Physical, dielectric, and C band microwave scattering properties of first‐year sea ice during advanced melt

Abstract

This paper investigates the influence of solar heating and intermittent cloud cover on the physical and dielectric properties of naturally snow‐free, warm (>−2°), first‐year sea ice (FYI) in the southeastern margin of the Beaufort Sea during advanced melt. A simple three‐layer physical model describing the surface is introduced and copolarized C band microwave signatures are simulated using a multilayer scattering model forced with four sets of measured surface parameters. Modeled backscatter signatures are compared to coincident surface‐based C band scatterometer signatures in order to elucidate the signature controlling properties of the ice. Results show that 50 MHz impedance probe dielectric measurements of desalinated upper ice layers exhibit statistically significant diurnal variations due to the link between solar forcing and the availability of free water in brine‐free upper ice layers. Enhanced downwelling longwave radiation to the surface from low‐level stratus clouds is positively linearly associated (r = 0.709) with volumetric moisture mv detected in upper ice layers. Model results show that desalinated upper ice layers contribute volume scattering from smooth, snow‐free FYI under the observed surface mv range. Sustained cloud‐free periods result in the formation of a 0.5–2.5 cm granular surface layer, composed of 5.2 mm ice grains, which enhances backscatter under relatively dry conditions. Sensitivity analyses show that layer thickness plays a significant role in scattering due to the increased number density of inclusions which act as discrete scatterers, and sufficient energy may penetrate to, and scatter from, the saline columnar ice layer under relatively dry conditions only (mv < 2%).