Hwang, C.; Wei, S.; Cheng, Y.; Peng, H.; Lee, J.; Tseng, K.; Chi, C.; Lo, Y.; Wang, Q. Rapid Thinning at a Glacier Terminus and Icefield of Mt. Tanggula, Tibet, Detected by TOPEX/Poseidon, and Jason-2/-3 Altimeters: Confirmation by Satellite Imagery. Preprints2018, 2018110347. https://doi.org/10.20944/preprints201811.0347.v1
Hwang, C., Wei, S., Cheng, Y., Peng, H., Lee, J., Tseng, K., Chi, C., Lo, Y., & Wang, Q. (2018). Rapid Thinning at a Glacier Terminus and Icefield of Mt. Tanggula, Tibet, Detected by TOPEX/Poseidon, and Jason-2/-3 Altimeters: Confirmation by Satellite Imagery. Preprints. https://doi.org/10.20944/preprints201811.0347.v1
Hwang, C., Yuan-Ni Lo and Qiu-Yu Wang. 2018 "Rapid Thinning at a Glacier Terminus and Icefield of Mt. Tanggula, Tibet, Detected by TOPEX/Poseidon, and Jason-2/-3 Altimeters: Confirmation by Satellite Imagery" Preprints. https://doi.org/10.20944/preprints201811.0347.v1
An oceanic radar altimeter such as TOPEX/Poseidon (T/P) is typically for observing elevation changes over the open oceans or large inland lakes/rivers, with limited applications over solid earth due to its large footprint and susceptibility to waveform contamination and slope effect. Here we demonstrate that it is possible to construct a long-term time series of glacier elevation change from T/P-series radar altimeters over two flat surfaces near a glacier terminus and an icefield (Sites A and B, with slopes of 2° and 0.8°) in Mt. Tanggula, Tibet, at elevations over 5400 m. We retracked radar waveforms using the subwaveform threshold algorithm, selected quality altimeter data (1/4 of the original) with nearly the same slope and adjusted the original elevations by fitting with a time-varying, 2nd order surface. The glacier elevation changes at the two sites from T/P (1993–2002) show seasonal elevation oscillations with linear rates at about −3 m/year and abnormal seasonal changes around the 1997–98 El Niño. Site A is over a deep valley in southern Tanggula. Its elevation dropped about 30 m over 1993–2002 (from T/P) and the glacier almost disappeared by 2016 (from altimeters and satellite images). Despite the sporadic Jason-2 and Jason-3 altimeter data, we also derived long-term rates of glacier elevation change over 1993–2017. Landsat-derived glacier area and elevation changes near the two sites confirm the rapid glacier thinning from the altimeters. The glacier meltwater near Site A supplied increasing source water to Chibuzhang Co west of Mt. Tanggula, contributing partially to its accelerated rising lake level. The glacier thinning at Site B (icefield) was correlated with the increased discharge of the Tuotuo River in eastern Mt. Tanggula, a source region of the Yangtze River. The successful detection of glacier thinning at the two sites shows that T/P-series altimeters can serve as a virtual station at a flat glacier spot to monitor long-term glacier elevation changes in connection to climate change. This virtual station concept is particularly useful for inaccessible glaciers, but its implementation faces two challenging issues: increasing the volume of quality altimeter data and improving the ranging accuracy over a targeted mountain glacier spot.
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