The effect of absolute humidity on GPS-positioning accuracy

Objective. Investigate the effect of absolute humidity on the GPS accuracy for different durations of observation. Methods. The GPS observations with different durations over spring-autumn period at 17 permanent stations in France and 8 stations in Switzerland were chosen for initial data. These observations used four GPS networks with a different number of points (from 5 to 8) and lengths of vectors (average length varied from 5.1 to 48.6 km). Values of absolute humidity were determined using the average values of air temperature, atmospheric pressure, and relative humidity, obtained from 06:00 to 22:00. For our investigation we selected only those days when absolute humidity varied significantly. The observations were processed by the Trimble Business Center software, changing the duration of the observations (1, 2, 4 hours). In total, 1,200 sessions were processed. By comparing the values of true coordinates of the network points and those determined by the results of observations, we obtained the RMS (root-mean-square) errors of the positions of the points. Results. The analysis of RMS position errors showed that there is a tendency for deterioration of the point’s position accuracy in the network when the absolute humidity is increasing. The values of the RMS, obtained at the lowest and highest values of absolute humidity, for all networks and the different durations of observations were compared. Thus, when the absolute humidity changed from 7,0 g/m3 to 13,8 g/m3 for the observation duration of 4 hours, the average values of RMS increased 1.6 times (from 4.4 mm to 7.0 mm), for the sessions of 2 hour duration the value of RMS increased 1.8 times (from 4.7 mm to 8.3 mm), and for a 1 hour duration – 2.1 times (6.1 mm to 13.0 mm). Scientific novelty and practical significance. The environment of satellite signals propagation remains one of the main sources of errors, in particular in the troposphere, which, in essence, "forms" the weather. Although today more attention is focused on weather forecasting using satellite navigation systems, there is also an inverse problem. The study suggests meteorological conditions, specifically absolute humidity, should be considered to increase the accuracy of GPS-measurements. The obtained results of the studies are quite reliable, since a large amount of data is used. It is advisable to choose the days for GPS observations, when the moisture content is minimal (no higher than 12 g/m3). From a practical point of view – the possibility of using observable meteorological parameters obtained from the weather forecasts are feasible.