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The scintillation data (S4-index) at the L-band frequency of 1.575GHz,recorded from a total of 18 GPS receivers installed at different locationsin India under the GAGAN project, have provided us with a unique opportunity, for thefirst time in the Indian region, to make a simultaneous study ofspatio-temporal and intensity characteristics of the trans-ionosphericscintillations during the 18-month, low sunspot activity (LSSA) period fromJanuary 2004 to July 2005. During this period, the occurrence ofscintillations is found to be maximum around the pre-midnight hours ofequinox months, with very little activity during the post-midnight hours. Nosignificant scintillation activity is observed during the summer and wintermonths of the period of observation. The intensity (S4 index) ofthe scintillation activity is stronger around the equatorial ionization anomaly(EIA) region in the geographic latitude range of 15° to 25° N in theIndian region. These scintillations are often accompanied by the TECdepletions with durations ranging from 5 to 25 min and magnitudes from 5to 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 to4 min, increasing the error bounds effecting the integrity of the SBASoperation. During the present period of study, a total of 395 loss of lockevents are observed in the Indian EIA region; this number is likely toincrease during the high sunspot activity (HSSA) period, creating moreadverse conditions for the trans-ionospheric communications and the GPS-based navigation systems

annales geophysicae

Study of spatial and temporal characteristics of L-band scintillations over the Indian low-latitude region and their possible effects on GPS navigation