Previous authors have reported on the morphology of GPS scintillations and irregularity zonal drift during the 2002 Conjugate Point Equatorial Experiment (COPEX) in Brazil. In this paper, we characterize the turbulent ionospheric medium that produced these scintillations. Using 10？Hz GPS carrier-to-noise measurements at Boa Vista (2.9°N, 60.7°W), Alta Floresta (9.9°S, 56.1°W), and Campo Grande (20.5°S, 54.7°W), we report on the variation of turbulent intensity, phase spectral index, and irregularity zonal drift as a function of latitude and local time for the evening of 1-2 November 2002. The method of analysis is new and, unlike analytical theories of scintillation based on the Born or Rytov approximations, it is valid when the scintillation index saturates due to multiple-scatter effects. Our principal findings are that (1) the strength of turbulence tended to be largest near the crests of the equatorial anomaly and at early postsunset local times, (2) the turbulent intensity was generally stronger and lasted two hours longer at Campo Grande than at Boa Vista, (3) the phase spectral index was similar at the three stations but increased from 2.5 to 4.5 with local time, and (4) our estimates of zonal irregularity drift are consistent with those provided by the spaced-receiver technique. 1. Introduction The distribution of free electrons in the ionosphere is dictated by production from solar radiation, transport, and loss through chemical recombination. It is also subject to instability mechanisms that generate large-scale depletions and irregularities in the ambient electron density over a wide range of spatial scales (plasma turbulence). Radio waves that propagate through these irregularities experience scattering and diffraction, causing random fluctuations in amplitude and phase referred to as scintillations. The scintillation of satellite signals has been shown to severely degrade the performance of satellite communications systems such as AFSATCOM [1, 2], satellite global navigation satellite systems (GNSS) such as the Global Positioning System (GPS) [3–5], and space radars used to conduct cloud-free, day-and-night observations of the Earth’s surface [6–8]. Scintillations associated with irregularities in the equatorial ionosphere are generally the most intense encountered worldwide, and the occurrence morphology depends on local time, season, longitude, solar cycle, magnetic activity, and exhibits a high degree of night-to-night variability [9]. Ionospheric irregularities and scintillations constitute one of the most important space weather
References
[1]
A. Basu, E. MacKenzie, and S. Basu, “Ionospheric constraints on VHF/UHF communications links during solar maximum and minimum periods,” Radio Science, vol. 23, no. 3, pp. 363–378, 1988.
[2]
K. Groves, S. Basu, E. Weber et al., “Equatorial scintillation and systems support,” Radio Science, vol. 32, no. 5, pp. 2047–2064, 1997.
[3]
K. M. Groves, S. Basu, J. M. Quinn, et al., “A comparison of GPS performance in a scintillating environment at Ascension Island,” in Proceedings of the 13th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS '00), pp. 672–679, Salt Palace Convention Center, Salt Lake City, Utah, USA, September 2000.
[4]
S. Datta-Barua, P. H. Doherty, S. H. Delay, T. Dehel, and J. A. Klobuchar, “Ionospheric scintillation effects on single and dual frequency GPS positioning,” in Proceedings of the 16th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS/GNSS '03), pp. 336–346, Portland, OR, USA, September 2003.
[5]
C. S. Carrano and K. M. Groves, “Temporal decorrelation of GPS satellite signals due to multiple scattering from ionospheric irregularities,” in Proceedings of the 23rd International Technical Meeting of The Satellite Division of the Institute of Navigation (ION GNSS '10), pp. 361–374, Oregon Convention Center, Portland, OR, USA, September 2010.
[6]
Z.-W. Xu, J. Wu, and Z.-S. Wu, “A survey of ionospheric effects on space-based radar,” Waves in Random Media, vol. 14, no. 2, pp. S189–S273, 2004.
[7]
N. Rogers and P. Cannon, “The synthetic aperture radar trans-ionospheric radio propagation simulator (SAR-TIRPS),” in Proceedings of the 11th International Conference on Ionospheric Radio Systems and Techniques (IRST '09), pp. 112–116, Edinburgh, UK, April 2009.
[8]
C. S. Carrano, K. M. Groves, and R. G. Caton, “Accuracy of phase screen models using deterministic screens derived from GPS and ALTAIR measurements,” in Proceedings of the Ionospheric Effects Symposium, Alexandria, Va, USA, May 2011.
