Geostatistical Analysis of Three Dimensional Current Patterns in Coastal Oceanography: Application to the Gulf of Lions (NW Mediterranean Sea)

Abstract

Two geostatistical methods are used to map hydrodynamic patterns in the Gulf of Lions (Mediterranean Sea). The aims are both methodological — mapping vectorial data raises some difficulties — and applied — sampling schemes from boat cruise are not convenient to get maps or to compare with model output. From a large data set that was obtained from a shipboard ADCP (Acoustic Doppler Current Profiler), stationary isotropic geostatistical models were fitted for several horizontal layers. Vectors of current are characterized by two components or by intensity and direction. A linear model of coregionalization was used on vector components and compared to a second approach that considers vectors as elements of the complex plane ¢. Then interpolated maps were computed by ordinary cokriging and by ordinary kriging in the complex plane for two different depths. Although some difficulties remain unsolved due to the effect of time in the sampling scheme or to some constrains (physical equations and limit conditions) that currents must satisfy, the first results are already satisfactory and allow a better understanding of spatial patterns than the simple plots of original data. The same data set were also used in parallel for hydrological modelling using a physical circulation model. Then the complex kriging approach was used to address the spatial analysis of the residuals, i.e. difference between predicted and observed current vectors. Residuals were highly structured in space. Geostatistical methods confirmed their potential as complementary tools in physical circulation model validation and error reduction for current pattern predictions.