volume | PIER Journals

Abstract

To meet the growing requirements of Standard Positioning Services (SPS) and Precision Services (PS), more and more GNSS systems operating at conventional GPS frequencies and higher frequency bands are launched. The Indian NavIC system is one of such systems transmitting navigational signals at S1 (2492.028 MHz) and L5 (1176.45 MHz) frequencies. For GPS at L-band frequencies, comprehensive research work has been conducted to analyze the ionospheric delay to estimate precise user position, although very little research work is available in the public domain at the navigational S-band level. The NavIC program provides opportunities to explore the ionospheric delay effect on S-band navigational signals. The precise position determination demands accurate estimation of the vertical ionospheric delay which is generally obtained using Vertical Electron Content (VTEC) of the ionosphere. The VTEC can be obtained by multiplying a mapping function to the Slant Total Electron Content (STEC). Conventionally a thin shell (also known as a single shell) model is used to map STEC to VTEC, but it introduces error at low elevation angles. This error is significant for the NavIC receivers, located in the northern part of India, as they observe elevation angles below 50° for most of the time, and thus there is a need to investigate the suitability of the mapping function model for the NavIC system. As the ionospheric shell height modifies the mapping function and results in a change in VTEC, the height and thickness of the thick shell have been investigated based on the ionospheric data taken from IRI 2016 and were estimated as 300 km and 250 km, respectively. In the present work, the thick shell model has been compared to thin shell model mapping functions to improve the accuracy of VTEC estimation at the low elevation. The reduction in vertical delay using the thick shell mapping function at low elevation indicates its suitability for the locations like Dehradun, India, which lies in the mid-latitude region. Furthermore, the temporal variability of vertical delay at S and L band frequencies has also been investigated to understand the diurnal and seasonal characteristics of ionospheric vertical delay over a period of 12 months to cover all the seasons during the year 2017-18. The vertical delay at the S-band frequency was found to be less than that at the L-band frequency and is almost constant over a month. This finding will be beneficial for single-frequency users and could be used to develop the Grid Ionospheric Vertical Delay (GIVD) map for the NavIC system to enhance positional accuracy.

1. Rao, K. N. S., "GAGAN - The Indian satellite based augmentation system," Indian Journal of Radio & Space Physics, Vol. 36, 293-302, Aug. 2007.

2. Hager, B. H., R. W. King, and M. H. Murray, Measurement of Crustal Deformation Using the Global Positioning System, Vol. 19, 351, Annual Review of Earth and Planetary Sciences, 1991.

3. Sun, Y., R. Xue, D. Zhao, and D. Wang, "Radio frequency compatibility evaluation of S band navigation signals for future beidou," Sensors (Switzerland), Vol. 17, No. 5, 1039, May 2017, doi: 10.3390/s17051039.
doi:10.3390/s17051039

4. Zhong, J., J. Lei, X. Dou, and X. Yue, "Assessment of vertical TEC mapping functions for space-based GNSS observations," GPS Solut., Vol. 20, No. 3, 353-362, Jul. 2016, doi: 10.1007/s10291-015-0444-6.
doi:10.1007/s10291-015-0444-6

5. Ratnam, D. V., T. R. Vishnu, and P. B. S. Harsha, "Ionospheric gradients estimation and analysis of S-band navigation signals for NAVIC system," IEEE Access, Vol. 6, 66954-66962, 2018, doi: 10.1109/ACCESS.2018.2876795.
doi:10.1109/ACCESS.2018.2876795

6. Schaer, S., "Mapping and predicting the earth's ionosphere using the Global Positioning System," Diss. Astron. Inst., 205, 1999, [online], available: https://www.researchgate.net/publication/252260542_Mapping_and_Predicting_the_Earth's_Ionos-phere_Using_the_Global_Positioning_System.

7. Radicella, S. M., B. Nava, P. Coïsson, L. Kersley, and G. J. Bailey, "Effects of gradients of the electron density on Earth-space communications," Ann. Geophys., Vol. 47, No. 2-3 suppl., 1227-1246, 2004, doi: 10.4401/ag-3296.

8. Bates, D. R., The Propagation of Radio Waves, Vol. 34, No. 6, K. G. Budden Cambridge University Press, 1985.

9. Abe, O. E., X. Otero Villamide, C. Paparini, S. M. Radicella, and B. Nava, "Analysis of a grid ionospheric vertical delay and its bounding errors overWest African sub-Saharan region," J. Atmos. Solar-Terrestrial Phys., Vol. 154, 67-74, Feb. 2017, doi: 10.1016/j.jastp.2016.12.015.
doi:10.1016/j.jastp.2016.12.015

10. Hernández-Pajares, M., et al. "The ionosphere: Effects, GPS modeling and the benefits for space geodetic techniques," J. Geod., Vol. 85, No. 12, 887-907, 2011, doi: 10.1007/s00190-011-0508-5.
doi:10.1007/s00190-011-0508-5

