Can GNSS-R help us to monitor the effects of inverse barometer in coastal areas ?

The GNSS Reflectometry is an innovative technique, largely developed in the last years, to monitor local sea level heights. The agreement between sea level measurements derived from SNR-based GNSS-R and tide gauges observations have demonstrated the performance of this approach. In the presented study, we are interested in a subtidal scale phenomenon, the Local Inverse Barometer effect (LIB) which consists in the response of the sea surface to atmospheric pressure changes. The LIB is, in fact, not well modelled in coastal regions where GNSS-R provide continuous observations. The sea level anomaly obtained as the difference between GNSS-R sea level measurements and a tide model, T_TIDE developed by Rich Pawlowicz, is analyzed in order to detect the local inverse barometer effect. For this purpose, we have used 1-year of GNSS data of two antennas of the existing national network, Port-Tudy (Groix island, France) and Lyttelton (eastern coast of the South Island, New-Zealand), where the LIB effect is expected to be significant due to their location outside the equatorial band.

On the whole time series, a trend between the sea level anomaly and the LIB effect can be observed at mid to low frequencies (lower than 0.5 cycle per day). Moreover, high barometric variations caused by the passage of strong depressions lead to good correlations (> 0.7) between these two parameters.

Our results suggest that the GNSS reflectometry allows the observation of subtidal scale phenomena such as the impact of atmospherical variations in complex coastal environments.