Direct sensing of total ocean surface currents with microwave Doppler signals is a growing topic of interest for oceanography, with relevance to several new ocean mission concepts proposed in recent years. Since 2014, the spaceborne C-band SAR instruments of the Copernicus Sentinel-1 (S1) mission routinely acquire microwave Doppler data, distributed to users through operational S1 Level-2 ocean radial velocity (L2 OCN RVL) products. S1 L2 RVL data could produce high-resolution maps of ocean surface currents that would benefit ocean observing and modelling, particularly in coastal regions. However, uncorrected platform effects and instrument anomalies continue to impact S1 RVL data and prevent direct exploitation.

In this paper, a simple empirical method is proposed to calibrate and correct operational S1 L2 RVL products and retrieve two-dimensional maps of surface currents in the radar line-of-sight. The study focuses on the German Bight where wind, wave and current data from marine stations and an HF radar instrumented site provide comprehensive means to evaluate S1 retrieved currents. Analyses are deliberately limited to Sentinel-1A (S1A) ascending passes to focus on one single instrument and fixed SAR viewing geometry. The final dataset comprises 78 separate S1A acquisitions over 2.5 years, of which 56 are matched with collocated HF radar data. The empirical corrections bring significant improvements to S1A RVL data, producing higher quality estimates and much better agreement with HF radar radial currents.

Comparative evaluation of S1A against HF radar currents for different WASV corrections reveal that best results are obtained in this region when computing the WASV with sea state rather than wind vector input. Accounting for sea state produces S1 radial currents with a precision (std of the difference) around 0.3 m/s at ∼1 km resolution. Precision improves to ∼0.24 m/s when averaging over 21 × 27 km², with correlations with HF radar data reaching up to 0.93. Evidence of wind-current interactions when tides and wind align and short fetch conditions call for further research with more satellite data and other sites to better understand and correct the WASV in coastal regions.

Finally, 1 km resolution maps of climatological S1A radial currents obtained over 2.5 years reveal strong coastal jets and fine scale details of the coastal circulation that closely match the known bathymetry and deep-water coastal channels in this region. The wealth of oceanographic information in corrected S1 RVL data is encouraging for Doppler oceanography from space and its application to observing small scale ocean dynamics, atmosphere and ocean vertical exchanges and marine ecosystem response to environmental change.

用微波多普勒信号直接检测总海面洋流是海洋学越来越感兴趣的话题，与近年来提出的几个新的海洋任务概念相关。自 2014 年以来，哥白尼哨兵一号（S1）任务的星载 C 波段 SAR 仪器定期获取微波多普勒数据，并通过业务 S1 2 级海洋径向速度（L2 OCN RVL）产品分发给用户。S1 L2 RVL 数据可以生成高分辨率的海面洋流图，这将有利于海洋观测和建模，特别是在沿海地区。然而，未校正的平台效应和仪器异常继续影响 S1 RVL 数据并阻止直接利用。

在本文中，提出了一种简单的经验方法来校准和校正可操作的 S1 L2 RVL 产品，并在雷达视线中检索表面电流的二维图。该研究的重点是德国湾，来自海洋站和一个 HF 雷达仪器站点的风、波浪和洋流数据提供了评估 S1 反演洋流的综合手段。分析特意限于 Sentinel-1A (S1A) 上升通道，以专注于单一仪器和固定的 SAR 观察几何。最终数据集包括 2.5 年间的 78 个单独的 S1A 采集，其中 56 个与并置的 HF 雷达数据匹配。经验修正为 S1A RVL 数据带来了显着改进，产生了更高质量的估计，并且与 HF 雷达径向电流的一致性更好。

针对不同 WASV 校正的 HF 雷达电流对 S1A 的比较评估表明，在使用海况而不是风矢量输入计算 WASV 时，在该区域获得了最佳结果。考虑海况产生 S1 径向流，精度（差异的标准值）约为 0.3  m/s， 分辨率约为1 km。 当平均超过 21  ×  27  km ^{2 时}，精度提高到 ~0.24 m/s ，与 HF 雷达数据的相关性达到 0.93。潮汐和风对齐时风-流相互作用的证据以及短距离条件要求使用更多卫星数据和其他站点进行进一步研究，以更好地了解和纠正沿海地区的 WASV。

最后， 在 2.5 年间获得的1公里分辨率的气候学 S1A 径向流图揭示了强烈的沿海急流和沿海环流的精细尺度细节，与该地区已知的水深测量和深水沿海通道密切匹配。校正的 S1 RVL 数据中的丰富海洋学信息对于从空间进行的多普勒海洋学及其在观测小尺度海洋动力学、大气和海洋垂直交换以及海洋生态系统对环境变化的响应方面的应用是令人鼓舞的。