11. Jiang, H., Z. Wang, J. An, J. Liu, N. Wang, and H. Li, "Influence of spatial gradients on ionospheric mapping using thin layer models," GPS Solut., Vol. 22, No. 1, Jan. 2018, doi: 10.1007/s10291-017-0671-0.
doi:10.1007/s10291-017-0671-0

12. Mannucci, A. J., B. D. Wilson, D. N. Yuan, C. H. Ho, U. J. Lindqwister, and T. F. Runge, "A global mapping technique for GPS-derived ionospheric total electron content measurements," Radio Sci., Vol. 33, No. 3, 565-582, 1998, doi: 10.1029/97RS02707.
doi:10.1029/97RS02707

13. Klobuchar, J. A., "Ionospheric time-delay algorithm for single-frequency GPS users," IEEE Trans. Aerosp. Electron. Syst., Vol. 23, No. 3, 325-331, 1987, doi: 10.1109/TAES.1987.310829.
doi:10.1109/TAES.1987.310829

14. Walter, T., et al. "Robust detection of ionospheric irregularities," Navig. J. Inst. Navig., Vol. 48, No. 2, 89-100, 2001, doi: 10.1002/j.2161-4296.2001.tb00231.x.
doi:10.1002/j.2161-4296.2001.tb00231.x

15. Ruffini, G., A. Flores, and A. Rius, "GPS tomography of the ionospheric electron content with a correlation functional," IEEE Trans. Geosci. Remote Sens., Vol. 36, No. 1, 143-153, 1998, doi: 10.1109/36.655324.
doi:10.1109/36.655324

16. Wen, D., Y. Yuan, J. Ou, K. Zhang, and K. Liu, "A hybrid reconstruction algorithm for 3-D ionospheric tomography," IEEE Trans. Geosci. Remote Sens., Vol. 46, No. 6, 1733-1739, 2008, doi: 10.1109/TGRS.2008.916466.
doi:10.1109/TGRS.2008.916466

17. Shukla, A. K., M. R. Sivaraman, and K. Bandyopadhyay, "A comparison study of voxel based multi- and two-layer ionospheric tomography models over the indian region using GPS data," Int. J. Remote Sens., Vol. 31, No. 10, 2535-2549, 2010, doi: 10.1080/01431160903019296.
doi:10.1080/01431160903019296

18. Shukla, A. K., S. Das, N. Nagori, M. R. Sivaraman, and K. Bandyopadhyay, "Two-shell ionospheric model for Indian region: A novel approach," IEEE Trans. Geosci. Remote Sens., Vol. 47, No. 8, 2407-2412, 2009, doi: 10.1109/TGRS.2009.2017520.
doi:10.1109/TGRS.2009.2017520

19. Komjathy, A., et al. "A new ionospheric model for wide area differential GPS?: The multiple shell approach," Network, 28-30, Jan. 2002.

20. Norsuzila, Y., M. Abdullah, and M. Ismail, "Determination of GPS total electron content using Single Layer Model (SLM) ionospheric mapping function," IJCSNS Int. J. Comput. Sci. Netw. Secur., Vol. 8, No. 9, 154-160, 2008, [online], available: http://paper.ijcsns.org/07_book/200809/20080922.pdf.

21. Tancredi, U., A. Renga, and M. Grassi, "Geometric total electron content models for topside ionospheric sounding," EESMS 2014 - 2014 IEEE Work. Environ. Energy Struct. Monit. Syst. Proc., 163-168, 2014, doi: 10.1109/EESMS.2014.6923285.

22. Niranjan, K., B. Srivani, S. Gopikrishna, and P. V. S. Rama Rao, "Spatial distribution of ionization in the equatorial and low-latitude ionosphere of the Indian sector and its effect on the pierce point altitude for GPS applications during low solar activity periods," J. Geophys. Res. Sp. Phys., Vol. 112, No. 5, 1-15, 2007, doi: 10.1029/2006JA011989.

23. Xiang, Y. and Y. Gao, "An enhanced mapping function with ionospheric varying height," Remote Sens., Vol. 11, No. 12, 1497, Jun. 2019, doi: 10.3390/rs11121497.
doi:10.3390/rs11121497

24. Lanyi, G. E. and T. Roth, "A comparison of mapped and measured total ionospheric electron content using global positioning system and beacon satellite observations," Radio Sci., Vol. 23, No. 4, 483-492, 1988, doi: 10.1029/RS023i004p00483.
doi:10.1029/RS023i004p00483

25. Hernàndez-Pajares , M., J. M. Juan, J. Sanz, and M. Garcia-Fernàndez, "Towards a more realistic ionospheric mapping function," XXVIII URSI Gen. Assem., Vol. 2002, 2002-2005, 2005.

