Numerical estimation of multiple leakage positions of a marine pollutant using the adjoint marginal sensitivity method

When abnormally high concentration of a pollutant is observed in the ocean, it is very important to search for leakage positions and fluxes of the pollutant. To reduce time and expense of such search effort in the ocean, a numerical method was proposed for estimating a leakage position and its flux using a limited number of observed concentration data. This method is called the adjoint marginal sensitivity method, which is a time-backward probabilistic method to estimate a leakage position and a flux. In this study, we improved the method to deal with multiple leakage positions and validated this newly developed method. In addition, we showed the conditions for successful estimation using the simulation results of a well-planned two-dimensional case studies by changing flow velocity, eddy diffusion coefficient, distance between two leakage positions, spatial observation range, and sensor spacing. Moreover, we applied this method to a three-dimensional case with real topography and obtained reasonably acceptable results, suggesting that the knowledge learnt in the two-dimensional case studies is effective.