HR: 10:25h
AN: C12B-01    [Abstracts]
TI: Variability of Decimetre and Centimetre Scale Ice Surface Roughness and the Potential Consequences on the CryoSat Radar Altimeter Signal
AU: * Cawkwell, F G
EM: fiona.cawkwell@ualberta.ca
AF: University of Alberta, Earth and Atmospheric Sciences, Edmonton, AB T6G 2E3 Canada
AU: Burgess, D O
EM: dob@ualberta.ca
AF: University of Alberta, Earth and Atmospheric Sciences, Edmonton, AB T6G 2E3 Canada
AU: Sharp, M J
EM: martin.sharp@ualberta.ca
AF: University of Alberta, Earth and Atmospheric Sciences, Edmonton, AB T6G 2E3 Canada
AU: Demuth, M
EM: mdemuth@nrcan.gc.ca
AF: Geological Survey of Canada, 601 Booth Street, Ottawa, ON K1A 0E8 Canada
AB: Snow and ice surface roughness affect the backscatter of the pulse emitted by a radar altimeter, and hence the accuracy of the surface elevation calculated from the waveform echo, but the influence of surface roughness has not been quantified. As part of the CryoSat calibration/validation field campaigns on the Devon Ice Cap in 2004, surface roughness measurements were made at 0.1-7km intervals along a 48km transect from near the summit to the southern margin. Measurements were made at the decimetre scale by surveying and at the centimetre scale using digital photography. The data collected were subjected to wavelet analysis to define characteristic roughness wavelengths, and the fractal dimension associated with each of these was calculated using the semi-variogram method. Vario functions were calculated for the photographic data. The survey results show that wavelength scales depend on orientation and distance from the ice cap summit, the fractal dimension depends on the wavelength scale and the orientation, and both are significantly affected by storm events. Profiles aligned with the easterly prevailing wind direction, and thus perpendicular to the predicted satellite track, proved to be more sensitive to meteorological events than those normal to the dominant winds. Wavelet and fractal analysis of the photographic data was less conclusive, potentially due to the `noisier' nature of the data at this scale, where `noise' is actually the superimposition of small scale wavelengths onto larger ones. Vario analysis showed the characteristic wavelengths at the centimetre scale to increase with distance from the summit, although the abrading effect of storm events caused a decrease in wavelength. The amplitude of the roughness also increases with distance from the summit, although following a period of calm this value is significantly decreased along the transect. Orientation with respect to the prevailing wind direction is also a significant factor. Analysis of the return waveforms acquired by an airborne radar altimeter concurrently with ground data will allow the impact of the different roughness scales and orientations to be assessed.
DE: 3322 Land/atmosphere interactions
DE: 3349 Polar meteorology
DE: 3250 Fractals and multifractals
DE: 1827 Glaciology (1863)
DE: 1640 Remote sensing
SC: Cryosphere [C]
MN: 2004 AGU Fall Meeting