[9]
J. Aarons, “Global morphology of ionospheric scintillations,” Proceedings of the IEEE, vol. 70, no. 4, pp. 360–378, 1982.
[10]
I. S. Batista, M. A. Abdu, A. J. Carrasco et al., “Equatorial spread F and sporadic E-layer connections during the Brazilian conjugate point equatorial experiment (COPEX),” Journal of Atmospheric and Solar-Terrestrial Physics, vol. 70, no. 8-9, pp. 1133–1143, 2008.
[11]
M. T. A. H. Muella, E. R. de Paula, I. J. Kantor, et al., “GPS L-band scintillations and ionospheric irregularity zonal drifts inferred at equatorial and low-latitude regions,” Journal of Atmospheric and Solar-Terrestrial Physics, vol. 70, no. 10, pp. 1261–1272, 2008.
[12]
M. A. Abdu, I. S. Batista, B. W. Reinisch et al., “Conjugate point equatorial experiment (COPEX) campaign in Brazil: electrodynamics highlights on spread F development conditions and day-to-day variability,” Journal of Geophysical Research A, vol. 114, no. 4, Article ID A04308, 21 pages, 2009.
[13]
J. H. A. Sobral, M. A. Abdu, T. R. Pedersen et al., “Ionospheric zonal velocities at conjugate points over Brazil during the COPEX campaign: experimental observations and theoretical validations,” Journal of Geophysical Research A, vol. 114, no. 4, Article ID A04309, 24 pages, 2009.
[14]
E. R. de Paula, M. T. A. H. Muella, J. H. A. Sobral et al., “Magnetic conjugate point observations of kilometer and hundred-meter scale irregularities and zonal drifts,” Journal of Geophysical Research A, vol. 115, no. 8, Article ID A08307, 15 pages, 2010.
[15]
A. Ishimaru, Wave Propagation and Scattering in Random Media, IEEE Press and Oxford University, New York, NY, USA, 1997.
[16]
C. L. Rino, “Power law phase screen model for ionospheric scintillation, 1 weak scatter,” Radio Science, vol. 14, no. 6, pp. 1135–1145, 1979.
[17]
C. L. Rino and C. S. Carrano, “The application of numerical simulations in Beacon scintillation analysis and modeling,” Radio Science, vol. 46, no. 3, Article ID RS0D02, 10 pages, 2011.
[18]
C. L. Rino, The Theory of Scintillation With Applications in Remote Sensing, John Wiley, New York, NY, USA, 2011.
[19]
B. M. Ledvina, P. M. Kintner, and E. R. de Paula, “Understanding spaced-receiver zonal velocity estimation,” Journal of Geophysical Research A, vol. 109, no. 10, Article ID A10306, 12 pages, 2004.
[20]
P. D. Welch, “The use of fast Fourier transform for the estimation of power spectra: a method based on time averaging over short, modified periodograms,” IEEE Transactions on Audio and Electroacoustics, vol. 15, no. 2, pp. 70–73, 1967.
[21]
N. Olsen, T. Sabaka, and L. T？ffner-Clausen, “Determination of the IGRF 2000 model,” Earth, Planets and Space, vol. 52, no. 12, pp. 1175–1182, 2000.
[22]
J. A. Secan, R. M. Bussey, E. J. Fremouw, and S. Basu, “Improved model of equatorial scintillation,” Radio Science, vol. 30, no. 3, pp. 607–617, 1995.
[23]
M. A. Cervera and R. M. Thomas, “Latitudinal and temporal variation of equatorial ionospheric irregularities determined from GPS scintillation observations,” Annales Geophysicae, vol. 24, no. 12, pp. 3329–3341, 2006.
[24]
C. S. Carrano, K. M. Groves, R. G. Caton, C. L. Rino, and P. R. Straus, “Multiple phase screen modeling of ionospheric scintillation along radio occultation raypaths,” Radio Science, vol. 46, no. 3, Article ID RS0D07, 14 pages, 2011.
[25]
N. C. Rogers, P. S. Cannon, and K. M. Groves, “Measurements and simulation of ionospheric scattering on VHF and UHF radar signals: channel scattering function,” Radio science, vol. 44, Article ID RS0A07, 10 pages, 2009.
[26]
F. R. Hoots and R. L. Roehrich, Spacetrack Report #3, Models for Propagation of the NORAD Element Sets, United States Air Force, Colorado Springs, Colo, USA, 1980.
