Digital Signal Processing Reference
In-Depth Information
mm
90
2600
60
2380
30
2160
0
1940
−30
1720
−60
−90
1500
0
60
120
180
240
300
360
Longitude (deg)
Fig. 3.4
Distribution of mean ZTD at global IGS sites
Fig. 3.5
Distribution of ZTD
with the latitude
2800
2600
2400
2200
2000
1800
1600
1400
-90
-60
-30
0
30
60
90
Latitude (deg)
the ZTD values decrease with increasing altitude. This is due to the atmospheric
pressure variations with the height increase. Atmospheric pressure is the pressure
above any area in the Earth's atmosphere caused by the weight of air. Air masses
are affected by the general atmospheric pressure within the mass, creating areas
of high pressure (anti-cyclones) and low pressure (depressions). Low pressure
areas have less atmospheric mass above their locations, whereas high pressure
areas have more atmospheric mass above their locations. As elevation increases,
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