Optical properties of deep ice at the South Pole: scattering
Abstract
Recently, absorption and scattering at depths 800 1000 m in South Pole ice have been studied with transit-time distributions of pulses from a variable-frequency laser sent between emitters and receivers embedded in the ice. At 800 1000 m, scattering is independent of wavelength and the scattering centers are air bubbles of size wavelength. At 1500 2000 m it is predicted that all bubbles will have transformed into air-hydrate clathrate crystals and that scattering occurs primarily at dust grains, at liquid acids concentrated along three-crystal boundaries, and at salt grains. Scattering on decorated dislocations, at ice ice boundaries, and at hydrate-ice boundaries will be of minor importance. Scattering from liquid acids in veins at three-crystal boundaries goes as 1 to 2 and should show essentially no depth dependence. Scattering from dust grains goes as 2 and should show peaks at depths of 1050, 1750, and 2200 m in South Pole ice. If marine salt grains remain undissolved, they will scatter like insoluble dust grains. Refraction at ice ice boundaries and at hydrate-ice boundaries is manifested by a multitude of small-angle scatters, independent of wavelength. The largest contribution to Rayleigh-like scattering is likely due to dislocations decorated discontinuously with impurities. Freshly grown laboratory ice exhibits a large Rayleigh-like scattering that we attribute to the much higher density of decorated dislocations than in glacial ice.
- Publication:
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Applied Optics
- Pub Date:
- June 1997
- DOI:
- Bibcode:
- 1997ApOpt..36.4181P