional ionospheric models by considering multi -source data. In view of this, an attempt is made to investigate Equatorial Ionization Anomaly (EIA) structures in low -latitudinal Indian region using multiinstrument data. Data observations from background model CODEGIM, available International GNSS Service (IGS) stations in India, GNSS receivers at KLEF and Tripura stations, FORMOSAT/COSMIC radio occultation and SWARM during geomagnetic storm period August 26-28, 2021 are used for the study. Spherical Harmonics Function (SHF) of order 4 is employed along with Weighted Least Squares analysis (WLS), where separate weight constraint is computed for each data source. TEC maps of spatial resolution 5 degrees x 5 degrees and temporal resolution of 1 h are generated to illustrate the dynamic behavior of ionosphere. The standard deviation for 3 days is obtained as 0.42, 0.61 and 1.43 TECU respectively. TEC depletions and enhancements are observed on August 27 and 28, with mean values of 12.74 and 15.27 TECU respectively, demonstrating negative and positive storm effects. (c) 2023 COSPAR. Published by Elsevier B.V. All rights reserved.
