While our inertial navigation systems are often used to measure the position and attitude of moving objects, one of our xNAV550s has recently been put to novel use when it was strapped to the Severn Bridge for three days in late July. The xNAV550, which is typically used for georeferencing in UAV applications thanks to its small size and low weight, was used as part of an on-going study conducted by a research group from the Nottingham Geospatial Institute into the deflection of bridges.
The xNAV550 was only part of the measuring equipment installed on the Severn Bridge—a motorway suspension that joins England and Wales. In previous studies, survey-grade GNSS receivers were used to gather sub-centimetre measurements from key points on the bridge. When coupled with other data sources—such as the speed and mass of vehicles travelling on the bridge and environmental data, a more detailed understanding of the bridge’s behaviour can be found. This data can then be used for anything from validating a Finite Element Model of the bridge to revealing previously unknown deflections.
But, while the survey-grade GNSS receivers provide the necessary accuracy, the effects of multi-path on them present a particular problem when operating at sub-centimetre while surrounded by numerous wires, metal towers and with an endless stream of high-sided vehicles passing in close proximity to the antennas. The effect of this is greatly reduced in the xNAV550 thanks to the internal Kalman Filter that can detect and reject erroneous GNSS signals from multi-path effects. Not just relying on GNSS measurements for its position solution, the xNAV550 instead blends measurements from a high-quality inertial measurement unit with its own survey-grade receivers to create a non-drifting, robust and accurate measurement system that can provide updates at up to 250 Hz.
The additional information provided by the xNAV may give researchers an interesting insight into the motion of the bridge, being able to directly measure accelerations and angular rates as it twists and sways with the wind and traffic. At the very least, the data will serve as an alternative source to corroborate and compare with their findings from the traditional GNSS receivers. For now though, it’s back to the labs again to start processing and analysing the data. We hope to catch up with the group at a later date to learn more about their findings with the xNAV.