Application Of Shipboard ADCP In Hydrodynamic Processes In The Bohai Sea And Yellow Sea

Coastal circulation and material transport can be obtained by effective tidal-residual separation,which can determine the capacity of water exchange,predict the source,migration and retention of nutrients and pollutants,and provide an important guarantee for marine environmental protection and sustainable utilization of resources.Shipboard ADCP is one of the important means to observe the velocity structure of the key sections and to obtain the circulation and material transport around coastal area.However,the de-tide technology has always been a difficult problem.In this paper,a systematic analysis method for quality control processing and de-tide method is established,and applied to the Bohai and Huanghai sea.The dynamic characteristics of tidal residual currents around observed areas are discussed.Firstly,processing steps of ship speed acquisition,sound speed calibration,misalignment angle correction,and profile data processing are summarized,and a systematic quality control procedure of shipboard ADCP observation data is established.Taking a shipboard ADCP observation around the Liaodong Bay as an application,the shipboard ADCP observation data was carried out according to the procedure established in this paper.Compared with the original ADCP observation data,the post-processed results show that 23.56% of the zonal velocity data and 25.96% of the meridional velocity data are incredible and these data are eliminated.The comparison of velocity before and after quality control indicates that the procedure effectively reduces the impact of random errors.Secondly,in order to explore the applicability and validity of various commonly used de-tide methods,based on the fixed-point ADCP observation data around the coastal area of Zhangzi Island,the de-tide effects of T_TIDE method,traditional method and L-curve method are compared by controlling sampling mode.The results show that under a fixed sampling frequency of 10 minutes/time,the T_TIDE method is effective in de-tiding from the observed data over 15 days.The traditional method can effectively separate the tidal current from the observed data over 2 days.The L-curve method is suitable for the observed data within 1 day.With the decrease of sampling interval,the better de-tiding effect of L-curve method is.The results of two random sampling experiments show that the randomness of sampling time distribution will affect the de-tiding effect of L-curve method.Finally,based on the repeated short-term shipboard ADCP surveys of three sections around the coastal area of Hongyanhe Nuclear Power Station,the L-curve method is used to separate tidal and residual current.The results show that the tidal current characteristics separated by L-curve method are in good agreement with the previous observations,and the pattern of residual current from coastal to South and offshore to north is consistent with the temperature and salinity distribution in the observed sea area.The regression values derived from the L-curve method are highly correlated with the measured instantaneous velocity.The root mean square error(RMSE)is about 3 cm/s,and the relative error was about 5.3%.L-curve method can be extended to de-tide at any critical sections to obtain the important information such as coastal circulation variation and material transport fluxes to estimate the water exchange and resident time.