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G(f)
G
+
∆G
M
G
−
∆f
f
+
f
A
f
f
−
∆ψ
(f)
*
∆ψ
0
∆ψ
f
A
f
Fig. 11.1.
Schematic plots of the amplitude spectral ratio
G
(
f
) and phase spectral
difference
∆ψ
(
f
) between two near-by stations, as predicted by the resonance theory
A.
G
(
f
A
)=
M
= 1 for frequency
f
c
=
f
A
(
x
c
), where the point
x
c
=(
x
1
+
x
2
)
/
2
is located at the midpoint between the stations;
B.
G
(
f
) reaches extreme values
G
+
and
G
−
at frequencies
f
+
and
f
−
which
correspond to the points
[
δ
2
+(
∆x/
2)
2
]
1
/
2
;
x
r
(
f
±
)=
x
±
=
x
c
±
C.
G
+
G
−
=1and
G
+
−
G
−
=
∆x/δ
;
D.
∆ψ
(
f
) reaches an extreme value
∆ψ
∗
= 2 arctan(
∆x/
2
δ
) at frequency
f
A
=
f
r
(
x
r
).
The properties (
A
) and (
D
) of functions
G
(
f
)and
∆ψ
(
f
) enable us to
estimate the FLR-frequency between the stations. We can also find the width
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