Ocean tide aliasing is one of the largest error sources in satellite gravimetry. Despite its importance, the aliasing mechanism of ocean tides in satellite gravimetry is only partially understood. This paper explains tidal aliasing as a two-step mechanism. The primary aliasing is caused by orbit undersampling of original tidal signals. The secondary aliasing is due to undersampling of the primary aliasing signals through gravity recovery in discrete time intervals. The two-step aliasing mechanism is demonstrated through a closed-loop numerical simulation. The aliasing of the tidal constituents \(M_2\), \(N_2\), \(S_2\), \(K_2\), \(O_1\), \(P_1\), \(Q_1\) and \(K_1\) in CHAMP, GOCE, GRACE and GRACE Follow-On missions is analysed. The primary alias periods of individual constituents change from a few to hundreds of days depending on the orbital geometry. The long-term \(S_2\) aliasing may cause bias in gravity fields derived by GOCE data if the \(S_2\) tide is not well-represented by the ocean tide model applied in the data processing. Comparing the primary aliasing properties of CHAMP with that of GRACE indicates that tuning orbit inclination can improve aliasing properties, i.e. shorter aliasing periods and less couplings with annual/semi-annual signals. The strict definition of secondary alias periods is compromised in case of GRACE and GRACE Follow-On due to non-constant recovery periods, which results in irregular sampling and blurs the sharp spectral lines that are described by the two-step mechanism. The two-step aliasing mechanism can also be used in understanding aliasing of other periodic signals observed by satellite gravimetry.

海洋潮汐混叠是卫星重力测量中最大的误差源之一。尽管它很重要，但卫星重力测量中海洋潮汐的混叠机制仅被部分了解。本文将潮汐混叠解释为两步机制。主要混叠是由原始潮汐信号的轨道欠采样引起的。二次混叠是由于在离散时间间隔内通过重力恢复对主要混叠信号进行了欠采样。通过闭环数值模拟演示了两步混叠机制。潮汐成分\(M_2\)、\(N_2\)、\(S_2\)、\(K_2\)、\(O_1\)、\(P_1\)、\(Q_1\)的混叠和\(K_1\)在 CHAMP、GOCE、GRACE 和 GRACE 后续任务中进行了分析。根据轨道几何形状，单个成分的主要别名周期从几天到几百天不等。长期\（S_2 \）混叠可能导致在通过GOCE数据导出的重力场偏置如果\（S_2 \）数据处理中应用的海洋潮汐模型不能很好地代表潮汐。将 CHAMP 的主要混叠特性与 GRACE 的主要混叠特性进行比较表明，调谐轨道倾角可以改善混叠特性，即更短的混叠周期和与年/半年信号的更少耦合。在 GRACE 和 GRACE Follow-On 的情况下，由于非恒定恢复周期，次级混叠周期的严格定义会受到影响，这会导致不规则采样并模糊由两步机制描述的尖锐谱线。两步混叠机制还可用于理解卫星重力测量观测到的其他周期信号的混叠。