A Gnss-based Tide Gauge for Local Sea Level Monitoring

It is important for human society to continuously monitor the sea level, since more than 50% of the world’s population live within 60 km of the coast [1]. Moreover, global climate change is believed to result in the melting of large masses of ice in Polar Regions. This will bring freshwater into the ocean [2] and thus change the sea level [3]. The traditional way to observe sea level is with tide gauges which results in measurements relative to the Earth’s crust [4]. However, the Earth’s crust is continuously moving and in order to fully understand sea level change processes, measurements of sea level in relation to the Earth’s center of gravity, are necessary. The motion of the Earth’s crust in relation to the center of gravity can be determined using satellite techniques [5], e.g., Global Navigation Satellite Systems (GNSS). A GNSS-based tide gauge was therefore proposed [6], which can obtain both relative and absolute sea level variations, by observing reflected GNSS-signals. Presented here, as a proof of concept, are results from the experimental installation compared with data from traditional tide gauges. Moreover, we anticipate to present new results at the IGARSS 2010 conference with long time series (weeks to months) of sea level from the permanent GNSS-based tide gauge installation that is currently under construction at the Onsala Space Observatory (OSO).