Digital Signal Processing Reference
In-Depth Information
Chapter 2
GNSS Atmospheric and Multipath Delays
2.1
Atmospheric Refractivity
The Earth's atmosphere is a kind of inhomogeneous medium. With increase of
height, atmospheric mass decreases. When the electromagnetic wave propagates
through the atmosphere, the deviation from a straight line occurs due to the variation
of the air mass or density, which is called the atmospheric refraction. The refractive
index
n
of a substance can be expressed as,
c
v
n
D
(2.1)
where
c
and
v
are the speeds of the electromagnetic waves propagating in a vacuum
and in some substance, respectively. The atmospheric refractivity
N
is defined as,
D
10
6
.n
1/
N
(2.2)
The atmospheric refractivity can be further described as a function of meteoro-
logical parameters, including both hydrostatic and non-hydrostatic (dry and wet)
components (Hopfield
1969
) with the empirical formulas (Smith and Weintraub
1953
; Hartmann and Leitinger
1984
),
D
N
d
C
N
w
N
(2.3)
p
T
D
C
1
N
d
(2.4)
e
T
C
C
3
e
T
2
N
w
D
C
2
(2.5)
where
N
d
and
N
w
are the dry and wet component refractivity, respectively.
p
is
the pressure of the dry gas of the atmosphere in hPa (Hectopascal),
e
is partial
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