Sea Level Records from Geodetic GPS Receivers: a New Coastal Sea Level Dataset

Conference poster, 2012

Global sea level rise and local sea level variations due to climate change has the potential for a significant impact on coastal societies. Thus, it is of great importance to monitor and understand how the sea level is changing. Existing techniques to measure sea level have provided important insights in this field during the last decades. However, further observations are necessary in order to fully understand the underlying processes. We present the possibility of a new coastal sea level dataset based on analysis of Signal-to-Noise Ratio (SNR) data from existing permanent GPS stations at the coast. For a GPS antenna close enough to the ocean, the multipath signals, reflected off the sea surface, interfere with the direct satellite signals. This becomes especially visible as oscillations in the recorded SNR data. The analysis of the SNR oscillations provides the distance between the sea surface and the GPS antenna phase center. Thus, such an installation can be called a GPS tide gauge and can be used to monitor sea level. The advantage of a GPS tide gauge is that it allows both determination of the sea level and determination of the position with respect to the International Terrestrial Reference Frame, using a single geodetic instrument. This is particularly valuable in areas with land surface motion where the usefulness of traditional tide gauges is restricted. The technique has been verified through comparison to traditional tide gauges at two sites. The comparison of more than three months long time series resulted in correlation coefficients of better than 0.97 for both sites. For the station with low and high tidal range, the root-mean-square agreement between the GPS results and the tide gauge records were better than 5 and 10 cm, respectively. In this presentation we show preliminary results for sea level records world wide by applying this technique to several existing permanent GPS stations.