[27]
H. Booker, J. A. Ferguson, and H. O. Vats, “Comparison between the extended-medium and the phase-screen scintillation theories,” Journal of Atmospheric and Terrestrial Physics, vol. 47, no. 4, pp. 381–399, 1985.
[28]
H. Booker and G. MajidiAhi, “Theory of refractive scattering in scintillation phenomena,” Journal of Atmospheric and Terrestrial Physics, vol. 43, no. 11, pp. 1199–1214, 1981.
[29]
E. J. Fremouw and J. A. Secan, “Modeling and scientific application of scintillation results,” Radio Science, vol. 19, no. 3, pp. 687–694, 1984.
[30]
K. C. Yeh and C. H. Liu, “Radio wave scintillations in the ionosphere,” Proceedings of the IEEE, vol. 70, no. 4, pp. 324–360, 1982.
[31]
A. Bhattacharyya, K. C. Yeh, and S. J. Franke, “Deducing turbulence parameters from transionospheric scintillation measurements,” Space Science Reviews, vol. 61, no. 3-4, pp. 335–386, 1992.
[32]
C. S. Carrano and C. L. Rino, “Split-step solution of the 4th moment equation for propagation through intense ionospheric disturbances,” in Proceedings of the International Conference on Electromagnetics in Advanced Applications (ICEAA '11), Turin, Italy, 2011.
[33]
R. Piessens, E. deDoncker-Kapenga, C. Uberhuber, and D. Kahaner, Quadpack: A Subroutine Package for Automatic Integration, vol. 1 of Computational Mathematics, Springer, 1983.
[34]
J. A. Nelder and R. Mead, “A simplex method for function minimization,” The Computer Journal, vol. 7, no. 4, pp. 308–313, 1965.
[35]
R. G. Caton, C. S. Carrano, C. M. Alcala, K. M. Groves, T. Beach, and D. Sponseller, “Simulating the effects of scintillation on transionospheric signals with a two-way phase screen constructed from ALTAIR phase-derived TEC,” Radio Science, vol. 44, no. 4, Article ID RS0A12, 9 pages, 2009.
[36]
C. L. Rino and J. Owen, “The time structure of transionospheric radio wave scintillation,” Radio Science, vol. 15, no. 3, pp. 479–489, 1980.
[37]
C. S. Carrano, A. Anghel, R. A. Quinn, and K. M. Groves, “Kaiman filter estimation of plasmaspheric total electron content using GPS,” Radio Science, vol. 44, no. 4, Article ID RS0Al0, 14 pages, 2009.
[38]
C. S. Carrano and K. Groves, “The GPS segment of the AFRL-SCINDA global network and the challenges of real-time TEC estimation in the equatorial ionosphere,” in Institute of Navigation, National Technical Meeting (NTM '06), pp. 1036–1047, January 2006.
[39]
M. Knight and A. Finn, “The effects of ionospheric scintillation on GPS,” in Proceedings of the Institute of Navigation (ION) GPS meeting, Nashville, Tenn, USA, 1998.
[40]
R. S. Conker, M. B. El-Arini, C. J. Hegarty, and T. Hsiao, “Modeling the effects of ionospheric scintillation on GPS/Satellite-based augmentation system availability,” Radio Science, vol. 38, no. 1, article 1001, 23 pages, 2003.
[41]
S. J. Franke and C. H. Liu, “Modeling of equatorial multifrequency scintillation,” Radio Science, vol. 20, no. 3, pp. 403–415, 1985.
[42]
M. T. A. H. Muella, E. A. Kherani, E. R. de Paula et al., “Scintillation-producing Fresnel-scale irregularities associated with the regions of steepest TEC gradients adjacent to the equatorial ionization anomaly,” Journal of Geophysical Research A, vol. 115, no. 3, Article ID A03301, 19 pages, 2010.
[43]
C. E. Valladares and P. H. Doherty, “The low-latitude ionosphere sensor network (LISN),” in Proceedings of the International Technical Meeting of The Institute of Navigation, pp. 16–24, Anaheim, Calif, USA, January 2009.
[44]
C. Valladares, “The low-latitude ionosphere sensor network (LISN): initial results,” in Proceedings of the 2011 Ionospheric Effects Symposium, Alexandria, Va, USA, May 2011.
