* School of Electrical, Electronics & Computer Engineering, Newcastle University, UK, rajesh.tiwari@ncl.ac.uk ** Space Science Laboratory Barkatullah University, Bhopal. *** National Institute of Technical Teachers' Training & Research, Bhopal, India 49 Abstract The marine navigation is one of the major applications of GPS-based navigation, and it require high level of precision, availability and reliability. However, the precision does depend on ionospheric conditions. The performance of GPS is not so effective in low and high latitude region. The ionosphere is composed of non-uniform charged particles, so it has different properties depending on geomagnetic latitude, season, and local time. GPS signal slows down in the ionospheric region with the actual velocity of light. A delay of about 5 – l00 ns in the zenith direction may be observed. The extra ionospheric delay produces a range error, which ultimately affect position accuracy. In this research paper, influence of the ionosphere on GPS accuracy over geomagnetic latitude (high, mid, and low latitude) has been investigated in dynamic mode for marine navigation in M.V. Emerald Sea, a Russian cargo ship during XXVI Indian Scientific Expedition for Antarctica (ISEA). A close correlation of magnitude of the rate of change of TEC (ROT) is established with navigational solution over three different geomagnetic regions. The ROT parameter is represented as ionospheric irregularities, and it also represents as GPS phase fluctuation. In this study, it is observed that high level of fluctuation in ROT effect the position solution. The higher fluctuation recorded in low- and high-latitude regions, and so as position errors, and sometime exceeding tolerable limits. Furthermore, the study also agree with theory of ionospheric disturbance is high in high and low geomagnetic region, whereas the mid-latitude seems to be moderate and the level of degradation of position solution in mid-latitude is comparatively lower Key words : GPS, POT, Phase fluctuation. INTRODUCTION The ionosphere is a region of charged particles: ions and electrons; that ranges from 50 km to 1000 km. These particles are produced by ionization of atmospheric gases. Furthermore, the level absorption also exit and both the process varies with solar intensity, season, and solar cycle, during intense solar flare, the solar particle produces bow shock to earth magnetic field and causes geomagnetic storms which eventually turns into ionospheric storm. The relation between magnetic and ionospheric storm is governed by Coupling Theory. With the effect of ionospheric storm, irregularities in ionosphere generated, thus the transionospheric radio waves changes their characteristics and delayed [1]. Furthermore, the state of ionosphere is not homogenous in three geomagnetic regions –high, mid and low latitude. This research obtained a practical approach to study the effect of ionosphere on GPS position accuracy in a ship journey from Antarctica (high latitude) to Goa, India (low latitude). Twenty four days of ship journey covers all region high, mid and low latitude to evaluate GPS performance. The GPS (Global Positioning System) is modern satellite based navigation tool developed by US in 1985, since then, the applications of GPS have been expanding its spectrum day to day. In addition, there are some applications, which need a high level of accuracy, precision, reliability and availability. However, when GPS signals from satellite propagate through a disturbed ionospheric medium, their characteristics in terms of amplitude or phase change depending on the level of ionospheric irregularities. There exists a correlation between ionospheric variations and the TEC derived from dual frequency GPS receivers. shows regular variation patterns in different regions. The irregular variations of the ionosphere over a particular region can be expressed by the rate of TEC (ROT). The ROT is the difference of the successive epochs in units of time [2]. In this chapter, irregular ionospheric variation has been studied at high, mid, and low latitude, as well as the effect on the GPS positioning. The effect of ionospheric irregularities as ROT on GPS position solution in equatorial anomaly region can be seen in [3]. In addition, the sudden irregular variations in the ionosphere can cause cycle slips in the GPS signal [4-6], which eventually loosing GPS services. In order to understand the overall effect of ROT, the experiment was conducted in dynamic state of ship from high to low latitude. The upcoming section discusses the experimental setup and methodology followed with result and discussion; and ended up with conclusion drawn from the experiment. IONOSPHERIC EFFECT ON GPS-BASED MARINE NAVIGATION Rajesh Tiwari*, Smita Tiwari*, Soumi Bhattacharya**, P. K. Purohit*** and A. K. Gwal** Recieved Aug. 14, 2010, Revised Aug. 26, 2010 ; Accepted Sep. 30, 2010 Tiwari etal./Journal of Engineering, Science and Management Education/Vol. 2, 2010/49-56 Fig.1 : Global VTEC between 10:00 and 12:00 UT. Latitude (degree) (TECU) Longitude (degree)