Abstract
Abstract. There are more than 1,000 lakes (> 1 km2) on the Tibetan Plateau and lake level is an important physical feature of lake changes. Lake level change is an important indicator to reflect changes of climate and environment in a certain area. The development of satellite altimetry has provided data support for the monitoring of lake level and effectively compensated for the deficiencies of traditional water level monitoring in alpine regions. In this study, the laser altimeter of ICESat-2 and the radar altimeter of CryoSat-2 are used to provide lake level of the Nam Co lake during the period of 2010–2020. The result showed that the standard deviation (SD) of ICESat-2 (0.0895 m) was lower than the SD of CryoSat-2 (0.2556 m) and the months with higher SD values were mostly during the ice period of Nam Co lake. ICESat-2 had a considerably decreased measurement uncertainty. There are systematic differences in lake levels extracted by different altimetry satellites and the mean bias between ICESat-2 and CryoSat-2 was around 0.45 m. After removing inter-altimeter biases, the continuous lake levels from 2010 to 2020 were constructed. The inter-annual changes in lake levels were flat or even slightly decreased and the lake level has dropped by about 0.80 m in general. The water level generally reached the highest from September to October of the year in terms of intra-annual changes. Besides, temperature and precipitation changes were closely related to lake level tendency.
Highlights
The Tibetan Plateau (TP) is the region with the most widespread glaciers, except for Antarctica, Arctic, and Greenland, so it is referred to as the third pole (Zhang et al, 2015)
2.2.1 CryoSat-2 altimetry data: CryoSat-2 is a radar altimetry satellite launched by European Space Agency (ESA) in 2010, characterized by three different modes, including low resolution mode (LRM), synthetic aperture mode (SAR) and synthetic aperture interferometric mode (SARIn) (Vieira et al, 2018)
We calculated the standard deviation (SD) after outlier removal of the two altimetry satellites and found the SD of ICESat-2 (0.0895m) was lower than that of CryoSat-2 (0.2556m), ICESat-2 had a considerably decreased measurement uncertainty compared with CryoSat-2 (Figure 3)
Summary
The Tibetan Plateau (TP) is the region with the most widespread glaciers, except for Antarctica, Arctic, and Greenland, so it is referred to as the third pole (Zhang et al, 2015). There are lots of satellite altimetry data to monitor lake levels, such as ERS-2(1995-2011), Envisat (2002-), ICESat(2003-2008), CryoSat-2(2010-), ICESat-2(2018-)(Jiang et al, 2017; Crtaux et al, 2011). Song et al (2015) and Zhang et al (2011) used the ICESat altimetry data over the period of 2003-2009 to monitor the lake levels on the TP. A continuous time series of lake level changes compiled by merging different altimetry data is uncertain due to the bias of different altimetry satellites. We analyzed lake level changes based on CryoSat radar altimetry and ICESat-2 laser altimetry during the period of 2010-2020. The focus of this paper is to remove inter-altimeter biases in order to obtain a more accurate continuous lake level and explore the relationship between temperature, precipitation, and lake level changes. The research will provide effective verification for the simulation of water balance in lake basins, and initially explore the relationship with climate factors
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