Evaluation of the Suitability of GNSS Instruments as Proxy Tide Gauges in a Tsunami Early-Detection Context

Abstract:

The use of a coastally-located GNSS (Global Navigation Satellite System) instrument as a relatively high accuracy proxy tide gauge, by employing multipath reflection analysis of incoming signals, has been demonstrated in recent studies. Inversion of positional GNSS data (coseismic displacements) from networks of multiple instruments is currently used to constrain tsunamigenic sources for forecasting in existing tsunami early-warning systems. However, the GNSS multipath reflection method has not yet been directly applied in a tsunami-warning context. This technique employs reflected signals arriving at the GNSS antenna, which are generally discarded as 'noise' in standard positional measurements. The signal-to-noise ratio data encoded in standard RINEX data are analyzed, allowing computation of the vertical distance from the antenna to the water surface using multipath reflection theory. GNSS instruments can be co-located with pre-existing physical (analog) tide-gauge instruments to create a comparative baseline to evaluate the suitability of this technique in the field. Sea level time series derived from GNSS data are compared with time series recorded by analog instruments in order to establish a correlation and margin of error in typical use. With the aid of three test sites bordering the Strait of Georgia, British Columbia, Canada, we will assess whether tsunami wave amplitudes and periods can be determined in near real time with sufficient accuracy for use in tsunami detection and early warning. The ultimate goal of this work is to deploy GNSS instruments independently as tide gauges in locations where analog tide gauges are not practical. An expanded network of coastal GNSS instruments would also provide valuable positional data for crustal deformation analyses, especially in regions with current sparse networks such as the west coast of Canada.