Preprints
https://doi.org/10.5194/egusphere-2024-2276
https://doi.org/10.5194/egusphere-2024-2276
06 Sep 2024
 | 06 Sep 2024
Status: this preprint is open for discussion.

Anisotropic Scattering in Radio-Echo Sounding: Insights from Northeast Greenland

Tamara Annina Gerber, David A. Lilien, Niels F. Nymand, Daniel Steinhage, Olaf Eisen, and Dorthe Dahl-Jensen

Abstract. Anisotropic scattering and birefringence-induced power extinction are two distinct mechanisms affecting the azimuthal power response in Radio Echo Sounding (RES) of ice sheets. While birefringence is directly related to the crystal orientation fabric (COF), anisotropic scattering can, in principle, have various origins. Although both mechanisms can appear separately, they often act jointly, complicating efforts to deduce the COF strength and orientation from RES signals. In this study, we assess the relative importance of anisotropic scattering and birefringence using quad-polarized ground-based RES measurements collected in the Northeast Greenland Ice Stream (NEGIS). We employ curve-fitting techniques to analyze the synthesized full azimuthal response, revealing insights into the dominance and orientation of the two different mechanisms at various depths between 630 m and 2500 m. We find that anisotropic scattering clearly dominates the radar signal in most depths larger than 1000 m, while birefringence effects are only important at shallower depths and in the vicinity of the ice- stream shear margins. We further find that the co-polarized power difference follows the ice-sheet stratigraphy with a notable transition in strength and/or direction at the Wisconsin-Holocene transition and in folded ice outside the ice stream, possibly indicating inverted stratigraphy in these folded units. We conclude that small-scale fluctuations in the horizontal COF eigenvalues is the most likely mechanism responsible for the anisotropic scattering observed in our survey area. Mapping the strength and orientation of scattering in quad-polarized measurements thus have the potential to provide independent estimates of the COF orientation and distinguish ice units with different scattering properties, e.g. from different climatic periods.

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Tamara Annina Gerber, David A. Lilien, Niels F. Nymand, Daniel Steinhage, Olaf Eisen, and Dorthe Dahl-Jensen

Status: open (until 02 Nov 2024)

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Tamara Annina Gerber, David A. Lilien, Niels F. Nymand, Daniel Steinhage, Olaf Eisen, and Dorthe Dahl-Jensen

Model code and software

anisotropicScattering-code Tamara Gerber https://github.com/tamaragerber/anisotropicScattering

Tamara Annina Gerber, David A. Lilien, Niels F. Nymand, Daniel Steinhage, Olaf Eisen, and Dorthe Dahl-Jensen

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Short summary
This study explores how anisotropic scattering and birefringence affect radar signals in ice sheets. Analyzing data from Northeast Greenland, we found anisotropic scattering, caused by small changes in ice crystals, dominates the azimuthal power response. We observe a strong link between scattering strength, orientation, and ice-sheet stratigraphy. Anisotropic scattering can thus be used to determine ice crystal orientation and distinguish ice units from different climatic periods.