Providing sub-metre positioning for autonomous river survey vessels.

  • Our customer used Acoustic Doppler Current Profilers (ADCPs) to monitor river flow to develop models used as part of flood defence planning
  • The ADCP can generate a relative trajectory however this is not georeferenced and is unreliable in deep waters, or where the river bed is moving, or has high silt levels
  • The requirement was to provide a compact GNSS antenna with sub-metre accuracy, located over the ADCP, with power and a wireless link, with a range of ~100m, to the shore where the data was being collected by the ADCP software
  • The ReACT antenna provided the required accuracy in a single environmentally robust package but lacked the internal battery and wireless communications so implemented a simple plug-in module featuring a removable, and rechargeable battery pack and a Bluetooth adapter
  • The ReACT was configured to track the EGNOS service to achieve sub-metre SBAS positioning and GLONASS to overcome issues with tree cover blocking open sky
  • Following successful deployment of the system, the range requirement was increased to 1km
  • We decided to move away from Bluetooth and use 869MHz xBee radios
  • In tests, with basic antennas, and no amplification, we observed transmission ranges in excess of 2km line of sight, as well as impressive performance when there were obstructions in the way, such as trees