Feature-oriented acoustic tomography: Upwelling at Cabo Frio (Brazil)

The Cabo Frio region (Brazil) presents a unique coastal-oceanic system. Among several interesting oceanic phenomena that occur in this region, the coastal upwelling is the most important coastal feature and is mainly forced by persistent winds northeast. An oceanic feature model which specifically describes the Cabo Frio upwelling process is used as a parameterization scheme to track the time evolution of the sound-speed field of a vertical slice of the coastal waters. The tracker processes the repeated measurements of broad-band, multi-frequency (220-880 Hz), full-field acoustic field on a vertical receiver array. The acoustic data are assimilated in the feature model to continuously correct the prediction of the upwelling slope of the temperature field. To cope with the nonlinearity between the environmental parameters and the acoustic propagation data, advanced nonlinear extensions of Kalman filters are necessary. It is shown that an ensemble Kalman filter (EnKF) continuously tracks the upwelling conditions, outperforming the extended Kalman filter (EKF).