Digital Signal Processing Reference
In-Depth Information
Fig. 4.12
Monthly averaged
diurnal NmF2 variation
percentage of the GPS
reconstruction with respect
to the IRI-2001 model
250
Jan
Apr
Jul
Oct
200
150
100
50
0
−50
−100
0
5
10
15
20
25
Local Time (hour)
The
TEC
(',,
h
), relating with latitude ', longitude and height
h
,isthe
integrated electron density along a path through the ionosphere, namely
Z
S
s
atellite
TEC .'; ; h/
D
N
e
.'; ; h/ ds
(4.32)
R
r
ecei
v
er
where
N
e
(',,
h
), ionospheric electron density, was obtained from GPS tomography
reconstruction in small cells (
i, j, k
)of0.5
ı
1.0
ı
25 km pixels. Therefore, the
vertical
TEC
(',,
h
) can be written as follows
VTEC .'; ; h/
D
X
i
X
X
.N
e
/
i;j;k
h
i;j;k
(4.33)
j
k
Thus, the vertical TEC can be obtained from the GPS reconstructed 3-D electron
density at any specific grid points. Although the IRI model can calculate the
TEC by really updating F2 peak parameters with measured peak values, we here
focus on evaluating the average behaviours of the IRI-2001 model with empirical
standard models' parameters. So we here didn't use the measured peak values
(e.g. ionosonde) and just used empirical standard models' peak values for IRI
TEC calculation. Figure
4.13
is the comparison of TEC at grid point (37.5
ı
N,
127.0
ı
E) estimated from GPS and IRI-2001 in different seasons. Both show the
diurnal behavior of the monthly TEC median of the ionosphere averaged over 1
month. Independently of the season, the maximum TEC values are arrived at about
the noon, between 11:00 and 15:00 LT. The IRI-2001 gives a smoother TEC than
GPS reconstruction. However, averaged monthly TEC medians from the IRI-2001
model are overestimated in daytime in winter, but underestimated in other time for
all seasons. In addition, the maximum GPS-derived TEC values are found during
equinoxes (spring equinox especially). Furthermore, the daytime TEC values in
winter (January) are slightly greater (about 5-16 %) than those in summer (July)
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