Abstract
CryoSat-2 altimetry has become a valuable tool for monitoring the water level of lakes. In this study, a concentrated probability density function (PDF) method was proposed for preprocessing CryoSat-2 Geophysical Data Record (GDR) data. CryoSat-2 altimetry water levels were preprocessed and evaluated by in situ gauge data from 12 lakes in China. Results showed that the accuracy of the raw GDR data was limited due to outliers in most of the along-track segments. The outliers were generally significantly lower than the in situ values by several meters, and some by more than 30 m. Outlier detection, therefore, improves upon the accuracy of CryoSat-2 measurements. The concentrated PDF method was able to greatly improve the accuracy of CryoSat-2 measurements. The preprocessed CryoSat-2 measurements were able to observe lake levels with a high accuracy at nine of the twelve lakes, with an absolute mean difference of 0.09 m, an absolute standard deviation difference of 0.04 m, a mean root mean square error of 0.27 m, and a mean correlation coefficient of 0.84. Overall, the accuracy of CryoSat-2-derived lake levels was validated in China. In addition, the accuracy of Database for Hydrological Time Series of Inland Waters (DAHITI) and HYDROWEB water level products was also validated by in situ gauge data.
Highlights
Lakes are a key component of the earth’s surface system and serve as a meeting point for the atmosphere, geosphere, hydrosphere, and biosphere
The CryoSat-2 altimetry measurements have been evaluated by in situ gauge data, and were found to accurately monitor water levels at many lakes [1,8,9,18,36]. These lakes are mainly located in Europe and North America, where gauge measurements are available for most lakes
Our results showed that the CryoSat-2 measurements were able to monitor robustly lake levels
Summary
Lakes are a key component of the earth’s surface system and serve as a meeting point for the atmosphere, geosphere, hydrosphere, and biosphere. Changes in lakes and their induced environmental evolutions are the result of global and regional climate events, to which they show great sensitivity. It is, important to continuously monitor the water levels of lakes. In situ gauge stations provide precise water-level observations, but they are limited to relatively few lakes because they are expensive, especially in remote areas. In situ water-level data are usually managed by government institutions who sometimes make data access difficult. Satellite altimetry has become a valuable tool to monitor the water levels of lakes
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