Research On Harmonic Analysis Method Of Short-term Tidal Level Data

The Yangtze River tidal river section starts from Datong Station in Anhui Province and reaches the river section between Xuliujing,Jiangsu Province,with a total length of about 600 kilometers.Located in the tidal reaches of the Yangtze River Delta,the Yangtze River Delta has developed manufacturing and aquaculture,and active social and economic activities,which have provided tremendous assistance to the country's economic development.However,the terrain of the delta area is flat and the average altitude is low.When encountering typhoons,heavy rains,etc.,the water level rises rapidly and it is prone to serious flood disasters.Therefore,analyzing and exploring the water level changes in the tidal rivers and summarizing the laws has become a hot issue that many experts and scholars in geography and hydrology have been paying attention to for many years.Harmonic analysis method is the main method for tidal and tidal forecasting and is applied to tidal research in various sea areas.According to the length of time of observation data,the harmonic analysis method is divided into three categories:long-term,medium-term and short-term.At present,most studies focus on analyzing long-term and medium-term data,and less analysis of short-term data.This paper explores the harmonic analysis method of short-term data to apply to the tidal reaches,and proposes an exploratory idea and method for the water level analysis of the tidal reaches,and constructs a water level forecast model for the tidal river.The water level of the tidal river is affected by the upstream runoff(especially the flood wave)and the tidal wave in the outer sea.The water level process is complicated.In this paper,the data of the water level station of the tidal reaches of the river is selected for short-term harmonic analysis,and the correlation between the harmonic constant and the upstream runoff is established.Based on this,the water level forecast model of the tidal reaches is constructed.Firstly,the Fourier analysis method is used to interpolate the tidal level data(generally hourly),and the accuracy of the interpolated data is guaranteed under the premise of the source data.Secondly,in order to overcome the shortcomings of short-term data and data during analysis,this paper explores the selection rules of tidal data from data length,tide type and starting point.Then,it is clear that the tidal level data within 120?135h of the average tide level of the middle tide is more suitable for short-term harmonic analysis.Thirdly,for the problem of the tidal confusion that may occur in the harmonic analysis of short-term tide level data,the solution to the application of the ridge regression analysis method is discussed.Considering that the method is a biased estimate,a method for correcting the prediction results is further proposed.Finally,using the tidal data selection rules of this paper,combined with the Fourier analysis method,the short-term harmonic analysis is carried out with the data of the Baimao water level site in the Yangtze River tidal reaches.Then the quantitative relationship between harmonic constant and runoff is analyzed,and the water level prediction model of Baimao station is constructed,and the rationality of the results is verified.By analyzing the data of the offshore tide level stations,this paper clarifies the short-term tide level data selection rules for harmonic analysis,and proposes a short-term tide level data harmonic analysis method based on ridge regression.The Baimao water level station of the tidal river section is used as an experimental site to explore the correlation between the harmonic constant and the upstream runoff,and on this basis,the water level prediction model of the tidal reaches is constructed.The experimental results are consistent with the trend of water level change,which verifies the effectiveness of the research method.