Study On The Correction Method Of Near-Shore Water Level Based On Regional Tidal Model And Residual Water Level

Water level correction is an important work in depth measurement.The purpose is to obtain the true sea surface position of the desired point at the time of sounding and to calculate it to the depth datum.At present,the sounding instruments and means have made a great breakthrough,the high resolution and high precision sounding method represented by the multi-beam system has been widely used in project,and the water level correction still remains in the traditional method,has become one of the main factors restricting the sounding accuracy.Aiming at the problems existing in the traditional water correction method carried on the thorough analysis,and use the area precision tidal model and residual water level with the method of realizing the nearshore waters to complex water correction,based on this,according to the characteristics of residual water level put forward by using empirical mode decomposition and BP model for short-term forecasting method.The main work of this paper is as follows:(1)Constructed a 1.2'×1.2' precise tidal model of Hangzhou bay area.The construction method and key steps of the regional tidal model are described in detail,including constructing the regional water depth model by using the measured water depth;The harmonic constant interpolation method is used to optimize the open boundary conditions for the global tidal model.Through a pair of tide station check showed that hydrodynamic equation and "blending" assimilation method based on POM model can effectively change the limitation of the water level correction method of linear interpolation,conform to the high degree of each tidal harmonic constant main contribution constituent of M2 tidal wave propagation law and NAO.99jb model,amplitude error accounts for only 2.75%of the whole,is superior to the traditional water correction method.(2)The main error sources of the traditional water level correction method are analyzed.It is found that the accuracy of two-station water level correction method is largely dependent on the distribution of tidal stations;Different from the traditional concept,the geographical distance between the tidal station and the waiting point is not the only condition to determine the correction accuracy of water level;In the optimal case,the distance between the two tidal stations and the point to be searched is close,and the line of tidal stations is perpendicular to the main tidal equal-amplitude line;The method of least square curve fitting is proposed,which can eliminate the influence of semi-diurnal tide and all-diurnal tide in water level to a great extent compared with the method of monthly and daily sliding;In addition,through the water level transfer experiments at stations B,H and A,it is found that the interpolation of tidal transfer parameters is the main source of errors in the least square curve fitting method.(3)The principal component,distribution law and short-term prediction method of residual water level were studied.The spectrum analysis of the residual water level after the measured water level of each station is removed by 9 constituents of tide shows that the shallow water tide and semidiurnal tide are the main components of the residual water level and their amplitude increases from the mouth of the bay to the top of the bay;It is worth noting that there are periodic oscillations of non-astronomical tides in the bay,the amplitude of which is about 8 cm;The median error of residual water level obtained by using the residual water level correction method is 6.9 cm.The median error of simulated water level and measured water level is 9.5 cm after superimposed the astronomical tide level and the average sea level of the regional tidal precision model,which is better than the traditional water level correction method;Based on the analysis of residual water level,a method for short-term prediction of residual water level was proposed.Based on the residual water level data of three groups of typical tidal stations in the lower Columbia estuary,the residual water level of different time periods in the future was predicted by the combination model of EEMD-BP neural network;The experimental results show that the prediction accuracy of residual water level of each station in the period of 6 h and 12 h has reached the centimeter level,and the prediction accuracy is close to the centimeter level in the period of 24 h,which proves the reliability of the method.