Geoscience Reference
In-Depth Information
10˚
20˚
30˚
6
70˚
70˚
5
4
3
65˚
65˚
2
1
60˚
60˚
0
55˚
55˚
−1
10˚
20˚
30˚
Fig. 15
Zenith wet delay trends in mm/decade estimated from GPS data in Sweden and Finland,
1997-2006. Modified from Nilsson and Elgered (
2008
)
vide the water vapor content with high enough spatial and temporal resolution. With
the establishment of relative dense GNSS networks the meteorological community
has started to be interested in assimilating zenith total delays or zenith wet delays
estimated from these GNSS networks in the numerical weather prediction models
(Gutman and Benjamin
2001
;Polietal.
2007
).
Several investigations of assimilating GNSS tropospheric delays in numerical
weather prediction models have been performed. For example, in Europe this has
been investigated in the projects COST-716 (Elgered et al.
2005
), TOUGH (Vedel
2006
), and E-GVAP (
http://egvap.dmi.dk/
)
. It has been shown that the quality of
the forecasts improve if GNSS data are assimilated, especially in cases of high
precipitation (Vedel and Huang
2004
; Karabati´cetal.
2011
).
6.3 GNSS Tropospheric Tomography
Tomography is a method which can be used to estimate the 2D or 3D structure of a
quantity frommeasurements of the integral of the quantity along different paths. It is
a method commonly used in medicine, seismology, material science, and a number
of other fields. Tomography can also be applied to atmospheric delay measurements
