DGPS走航测深验潮技术中的潮位信息提取方法

提出了一种提取观测海域潮位信息的新方法--DGPS走航测深验潮技术,即在走航ADCP重复测量断面潮周期流场观测的同时获取潮位信息,并实现水下地形的潮位改正.该方法通过重复测量点瞬时水深数据选取、潮位差数据计算、叠加拟合和迭代逼近等预处理与算法,可在潮差约1.6 m、地形起伏高达10～20 m的台湾浅滩沙波区,获取均方根误差小于0.1 m的潮位观测结果.

Retrieval of tide information from repetition sounding area

Underwater topography measured by a depth-sounder is affected by time series of tide level,so it is very important to remove tidal effect.Tide gauges setting at the adjacent costal station or mooring on nearby seabed are two regular ways to observe tide level data,but these two methods have some limitations.During the Taiwan Strait "Yanping No.2" joint cruise from 27th August to 1st September,2006,a 28-hour series repetition underwater topography measurement over the sandwaves of the Taiwan Bank,was carried out using the ship borne bottom track ADCP and isometer sounding along with GPS-time and DGPS-position.This article mainly put forward a new algorithm to retrieval time series of tide level from the time series of water depth over the repetition transects.The principle of this algorithm mainly base on the assumption that time series in every measuring point can be interpreted as equivalent to nestification of momentary tide level and corrected water depth,which can produce tide level data to obtain more accurate isobath map.The method mainly include several steps:the step for selecting points of repetition measurement by the position of points,the step for calculating difference of water depth,the step to integral approximate tide level,the step of iterative to approach accurate tide level,and the step for B-spline approximate and zero adjustment.Firstly,the difference of water depth of two close points equal to their difference of time tide level was assumed,while after setting tide level information of a series of time series point,we try to determine tide level information of other time series points using some mathematical fitting method.Furthermore,time series of tide level were retrieved repeatedly to get more accurate tide level data using iterative approach method.Finally,the total time series of tide level information were obtained based on the method of B-spline interpolating approach.In this paper we have adopted two ways to checking the feasibility of this approach.Calculation by both positive and negative direction and calculation by adopt two different data of bottom track ADCP and single-frequency sounder,the results show that the method proposed in the paper is reasonable and feasible.Great deals of work have carried on quality control.The flat and stable topography of the quasi-repeated measurement point can restrain the improvement of survey accuracy.We may achieve much better effect measuring accuracy in flat and stable area than fluctuant sand waves.However,the algorithm consists of many mathematical steps still remains to further improvement,It should be made to refine the process capacity of individual bad points,in an effort to become a more stable and accurate algorithm.In a word,This method is preformed as a good tool to measure an calculated tide curve with RMS of less than 0.1 m,even though the studying area is cover a series of sand waves over the Taiwan Bank.