Study On Synchronization Of Marine Environmental Monitoring Data Obtained By Underway Measurement

Marine environmental monitoring is the basis of investigating and exploiting the ocean. At present, the most widely used means of marine environmental monitoring is underway measurement, by which the observation data is nonsynchronous. In offshore and coastal areas where material motion is strenuous, synchronization problem of data is quite prominent. Research on marine environmental monitoring data obtained by underway measurement helps to correctly understand the spatial distribution of monitoring substance, and has a certain theoretical and applicable significance.In this paper, take water quality monitoring data as an example for synchronization calculations. Considering movements with fluid of particles and changes of pollutant concentration, use different numerical methods to correct synchronization error caused by these two factors. Based on the2-dimensional hydrodynamic model established by Delft3D, build up a particle tracking model to simulate the trajectory of the fluid particles, eliminating the effect of tidal displacement, and apply a convection-diffusion model to simulate changes of pollutant concentration, correcting concentration error by two different methods. The main research results and conclusions are:(1) In synchronization calculation of station location, Lagrange particle tracking method is used, which can reflect the real situation of water flow to a great extent. We use fourth-order Runge-Kutta method to calculate the Lagrange differential equation of motion, which can ensure calculation precision. So Lagrange particle tracking method can effectively correct position deviation of stations.(2) In synchronization calculation of pollutant concentration, two methods are used. We call the first method "statistical method":according to the results of the convection-diffusion model, calculate concentration variation from the sampling time to synchronization time in trajectory of one certain fluid particle, and in proportion to the variation correct concentration value at synchronization time by the measured one. The second method is "iterative method":calculated the initial condition used for synchronization by iterative method, and then use this condition to compute concentration value at synchronization time, which is the concentration correction.(3) When using "statistical method" to modify the concentration error, the correcting results depend on accuracy of water quality model, which is verified by nonsynchronous monitoring data, so this method is applicable to the case that the sampling interval is short,"iterative method" proceeds from the initial condition of convection-diffusion model, and by this method the sampled data can be validated separately at different times, unrestrained by sampling interval. The second method has a wider range of application in synchronization calculation of marine environmental monitoring that obtained by underway measurement.