Global Positioning System Reference
In-Depth Information
mm
90
125
60
105
30
85
0
65
-30
45
-60
25
-90
5
0
60
120
180
240
300
360
Longitude (deg)
Fig. 5. Annual variation amplitude of ZTD at globally distributed 150 GPS sites
120
100
80
60
40
20
0
-90
-60
-30
0
30
60
90
Latitude (deg)
Fig. 6. Distribution of annual ZTD variation amplitude with the latitude
The mean amplitude of semiannual ZTD variations is much smaller than annual variations
with about 10 mm. The amplitudes of the semiannual oscillations are much smaller on the
Southern Hemisphere than on the Northern Hemisphere. The distribution of the semiannual
variation phase with the latitude has no clear symmetry. For example, at the latitudes of
40°N-50°N in the Northern Hemisphere, the semiannual phase is about 30° (about January),
while at the latitudes of 40°S-50°S in the Southern Hemisphere, the semiannual phase is
about 330° (November).
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