Abstract Satellite nadir radar altimeters have been widely used to measure river and lake surface water elevations. They can now retrieve the elevations of some rivers The Jason-3 altimetry mission, launched in January 2016, has an alternative instrument operation mode, the so called Open-Loop (OL) or Digital Elevation Model (DEM) tracking mode. This mode is intended to help overcome this issue, by using an on-board DEM. However it was not used in 2016 as the operational mode because of difficulties in defining an accurate on-board global-scale DEM. Mainland France has been chosen to test the OL tracking mode, as water masks and DEMs of sufficient accuracy are available. Following the launch of Jason-3, Jason-2 (its predecessor) was maintained on the same nominal orbit as its follow-on, for more than 6 months. During this tandem period, data from the first 10 Jason-3 cycles (a Jason-2/-3 cycle corresponds to 10 days) were acquired in the traditional Closed-Loop (CL) tracking mode. Jason-3 data from the last 13 cycles were acquired in OL tracking mode. Jason-2 was always in CL tracking mode. Compared to nearby in situ gages and for river wider than 100 m, Jason-3 water elevation anomalies have a RMSE between 0.20 and 0.30 m for most reaches. Jason-3 performance over narrow rivers is similar to that of Jason-2. In CL tracking mode, Jason-3 altimeter tends to be locked over the surrounding topography more frequently than Jason-2 (due to the specific post-launch Jason-2 altimeter tuning). This study shows that Jason-2 observed 60% of river reaches studied (48 of 86 reaches), whereas Jason-3 in OL tracking mode was able to measure all river reaches for every cycle. This result clearly highlights the significant advantages of the OL tracking mode for observation of steep-sided rivers. However, further investigations are required to compute an accurate on-board global-scale DEM and to determine those locations where the use of OL tracking mode is or is not appropriate.

中文翻译：

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在法国河流上验证 Jason-3 跟踪模式

摘要 卫星天底雷达高度计已广泛用于测量河流和湖泊的地表水位。他们现在可以检索一些河流的高程 Jason-3 测高任务于 2016 年 1 月启动，具有替代仪器操作模式，即所谓的开环 (OL) 或数字高程模型 (DEM) 跟踪模式。此模式旨在通过使用板载 DEM 帮助克服此问题。然而，由于难以定义准确的机载全球规模 DEM，因此在 2016 年并未将其用作操作模式。选择法国大陆来测试 OL 跟踪模式，因为有足够准确的水面罩和 DEM。在 Jason-3 发射之后，Jason-2（它的前身）与其后续卫星保持在同一标称轨道上超过 6 个月。在这个串联期间，前 10 个 Jason-3 周期（Jason-2/-3 周期对应 10 天）的数据是在传统的闭环 (CL) 跟踪模式中获取的。来自最后 13 个周期的 Jason-3 数据是在 OL 跟踪模式下获取的。Jason-2 始终处于 CL 跟踪模式。与附近的原位测量仪和宽度超过 100 m 的河流相比，Jason-3 水位高程异常在大多数河段的 RMSE 介于 0.20 和 0.30 m 之间。Jason-3 在狭窄河流上的表现与 Jason-2 相似。在 CL 跟踪模式下，Jason-3 高度计往往比 Jason-2 更频繁地锁定在周围地形上（由于特定的发射后 Jason-2 高度计调整）。这项研究表明，Jason-2 观察了 60% 的河段（86 个河段中的 48 个），而处于 OL 跟踪模式的 Jason-3 能够测量每个周期的所有河段。这一结果清楚地突出了 OL 跟踪模式在陡峭河流观测方面的显着优势。但是，需要进一步调查以计算准确的机载全球尺度 DEM 并确定使用 OL 跟踪模式是否合适的位置。