Synergy between surface drifters and altimetry to increase the accuracy of sea level anomaly and geostrophic current maps in the Gulf of Mexico

•Processing of three different kinds of drifters to extract the geostrophic component.•The use of drifters leads to a higher improvement than an additional altimeter.•Improvement is of 1% in SLA and 10% in meridional velocities.•Both components of the velocity vector have similar accuracy.