The Sentinel-6 (or Jason-CS) altimetry mission provides a long-term extension of the Topex and Jason-1/2/3 missions for ocean surface topography monitoring. Analysis of altimeter data relies on highly-accurate knowledge of the orbital position and requires radial RMS orbit errors of less than 1.5 cm. For precise orbit determination (POD), the Sentinel-6A spacecraft is equipped with a dual-constellation GNSS receiver. We present the results of Sentinel-6A POD solutions for the first 6 months since launch and demonstrate a 1-cm consistency of ambiguity-fixed GPS-only and Galileo-only solutions with the dual-constellation product. A similar performance (1.3 cm 3D RMS) is achieved in the comparison of kinematic and reduced-dynamic orbits. While Galileo measurements exhibit 30–50% smaller RMS errors than those of GPS, the POD benefits most from the availability of an increased number of satellites in the combined dual-frequency solution. Considering obvious uncertainties in the pre-mission calibration of the GNSS receiver antenna, an independent inflight calibration of the phase centers for GPS and Galileo signal frequencies is required. As such, Galileo observations cannot provide independent scale information and the estimated orbital height is ultimately driven by the employed forces models and knowledge of the center-of-mass location within the spacecraft. Using satellite laser ranging (SLR) from selected high-performance stations, a better than 1 cm RMS consistency of SLR normal points with the GNSS-based orbits is obtained, which further improves to 6 mm RMS when adjusting site-specific corrections to station positions and ranging biases. For the radial orbit component, a bias of less than 1 mm is found from the SLR analysis relative to the mean height of 13 high-performance SLR stations. Overall, the reduced-dynamic orbit determination based on GPS and Galileo tracking is considered to readily meet the altimetry-related Sentinel-6 mission needs for RMS height errors of less than 1.5 cm.

Sentinel-6（或 Jason-CS）测高任务为海洋表面地形监测的 Topex 和 Jason-1/2/3 任务提供了长期扩展。高度计数据的分析依赖于轨道位置的高精度知识，并且要求径向 RMS 轨道误差小于 1.5 厘米。为了精确确定轨道 (POD)，Sentinel-6A 航天器配备了双星座 GNSS 接收器。我们展示了 Sentinel-6A POD 解决方案在发布后的前 6 个月内的结果，并展示了双星座产品的含模糊度固定的仅 GPS 和仅伽利略解决方案的 1 厘米一致性。在比较运动学轨道和缩减动态轨道时，实现了类似的性能（1.3 cm 3D RMS）。虽然伽利略测量的 RMS 误差比 GPS 的误差小 30-50%，POD 受益于组合双频解决方案中卫星数量的增加。考虑到 GNSS 接收机天线任务前校准的明显不确定性，需要对 GPS 和伽利略信号频率的相位中心进行独立的飞行校准。因此，伽利略观测无法提供独立的比例信息，估计的轨道高度最终取决于所采用的力模型和航天器内质心位置的知识。使用来自选定高性能站的卫星激光测距 (SLR)，SLR 法线点与基于 GNSS 的轨道的一致性优于 1 cm RMS，当针对站位调整站点特定校正时，该一致性进一步提高到 6 mm RMS和范围偏差。对于径向轨道分量，从 SLR 分析中发现相对于 13 个高性能 SLR 站的平均高度的偏差小于 1 mm。总体而言，基于 GPS 和伽利略跟踪的缩减动态轨道确定被认为可以轻松满足与高度测量相关的 Sentinel-6 任务对 RMS 高度误差小于 1.5 cm 的需求。