Inadequate sampling of oceanic motions, which commonly occurs for both oceanic measurements and simulations, can cause peculiar spectral features and potentially leads to misinterpretations. Here, we combine an extremely high-frequency moored velocity record and a high-resolution numerical simulation with the basic signal-processing theory to quantitatively explore how varying sampling rates affect the ability to represent oceanic motions, especially internal gravity waves (IGWs). The moored measurements and simulations demonstrate that hourly sampling is sufficient to capture horizontal internal tidal velocities, but inadequate to faithfully characterize the vertical velocity for nearly all frequencies. The daily-sampled model simulation shows a complicated frequency-wavenumber spectral pattern of IGWs. Due to contrasting periodicities in time and space, temporal subsampling tends to retain the total variance of original IGWs, while spatial subsampling directly induces spectral energy loss. This study sheds light on data applications of the upcoming satellite altimetry missions.

中文翻译：

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解释海洋运动采样不足的后果

海洋运动的不充分采样通常发生在海洋测量和模拟中，可能会导致特殊的光谱特征并可能导致误解。在这里，我们将超高频系泊速度记录和高分辨率数值模拟与基本信号处理理论相结合，定量探索不同的采样率如何影响表示海洋运动的能力，尤其是内部重力波 (IGW)。系泊测量和模拟表明，每小时采样足以捕获水平内部潮汐速度，但不足以忠实地描述几乎所有频率的垂直速度。每日采样模型模拟显示了 IGW 的复杂频率波数光谱模式。由于时间和空间的对比周期性，时间子采样倾向于保留原始IGW的总方差，而空间子采样直接导致光谱能量损失。这项研究揭示了即将到来的卫星测高任务的数据应用。