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.  She was deputy-coordinator in the EU projects (AMOC (1998-2001) and ACOBAR (2008-2013)), and she led the follow up ACOBAR II project funded by RCN project.

Sagen has led the development of the acoustic tomography system in the Fram Strait, and coordinated annual ocean/acoustic cruises to the Fram Strait since 2007 (involving open ocean vessel, icebreakers and aircraft missions). Currently, Sagen lead the   UNDER-ICE – Arctic Ocean under melting ice; and she is the deputy coordinator of the EU project INTAROS - Integrated Arctic Observation System.  Sagen has a strong international network in USA, and Europe within research and technologies.    

Sagen is a member of the Acoustical Society of America and she is a member of the Norwegian Scientific Academy for Polar Research. 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 is member of the ITU/WMO/UNESCO-IOC Joint Task Force (JTF) - Green Cables sin 2013 and of the scientific steering committee of the International Quiet Ocean Experiment (SCOR committee) from 2016.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.