26. Brunini, C., E. Camilion, and F. Azpilicueta, "Simulation study of the influence of the ionospheric layer height in the thin layer ionospheric model," J. Geod., Vol. 85, No. 9, 637-645, 2011, doi: 10.1007/s00190-011-0470-2.
doi:10.1007/s00190-011-0470-2

27. Prasad, S. N. V. S., P. V. S. Rama Rao, D. S. V. V. D. Prasad, K. Venkatesh, and K. Niranjan, "On the variabilities of the Total Electron Content (TEC) over the Indian low latitude sector," Adv. Sp. Res., Vol. 49, No. 5, 898-913, 2012, doi: 10.1016/j.asr.2011.12.020.
doi:10.1016/j.asr.2011.12.020

28. Acharya, R., et al. "Ionospheric studies for the implementation of GAGAN," Indian J. Radio Sp. Phys., Vol. 36, No. 5, 394-404, 2007.

29. Ratnam, D. V., J. R. K. K. Dabbakuti, and S. Sunda, "Modeling of ionospheric time delays based on a multishell spherical harmonics function approach," IEEE J. Sel. Top. Appl. Earth Obs. Remote Sens., Vol. 10, No. 12, 5784-5790, 2017, doi: 10.1109/JSTARS.2017.2743695.
doi:10.1109/JSTARS.2017.2743695

30. Smith, D. A., E. A. Araujo-Pradere, C. Minter, and T. Fuller-Rowell, "A comprehensive evaluation of the errors inherent in the use of a two-dimensional shell for modeling the ionosphere," Radio Sci., Vol. 43, No. 6, n/a-n/a, 2008, doi: 10.1029/2007rs003769.
doi:10.1029/2007RS003769

31. Maruyama, T., K. Hozumi, and G. Ma, "Ionospheric total electron content derived from gnss signals by double thin-shell model near the magnetic equator and implication in the meridional wind," 2019 Russ. Open Conf. Radio Wave Propagation, RWP 2019 - Proc., Vol. 1, No. 3, 139-140, 2019, doi: 10.1109/RWP.2019.8810250.
doi:10.1109/RWP.2019.8810250

32. Sinha, S., R. Mathur, S. C. Bharadwaj, A. Vidyarthi, B. S. Jassal, and A. K. Shukla, "Estimation and smoothing of tec from navic dual frequency data," 2018 4th Int. Conf. Comput. Commun. Autom. ICCCA 2018, 1-5, 2018, doi: 10.1109/CCAA.2018.8777665.

33. Bhardwaj, S. C., A. Vidyarthi, B. S. Jassal, and A. K. Shukla, "Study of temporal variation of vertical TEC using NavIC data," 2017 International Conference on Emerging Trends in Computing and Communication Technologies, ICETCCT 2017, Vol. 2018-Janua, 1-5, 2018, doi: 10.1109/ICETCCT.2017.8280317.

34. Zaminpardaz, S., P. J. G. Teunissen, and N. Nadarajah, "IRNSS stand-alone positioning: First results in Australia," J. Spat. Sci., Vol. 61, No. 1, 5-27, 2016, doi: 10.1080/14498596.2016.1142398.
doi:10.1080/14498596.2016.1142398

35. Bilitza, D., et al. "International reference ionosphere 2016: From ionospheric climate to real-time weather predictions," Sp. Weather, Vol. 15, No. 2, 418-429, 2017, doi: 10.1002/2016SW001593.
doi:10.1002/2016SW001593

36. Venkatesh, K., P. V. S. R. Rao, D. S. V. V. D. Prasad, K. Niranjan, and P. L. Saranya, "Study of TEC, slab-thickness and neutral temperature of the thermosphere in the Indian low latitude sector," Ann. Geophys., Vol. 29, No. 9, 1635-1645, 2011, doi: 10.5194/angeo-29-1635-2011.
doi:10.5194/angeo-29-1635-2011

37. Bagiya, M. S., H. P. Joshi, K. N. Iyer, M. Aggarwal, S. Ravindran, and B. M. Pathan, "TEC variations during low solar activity period (2005-2007) near the Equatorial Ionospheric Anomaly Crest region in India," Ann. Geophys., Vol. 27, 1047-1057, 2009.
doi:10.5194/angeo-27-1047-2009

38. Bhardwaj, S. C., A. Vidyarthi, B. S. Jassal, and A. K. Shukla, "Estimation of temporal variability of differential instrumental biases of NavIC satellites and receiver using Kalman filter," Radio Sci., Jun. 2020, doi: 10.1029/2019RS006886.

39. Sunehra, D., "TEC and instrumental bias estimation of GAGAN station using Kalman filter and SCORE algorithm," Positioning, Vol. 7, No. 1, 41-50, 2016, doi: 10.4236/pos.2016.71004.
doi:10.4236/pos.2016.71004

40. Kashcheyev, A., B. Nava, and S. M. Radicella, "Estimation of higher-order ionospheric errors in GNSS positioning using a realistic 3-D electron density model," Radio Sci., Vol. 47, No. 4, 1-7, 2012, doi: 10.1029/2011RS004976.
doi:10.1029/2011RS004976

Dr. Sharat Chandra Bhardwaj

Dr. Anurag Vidyarthi

Dr. Bhajan Singh Jassal

Dr. Ashish Kumar Shukla