Low-cost multi-GNSS, single-frequency RTK averaging for marine applications: accurate stationary positioning and vertical tide measurements

The use of Real Time Kinematic (RTK) Global Navigation Satellite System (GNSS) for accurate horizontal and vertical measurements in the marine environment has been considered since the late-1980's and tested from the 1990's when GPS and GLONASS were the only operational constellations available and high-cost multi-frequency receiver equipment was required. This paper modernizes the conversation using multi-constellation, low-cost, single-frequency RTK GNSS measurements and proves their value with accurate positioning and tide measurements. Our tests show average stationary horizontal positioning measurements using this equipment are suitable (95% CI) for the most stringent International Hydrographic Organization (IHO) Standard S-44 'Exclusive Order' at base station ranges of up to 27 km. Vertical observations on a moving platform, smoothed using a baseline distance-dependent moving average filter show the equipment and method are comparable with traditional electronic tide gauge observations over the same base station range. All of our measurement results show the potential to improve total uncertainty calculations undertaken by hydrographers, engineers and scientists in the marine realm, while the low-cost equipment raises the possibility that more measurements can be taken, leading to improvements in monitoring, modelling and understanding the marine environment.