GNSS Data Results
Development of Single Frequency Ionospheric correction & plasma bubble detection algorithms using GPS Aided GEO Augmented Navigation (GAGAN) & Navigation Indian Constellation (NavIC) TEC observations
Researchers from the Department of ECE, Koneru Lakshmaiah Education Foundation (KLEF), Greenfields, Vaddeswaram, Guntur, deemed to be university have developed a Single Frequency Ionospheric correction & plasma bubble detection algorithms using GPS Aided GEO Augmented Navigation (GAGAN) & Navigation Indian Constellation (NavIC) TEC observations.
ASHF ionospheric model carried out with dual and single frequency ionospheric models like as Klobuchar model, Centre for Orbit Determination in Europe (CODE) Klobuchar model, NeQuick G model, BeiDou System (BDS2) model and CODE Global Ionospheric Maps (GIM) models. The outcome of the results indicates that the 4th Order ASHF ionospheric model would be the potential for single and dual-frequency ionospheric models for GNSS and SBAS systems.
The regional ionosphere TEC broad model based on the 4th order ASHF model is constructed for estimating the vertical ionospheric delay at different grid points using empirical data collected from 26 GPS TEC stations distributed throughout India. It is suggested that a one-hour update interval of ASHF model coefficients for the GNSS/NavIC system is sufficient to represent dynamic and random ionospheric spatial-temporal variations in the Indian region.
The regional ionospheric Total Electron Content (TEC) model is necessary for High Frequency (HF), communication, and navigation applications to characterize local spatial-temporal and dispersive properties of the ionosphere
A novel Adjusted Spherical Harmonics Ionospheric Model (ASHF) for Indian region is developed by KLEF, Space Technology and Atmospheric Research (STAR) group, Department of ECE, KLEF University.
ASHF model estimates ionospheric delay using the Fourier series expansion method with the sum of latitudinal Legendre function and longitudinal sine and cosine terms. The mathematical expression for mapping the regional vertical total electron content (VTEC) using the adjusted spherical harmonics function (ASHF) model. The TEC model is successful in capturing day-to-day variability in Equatorial Ionization Anomaly (EIA) over the Indian region. The ASHF model coefficients are obtained for orders 2, 3, 4 and 5. The spatial resolution is 1ox1o and temporal resolution is 1 hour for the ASHF model.
Conclusions drawn from the proposed model:
1. The performance of the proposed ASHF model validated in capturing the Equatorial Ionization Anomaly (EIA) patterns over the Indian region during the geomagnetic storm and quiet periods for the 2015 data.
2. The proposed ASHF model TEC would be useful for providing ionospheric corrections to single-frequency GNSS users.
3. The 4th order ASHF order driven by 25 coefficients alone and has the feasibility to act as regional GPS ionospheric broadcast model, i.e., broadcasting of these coefficients to NavIC/GNSS users.
4. The presented results show that adjusted spherical harmonics expansion model (with order = 4) estimates the ionospheric delays with high accuracy for SBAS application.
Publications:
1. K. S. Krishna, D. V. Ratnam, M. Sridhar, P. B. S. Harsha and G. Sivavaraprasad, "Performance Evaluation of Adjusted Spherical Harmonics Ionospheric Model Over Indian Region," in IEEE Access, vol. 8, pp. 172610-172622, 2020.
2.Abhigna, M.S.R., Sridhar, M., Harsha, P.B.S., Krishna, K.S. and Ratnam, D.V., 2021. Broadcast ionospheric delay correction algorithm using reduced order adjusted spherical harmonics function for single-frequency GNSS receivers. Acta Geophysica, 69(1), pp.335-351.