Thin sea ice thickness as inferred from passive microwave and in situ observations

Abstract

[1] Microwave radiometric signals from sea ice strongly reflect physical conditions of a layer near the ice surface. This study examines the extent to which the relationships of thickness with brightness temperature and with emissivity hold for thin sea ice, approximately <0.2-0.3 m, and how those relationships may arise from changes in brine characteristics through modification of dielectric properties near the ice surface. In order to address these questions we made concurrent measurements of sea ice thickness in the Sea of Okhotsk from a ship and passive microwave radiometry from an over-flying aircraft. The results show that the brightness temperature and emissivity increase with thickness approximately within the thin ice for a frequency range of 10-37 GHz. The relationship is more pronounced at lower frequencies and at the horizontal polarization. We also established an empirical relationship between ice thickness and salinity in the layer near the ice surface from a field experiment, which qualitatively supports the idea that changes in the near-surface brine characteristics contribute to the observed thickness-brightness temperature/emissivity relationship. On the basis of our results, we conclude that for thin ice, passive microwave radiometric signals likely contain indirect information on ice thickness through the dependence of dielectric properties on brine, which provides a plausible and common explanation for previously proposed passive microwave thickness algorithms.

An Assessment of Sea-Ice Thickness Along the Labrador Coast From AMSR-E and MODIS Data for Operational Data Assimilation

“…For sea ice, this can be explained in part on the desalination of the ice as the ice becomes thicker [9]. A fairly robust measurement used to determine the ice thickness is the polarization ratio, which can be interpreted as a normalized difference between the horizontally and vertically polarized emissions at a given frequency.…”

“…Methods have been presented in the literature to calculate the sea-ice thickness from various sensors [9]- [12]. Estimates of sea-ice thickness can be calculated at a resolution of approximately 1 km using data from visible/infrared (VIS/IR) sensors [11], with the limitation that this source of data cannot be used during cloudy conditions.…”

SMOS-derived thin sea ice thickness: algorithm baseline, product specifications and initial verification

“…The thin ice thickness retrieval algorithms are linear or exponential regression equations between polarization ratios (PR) or the V-to H-polarization ratios (R) and AVHRR or Moderate Resolution Imaging Spectroradiometer (MODIS) thicknesses. Naoki et al (2008) suggested that the observed decrease of near ice surface salinity as a function of ice thickness, which results in the modification of the ice dielectric properties and further ice emission (i.e., brightness temperatures), is the main reason for the observed relationship between brightness temperature and ice thickness. In addition, the relationship between brightness temperature and ice thickness is more pronounced for H-polarization and for a lower frequency (e.g., 10.7 GHz).…”

Sea Ice Surface Temperature Estimation Using MODIS and AMSR-E Data Within a Guided Variational Model Along the Labrador Coast

“…Weather forecasts near ice-covered regions are significantly improved when the accurate information regarding the ice state is available [2]. Sea ice thickness can be estimated using the data from passive microwave and visual/infrared (VIS/IR) sensors [3], [4] and radar and laser altimetry [5], [6]. Estimates from VIS/IR sensors are of particular interest because these sensors typically provide global coverage on a daily basis, at a relatively fine resolution ( ).…”