Morphological Characteristics of L-Band Scintillations and Their Impact on GPS Signals - A Quantitative Study on the Precursors for the Occurrence of Scintillations
Abstract
The scintillation data (S4-index) at the L-band frequency of 1.575 GHz recorded from 18 GPS receivers installed at different locations in India under the GAGAN project has given an 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 low sunspot activity (LSSA) period from January 2004 to July 2005. During this period the occurrence of intense (S4 > 0.45 H 10 dB) scintillations are found to be mostly confine to the pre-midnight hours of equinoctial months and around the equatorial ionization anomaly (EIA) region of geographic latitudes from 15o to 25o N in the Indian sector. These scintillations are often accompanied by the TEC depletions with durations ranging from 5 to 25 minutes and magnitudes from 5 to 15 TEC units that are found to affect the positional accuracy of GPS by about 1 to 3 meters. Further, during the times of intense scintillations, the GPS receivers are found to loose their lock for a short duration of 1 to 4 min increasing the error bounds and thus effecting the integrity of the SBAS operation, which may substantially increase during the high sunspot activity periods. The pre-reversal enhancement (PRE) in ExB drift is the most important parameter in controlling the occurrence of scintillations. Also, these drifts are found to decrease with increasing geomagnetic activity (Kp), more significantly during equinoctial months. On a day-to-day basis, it is found that an upward drift velocity e 30 m/s at the equator, is the necessary condition for strong scintillations to occur over Waltair (20oN dip) on magnetically quiet days with average Kp d 2 (6 hrs prior to the local sunset) during the high sunspot year of 2001. This threshold value of the upward drift reduces to 20 m/s during the low sunspot activity year of 2004.
Document Details
- Document Type
- Technical Report
- Publication Date
- Jun 01, 2006
- Accession Number
- ADA476986
Entities
People
- D. S. Prasad
- K. Niranjan
- P. V. Rao
- S. G. Krishua
- S. T. Ram
Organizations
- Andhra University