Microwave penetration in polar snow and ice: Implications for GPR and SAR

• Published in: Annals of Glaciology
• Main Author: Müller, Karsten
• Other Authors: Svein-Erik Hamran, Jon-Ove Hagen
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: 2011
• Subjects: VDP::450; Antarctic; Arctic; East Antarctica; Svalbard; Annals of Glaciology; Antarc*; Antarctica; glacier
• Online Access: http://hdl.handle.net/10852/12329; http://urn.nb.no/URN:NBN:no-29265

The state of the continental ice masses has a direct impact on the global sea level. Changes in the polar regions will not only impact the people living in the Arctic, but also people living along coastlines around the world. Monitoring the current and future state of the global ice masses is therefore of greatest interest. Microwave remote sensing of the cryosphere from ground, air or space is an active and fast developing field of research. In this thesis we investigate the interaction of microwaves with snow and ice by means of ground penetrating radar (GPR) and relate the findings to observations from space-borne radars (SAR or InSAR). We applied GPR to extend the 200 year mean surface mass balance (SMB) measurement from firn cores in a previously unmapped part of East Antarctica. Our findings show up to 50% lower values than estimated from modelling or remote sensing. However, our evaluated time period is much longer and our spatial resolution much finer. We relate our SMB values to radar backscatter from space-borne radar and use this correlation to further extend the SMB estimate over a 76000 km2 large area on the East Antarctic plateau. We investigate the position of the GPR phase center (zö) in snow, firn and ice in the interior and exterior of the East Antarctic Plateau and a glacier on Svalbard. Values of zö exceed 40 m in the dry firn of the East Antarctic Plateau at frequencies of 1.75 GHz. Thus, we have to expect a potential bias when measuring topography by means of InSAR in these areas. In coastal Antarctica and on an Arctic glacier zö often exceeds 5 m even at C-band. Consequently, deriving mass-balance estimates through monitoring elevation changes with radar are difficult to interpret. However, we find that zö aligns with the previous summer surface in the ablation zone of the glacier for S- and C-band frequencies. Thus, in this part of the glacier elevation changes can be monitored with InSAR. We attribute the difference in zö from the ablation zone to the firn zone of the glacier to a change in scattering mechanisms, which results in stronger radar backscatter from the firn zone. We use this difference to map the extent of the firn area by a simple threshold classification.