This paper describes first results obtained from the SWIM (Surface Waves Investigation and Monitoring) instrument carried by CFOSAT (China France Oceanography Satellite), which was launched on October 29th, 2018. SWIM is a Ku-Band radar with a near-nadir scanning beam geometry. It was designed to measure the spectral properties of surface ocean waves. First, the good behavior of the instrument is illustrated. It is then shown that the nadir products (significant wave height, normalized radar cross-section and wind speed) exhibit an accuracy similar to standard altimeter missions, thanks to a new retracking algorithm, which compensates a lower sampling rate compared to standard altimetry missions. The off-nadir beam observations are analyzed in details. The normalized radar cross-section varies with incidence and wind speed as expected from previous studies presented in the literature. We illustrate that, in order to retrieve the wave spectra from the radar backscattering fluctuations, it is crucial to apply a speckle correction derived from the observations. Directional spectra of ocean waves and their mean parameters are then compared to wave model data at the global scale and to in situ data from a selection of case studies. The good efficiency of SWIM to provide the spectral properties of ocean waves in the wavelength range [70m-500m] is illustrated. The main limitations are discussed, and the perspectives to improve data quality are presented.

中文翻译：

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来自 SWIM 雷达车载 ​​CFOSAT 的新观测结果：仪器验证和海浪测量评估

本文描述了从2018年10月29日发射的CFOSAT（中法海洋卫星）携带的SWIM（Surface Waves Investigation and Monitoring）仪器获得的初步结果。 SWIM是一种具有近天底扫描波束的Ku波段雷达几何学。它旨在测量表面海浪的光谱特性。首先，说明仪器的良好行为。然后表明，由于新的重新跟踪算法，与标准高度测量任务相比，最低点产品（有效波高、归一化雷达截面和风速）表现出与标准高度计任务相似的精度，该算法补偿了较低的采样率。对偏离天底光束的观测进行了详细分析。正如文献中先前研究所预期的那样，归一化雷达截面会随着入射角和风速而变化。我们说明，为了从雷达后向散射波动中检索波谱，应用从观测中得出的散斑校正至关重要。然后将海浪的方向谱及其平均参数与全球尺度的波浪模型数据和来自精选案例研究的现场数据进行比较。说明了 SWIM 在提供波长范围 [70m-500m] 内海浪光谱特性方面的良好效率。讨论了主要限制，并提出了提高数据质量的观点。应用从观察中得出的散斑校正至关重要。然后将海浪的方向谱及其平均参数与全球尺度的波浪模型数据和来自精选案例研究的现场数据进行比较。说明了 SWIM 在提供波长范围 [70m-500m] 内海浪光谱特性方面的良好效率。讨论了主要限制，并提出了提高数据质量的观点。应用从观察中得出的散斑校正至关重要。然后将海浪的方向谱及其平均参数与全球尺度的波浪模型数据和来自精选案例研究的现场数据进行比较。说明了 SWIM 在提供波长范围 [70m-500m] 内海浪光谱特性方面的良好效率。讨论了主要限制，并提出了提高数据质量的观点。