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Improved ionospheric correction for DGPS by taking into account the horizontal gradient effect over the equatorial region

Nagarajoo, K (2010) Improved ionospheric correction for DGPS by taking into account the horizontal gradient effect over the equatorial region. In: International Conference on Experimental Mechanics 2010, 29 November - 01 December 2010, Kuala Lumpur.

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Differential Global Positioning System or known as dGPS is a system where the range error at a reference station will be eliminated from the range measurement at the user, which ‘view’ the same satellite, presuming that the satellite’s path to both the reference station and the user experience common errors due to the ionosphere, clock errors, multipath etc. In this assumption, the error due to the ionospheric refraction is assumed to be the same for the two closely spaced paths (such as a baseline length between reference station and the user is 10km) and thus the presence of ionospheric horizontal gradient is ignored. If a user’s path is exposed to a drastically large ionosphere gradient (i.e., over the equatorial region), the large difference of ionosphere delays between the reference station and the user can result in significant position error for the user. Apart from that, the difference in the elevation angle at the reference and the user that ‘view’ the same satellite to get the range measurement does also introduce some millimetre to centimetre of range difference. The neglect of the effect due to the presence of an ionospheric horizontal gradient and the elevation angle’s difference (at both ends of the baseline) will cause a significant amount of error in the final dGPS user positioning. In this work, those two effects have been investigated in order to obtain a more accurate ionospheric correction for dGPS and have been found to be roughly comparable showing that they are both important. By performing ray-tracing calculations (using Jones 3-D Ray Tracing program) with and without a linear horizontal ionosphere gradient, the effects of elevation angle and horizontal gradient have been separated and a final positioning improvement of about 8cm has been shown at the user of a DGPS system over the equatorial region. Empirical models have been introduced to model these variations based on the ray tracing results. This is quite a good positioning improvement at the user location which really needs to be considered in applications such as geophysics, surveying and navigation. The geometric dilution of precision or GDOP factor also has been taken into account to get the best formation (geometry) of GPS satellites in order to do the DGPS positional improvement at the user station.

Item Type: Conference or Workshop Item (Paper)
Uncontrolled Keywords: ionospheric correction; dGPS; horizontal gradient; GDOP; user positioning improvement
Subjects: Q Science > QE Geology
Divisions: Faculty of Electrical and Electronic Engineering > Department of Communication Engineering
Depositing User: Normajihan Abd. Rahman
Date Deposited: 22 Jan 2013 12:42
Last Modified: 21 Jan 2015 07:26
URI: http://eprints.uthm.edu.my/id/eprint/2991
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