Abstract
This paper estimates lake level variations over two small and adjacent lakes in the Tibetan plateau (TP), namely Gemang Co and Zhangnai Co, as well as the inland Dianchi Lake in China using CryoSat-2 SARIn-mode and LRM 20-Hz waveforms over the period of 2011–2018. Different retrackers and a dedicated data editing procedure have been used to process CryoSat-2 data for determining the lake level time series. The lake level estimations are indirectly validated against those from Jason-2 in TP and from in situ data in Dianchi Lake, both showing good agreement with strong correlation coefficients >0.74. The results of this paper suggest that the official ICE retracker for LRM data and APD-PPT retracker for SARIn-mode waveforms are the most appropriate retrackers over Dianchi Lake and TP lakes, respectively. The trend estimates of the time series derived by both retrackers are 61.0 ± 10.8 mm/yr for Gemang Co and Zhangnai Co in TP, and 30.9 ± 64.9 mm/yr for Dianchi Lake, indicating that the lake levels over three lakes were continuously rising over the study period. The results of this study show that CryoSat-2 SARIn-mode data can be used for monitoring many small lakes that have not been measured by other altimetry missions in TP.
Highlights
There are approximately 1400 lakes in the Tibetan Plateau (TP) [1] and 40 lakes in the Yunnan plateau [2] with water surface area larger than 1.0 km2
low-resolution mode (LRM) operates like a conventional altimeter in the pulse-limited mode over oceans, land and flat ice sheets; SAR mode mainly works over sea ice and a few ocean areas; and SAR interferometric (SARIn) mode is used around ice sheet margins and over mountain glaciers
CryoSat-2 operates in the LRM over Dianchi Lake, and measurements taken withinan analtimeter altimeterfootprint footprint width width of measurements areare taken within of 1.65
Summary
There are approximately 1400 lakes in the Tibetan Plateau (TP) [1] and 40 lakes in the Yunnan plateau [2] with water surface area larger than 1.0 km. The temporal and spatial variations in water levels of these lakes provide a significant indicator of changes in regional hydrology, ecosystem and climate systems. Since 1992, data from conventional satellite altimetry missions (e.g., TOPEX/Poseidon, Envisat, Jason-1/2/3, SARAL/AltiKa and ICESat) and new generation altimetry missions (e.g., CryoSat-2, Sentinel-3A and ICESat-2) have been used to monitor the temporal lake levels in TP, e.g., [1,3,4,5,6,7,8,9,10,11,12,13]. LRM operates like a conventional altimeter in the pulse-limited mode over oceans, land and flat ice sheets; SAR mode mainly works over sea ice and a few ocean areas; and SARIn mode is used around ice sheet margins and over mountain glaciers.
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