Monitoring water level changes from retracked Jason-2 altimetry data: a case study in the Yangtze River, China

Although initially designed and developed for studying large-scale open ocean dynamics, radar altimetry has proven to have the potential for monitoring coastal and inland water-level changes. However, for rough and heterogeneously reflecting surface, the shape of a waveform contains multiple peaks and traditional retracking methods do not perform well. In this study, we proposed a novel Multi-subwaveform Multi- weight Threshold Retracker (MSMWTR) method, which was applied to Jason-2 waveforms over the Yangtze River (about 1.70 km wide) during 2008-2015. Several traditional waveform retracking algorithms, including Ice-1, offset centre of gravity (OCOG) and 50% Threshold algorithms, were also used to compute water levels. By comparing retracked water levels with nearby Hankou daily gauge records, the results show that the proposed MSMWTR method can significantly improve the accuracy of the estimated water levels compared with other retrackers, especially in the dry season. After applying the MSMWTR algorithm, the root mean square of the errors decreased significantly from 9.06 to 0.34 m. The new method can significantly broaden the application of radar altimeter over relatively wide rivers.