This paper describes an innovative method for processing nadir altimeter data acquired in Synthetic Aperture Radar (SAR) mode, enhancing the system performances over open ocean. Similarly to the current SAR data processing scheme, the so-called LR-RMC (Low Resolution with Range Migration Correction) method, originally designed by Phalippou and Demeester (2011), includes Doppler beam forming, Doppler shift correction and range correction. In LR-RMC, however, an alternative and less complex averaging (stacking) operation is used so that all the Doppler beams produced in a radar cycle (4 bursts of 64 beams for the open-burst Sentinel-3-mode altimeter) are incoherently combined to form a multi-beam echo. In that manner, contrarily to the narrow-band SAR technique, the LR-RMC processing enlarges the effective footprint to average out the effects of surface waves and particularly those from small sub-mesoscale structures (<1 km) that are known to impact SAR-mode performances. On the other hand, the number of averaged beams is as high as in current SAR-mode processing, thus providing a noise reduction at least equally good. The LR-RMC method has the added benefit of reducing the incoherent integration time with respect to the SAR-mode processing (50 ms compared to 2.5 s) limiting possible surface movement effects. By processing one year of Sentinel-3A SRAL SAR-mode data using the LR-RMC method, it is shown that the swell impact on the SAR altimeter performances is totally removed and that an improvement of 10–50% is obtained in the measurement noise of the sea surface height and significant wave height with respect to SAR mode. Additionally, observational capabilities over the middle scales are enhanced potentially allowing the ocean mesoscale features to be retrieved and observations assimilated more usefully in ocean models.

本文介绍了一种创新的方法来处理以合成孔径雷达（SAR）模式获取的最低海拔高度数据，从而提高了公海上的系统性能。与当前的SAR数据处理方案相似，最初由Phalippou和Demeester（2011）设计的所谓LR-RMC（带距离偏移校正的低分辨率）方法包括多普勒波束形成，多普勒频移校正和距离校正。但是，在LR-RMC中，使用了一种替代性的且不太复杂的平均（堆叠）操作，以使雷达周期中产生的所有多普勒波束（对于开放式Sentinel-3模式高度计而言，有4束突发脉冲，共64束）。组合形成多波束回波。以这种方式，与窄带SAR技术相反，LR-RMC处理扩大了有效覆盖范围，以平均化表面波的影响，尤其是来自小型亚中尺度结构（<1 km）的已知影响SAR模式性能的表面波的影响。另一方面，平均波束的数量与当前的SAR模式处理中的波束数量一样多，因此提供了至少同样好的降噪效果。LR-RMC方法具有减少SAR模式处理的非相干积分时间的优势（与2.5 s相比，缩短了50 ms），从而限制了可能的表面运动效果。通过使用LR-RMC方法处理一年的Sentinel-3A SRAL SAR模式数据，结果表明，完全消除了对SAR高度计性能的影响，相对于SAR模式，海面高度和显着波高的测量噪声提高了10–50％。此外，中尺度的观测能力得到了增强，有可能使海洋中尺度特征得到恢复，并且在海洋模型中更有效地吸收观测结果。