TITLE:
An Assessment of Ionospheric Error Mitigation Techniques for GNSS Estimation in the Low Equatorial African Region
AUTHORS:
Isioye Olalekan Adekunle
KEYWORDS:
Global Ionosphere Map (GIM); Single Frequency Precise Point Positioning (SFPPP); GNSS; Dual Frequency Measurement; Klobuchar Model; Position Accuracy
JOURNAL NAME:
Positioning,
Vol.5 No.1,
February
21,
2014
ABSTRACT: Single
frequency GNSS receivers are the most widely used tools for tracking,
navigation and geo-referencing around the world. It is estimated that over 75%
of all GNSS receivers used globally are single frequency receivers and users
experience positioning error due to the ionosphere. To enable GNSS Single Frequency Precise Point
Positioning (SFPPP), accurate a-prior information about the ionosphere is needed. The variation of the ionosphere is
larger around the magnetic equator and therefore depends on latitude. It will be expected that SFPPP works better on
latitude further from the magnetic equator. This present study aims to
investigate the accuracy of some ionospheric error mitigation approaches used
in single frequency precise point positioning (SFPPP) at several GNSS station
in the new Nigerian GNSS Network (NIGNet) and two IGS sites in the low
equatorial African region. This study covers two epochs of observation. The first consists of observation from three
consecutive days (GPS week 1638; days 0, 1 and 2) that belongs to a period of low solar
activities. The second epoch consists of observation from three consecutive
days (GPS week 1647; days 2, 3 and 4) that belongs to a high solar activity and
intense geomagnetic conditions. The estimated position for the GNSS stations
from dual frequency measurement and their known ITRF solutions were used as a benchmark to assess the accuracy of SFPPP under
four conditions i.e., SFPPP without
ionospheric correction, SFPPP using final GIM models from the Centre for Orbit Determination in
Europe( CODE), SFPPP with
Klobuchar model, and SFPPP with a computed (local) model at each station. All
computation was done using Leica Geo-office software. The result of the study clearly demonstrates the
significance of removing or correcting for the effect of the ionosphere, which
can result in up to 7 m displacement. It was recommended that GIMs from different organization should be investigated and also efforts should be
towards improvement in algorithms and clock error modeling.