Estimating High Amplitude Water Level Variations During Asymmetric Tides in the Garonne River with GNSS-Reflectometry

Signal to Noise Ratio (SNR) time series acquired by a single Global Navigation System Satellites (GNSS) antenna are used to retrieve water levels during asymmetric tides and tidal bores in the Garonne River. As height variations are important, a dynamic SNR approach was applied, instead of the static case, to estimate the relative antenna height from the dominant frequencies. Evaluation of the results is performed against pressure measurements. Results on asymmetric tides are quite good overall $\text{(ubRMSD}=0.55\mathrm{m}$ ), and way better in the falling tide $(\text{ubRMSO}=0.12\mathrm{m}$ ), where the vertical velocity of the reflecting surface $h$ . is lower than in the rising part $\text{(ubRMSD}=0.59\mathrm{m}$ ). The dynamic SNR method is limited for high h values as it is not able to extract the correct frequencies. For this reason, extremely rapid variations of the river surface during the tidal bore could not be retrieved.