Firn density profiles from Radar inversion using forward modelling

Sammanfattning

The Greenland ice sheet is rapidly changing. To monitor this change, remote sensing presently provides a powerful tool in some applications, but many aspects are not yet determinable. In this thesis, the potential of using Radar forward modelling to invert Radar echoes to firn profiles on Greenland is investigated. The temperature in the profiles is dismissed as an uninfluential factor, and strong contrast in the firn density corresponding to annual densification layers are identified as a signal that can be detected and used in this inversion. As a consequence, the density profile is parameterized as a linearly increasing density with depth, with high density layers superimposed. By introducing a constraint between the average slope of the profile and the position of density contrasts, based on the solution of a simpler density profile, a method which produce accurate estimations of the slope is developed and verified on purely simulated Radar echoes and one real airborne Radar echo from the IceBridge campaign. The position and magnitude of density contrasts are also found by inverting single Radar echoes, and by combining several inversions separated only temporally. This has produced density profiles containing the correct amount of contrasts, but of questionable accuracy in terms of shape and magnitude of the contrasts using simulated echoes. The correct location of the contrasts has been produced in most cases.