Structure and dielectric properties at 4.8 and 9.5 GHz of saline ice

Abstract

The structure and salinity characteristics of saline ice slabs removed from ice sheets grown in an outdoor pool have been studied and related to the complex relative dielectric permittivity measured, utilizing free space transmission techniques, at 4.8 and 9.5 GHz. The saline ice closely simulated Arctic sea ice in its structural and salinity characteristics which were regularly monitored in a number of ice sheets grown during the winters of 1983–1984 and 1984–1985. In‐situ transmission measurements at similar frequencies were also made on the ice sheet itself using antennas located above and beneath the ice. The slab measurements were made during warming from −28°C to −2°C on slabs grown during the winter of 1983–1984 (4.75 GHz) and during a warming and cooling cycle over a slightly larger temperature range on slabs grown during the winter, 1984–1985 (4.80 and 9.50 GHz). The 1983–1984 results show both the real εr′ and imaginary εr″ parts to vary almost in direct proportion to the brine volume νB at values less than about 50‰. The 1984–1985 slabs showed only εr′ to depend strongly on νB while values of εr″ were considerably less than in the previous year. This difference may have been due to greater electrical conductivity in the 1983–1984 slabs, which could be related to distinct differences seen in brine pocket structure between the two winters. Values of εr′ as a function of νB were slightly lower on the average at 9.50 GHz than at 4.80, and most values of εr′ agreed with the results of others when their temperature and salinity values were converted to values of νB. Changes in εr′ due to thermal modification (laboratory warming) seem more strongly related to a gain in air volume due to brine drainage than to the redistribution of brine inclusions. The in‐situ measurements showed extremely high attenuation for the young (<12 cm) brine‐rich ice. Good agreement was found between data for the more desalinated samples and theoretical values predicted by a previously proposed dielectric mixing model that was modified to account for the brine pocket geometry observed in thin sections, and also by including a bulk conductivity term to account for the observed loss.

Bounds on the complex permittivity of polycrystalline materials by analytic continuation

“…e T k Re k ). This information is available for the set of data in [52] as it is accompanied by a detailed analysis of the crystalline structure of the ice.…”

“…Here the polycrystalline bounds derived in the current work are applied to sea ice composite, and the results are compared with the measured effective permittivity of sea ice in [52]. This dataset is obtained from primarily columnar sea ice; it was previously used to compare effective permittivity of sea ice with the bounds for the effective property of a two-component material [14,54], of a statistically isotropic two-component composite [14,54] and of a two-component matrix-particle material [9,21].…”

“…The big picture is that granular ice (typically found in the top layer of a column of sea ice [58]) has an essentially random uniform distribution across all angles, whereas columnar ice has a strongly preferred vertical orientation. The effective complex permittivity dataset from Arcone et al [52] is largely columnar and crosssectional slices show that the sea ice is transversely isotropic. Examining the orientation statistics [58], it is very reasonable to conclude that the average crystal orientation e T k Re k for the largely columnar ice structure used in [52], is between 0 • and 30 • off the vertical axis.…”

Retrieval of the thickness of undeformed sea ice from simulated C-band compact polarimetric SAR images

“…The functional forms of F 1 and F 2 can be found from the work of Cox and Weeks (1983). (Arcone et al, 1986;Vant et al, 1978) f vb is the relative brine volume fraction. surface roughness parameters s, l, and σ are set to different values considering the validity range of the X-SPM model (Ulaby et al, 1982;del Monaco et al, 2009;Iodice et al, 2011).…”

“…The complex permittivity of brine inclusions is ε b , and their fractional volume is f v . The relative permittivity of the sea ice ε eff is a function of the volume fraction of brine inclusions (Arcone et al, 1986;Vant et al, 1978). The ice surface roughness is described by the correlation length l, rms height s, and the standard deviation of surface slope σ .…”