GNSS Atmospheric and Multipath Delays - GNSS Remote Sensing: Theory, Methods and Applications - page 24

Fig. 2.3 Ionospheric
structures on a summer day
and night in the middle
latitude and the main
ionization regions (Pulinets
and Boyarchuk 2004 )

so on. On account of the physical characteristics and chemical processes responsible
for the ionosphere formation varying from the altitudes, generally, the ionosphere
is divided into four different layers, i.e., D, E, F1 and F2 from the bottom to
the top of the ionosphere. Figure 2.2 shows the typical midlatitude profile of
neutral atmospheric temperature (Kelley 2009 ). Obviously, temperature of Earth's
ionosphere is changing with the altitude increasing. The vertical structure and
electron density of each ionospheric layer are shown in Fig. 2.3 (Pulinets and
Boyarchuk 2004 ).

2.3.2 GNSS Ionospheric Delay

The ionosphere is a complex and changing system. As an important component
of Earth space environment, the ionosphere has significant effect\ on radio science
and human's space exploration and activities. With the booming development
of modern communication techniques, computer science, space science, and so
on, the ionosphere influence on human's life has been greatly growing since the
1950s, particularly the existence of Global Navigation Satellite Systems (GNSS).
The ionospheric delay is one of the important error sources in GNSS navigation,
positioning and timing. In contrast, the ionospheric delays can be extracted from
dual-frequency GNSS observations, which have a wide application in space weather
and space physics. As we known, Earth's ionosphere is a dispersive medium. When