HR: 1340h
AN: PP33C-1594    [Abstracts]
TI: Spatial Distribution of Stratigraphic Density Variations in Arctic Firn Mapped by Ground Penetrating Radar and Coring
AU: * Brandt, O
EM: ola.brandt@npolar.no
AF: Norwegian Polar Institute, Polarmiljøsenteret, Tromsø, NO-9296 Norway
AU: Kohler, J
PP33C-1594 AF: Norwegian Polar Institute, Polarmiljøsenteret, Tromsø, NO-9296 Norway
AU: Langley, K
PP33C-1594 AF: Department of Geosciences, University of Oslo Blindern PO Box 1047, Oslo, NO-0316 Norway
AB: Ice or firn cores provide point estimates of down-core properties which are known to vary spatially. An inevitable question is how representative are cores in time and space? Here we use Ground Penetrating Radar (GPR) to map firn properties (in particular, density) over a larger area, and compare properties inferred from the imagery to those measured on firn cores. Each spring in 2003-2005, five firn cores have been recovered from the same location on the high arctic glacier Kongsvegen, Svalbard. The site is situated at 670 m asl, in the percolation/wet-snow zone, and has an average specific net mass balance of 0.5 m w.eq. for the period 1986-2004. Cores were drilled on a grid with horizontal spacing of 5-20 m, to a depth of ~10 m. At the same time GPR data were collected on a grid with a spacing of 0.25-5 m, at various frequencies (350, 500 and 900MHz). The electromagnetic wave velocity was determined from common midpoint (CMP) surveys. Core stratigraphy is characterized using both dielectrical profiling (DEP) of the whole core, at three different frequencies (50, 250 and 900kHz), and high-resolution digital imaging of the sliced core. Permittivity records are derived from the DEP records. There is a high degree of similarity between the digital imagery and the core permittivity. Comparing GPR profiles and neighboring cores shows there is a high degree of heterogeneity of stratigraphic features finer than ~0.05m; cores are similar when comparing the most prominent features and patterns, typically high density layers thicker than ~0.15 m. The permittivity records are used to simulate radargrams using both a plane-wave convolution approach and FDTD modeling. There is reasonable agreement between simulated and observed radargrams, in the sense that the simulated radargrams are plausible realizations within the population of observed radargrams.
DE: 0600 ELECTROMAGNETICS
DE: 0724 Ice cores (4932)
DE: 0758 Remote sensing
DE: 0776 Glaciology (1621, 1827, 1863)
DE: 6969 Remote sensing
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005