你的问题实际上是一个由三部分组成的问题,我不能回答所有部分,但让我告诉你我所知道的。# #第1部分:是什么原因导致垂直位置变化的上下文中提到的句子吗?# #如果你仔细阅读部分更多与其说是海底深度的变化,但变化的_measurement_海底深度。使用已知的固定结构的海床上他们发现不同的运行给这些结构的不同垂直位置。让我扩大你的引用:> […)重复抽样稳定的固定海底结构(钓鱼drag-board痕迹,沉船)表明,重建的整体垂直位置对一个固定的海图深度基准面可能不同从调查,调查10厘米以上。这种变化的原因还没有被解决。因此,没有一个垂直参考目前在调查区域内整体变化海底不到20厘米不能得到明确的时间超过几个月。相比之下,使用一个固定的海底结构垂直参考多波束数据的精度可以不到半米的水平和1厘米在垂直[…),这意味着在不稳定情况下垂直参考测量在不同的时间不能轻易相比,并简单地减去床高度不一定会给时间床层高度的变化。 However, when there are stable structures, such as a ship's wreck, you can use the difference in the measurements of the vertical position of that structure to correct measurements of the entire seabed, giving a much better vertical precision. ## Part 2: What causes variations in the measurements between measurement runs? ## The section referenced mentions that the exact causes of the different measurements have not been resolved. Most likely it is a combination of inaccuracies of the used instruments, on which I'm definitely not an expert, and I'm not even sure this is the right Stack Exchange to ask that question. ## Part 3: What causes true variations in the absolute seabed height? ## This is an entire field of research on its own, called coastal morphodynamics, which is too broad to be answered in a single Stack Exchange answer. Without a specific question you wouldn't get a more sensible answer than it a depends on the seabed composition and water flow.