Since IGY (International Geophysical Year),
through coordinated global observations, ionospheric research has been carried
out by many countries. This effort primarily helped in the design and operation
of HFradio wave communication
systems. The Indian region covers a highly
variable part of the equatorial electrojet and EIA (Equatorial Ionisation
Anomaly) phenomena making its predictability difficult. With the advent of
satellite communication and navigation, the need for accurate ionospheric TEC
(Total Electron Content) models at global and regional scales has been
stressed. The GAGAN (GPS Aided Geo Augmented Navigation) project jointly
undertaken by the Indian Space Research Organisation (ISRO) and the Airport Authority
of India (AAI) aims at effectively utilising the Global Navigational Satellite
System (GNSS) to determine position coordinates accurately for aircraft
precision landing applications. For this purpose the range errors are estimated
by using a ground network of TEC stations spread over Indian region. The near simultaneous data collected from these dual frequency GPS stations can be used to generate the geo-referenced TEC values
for various applications. The author has developed necessary algorithm and associated
computer programmes for a real-time vertical TEC (VTEC) model based on TEC data
collected from the GAGAN ground based network stations. The model has been
tested and sample results presented here show that it adequately provides for
the latitudinal resolution of 1° for the entire longitude span and also for two
longitude blocks (73 - 83 & 83-93°E)
separately. Cubic spline and bilinear interpolation techniques are used for
filling up temporal and spatial data gaps. The model provides tabulated output
of hourly average VTEC data with latitude for ready use, as well as graphical
displays of VTEC maps and contours for monitoring purpose. The real-time model
and its extensions are also being used for detailed scientific studies;
examples of these show small day to day variability of VTEC without any change
in solar activity and indication of the change in the shape of the VTEC diurnal
curve with season. The present model will be used for further studies to derive
the monthly average variation of the diurnal pattern and the relationship
between VTEC peak amplitudes with changes in solar activity. The
References
[1]
H. Rishbeth and O. K. Garriott, “Introduction to Ionospheric Physics,” Academic Press, Waltham, 1969.
[2]
M. C. Kelley, “The Earths Ionosphere: Plasma Physics and Rlectrodynamics,” International Geophysics Series, Vol. 43, Academic Press, Waltham, 1989.
[3]
L. F. McNamara, “The Ionosphere: Communications, Surveillance, and Direction Finding,” Kruger Pub. Co., Malabar, 1991.
[4]
R. G. Cracknell and R. A. Whiting, “Twenty-One Years of TE, 1. Transequatorial Radio Wave Propagation,” Radio Communication, Vol. 56, No. 6-7, 1980, pp. 626-634.
[5]
J. K. Hargreaves, “The Solar Terrestrial Environment,” Cambridge University Press, Cambridge, 1992. http://dx.doi.org/10.1017/CBO9780511628924
[6]
S. Chapman, “Some Phenomena of the Upper Atmosphere,” Proceedings of the Physical Society of London, Vol. B64, No. 10, 1951, pp. 833-843.
[7]
S. K. Mitra, “Geomagnetic Control of Region F2 of the Ionosphere,” Nature, Vol. 158, No. 4019, 1946, p. 668. http://dx.doi.org/10.1038/158668a0
[8]
D. F. Martyn, “Large Scale Movements of Ionization in the Ionosphere,” Journal of Geophysical Research, Vol. 64, No. 12, 1959, pp. 2178-2179. http://dx.doi.org/10.1029/JZ064i012p02178
[9]
S. Chapman, “The International Geophysical Year,” Transactions, American Geophysical Union, Vol. 10, No. 2, 1958, pp. 112-119. http://dx.doi.org/10.1029/TR040i002p00112
[10]
K. Davies, et al., “ATS-6 Satellite Radio Beacon Measurements at Ootacamund, India,” Radio Science, Vol. 14, No. 1, 1979, pp. 85-95. http://dx.doi.org/10.1029/RS014i001p00085
[11]
A. P. Mitra, “Indian Programme on Middle Atmosphere: Some Results,” Advances in Space Research, Vol. 10, No. 10, 1990, pp. 123-132. http://dx.doi.org/10.1016/0273-1177(90)90020-Z
[12]
G. Rostoker, “Solar-Terrestrial Energy Program 1990-1995: A Study of Energy Transfer Mechanisms in the Solar-Terrestrial System,” Eos Transactions American Geophysical Union, Vol. 70, No. 14, 1989, pp. 209-216. http://dx.doi.org/10.1029/89EO00110
[13]
A. R. Jain, D. N. Rao and P. B. Rao, “Indian MST Results,” Indian Journal of Radio & Space Physics, Vol. 29, No. 4, 2000, pp. 149-171.
[14]
S. C. Garg, et al., “RPA Aeronomy Experiment Onboard the Indian Satellite SROSS-C2: Some Important Aspects of the Payload and Satellite,” Indian Journal of Radio & Space Physics, Vol. 32, No. 1, 2003, pp. 5-15.
[15]
P. B. Rao, et al., “An Overview of CAWES-India Program with Emphasis to Equatorial Atmospheric Coupling Pro-cesses,” Journal of Atmospheric and Solar-Terrestrial Physics, Vol. 75-76, 2012, pp. 98-114. http://dx.doi.org/10.1016/j.jastp.2011.08.005
[16]
K. N. Suryanarayana Rao, “GAGAN—The Indian Satellite Based Augmentation System,” Indian Journal of Radio & Space Physics, Vol. 36, No. 4, 2007, pp. 293-302.
[17]
N. Jakowski, M. Hoque and M. C. Mayer, “A New Global TEC Model for Estimating Trans-Ionospheric Radio Wave Propagation Errors,” Journal of Geodesy, Vol. 85, No. 12, 2011, pp. 965-974. http://dx.doi.org/10.1007/s00190-011-0455-1
[18]
J. Klobuchar, “Ionospheric Time-Delay Algorithm for Sin- gle Frequency GPS Users,” IEEE Transactions on Aerospace and Electronic Systems, Vol. AES-23, No. 3, 1987, pp. 325-331.
[19]
N. Jakowski, S. M. Stankov and D. Klaehn, “Operational Space Weather Service for GNSS Precise Positioning,” Annals of Geophysics, Vol. 23, No. 9, 2005, pp. 3071-3079.
http://dx.doi.org/10.5194/angeo-23-3071-2005
[20]
S. C. Chakravarty, “Real Time TEC Model over Indian Region,” Indian Patent No. 2229/CHE/2010 (applied by ISRO), 2010.
[21]
R. Acharya, et al., “Ionospheric Studies for the Implementation of GAGAN,” Indian Journal of Radio & Space Physics, Vol. 36, No. 5, 2007, pp. 394-404.
[22]
P. V. S. Rama Rao, K. Niranjan, D. S. V. V. D. Prasad, S. Gopi Krishna and G. Uma, “On the Validity of the Iionospheric Pierce Point (IPP) Altitude of 350 km in the Indian Equatorial and Low-Latitude Sector,” Annals of Geophysics, Vol. 24, 2006, pp. 2159-2168. http://dx.doi.org/10.5194/angeo-24-2159-2006
