Exploring the synergy between along-track altimetry and tracer fronts to reconstruct surface ocean currents

High-frequency along-track altimetric data only provide direct information on the geostrophic currents orthogonal to the track. A new approach is proposed that combines these across-track current estimates with directional information from remotely-sensed tracer fields, such as surface chlorophyll concentration and sea surface temperature. The analysis focuses on the South Madagascar region characterised by the strong East Madagascar Current and sharp gradients of surface tracers. The results are compared with in-situ observations from three moorings along the Jason-1 track 196. Accurate information on the total velocity direction is the key factor for obtaining accurate estimates of along-track velocities. Surface tracer fronts can be successfully used to retrieve such information, especially when currents intersect the satellite track at low incidence angles (within ± 60° from the perpendicular direction). Errors in the reconstructed total velocities tend to grow rapidly for higher angles. Best performance is obtained by retaining information from the strongest fronts only. However, this significantly limits the resolution at which total currents can be reconstructed along the altimeter track.