Mask Angle Effects on GNSS Speed Validity in Multipath and Tree Foliage Environments

Abstract

Global Navigation Satellite System (GNSS) receivers are now widely used for speed measurements. Theoretical studies suggest that speed accuracy parameter of the receivers might be improved by simple elevation of the receiver’s mask angle. However, little practical information is provided regarding a link between the speed accuracy parameter and the specific mask angle values. Also, little practical research activities were conducted to determine how tree foliage can degrade the speed accuracy parameter and whether or not attenuation of GNSS signal caused by tree foliage represents a higher challenge for GNSS receivers than multipath.  Finally, no activities were conducted to understand if enabling more constellations, for example, Globalnaya Sputnikovaya Navigatsionnaya Sistema (GLONASS) provides any value in speed accuracy in the environment where tree foliage is present. To cover the above gaps, this research firstly aims to practically estimate the performance of high end GNSS receivers for measuring speed in multipath environment and determine if elevation of mask angle can always lead to speed accuracy improvements. Secondly, the research also aims to determine if the receivers with higher mask angle perform better in tree foliage environment. The next goal of the research is to discover whether tree foliage or multipath related environment is the most challenging for GNSS speed measurements. The last aim of the research is to practically determine if adding GLONASS on top of GPS provides any value in speed accuracy determination in the environment when tree canopies cause multiple scattering and absorption of GNSS signal. A calibrated test vehicle was used to conduct two tests with four identical high end GPS/GNSS receivers having different mask angles in the environments where multipath and tree foliage are present.  The main contributions can be summarised as follows: firstly, it was identified that elevation of the mask angle in GNSS receivers may not necessarily improve the speed accuracy parameter both in multipath and tree foliage related environments. Secondly, the research also determined that attenuation and scattering of GNSS signal in tree foliage environment may represent a higher threat for GNSS speed measurements compared to multipath related environment.  Third, for a specific receiver adding GLONASS might not necessarily improve the performance in speed accuracy in the environments when tree canopies or overpasses are present. Forth, it was practically validated that the average single tree attenuation at GNSS band frequency may not be handled well by even high end GPS/GNSS receivers when conducting speed measurements. The research recommends that every GNSS receiver shall be individually tested in tree foliage and multipath related environments to determine the degradation in speed accuracy parameter.