Sagen is a researcher at the Nansen Environmental and Remote Sensing Center. Her expertise is in applied mathematics specialized within ocean acoustic. Her research interests are focused on using new technologies for observing the Arctic environment, such as acoustic tomography, passive acoustics, floats and gliders. Currently, she is the deputy-coordinator of the EU funded project ACOBAR (2008-2012) (http://acobar.nersc.no). As part of ACOBAR she leads the implementation of a multi-purpose acoustic system in the Fram Strait for tomography, navigation of gliders and passive acoustic, and the development of assimilation of acoustic data into ice-ocean models. She plans and implement field experiments in the Arctic, and has been chief scientist on 9 cruises since 2007 in Arctic marginal ice zone experiments.

Sagen is a member of the Acoustical Society of America and the AO Subcommittee on Integrated Acoustics Systems for Ocean Observatories (IASOO). She has served as member in research programmes committees in the Norwegian Research Council, and is a former member of the Norwegian National International Polar Year Committee (2004-2005). She received her Cand.mag. in 1985, Cand. Scient.  in 1987 and Dr. Scient.  in 1998 in applied mathematics from the University of Bergen, Norway.