Envisat altimetry radar waveform retracking of quasi-specular echoes over the ice-covered qinghai lake

Kuo Hsin Tseng, C. K. Shum, Yuchan Yi, Hok Sum Fok, Chung Yen Kuo, Hyongki Lee, Xiao Cheng, Xianwei Wang

Research output: Contribution to journalArticlepeer-review

25 Scopus citations


The use of satellite radar altimetry has long been extended to areas other than the deep-ocean primarily because of the advances in radar waveform retracking methodologies. However, the retracking algorithms are limited to a handful shapes of return echoes over assumed known surfaces, while numerous unknown waveforms exist due to the complexity of real-world land cover and other surfaces. Measurements over a surface with seasonal or ephemeral patterns could thus degrade in accuracy due to varying characteristics from the corresponding radar backscatters. In this study, we demonstrate that the Qinghai Lake, an alpine water body with distinct seasonal variation between water and ice causes inaccurate surface-height estimates when using Envisat radar altimetry and conventional retracking techniques. Following the characterization of the lake surface using EO-1 and Landsat multispectral analysis, we hypothesize that the overestimation of the lake level during winter and early spring is not from the snow accumulation; rather it is due to an error of the onboard retracker (ICE-1) which is unable to properly model the quasi-specular waveforms. Hence, we first build a classification algorithm to identify the anomalous waveforms, and then use an empirical retracking gate correction to mitigate the ice contamination. The accuracy of the 20% threshold retracker (TR) after applying suggested gate correction has a significant improvement with a root-mean-square error (RMSE) of 6 ± 7 cm and a correlation of 0.98 compared with the in situ gauge data. The improvement in accuracy is 54% better than the ICE-1 and 85% than the OCEAN retrackers, respectively.

Original languageEnglish
Pages (from-to)615-627
Number of pages13
JournalTerrestrial, Atmospheric and Oceanic Sciences
Issue number4 PART1
StatePublished - Aug 2013


  • Lake ice
  • Qinghai lake water level
  • Satellite altimetry
  • Specular echoes
  • Tibetan plateau
  • Waveform retracking


Dive into the research topics of 'Envisat altimetry radar waveform retracking of quasi-specular echoes over the ice-covered qinghai lake'. Together they form a unique fingerprint.

Cite this