Abstract Satellite radar altimetry has been widely used in the monitoring of water levels of lakes, rivers and wetlands in the past decades. The conventional pulse-limited radar altimeters have a relatively large ground footprint, which limits their capability to retrieve surface elevation information over small and medium-sized water bodies. A new generation of satellite radar altimeter system, a dual-frequency SAR radar altimeter (SRAL) onboard the Copernicus Sentinel-3 satellite, has produced densely sampled elevation measurements with a smaller footprint for the Earth's surfaces since June 2016, owing to the Delay-Doppler processing technique. Four standard SRAL SAR altimetry waveform retracking algorithms (known as retrackers) have been designed to retrieve elevation measurements for different types of surfaces: Ice-Sheet retracker for polar ice sheets, SAMOSA-3 retracker for open ocean and coastal zones, OCOG retracker for sea-ice margins, and Sea-Ice retracker for sea ice. In this research, we evaluated the performances of the Sentinel-3 SRAL SAR altimetry retrackers over lakes, particularly over seasonally ice-covered lakes in one hydrological cycle. For 15 lakes and reservoirs with different sizes and at varying latitudes in the northern hemisphere, we compared the lake water levels estimated by each of standard SRAL SAR retrackers against in-situ water level measurements for different seasons (a full hydrologic cycle) during 2016–2017. Our evaluation shows that Sea-Ice retracker was unable to provide continuous estimates of lake water levels, as a result of the high rate of missing data. Although the precision and relative accuracy of lake water level estimates from these three standard SRAL SAR retrackers are similar, the SAMOSA-3 retracker has the least bias in comparison with ground-based gauge measurements. When the lakes in the mid- and high-latitude regions were covered by ice in the winter season, these three standard SAR retrackers generated erroneous lake water level measurements, significantly lower than the true lake water levels recorded by in-situ gauge stations. The measurement errors of these three standard retrackers increase with the growth of the lake ice thickness. To address the negative effect of the seasonal ice cover, we developed a new bimodal correction algorithm. We demonstrate that our bimodal correction algorithm can retrieve the ice thickness and reliably estimate water levels for the ice-covered lakes in winter, hence enabling the generation of temporally consistent lake water level measurements throughout all seasons for lake hydrological analysis.

中文翻译：

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Sentinel-3 SAR 测高波形重跟踪算法的分析，用于推导冰覆盖湖泊上时间一致的水位

摘要 卫星雷达测高在过去几十年中被广泛应用于湖泊、河流和湿地的水位监测。传统的脉冲受限雷达高度计具有相对较大的地面足迹，这限制了它们在中小型水体上检索表面高程信息的能力。新一代卫星雷达高度计系统，即哥白尼哨兵 3 号卫星上的双频 SAR 雷达高度计 (SRAL)，自 2016 年 6 月以来已产生密集采样的高程测量，地球表面的足迹较小，这是由于延迟多普勒处理技术。四种标准的 SRAL SAR 测高波形重跟踪算法（称为重跟踪器）旨在检索不同类型表面的高程测量值：Ice-Sheet Retracker 用于极地冰盖，SAMOSA-3 用于开阔海洋和沿海地区，OCOG 用于海冰边缘，Sea-Ice 用于海冰。在这项研究中，我们评估了 Sentinel-3 SRAL SAR 测高仪在湖泊上的性能，特别是在一个水文循环中季节性冰雪覆盖的湖泊上的性能。对于北半球不同大小和不同纬度的 15 个湖泊和水库，我们将每个标准 SRAL SAR 重新跟踪器估计的湖水位与 2016 年期间不同季节（一个完整的水文循环）的原位水位测量值进行了比较– 2017 年。我们的评估表明，由于数据丢失率很高，海冰重新跟踪器无法提供湖水位的连续估计。尽管这三个标准 SRAL SAR 再跟踪器估计湖水位的精度和相对准确度相似，但 SAMOSA-3 再跟踪器与地面测量仪测量值相比偏差最小。当冬季中高纬度地区的湖泊被冰层覆盖时，这三个标准 SAR 再跟踪器产生了错误的湖水位测量值，明显低于原位测量站记录的真实湖水位。这三种标准重跟踪器的测量误差随着湖冰厚度的增加而增加。为了解决季节性冰盖的负面影响，我们开发了一种新的双峰校正算法。