Signal Distortion in High Precision GPS Surveys

The aim of this paper is to show that GPS signal distortions can significantly influence the accuracy of the results of a GPS survey. Signal distortions may occur if the satellite signals propagate through a diffuse obstacle such as a bush and the distorted carrier phases arrive at the GPS antenna. As a result errors in the horizontal position of up to 2 cm and in the vertical position of up to 5 cm can occur. The results of several experiments will be shown. Different GPS choke ring antennas and receivers as well as different GPS processing software packages were used in order to prove that this effect is hardware and software independent. The signal distortion was evident in all experiments. The detailed investigation of the double difference phase data allowed the removal of the affected data which subsequently yielded the correct GPS results.