The impact of the electromagnetic environment of the antenna on GPS

Conference poster, 2008

Measurements and analysis of the amount of atmospheric water vapour are of the importance in meteorology and climatology. As one of the dominating greenhouse gases, water vapour plays an important role for our climate, especially for global warming effect. The radio signals will undergo path distortions when traversing the atmosphere of the Earth due to water vapour [Elgered,1993]. Based on the timing of radio signals propagating through the atmosphere, the Global Positioning System (GPS) can be used to determine the amount of atmospheric water vapour. In Sweden a geodetic reference network—SWEPOS installed in 1993—is used in surveying and geophysical research. The network consists of 21 geodetic stations. Each station has a GPS antenna mounted on a concrete pillar and protected by a radome from severe weather conditions, e.g. snow and rain. The effects due to the geometry of the GPS pillar, antenna, and radome on the estimated time series of atmospheric water vapour are of fundamental importance since it may change over long time scales. We present a first assessment of the impacts from a changing geometry of the nearby antenna environment. The long term goal is to be able to quantify the required specifications on the geometric stability in order to detect variations in the water vapour content of the order of 0.01 mm/yr.