VHF Doppler radars have been used by LSEET for the measurements ofEulerian superficial currents in coastal zones (between 1to 30 km from the shore). For radar frequencies close to 50 MHz, the velocity measured is integrated over a depth of 25 cm, over an area of a few hundred square metres, and for times of one to ten minutes.The accuracy of the velocity measurements is better than 5 emis.1be radars are set up on the sea-shore and their maximum range,depending upon sea-state, is of 20 - 30 km.Two radars are needed to obtain a mapping of current vectors. These measurcmcnts don't account for vclocity fluctuations at scales less than the mesh size, which are generally described by a diffusion coefficient (Kh). On the other band, Lagrangian measurements can be made by tracking surface drifters.The same VHF radars can be used for such tracking by using radio beacons plaœd on the drifters. This paper proposes a method for using both the Eulerian velocity field (usual product ofVHF radars) and the Lagrangian trajectories of severa! drifters in order to estimate the horizontal diffusion coefficient. This method consists of comparing the statistical characteristics of the observed drifters distribution with those obtained by numerical simulations based on a random walk mcthod. Numerical experiments concerning the influence of the accuracy and the spatial resolution of current measurements and the elfect of the nurnber of drifters on the accuracy of dispersion estimate have been carried out. ln the particular case of a river plume with an outflow of the order of 1000 m3fs, we have shown that the accuracy of the horizontal diffusion coefficient estimation is of the order of 35 % for the l'Calistic number of 5drifters, with a spatial resolution of 500 x 500 m2.