Name Internal Tide Measurements with Acoustic Tomoghrapic
Funding Reference FCT - PRAXIS project, contract n degree 2/2.1/MAR/1698/95
Dates 1997|2000

Today acoustics one of the main tools for ocean exploration. Inspired by a technique from biomedical engineering, ocean acoustical tomography (OAT) consists of the use of one or more acoustic sensors/sources strategically distributed in a volume of water and simultaneously emitting and receiving coded signals. The comparison of the emitted and received signals allows for the acoustical characterization of the environment in between the source(s) and receiver(s). The experiments that have been performed to date, mainly in deep water, showed that it is possible to estimate: (1) the temperature over the water column, (2) the physical characteristics of the seabottom and (3) the velocity and direction of currents.

Due to the large water mass involved and its periodic nature, internal tides signatures have been frequently observed during ocean tomography experiments in the Bay of Biscay. In the continental shelf, internal tides are extremely important to the study of the coastal dynamics with a very special relevance close to the shelf break and to topographic irregularities like submarine canyons. This project aims at providing the concept of using vertical arrays of sensors and acoustic sources in the band 50 – 400 Hz for tomographic estimation of the oceanographic characteristics of internal tides on the continental shelf up to 200 m of water depth. During the project, areas of interest near the portuguese coast will be selected for at sea testing including the validation of the tomographic results with ground truth measurements. The conclusions of this study are hoped to bring a better knowledge of the internal tide phenomena and its impact on the portuguese coastal dynamics. This should lead to improved prediction accuracy for coastal dynamical models and to a better management of existing resources. The results will also be important in providing more refined predictions of the impact of potential ecological accidents and climate changes.

Research Groups Signal and Image Processing Group (SIPG)
Project Partners Instituto Hidrográfico (Lisbon, Portugal), Centre Militaire Oceanographique - Service Hydrographique et Oceanographique de la Marine (Brest, France)
ISR/IST Responsible
Sérgio Jesus
Cristiano Soares
Orlando Rodriguez
Nelson Martins