Caring about the future

EMNOCM-ElectroMagnetic Network for Oceanic Currents Monitoring
Coordinator - Fernando Acácio Monteiro dos Santos
CESAM Responsible researcher - João Miguel Dias (com a participação de Jesús Dubert)
Programme - POCTI
Execution dates - 2005-03-01 - 2008-06-30 (40 Months)
Funding Entity - FCT
Funding for CESAM - 19400 €
Total Funding - 100000 €
Proponent Institution - Centro de Geofísica da Universidade de Lisboa
Participating Institutions
Universidade de Aveiro

Project Description

Motionally induced voltage (MIV) were widely taken up in oceanographic studies during last decade (e. g. Flosadottir and Taira, 1997). The most effective tools for long-term measurements of an electric field in ocean are cross-stream submarine cables, for such cables, the measured voltage is approximately proportional to integral water transport (e. g. Larsen, 1992). However, as ocean bottom cables are limited in number and location, the idea is to find a suitable method to derive oceanic currents from on-shore measurement of electromagnetic fields. Previous theoretical and practical results showed that electric field measurements with receiving antennas (electrical dipoles) located on the coastal line give possibility to get experimental estimations of non-local MIV and are a promising tool for studying temporal variability of sea currents (see e.g. Junge, 1988, Palshin et al., 2002). In particular this technique could be used for studying tidal currents, residual tidal circulation, wind-driven currents and other shelf/slope alongshore currents driven by other mechanisms. This method will also allow studying the seasonal variability, and long term (inter-annual) variability of the transports. In this project the installation of on-shore antennas for MIV observations at six sites located in Portuguese mainland is proposed. The calibration of the data obtained in the network will be done based on the knowledge of the tidal component of the currents, given by numerical models of the hydrodynamical equations. These models will provide the tidal transport between the coast and the open ocean. Thus, with the knowledge of the tidal transport and the electromagnetic fields, a transfer function between them will be computed, in order to obtain an estimation of the oceanic transports for low frequency flows. The data collected in this network will be still correlated with those obtained in the CAM1 submarine cable (installed between Sesimbra and Madeira Island) in order to complement the calibration process for obtaining the long-term oceanic transports. Thus, one of the final products will be an estimation of the longitudinal transports of volume in the portuguese coastal transition zone. The six stations will allow us to obtain an excellent temporal resolution. It should be noted that this information would be of great importance for the knowledge of the alongshore transports with an efficient and low cost method. Those transports are very difficult to measure with conventional instrumentation (currentometry), and in this region the satellite altimetry fails to give the sea surface slope. The project has the potential to provide valuable information for all organisations (national and international) that directly or indirectly are related to the long-term ocean behaviour, mainly that one involved in "global change" studies.

CESAM members on this project
João Miguel Dias

CESAM Funding: UIDP/50017/2020 + UIDB/50017/2020 + LA/P/0094/2020