Global Positioning System Reference
In-Depth Information
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the slant group delay directly in meters. The algorithm presented here compensates
for 50-60% of the actual group delay.
The Klobuchar algorithm is based on the “shell model” or single-layer model
of the ionosphere. The implicit assumption is that the TEC is concentrated in an
infinitesimally thin spherical layer at a certain height, e.g., 350 km. The model further
assumes that the maximum ionospheric disturbance occurs at 14:00 local time. The
factor
F
in Table 6.3 is the mapping function that converts the vertical ionospheric
delay at the ionospheric pierce point to the slant delay at the receiver location. The
ionospheric pierce point is the intersection of the line of sight and the ionospheric
layer. The geomagnetic latitude of the ionospheric pierce point is
φ
, and its geodetic
latitude and longitude is
ϕ
IP
and
denotes the earth's central angle
between the user and the ionospheric pierce point,
t
is the local time,
P
is the period
in seconds,
x
is the phase in radians, and
A
denotes the amplitude in seconds.
λ
IP
. The angle
ψ
[22
TA
BLE 6.3
The Broadcast Ionospheric Model
Lin
—
1.2
——
Lon
PgE
ϕ,
λ
geodetic latitude and longitude of receiver [SC]
T
=
GPS time [s]
p
k
,
p
k
azimuth and altitude of satellite [SC]
α
β
α
n
,
γ
n
broadcast coefficients
=
1
+
16
0
.
53
− β
k
3
0
.
0137
p
F
(a)
ψ =
0
.
11
−
0
.
022
(b)
p
k
α
+
1
2
p
k
ϕ
+ ψ
cos
α
if
|
ϕ
IP
| ≤
0
.
416
p
k
cos
ϕ
IP
λ
IP
= λ +
ψ
sin
α
[22
ϕ
IP
=
0
.
416
if
ϕ
IP
>
0
.
416
(c)
(d)
−
0
.
416
if
ϕ
IP
<
−
0
.
416
φ =
ϕ
IP
+
0
.
064 cos
(
λ
IP
−
1
.
617
)
(e)
1
2
λ
IP
4
.
32
×
10
4
+
T
if 0
≤
t<
86400
λ
IP
4
.
32
×
10
4
t
=
+
T
−
86400
if
t
≥
86400
(f)
λ
IP
4
.
32
×
10
4
+
T
+
86400
if
t<
0
2
π
(t
−
50400
)
P
x
=
(g)
1
2
1
2
3
3
n
n
0
γ
n
φ
if
P
≥
72000
0
α
n
φ
if
A
≥
0
P
=
(h)
A
=
(i)
n
=
n
=
72000
if
P<
72000
A
=
0if
A<
0
1
2
cF
5
×
10
−
9
A
1
−
if
|
x
2
2
+
x
4
24
+
x
|
<
1
.
57
I
k,
1
,P
=
(j)
cF
5
×
10
−
9
if
|
x
|
>
1
.
57
Conversion of SC unit: 1 SC
=
180°
