Water Level Measurement and Tidal Datum Transfer Using High Rate GPS Buoys

SUMMARY The transfer of tidal datums using high rate GPS buoys offers advantages over traditional techniques, which may be limited by their practicality, efficiency and cost. This paper describes an experiment where two GPS buoys were deployed simultaneously near two tide gauges within Otago Harbour, New Zealand. The tide gauge records were used to verify, first, that GPS buoys can measure water levels, and second, test the accuracy to which a tidal datum can be transferred based on water levels estimated by the buoy. It was found that a datum could be transferred at similar accuracy to previous experiments, concluding that GPS buoys are a viable means of tidal datum transfer. With rising sea levels and an increasing demand for coastal properties, cadastral surveyors and engineers need to be able to readily define cadastral boundaries both reliably and accurately. The use of GPS buoys has the following advantages for tidal datums transfer:  Efficient datum connections between the GPS buoy and benchmark.  Expedient and relatively easy data collection.  Existing GPS equipment can be used.  GPS buoys can be deployed in close proximity to the shore and do not have to be attached to an existing tide gauge instrument.