STARTWAVE

STudies in Atmospheric Radiative Transfer
and Water VApour Effects

Water vapour information from the GPS receiver network

GPS IWV anomaly in percent

Interpolated column water vapour anomaly from GPS measurements

The above image shows the GPS IWV anomaly (respective to the monthly mean) in percent at 2 hourly intervals for the last available day for which there is data for central Europe. New GPS observations arrive with a delay of 3 to 6 weeks.

A GPS receiver is capable of estimating the total amount of water vapour in the atmosphere. The signals sent by GPS satellites are delayed as they travel through the atmosphere. Part of the delay is due to the dry components in the atmosphere and can be estimated from air pressure at the antenna position. The other part is due to water vapour and this so-called 'Wet Delay' can be used to estimate column water vapour.

Of course, if you want to use a GPS receiver to estimate water vapour, you have to first of all have an accurate measurement of the position of the GPS receiver and water vapour estimates are only possible from a network of fixed GPS receivers. Such a network exists in Switzerland and is run by Swiss Topography. The AGNES GNSS network consists of 30 GPS receivers across the country all of which can provide total column water vapour estimates. The Institute of Applied Physics at Bern operates an additional GPS receiver.

The GPS sensors in Switzerland are situated at varying altitudes, from less than 400 m to over 3500 m (Jungfraujoch). Water vapour decreases with height in the atmosphere and the GPS network allows us to observe this effect. However, because the GPS stations are also situated at different geographical locations, the combined variation in both altitude and geographical position provides a challenge for interpreting the measurements. The low column water vapour amounts over the high alpine stations can be clearly seen in the map of interpolated water vapour above.

More details on GPS water vapour estimation are given in an IAP internal report by Guergana Guerova.

Positions of the GPS stations

Click on a GPS station to get position information

Station ID:
Station name:
Latitude (deg):
Longitude (deg):
Altitude (m):
GPS stations

Data download

IMPORTANT: All GPS data before mid-2014 have been reprocessed within the EUREF Permanent Network (EPN) reprocessing campaign. Data that have been downloaded here before the 2 March 2020 have not been reprocessed. In case that you downloaded GPS data before this date, please consider downloading the data again. For more information, please contact the database administrator.

GPS Zenith Total Delay (ZTD) data are converted to IWV using surface pressure and temperature measurements provided by the Meteo Swiss ANETZ network. Where there is no coincident ANETZ and AGNES station, the pressure measured by the closest ANETZ station is interpolated to the GPS station height.

One of the main data quality problems in GPS processing is noise in the data. At present, all GPS ZTD measurements are screened to eliminate noisy data before calculating IWV.

The high altitude station Jungfraujoch has a more or less constant bias of -1.3 mm due to an incorrect antenna model used in the ZTD correction. We recommend that users apply a correction based on a comparison with the PFR data:

For period up to 2005-4-3 (when change in GPS processing occurred):

GPS_IWV_Jungfraujoch=(GPS_IWV_Jungfraujoch/0.99)+1.32

For period after 2005-4-3:

GPS_IWV_Jungfraujoch=(GPS_IWV_Jungfraujoch/1.086)+1.8

> Download hourly data

Contactlast update: March 2020