Lake Level Variations From Satellite Altimetry

The instantaneous sea surface height surveyed by satellite altimetry over open water can have the precision of ±5cm. For inland lakes with bigger areas, the lake surface has similar reflective characteristics as sea surface, which makes it possible to monitor the water level variation over inland lakes by satellite altimetry. In this paper, based on the former researches, satellite altimetry is used to monitor the water level changes of seven inland lakes in China. The contents and conclusions of this research are as following:1. Based on the characteristics of altimetric waveform, methods of improved waveform retracking are put forward. DEM or DTM model is introduced as the standard to estimate the retracked range for waveform retracking. The waveform retracking software is designed using Fortran language. Taking Hulun Lake as an example, the waveform of the 27th pass near the bank from TOPEX is retracked by waveform retracking software. The results indicate that the mean square error has improved three times than that of geophysical data records (GDRs). It is proved that the waveform retracking can improve the precision of altimetric data over inland lake, because the waveform retracking can decrease the influence of contamination from land topography, adlittoral area, AGC and so on.2. The altimeter waveform data of TOPEX over Hulun Lake are analyzed. A conclusion can be obtained that most of the altimeter waveforms are peaks or spikes during the frozen time in winter, while the waveform energy is lower than that in summer owing to the influence by snow and ice on the lake surface in winter.3. Data editing principles are put forward when the level change of the lake is monitored using GDRs. The method to reduce GDR data to referenced track among different cycles is improved.4. Lake level anomaly from satellite altimetry is studied. Comparing the annual mean level anomaly of Hulun Lake with the in situ annual lake level, the mean square error is 10.2cm and the biggest difference is -14.5cm. Therefore, it is proved that it is possible to monitor land lake level variation by satellite altimetry.5. Time series of lake level anomaly from TOPEX/Poseidon and Jason-1 are studied using the wavelet analysis. By analyzing the wavelet coefficient diagram, the Cycs of yearly lake level variation of 7 lakes including Hulun Lake are shown. Finally, the relationship between lake level variation and ENSO is proved.