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Ann. Geophys., 24, 1567-1580, 2006
www.ann-geophys.net/24/1567/2006/
© European Geosciences Union 2006
Study of spatial and temporal characteristics of L-band scintillations over the Indian low-latitude region and their possible effects on GPS navigation
P. V. S. Rama Rao, S. Gopi Krishna, K. Niranjan, and D. S. V. V. D. Prasad
Space Physics Laboratories, Department of Physics, Andhra University, Visakhapatnam 530 003, India
Abstract. The scintillation data (S4-index) at the L-band frequency of 1.575GHz,
recorded from a total of 18 GPS receivers installed at different locations
in India under the GAGAN project, have provided us with a unique opportunity, for the
first time in the Indian region, to make a simultaneous study of
spatio-temporal and intensity characteristics of the trans-ionospheric
scintillations during the 18-month, low sunspot activity (LSSA) period from
January 2004 to July 2005. During this period, the occurrence of
scintillations is found to be maximum around the pre-midnight hours of
equinox months, with very little activity during the post-midnight hours. No
significant scintillation activity is observed during the summer and winter
months of the period of observation. The intensity (S4 index) of
the scintillation activity is stronger around the equatorial ionization anomaly
(EIA) region in the geographic latitude range of 15° to 25° N in the
Indian region. These scintillations are often accompanied by the TEC
depletions with durations ranging from 5 to 25 min and magnitudes from 5
to 15 TEC units which affect the positional accuracy of the GPS by 1 to 3 m.
Further, during the intense scintillation events (S4>0.45≈10 dB),
the GPS receiver is found to lose its lock for a short duration of 1 to
4 min, increasing the error bounds effecting the integrity of the SBAS
operation. During the present period of study, a total of 395 loss of lock
events are observed in the Indian EIA region; this number is likely to
increase during the high sunspot activity (HSSA) period, creating more
adverse conditions for the trans-ionospheric communications and the GPS-based navigation systems.
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