Waveform Analysis,Retracking And Application Of Satellite Altimetry Considering Reflection Defference In Lake Area

Lakes are sensitive to climate change and human activities.And any changes to lake will have an impact on natural ecosystems and socio-economic systems.Water level is an important index reflecting lake changes.Traditional water level measurement is mainly done by hydrological stations.Due to high maintenance costs,lack of data in remote areas and the difficulties of data sharing,there are certain obstacles in relevant scientific research.Satellite altimetry techniques have now become a new means of monitoring lake water level changes.Since satellite altimetry technology was originally designed for marine missions,it may create problems when applied to inland lakes.Radar waves may touch things outside the lake since inland lakes are generally small.When radar waves are received,it may be contaminated,and then causing distance tracking errors.This paper analyzes the surface factors affecting the waveform formation and analyzes the waveform formation mechanism in flat and steep terrain.Corresponding waveform retracking algorithms is designed.And the waveforms of typical lakes are analyzed.The main contents and conclusions are as follows:(1)The satellite altimeter echo model is analyzed.Two surface factors are found affecting the waveform,mainly the scattering cross section(ie,the reflection capability)and the topography.When the radar illuminates an area with a variety of features and undulating terrain,the waveform will be affected.(2)The waveform of flat area is mainly affected by the scattering cross section.When the radar illumination area contains both water and non-water surfaces,if the non-water surface reflection ability is strong,the non-water surface signal of the waveform will be highlighted.The formed waveform has a small leading edge and retracking of this type of waveform is error-prone.Corresponding waveform retracking algorithm is designed for this waveform.(3)The waveform of steep terrain area is affected by both scattering cross section and topography.When the radar illumination area contains both water and non-water surfaces,if the terrain around the lake is rough,the waveform will be affected.There are two leading edge,and the latter is produced by water.For this situation,a special waveform retracking software has been developed to perform waveform retracking under manual intervention.(4)Some typical lakes are selected for analysis.The terrain around Hongze Lake is flat.And the waveform is mainly affected by the scattering cross section.The affected waveform has the characteristics of a small leading edge.After the waveform retracking,the water level returns to normal and the standard deviation of the water level is 0.09m.The terrain around Lake Victoria is rough,so the waveform is affected by both the scattering cross section and topography.The affected waveform has two leading edge.The leading edge produced by water is difficult to track properly.The water level returned to normal after retracking by the waveform retracking software developed for this situation.The lake level database established using satellite altimetry data was analyzed.The water level of Hongze Lake in the GRLM database was verified and compared with the measured data at the hydrological station.It was found that the database had errors in the water level of Hongze Lake.The reason for this situation may be that the affected waveform was not retracking.Therefore,the results of this paper can be used to improve the global lake water level database.