On the 26th August 2015 the GO! partners carried out measurements at the Rail & Logistic Center Wustermark to study the environmental effects on the precision of GNSS measurements in a real track areas. The Rail & Logistic Center Wustermark is a marshalling yard located 30 kilometers west of Berlin.
The environment can influence the measurement when large objects in the surrounding of the sensor cover the direct sight to satellites or reflect their signals. This decreases the number of information or the information quality to calculate the local position.
In order to figure out which structural objects (e.g. buildings, bridges, forest, overhead wiring) worsen the GNSS measurements a Septentrio RTK-Receiver was placed onto a locomotive which moved through the marshalling yard. Different objects like buildings, other trains, masts, bridges and forest sections were passed. A video camera documented the path of the train and it’s surrounding (Fig 1). During measurements GNSS position, acceleration, velocities, among other sensor data, were saved.
Afterwards, an evaluation was done and a Video was created, which displays the correlations between surroundings and precision of GNSS measurements (Fig. 2). Using data of the GNSS receiver, the number of visible satellites, the precision of the measurement, and also the vehicle velocity can be determined. All these pieces of information are displayed in the bottom bar and the bottom right map of the Video and Fig. 2, respectively. Within the embedded open street map (OSM) the rails are coloured green, buildings and streets are White, and the current vehicle position is marked by a red dot. The red graph on the right side in Fig. 2 shows the development of GNSS’s 3D-precision. The blue and green graphs describe the accelerations in x- and y-direction.
In Fig. 2 a bridge passage is depicted. It can be seen that the precision becomes worse, when the locomotive passes the bridge. For measurements with enabled differential GNSS, the 3D-precision increases from 0.2 meters to almost 6 meters passing the bridge (Fig. 2). During another mesurement run, but this time without differential correction of the GNSS signals, the 3D-precision increases from 5 meters to over 100 meters in the same bridge crossing situation.
A correlation between the 3D-precision and other objects in the environment , such as buildings, forest, overhead wiring, could not be detected.