==== GPS (GOP-5) ====
Ground-based GPS receivers measure the Zenith Total Delay (**ZTD**) in mm which is the sum of the Zenith Hydrostatic Delay (**ZHD**) caused by the atmospheres dry components and the Zenith Wet Delay (**ZWD**) resulting mainly from atmospheric water vapor. 

**ZTD = ZHD + ZWD**

Knowing the atmospheric pressure **ZWD** can be derived and in a second step converted to the Integrated Water Vapor (**IWV**). 
^ Name ^ Code ^ PI ^ Location ^ Temp. Reso. ^ No. stations ^Products ^ Data/Day ^ Availability ^ 
|GFZ GPS Standard net | [[gps_gfzn]] | [[:participants|Dick]] | Central Europe | 15 min | ∼200 | ZTD, ZWD, IWV | ∼100 KB | [[status:gop5_gps_gfzn|check]] | 
|GPS Standard Switzerland | gps_swit | [[:participants|Brocard]] | Switzerland | 1 h | ∼30 | ZTD, ZWD, IWV | ∼80 KB | [[status:gop5_gps_swit|check]] | 


 --- //[[crewell@meteo.uni-koeln.de|Susanne Crewell]] 2007/03/25 12:04//