Altimetry Combined with Hydrography for Ocean Transport Estimation

A method to estimate mass and heat transports across hydrographic sections using hydrography together with altimetry data in a geostrophic inverse box model is presented. Absolute surface velocities computed from Archiving, Validation, and Interpretation of Satellite Oceanographic data (AVISO) altimetry products made up of a combination of sea surface height measurements and geoid estimate are first compared to ship acoustic Doppler current profiler (S-ADCP) measurements of the Observatoire de la Variabilité Interannuelle et Décennale (OVIDE) project along hydrographic sections repeated every 2 yr in summer from Portugal to Greenland. The RMS difference between S-ADCP and altimetry velocities averaged on distances of about 100 km accounts for 3.3 cm s−1. Considering that the uncertainty of S-ADCP velocities is found at 1.5 cm s−1, altimetry errors are estimated at 3 cm s−1. Transports across OVIDE sections previously obtained using S-ADCP data to constrain the geostrophic inverse box model are used as a reference. The new method is found useful to estimate absolute transports across the sections, as well as part of their variability. Despite associated uncertainties that are about 50% larger than when S-ADCP is used, the results for the North Atlantic Current and heat transports, with uncertainties of 10%–15%, reproduce the already observed variability. The largest uncertainties are found in the estimates of the East Greenland Irminger Current (EGIC) transport (30%), induced by larger uncertainties associated with altimetry data at the western boundary.