论文部分内容阅读
一、前言实际的水位变化除包括天文潮变化外,还含有非天文因素影响而产生的非潮汐性质的水位变化。用一日24小时逐时水位平均求得的日平均水位,基本上滤去了日周期以下的高频分潮,而非潮汐性质的水位变化仍包括在日平均水位变化之中。不过这儿要指出,日平均水位仍包含日和半日以及更高频的潮汐成份,这必然形成Nyquist折叠现象,会使谱分析中形成的极值出现虚像。但是在研究大尺度的低频波动还常采用日平均水位
I. INTRODUCTION In addition to the changes in astronomical tide, the actual water level changes also include the non-tidal water level changes that are caused by non-astronomical factors. The average daily water level obtained from the hourly hourly water level on a 24-hour day basically removes the high-frequency tidal currents below the daily level, whereas the tide-free water level changes are still included in the daily average water level changes. However, it should be pointed out here that the daily mean water level still contains tidal components of day, half-day and higher frequencies, which inevitably result in Nyquist folding, causing a virtual image to appear at the extreme values of the spectral analysis. However, daily average water levels are often used in the study of large-scale low-frequency fluctuations