Geophysical challenges in using large-scale ocean-generated EM fields to determine the ocean flow

For some time, oceanographers have used measurements of the small electromagnetic fields generated by the flow of the electrically conductive oceans through the Earth's main magnetic field to infer values for the ocean flow velocities. An overview of the process of motional induction is given including a description of the global electromagnetic fields generated by a global model ocean. We describe how electromagnetic methods are currently used in oceanography and outline the most important challenges presently faced.