HR: 0800h
AN: C51B-0301    [Abstracts]
TI: A Ground-Based Radar Backscatter Investigation on the Greenland Ice Sheet
AU: * Scott, J B
EM: j.b.t.scott@abdn.ac.uk
AF: Department of Geography and Environment, School of Geosciences, University of Aberdeen, Elphinstone Road, Aberdeen, AB24 3UF United Kingdom
AU: Mair, D
EM: d.mair@abdn.ac.uk
AF: Department of Geography and Environment, School of Geosciences, University of Aberdeen, Elphinstone Road, Aberdeen, AB24 3UF United Kingdom
AU: Nienow, P
EM: pnienow@geo.ed.ac.uk
AF: Department of Geography, School of Geosciences, University of Edinburgh, Drummond Street, Edinburgh, EH8 9XP United Kingdom
AU: Parry, V
EM: V.L.Parry@sms.ed.ac.uk
AF: Department of Geography, School of Geosciences, University of Edinburgh, Drummond Street, Edinburgh, EH8 9XP United Kingdom
AU: Morris, L
EM: emmo@bas.ac.uk
AF: Scott Polar Research Institute, University of Cambridge, Lensfield Road, Cambridge, CB2 1ER United Kingdom
AB: Satellite radar measurements over the ice sheets experience backscatter from the surface and from within the snowpack, termed surface and volume backscatter respectively. As part of the validation campaign for the ESA CryoSat mission, a ground-based step-frequency radar was deployed in the percolation zone of the Greenland Ice Sheet at ~1945m elevation (69 51N, 47 15W). Previous measurements in this region undertaken prior to summer melt events, have detected the strongest backscatter from buried ice features at around 1 m depth caused by the previous end of summer surface. In autumn 2004, radar measurements in the Ku band at bandwidths of 1 and 8 GHz were made alongside detailed glaciological studies. Results from both radar and shallow core/snowpit data reveal no continuous reflecting horizons in the upper 3.5 m of the firn. An average electromagnetic wave velocity of 2.11 ± 0.05 × 10⁸ m s^-1 was determined for the upper metre of the firn from 6 snowpits. Surface and volume backscatter at vertical incidence were calculated using a standard model. The contribution of the surface backscatter to the total backscatter was found to be an average of 6 dB higher than the volume backscatter. However, at the higher 8 GHz bandwidth the strongest return was frequently observed to originate not from the surface but from within the upper 30 cm of the snowpack, most probably from thin ice layers. These ice layers were not always resolved as separate events at 1 GHz bandwidth. Modelling using density and thickness measurements from shallow cores and snow-pits showed that the backscatter from these shallow, thin ice layers could be stronger than the surface return due to constructive interference from the top and base of the layers. In order to assess errors in satellite altimeter measurements, it is vital to know where the return is originating from in the snowpack.
DE: 0726 Ice sheets
DE: 0758 Remote sensing
SC: Cryosphere [C]
MN: Fall Meeting 2005