Earth Planets Space, Vol. 61 (No. 5), pp. 633-635, 2009LETTER
K. Ravi Chandra, V. Satya Srinivas, and A. D. Sarma
Research and Training Unit for Navigational Electronics, Osmania University, Hyderabad, India
(Received October 29, 2007; Revised July 21, 2008; Accepted September 28, 2008; Online published May 29, 2009)
To cater to the needs of aviation applications, GPS Aided GEO Augmented Navigation (GAGAN) system is being implemented over the Indian region. The most prominent parameter affecting the navigation accuracy of GAGAN is ionospheric delay which is a function of TEC. In the equatorial and low latitude regions such as India, TEC is often quite high with large spatial gradients. Carrier phase data from the GAGAN network of Indian TEC Stations is used for estimating ionospheric gradients in multiple viewing directions. Rate of TEC (ROT) and Rate of TEC Index (ROTI) are calculated to identify the ionospheric gradients. Among the satellite signals arriving in multiple directions, the signals which suffer from severe ionospheric gradients are identified and avoided for improving GAGAN positional accuracy. The outcome of this paper will be helpful for improving GAGAN system performance.
Key words: GAGAN, ionospheric gradients, ROT, ROTI.