Monitoring the Fluctuation of Lake Qinghai Using Multi-Source Remote Sensing Data

Wenbin Zhu,Shaofeng Jia,Aifeng Lv

doi:10.3390/rs61110457

Abstract

The knowledge of water storage variations in ungauged lakes is of fundamental importance to understanding the water balance on the Tibetan Plateau. In this paper, a simple framework was presented to monitor the fluctuation of inland water bodies by the combination of satellite altimetry measurements and optical satellite imagery without any in situ measurements. The fluctuation of water level, surface area, and water storage variations in Lake Qinghai were estimated to demonstrate this framework. Water levels retrieved from ICESat (Ice, Cloud, and and Elevation Satellite) elevation data and lake surface area derived from MODIS (Moderate Resolution Imaging Spectroradiometer) product were fitted by linear regression during the period from 2003 to 2009 when the overpass time for both of them was coincident. Based on this relationship, the time series of water levels from 1999 to 2002 were extended by using the water surface area extracted from Landsat TM/ETM+ images as inputs, and finally the variations of water volume in Lake Qinghai were estimated from 1999 to 2009. The overall errors of water levels retrieved by the simple method in our work were comparable with other globally available test results with r = 0.93, MAE = 0.07 m, and RMSE = 0.09 m. The annual average rate of increase was 0.11 m/yr, which was very close to the results obtained from in situ measurements. High accuracy was obtained in the estimation of surface areas. The MAE and RMSE were only 6 km2, and 8 km2, respectively, which were even lower than the MAE and RMAE of surface area extracted from Landsat TM images. The estimated water volume variations effectively captured the trend of annual variation of Lake Qinghai. Good agreement was achieved between the estimated and measured water volume variations with MAE = 0.4 billion m3, and RMSE = 0.5 billion m3, which only account for 0.7% of the total water volume of Lake Qinghai. This study demonstrates that it is feasible to monitor comprehensively the fluctuation of large water bodies based entirely on remote sensing data.

Highlights

Land surface water is an important part of the water cycle
It is obvious that similar accuracy was achieved in the estimation of water level variations, the equation established in our study provided a much more accurate estimation of the absolute water level
Lake Qinghai was taken as an example in this paper to demonstrate the potential of remote sensing in the monitoring of ungauged lakes

Summary

Introduction

Lakes and rivers only account for 0.007% of the Earth’s water budget, they are the most accessible inland water resources available for ecosystems and human consumption [1]. For these reasons, many countries operate a number of inland water level stations to collect information for water resources management. Even in areas where gauging stations exist, the water level in lakes is in most cases the only data that is measured routinely, while another two important parameters, namely water areas and volume, are often left ungauged. On the Tibetan Plateau (TP), known as the “Water Tower of

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