| Inland waters are not only an important part in global water cycle,but also are closely related to human life and production.It palys an important role in local economy and climate change.However,there are many rivers and lakes are not monitored around the world,especially for the inaccessible remote areas.What's more,even though they are monitored,some of them are not shared due to many kinds of reasons.How to monitor inland waters by the aid of remote sensing technology is an important subject,which is valuable in data poor,remote regions.Compared to traditional optical remote sensing technology,radar altimetry has the advantage of all-time and all-weather observation,strong penetrability,and can be less affected by clouds.Therefore,it has been widely used for rivers and lakes water level monitoring and related river discharge and lake storage estimation studies.However,due to the large footprint of radar altimeter,the radar signal returned from the inland waters is likey to be contaminated by the surrounding land.Our goal of the research is to answer two questions: 1.how to improve the performance of radar altimeter over inland waters? 2.how to combine radar altimetry data with optical images to estimate river discharge and lake volume? The main research content and conclusions of this dissertation are as follows:1.As for the Hankou section of the Yangtze River,a water level extraction workis conducted and a Multi-subwaveform Multi-weight Threshold Retracker (MSMWTR)is developed,which can effectively improve the accuracy of the derived water levels and decrease the root mean square from 9.06 m to 0.34m.2.In the middle reach of Yantze River,river discharge estimation work is carried out whether the in situ river discharge data is available or not.Especially, when the in situ discharge data is not available,we develop the method of reconstructing the river cross-section after combing optical images with radar altimetry data.Results show that the proposed method can be successfully used to estimate the river discharge,and the Relative Root Mean Suqare Error(RRMSE)reaches 12.83%.3.As for Lake Hulun,a waveform classification based targeted waveform retracking strategy is adopted,which can alleviate the waveform pollution problem.Meanwhile,by combining Landsat images with Jason series radar altimetry data,the lake storage dynamics is monitored.Results show that the water storage of the lake has changed dramatically during the past 15 years.The main innovations are as follows: 1.As for medium width rivers under rough and heterogeneous surfaces,we have firstly proposed the MSMWTR.Different from traditional retracking methods,the new method have taken more than one subwaveforms comprising the complex waveform into account,which can make full use of the information contained in the return echoes.This mehod can improve the performance of radar altimetry over medium width rivers to some degree.2.For the variable waveforms returned from lake surface,several waveform shape related feature indexes are designed.After collecting small amout of samples and using a Support Vector Machine,these waveform feature indexes can be successfully used for automatic waveform classification. |
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