Stéphane Calmant (LEGOS, Toulouse, France); Michel Calzas (DT-INSU, CNRS, Plouzané, France); Valérie Ballu (LIENSs, Université de La Rochelle, France); Laurent Testut (LEGOS, Toulouse, France); Pierre Valty (DITTT, Nouméa, New Caledonia); Yann Krien (LARGE, Université Antilles-Guyane, France); Pascal Bonnefond (Observatoire de Paris - SYRTE, France); Fabrice Papa (LEGOS, IRD, France)

The Bay of Bengal is home to massive continental freshwater supply during the summer monsoon season. During this season only, about 800 km3 of freshwater flow through the Bengal delta into the northern Bay, provided by the Ganges-Brahmaputra river system. Although the ocean tide is expected to play a strong role in the spreading of this freshwater, the spatio-temporal evolution of this seasonal plume as well as the exact processes governing its dispersal in the open ocean remain largely unknown, due to the lack of in situ observations.
To try to shed light on this issue, we conducted a pilot experiment in the near-shore region of the northern Bay of Bengal in the post-monsoon season of 2014, along SARAL track#810. Our observational strategy is based on an original ship-borne towed GNSS device: CalNaGeo. This device is designed to measure the absolute sea surface height within a few centimeters accuracy. Unfortunately, it was not possible to conduct the cruise during a SARAL overpass for validation of the SARAL measurements. However, our data are shown to capture multi-scale variability of sea surface height, from horizontal scales of a few meters to dozens of km. Our dataset evidences the signature of an hydrological front in the de-tided GNSS record, taking the form of a steric stair separating coastal (warm and fresh) waters from off-shore (cooler and salty) waters. We also assess the capability of along-track altimetry to capture the steric height gradient associated to this hydrological front.