Abstract
Zhari Namco, a large lake in the Tibetan Plateau (TP), is sensitive to climate and environmental change. However, it is difficult to retrieve accurate and continuous lake levels for Zhari Namco. A robust strategy, including atmospheric delay correction, waveform retracking, outlier deletion, and inter-satellite adjustment, is proposed to generate a long-term series of lake levels for Zhari Namco through multi-altimeter data. Apparent biases are found in troposphere delay correction from different altimeter products and adjusted using an identical model. The threshold (20%) algorithm is employed for waveform retracking. The two-step method combining a sliding median filter and 2σ criterion is used to eliminate outliers. Tandem mission data of altimeters are used to estimate inter-satellite bias. Finally, a 27-year-long lake level time series of Zhari Namco are constructed using the TOPEX/Poseidon-Jason1/2/3 (T/P-Jason1/2/3) altimeter data from 1992 to 2019, resulting in an accuracy of 10.1 cm for T/P-Jason1/2/3. Temperature, precipitation, lake area, equivalent water height, and in situ gauge data are used for validation. The correlation coefficient more than 0.90 can be observed between this result and in situ gauge data. Compared with previous studies and existing database products, our method yields sequences with the best observational quality and the longest continuous monitoring in Zhari Namco. The time series indicates that the lake level in Zhari Namco has increased by ∼ 5.7 m, with an overall trend of 0.14 ± 0.01 m/yr, showing a fluctuating rate (1992–1999: −0.25 ± 0.05 m/yr, 2000–2008: 0.26 ± 0.04 m/yr, 2009–2016: −0.05 ± 0.03 m/yr, 2017–2019: 1.34 ± 0.34 m/yr). These findings will enhance the understanding of water budget and the effect of climate change in the TP.
Highlights
There are ∼1400 lakes greater than 1 km2 over the Tibetan Plateau (TP), most of which are closed and rarely disturbed by human activities (Ma et al, 2010)
The changes of lake level in 111 lakes on the TP are successfully extracted by ICESat/ICESat-2, and it is found that the lake level has a significant upward trend (Zhang et al, 2011, 2019a; Phan et al, 2012)
The objective of this paper is to show a technique for computing lake level changes in Zhari Namco from T/PJason1/2/3 altimeters
Summary
There are ∼1400 lakes greater than 1 km over the Tibetan Plateau (TP), most of which are closed and rarely disturbed by human activities (Ma et al, 2010) These high-altitude lakes are extremely sensitive to global climate change, and digesting their evolution is important for both hydrological and climatic analysis (Song et al, 2014). SAR Interferometry (SARIn), a new sort of satellite altimetry (e.g., CryoSat-2), can gather worthwhile data for monitoring lake level changes on the TP (Kleinherenbrink et al, 2015; Jiang et al, 2017). Both ICESat/ICESat-2 and CryoSat-2 use non-repetitive orbits. This feature makes them improper for detecting periodic lake level alteration
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