Comparision of retrackers' performances over inland water bodies

The water level of inland water bodies plays an essential role in water balance management. Satellite altimeters can play an important role in monitoring water level, namely in remotely access places. However, satellite altimeters are normally designed to monitor homogeneous surfaces such as oceans or ice sheets, which results in poor performance over small inland water bodies because of the land contamination contribution in the returned waveforms. This paper presents three specialized algorithms or retrackers to retrieve water levels from radar altimeter data over inland water bodies dedicated to restricting the land contamination of the signal. The performances of the waveform portion selection method and the three retrackers which are the threshold retracker, Offset Center of Gravity (OCOG) retracker and 2-step analytical retracker are compared. Time series of water level results are retrieved over water bodies in Ebre river basin (Catalunya, Spain) and Lake Volta (West Africa). The standard deviation for 2-step analytical retracker combined with the waveform portion selection ranges from 0.02m to 0.05m, for OCOG retracker ranges from 0.07m to 0.13m, and for threshold retracker, it ranges from 0.05m to 0.1m over Lake Volta. The results show good accuracy with the insitu measurements over lake Ebre and Ribarroja reservoir with RMSE about 0.44 m and 0.18 m separately. All performances of the three retrackers are compared with the onboard retracker as well.